Wm i i»t»v THE JOURNAL OF ANIMAL BEHAVIOR VOLUME 5, 1915 EDITORIAL BOARD Madison Bentley University of Illinois Harvey A. Carr The University of Chicago Editor of Reviews Gilbert V. Hamilton Santa Barbara, California Samuel J. Holmes The University of California Walter S. Hunter The University of Texas Herbert S. Jennings The Johns Hopkins University Edward L. Thorndike Teachers College, Columbia University Margaret F. Washburn Vassar College John B. Watson The Johns Hopkins University William M. Wheeler Harvard University Robert M. Yerkes, Harvard University Managing Editor Published Bi-monthly at Cambridge, Boston, Mass. HENRY HOLT & COMPANY 34 West 33d Street, New York G. E. STECHERT & CO., London, Paris and Leipzig, Foreign Agents Entered as second-class matter March 7, 1911, at the post-office at Cambridge, Boston, Massachusetts, under the act of March 3, 1879 ^ 30 CONTEXTS OF VOLUME 6, 191 5 Number i, January-February pages Vincent, Stella B. The white rat and the maze problem. I. The introduction of a visual control 1-24 Yerkes, Robert M., assisted by Eisenberg, A. M. Prelimi- naries to a study of color vision in the ring dove Tutor risorius 2 5 _ 43 White, Gertrude M. The behavior of brook trout em- bryos from the time of hatching to the absorption of the yolk sac 44-60 Bittner, L. H., Johnson, G. R., and Torrey, H. B. The earthworm and the method of trial 61-65 Hubbert, Helen B. Elimination of errors in the maze. . . . 66-72 McDermott, F. Alex. Note on the reaction of the house- fly to air currents 73 _ 74 Financial statement for 1914 Number 2, March- April Coburn. Charles A., and Yerkes, Robert M. A study of the behavior of the crow Corvus Americanus And. by the multiple choice method 75-114 DeVoss, J. C, and Ganson, Rose. Color blindness of cats, 115-130 Vincent, Stella B. The white rat and the maze problem. II. The introduction of an olfactory control 140-157 Cole, L. W. The Chicago experiments with raccoons. . . . 158-173 Number 3, May-June Vincent, Stella B. The white rat and the maze problem. III. The introduction of a tactual control 175-184 Yerkes, Robert M., and Coburn, Charles A. A study of the behavior of the pig Sits scrofa by the multiple choice . method 185-225 Schwartz, Benjamin, and Safir, S. R. Habit formation in the fiddler crab 226-239 Rau, Phil. The ability of the mud-dauber to recognize her own prey (Hymen) 240-249 (JHo b CONTENTS iii Hargitt, Charles W. Observations on the behavior of butterflies 250-257 Yerkes, Robert M. The role of the experimenter in com- parative psychology 258 Number 4, July-August Walton, Arthur C. The influences of diverting stimuli during delayed reaction in dogs 259-291 Barber, Alda Grace. The localization of sound in the white rat 292-31 1 Hunter, Walter S. The auditory sensitivity of the white rat 3 I2 -329 Dodson, J. D. The relation of strength of stimulus to rapidity of habit-formation in the kitten 33 ~336 Turner, C. H. The mating of Lasius nigcr L 337~340 Number 5, September-October Mast, S. O. The behavior of fundulus, with especial refer- ence to overland escape from tide-pools and locomotion on land 341-350 Sturtevant, A. H. Experiments on sex recognition and the problem of sexual selection in drosophila 35 I- 366 Vincent, Stella B. The white rat and the maze problem. IV. The number and distribution of errors — a com- parative study 36/-374 Redfield, Elizabeth S. P. The grasping organ of Dendro- cocluni lacteum 375 - 38o Essenberg, Christine. The habits and natural history of the backswimmers Notonectidae 381-390 Shepherd, W. T. Some observations on the intelligence of the chimpanzee 39 x -396 Essenberg, Christine. The habits of the water-strider Gcrris remiges 397 _ 4° 2 Yerkes, Robert M. Maternal instinct in a monkey 403-405 Hunter, Walter S. A reply to Professor Cole 406 Number 6, November-December Holmes, S. J. Literature for 1914 on the behavior of the lower invertebrates 407~4 I 4 iv CONTENTS Turner, C. H. Literature for 1914 on the behavior of spiders and insects other than ants 415-445 Vincent, Stella B. Literature for 1914 on the behavior of vertebrates 446-461 Thorndike, E. L., and Herrick, C. Judson. Watson's " Behavior " 462-470 Herrick, C. Judson. Dunlap's " An Outline of Psycho- biology " 471-472 Hunter, Walter S. Hachet-Souplet's " De l'Animal a l'Enfant 473-474 Hunter, Walter S. Kafka's " Einfiihrung in die Tiers- psychologie " 475-479 Rahn, Carl. Cesaresco's psychology and training of the horse 480-481 Subject and Author Index VOLUME 5 Original contributions are marked by an asterisk ( lexander, C. P. Biology of flies, 441. Allee. W. C. Reactions of isopods, 407, 413, * Amphibians, literature on, 449. Andrews, E. A. The Bottle- Animal- cule, 408, 413. *Ant, mating in, 337. f Ape. intelligence of, 391. * Association, literature on, 440. Aubin, P. A. The buzzing of diptera, 436, 441. R ack. Life history of melon-flv, 441. Banta, A. M. Sex recognition in frog, 454, 460. *Barber, A. G. Audition in rat, 292. Basset, G. C. Habit formation in rat, 456, 460. Baumberger, J. P. Longevity of in- sects, 438, 441. Baunacke, W. Function of statocyst, 408, 413. Becker, G. G. Migration in Seiara, 433, 441. Beutel-Eeepen, v. Senses of bees, 416, 441; ancestry of bees, 428, 441. Bingham, H. C. Definition of form, 446, 460. *Bird, literature on, 450. *Bittner, L. H. Habit in earthworm, 61. Bloeser, W. Life history of Siphona, 429, 441; a parasite of Siplwna, 435, 441. Boving, A. Larva of Hydroscapha, 441. Branch, H. E. The biologv of Entyla, 427, 441. Bromlev, S. W. Food of asilids, 429, 44i. Browne, F. B. Life history of beetle, 441. Buddenbrock. W. v. Orientation of crab, 408, 413. ^Butterfly, behavior of, 250. Cameron, A. E. Biology of leaf- miner, 441. Campion, H. Dragon flies, 429, 441. Carr, H. Selection in animal learning, 459, 460. *Cat, color-blindness in, 115; *habit formation in, 330. Cesaresco, E. M. " Psvchologv of Horse," 480. Chapman, T. A. Life history of Agri- ades, 442. "Chimpanzee, intelligence of, 391. Coad, B. R. Behavior of boll weevil. 429, 442. *Coburn, C. A. Behavior of crow, 75 ; *behavior of pig, 185; behavior of crow, 450, 460. *Cole, L. W. Experiments with rac- coons, 158; *reply to, 406. Comstock, A. B. Cricket music, 436, 442. Cowles, E. P. Reactions of starfish, 408, 413. *Cral). tiddler, habit in, 226. Craig, W. Doves reared in isolation, 454, 460. *Crow, behavior of, 75. Cummins, H. A mite in the cat, 435, 442. Davidson, J. Habits of Aphis, 439, 442. ^Delayed reaction, in dog, 259. Demuth, G. S. Temperature of honey cluster, 438, 443. *DeVoss, J. C. Color-blindness in cat, 115. Dice, L. R. Movements of daphnia, 408, 413. Disease, relation of insects to, 434; *spreading, literature on, 434. *Dodson, J. D. Habit formation in kit- ten, 330. *Dog, delayed reaction in, 259. Draper, B. M. Box for insects, 440, 442. *Drosophila, sex recognition in. 351. Dunlap, K. " Psychobiology," 471. VI INDEX "Duration of life, literature on, 438. Dyer, H. G. Life history of caterpil- lar, 442. "[7 arthworm, habit formation in, 61. *Eisenberg, A. M. Color vision of ring- dove. 25. Emery, W. T. Biology of Simulium, 429, 442. "Essenberg, C. Habit in backswimmers, 381; "habit in water-strider, 397. Ewald, W. F. Light reactions of in- vertebrates, 409, 413. Fabre, J. H. The mason-bee, 426, 442. Fasten. X. Fertilization in the cope- pod, 409, 414. Ferton, C. Instinct of bee, 442. "Fish, behavior of, 44, 341. literature on, 449. *Fly, reaction of, 73. Frevtag, F. Vision in animals, 449, *460. Frohawk, F. W. Sleeping attitude of butterflies, 439, 442. Galiano, F. F. Chemotaxis of Para- mecium, 409, 414. *Ganson, R. Color-blindness in cat, 115. Gates, B. N. Temperature of bee col- ony, 439, 442. Girault, A. A. North American in- sects, 429, 442. Graham-Smith, C. 8. Flies in relation to disease, 434, 442. Guvenot, E. Behavior of fruit fly, ' 429. 442. k *T J abit, formation of, in earthworm. 11 61; *in fiddler crab, 226; *and strength of stimulus, 330 ; *in hemiptera, 381 ; *in water-strider, 397; "literature on, 453. Haehet-Souplet, P. " From Animal to Child," 473. Haempel, O. Vision in fishes, 449, 460. Haenel, II. Elberfeld horses, 458, 460. Hahn, W. L. Hibernation, 454, 460. Hamilton, G. V. Sexual tendencies in monkeys, 453, 460. Hanliam, A. \Y. Flowers and insects, 442. "Hargitt, ('. W. Behavior of butterfly, 250. Harms. B. Insects and diseases, 434, 442. Hartung, YV. J. Life history of melon fly, 428, 444. Hays, G P. Orientation of Porcellio, ' 413, 414. Headlee, T. J. Temperature, moisture, and insects, 442. *Hearing, in rat,' 292, 312; "literature on, 419, 451. Heath, E. F. Food of phalangid, 429, 442. "Herrick, C. J. Watson's " Behavior," 462; *Dunlap"s " Psychobiology," 471. Herrick, G. W. ' Apple pest, 428, 442. Herwerden, M. A. v. Vision in daph- nia, 409, 414. Hess, C. Vision in invertebrates, 409, 414. Hewitt, G. Habits of Scatophagy 42'.>. 442. "Hibernation, literature on, 4oi.. "Holmes, S. J. Behavior of lower in- vertebrates, 407. Houser, J. S. Life history of Con- wentzia, 429, 442. Howard, S. M. Honey bees, 439. 442. "Hubbert, H. B. Errors in maze. 66; time and distance in learning, 458, 460. Hudson, G. V. Memory and reasoning in wasp, 440, 442. Hueguenin, J. C. Insectivorous larva, 430, 443. Hungerford, H. B. Notes on coleop- tera, 427, 445. Hunter, S. J. Sand fly and Pellagra, 435, 443. "Hunter. W. S. Hearing in rat. 312; "reply to Cole, 406; hearing in white rat, 451, 460; "Haehet-Souplet's " From Animal to Child," 473; "Kafka's " Introduction to Animal Psychology," 475. Huxlev. J. Courtship of grebe, 454, 460. Hyde, R. B. Inheritance of length of life, 442. *T deational behavior, in crow, 75; "in pig, 185; *in dog, 259. "Insects, sex recognition in. 351; -natural history of, 3S1 ; INDEX vn •literature on, 415. "Instinct, mating, in ant, 337 ; *sex recognition, 351; *maternal, in monkey, 403 ; *mating, 426; *defensive, 429; •literature on, 453. "Intelligence, of chimpanzee, 391. "Invertebrates, literature on, 407. Isley, D. Biology of wasp, 427, 443. Jennings, A. H. Insects in relation to Pellagra, 443. •Johnson, G. R. Habit in earthworm, 61. Johnson, H. M. Form perception, -±46, 460. Jones, T. H. Life history of Lauron, 443. Jordan, H. Beflexes of Holothurians, 410, 414. Just, E. E. Habits of worm, 410, 414. Kafka, G. Animal psychology, 410, 414; " Introduction to Animal Psychol- ogy," 475. Kanda, S. Orientation of paramecium, 410, 414; geotropism of worm, 411, 414. Kellogg, C. E. Graphic maze, 458, 461. King, L. A. L. Habits of mites, 426, 443. Kolmer, W. Vision in fishes, 449, 460. Kiihn, W. Biology of snail, 411, 414. Lashley, K. S. Persistence of an in- stinct, 454, 460. Laurens, H. Reactions of amphibian larvae, 449, 460. •Learning, literattire on, 456. Lillie, F. E. Habits of butterfly, 432, 443. Lloyd, L. Insects and disease, 434, 443. Lohner, L. Death feigning in arthro- pods, 411, 414. Lovell, J. H. Oligotropism of bee, 417, 443; vision in bees, 424, 443. Ludlow. C. S. Insects and disease, 434, 443. Lund, E. J. Food of Bursaria, 411, 414. MacGregor learning acGregor, M. Learning and re- lg in mice and rats, 456, 460. Maday, S. v. Tbinking in man and horse, 451, 460. *Mast, S. O. Behavior of fundulus, 341; orientation in Euglena, 412, 414. •Mating instinct, in ant, 337. •Maze, for rat, 1, 140, 175, 367; •errors in, 66. •McDermott, F. A. Reaction of house fly, 73; vision, in insects, 426, 443. Mclndoo, N. E. Smell in insects, 421, 443. •Memory, literature on, 440. Merrill, D. E. Food of Clerid larva, 430, 443. Metalnikov, S. Choice of food by Para- mecium, 412, 414. •Method, maze, 1, 140, 175, 367; *in comparative psychology, 258. •Migration, of fundulus, 341. Moekel, P. The Mannheim dog, 457, 460. •Monkey, maternal instinct, in, 403. Morgulis, S. Hearing in dog, 451, 460; Pawlow's theory of nerve functions, 459, 460. Muir, F. Insect parasitism, 435, 443. •Multiple choice method, for crow, 75 ; •for pig, 185; Murphv, R. C. Reactions of spider, 443. 'N atural history, of wasp, 240; •of backswimmer, 381. ^Nicholson, C. Respiration of insects, 443. Noyes, A. A. Biology of trichoptera, 432, 443. 'Kane, C. Experience with insectary, 440, 443. Orton, J. H. Food-taking mechanisms, 412, 414. Palmer, M. A. Life history of lady beetle. 429, 443. ^Parasitism, literature on, 435. Parker, J. R. Life history of root louse, 443. Pax, F. Natural history of actinians, 412. 414. Peairs, L. M. Temperature ana insect life. 438, 444. Pearl, R. The brooding instinct, 455, 460. Vlll INDEX Pearse, A. S. Habits of fiddler crab, 412, 414. Pemberton. Life history of melon fly, 441. Phillips, E. F. Temperature of honey cluster, 438, 443. *Phototropism, in earthworm, 61. Pieron, H. Thinking animals, 458, 460. *Pig, behavior of, 185. Poulton, E. B. Marriage in wasp, 444. Powers, E. B. Reactions of crayfish, 412, 414. Putter, A. Sensibility of protozoans, 413, 414. •R. .accoons, experiments with, 158. *Rahn, C. Cesaresco's " Psychology of Horse," 480. *Eat, reactions to maze, 1, 140, 176, 367; •hearing in, 292, 312. *Rau, P. Behavior of wasp, 240. Ran, P. and N. Longevity of moth, 438, 444. Reasoning, in wasp, 440, 442. *Redfield, E. S. P. Grasping organ in dendrocoelum, 375. Regen, J. Sex behavior of cricket, 436, 444. Rilev, W. A. Insects and disease, 434, "444. *Ring-dove, color vision in, 25. Risser, J. Smell in amphibians, 452, 461. Robertson, C. Oligotrophy of bee, 416, 444. Rogers, St. A. Scent of butterflies, 444. Oafir, S. R. Habit in crab, 226. Sanderson, E. D. Temperature and in- sect life, 438, 444. Schinz, J. Learning and relearning in mice and rats, 456, 460. Schmidt, P. Catalepsy in Pliasmides, 444. Schroeder, C. The reckoning horses, 458, 461. "Schwartz, B., Habit in crab, 226. Schwarz, E. Hearing in moths, 419, 444. Severin, H. H. P. and H. C. Reactions of fruit-fly, 415, 444. *Sex recognition, 351. Shannon, R. C. Habits of Tachimdae, 444. bnarp, R. G. Nervous system of in- fusoria, 413, 414. Shelford, V. E. Evaporation and in- sect behavior, 439, 444; modification of behavior, 452, 461; animal community, 433, 444. ^Shepherd, W. T. Intelligence of chim- panzee, 391; hearing in cats, 451, 461. Sherman, A. Feeding humming birds, 455, 461. •Smell, in rat, 140; •literature on, 421, 452. *Sound production, literature on, 436. *Spiders, literature on, 415. Strand, E. Nest of wasps, 427, 444. Strong, R. M. Behavior oi Herring- gull, 456, 461. •Sturtevant, A. H. Sex recognition in drosophila, 351. Szymanski. J. S. Habit formation in rat, 447, 461. Tashiro, S. Reactions of isopods, 407, 413. *Thorndike, E. L. Watson's - Be- havior," 462. *Torrev, H. B. Habit in earthworm, 61. orientation of Porcellio, 413. 414. *Touch, in rat, 176. Tower, D. G. Life history of Prose- paltella, ^4l. Triggerson, C. J. Courtship of Dryo- phanta, 426, 444. *Tropisins, literature on, 415. •Trout, behavior of, 24. Trowbridge, C. C. Flocking habits of birds, 455, 461. Tugman, E. F. Vision in sparrow, 450, 461. ^Turner, C. H. Mating in ant, 337; •behavior of spiders and insects, 415; hearing in moths, 419, 444. Tyler, W. M. Nest life of brown creeper, 456, 461. u rban, C. Life history of Kaefer, 444. Venerables, E. P. Food habits of saw-fly, 430, 444. •Vertebrates, literature on, 446. *Vincent, S. B. White rat in maze, 1, 140, 175, 367; •behavior of vertebrates, 446. *Vision, of rat, 1 ; *color, in ring-dove, 25; •color-blindness, in cat, 115; INDEX IX in invertebrates, 400, 414; "literature on, 424. Wadsworth, J. T. Life history of gall-fly, 444. * Walton, A. C. Delayed reaction in dog, 250. Wardle, R. A. Life history of Zen- tilla. 444. '""Wasp, behavior of, 240. Waterson, J. Bird lice, 4:50. 444. *Water-strider, habits of, 397. Watson, J. B. Circular maze with camera lucida, 45!>. 4til ; " Behavior." 402. "Webster, R. L. Life history of Cono- trachelus, 434, 445. Weiss, H. B. Pain in insects, 416, 445; eggs of Paratenodera, 427, 445. Welch. P. S. Life history of Hydro- myza, 420, 445. Wevland, If. Chemotaxis oi Colpi- ' (limn. 413, 414. *White, Xi b/0 s 3 5 4 1 2 3 3 3 4 1 1 1 2 1 2 2 3 2 2 3 4 5 2 6 1 4 8 5 5 2 5 5 4 7 5 2 3 10 6 1 10 10 10 10 6 9 6 r g Date 7Mar. 3 Gen 5 " 4 " 6 " 7 " 4 " 9 " 3 " 10 " 5 " 11 " 2 " 12 " 2 " 13 " 2 " 14 " 1 " 16 " 5 " 17 No j 4 " 18 " 4 " 19 " 4 " 20 " 3 " 21 " 4 " 23 No i 3 " 24 " 3 " 25 " 2 " 26 " 3 " 27 " 3 " 28 " 2 " 30 " 6 " 31 " 5Apr. 1 Gen. 8 " 2 " 4 " 3 " 9 " 4 " 6 " 6 " 2 " 8 " 5 " 9 " 5 " 10 " 8 " 11 " 5 " 13 " 5 " 14 " 6 " 16 " 3 " 17 " 5 " 18 " 8 " 20 * 7 " 21 " " 23 " 4 " 24 " 9 " 25 " " 27 " " 28 " " 29 " " 30 " 4May 1 " 1 " 2 " 4 " 2 " a 4 it It g u u n a it U « )ove Nu Condi . ilium it it u ii it it mber 2, tions & -t-J H "So 2 2 2 2 2 2 2 2 2 1 2 2 1 2 1 2 1 5 4 4 4 5 5 5 6 7 4 6 4 4 5 6 5 5 5 7 4 7 3 10 5 9 6 9 5 6 10 10 10 9 8 5 G 2 3 3 3 3 3 3 3 5 3 3 4 3 " 4 ii " 7 it " 9 u " 10 u " 11 u " 12 u it " 13 It it " 14 ll a " 16 ll ?en. illui a it it it ii ti ti it ?en. ill., it it U ll ll ll ll ll ll It ll It a it ilium n " 17 gen. ilium it ii u it n it ii ii gen. ill., el it it ti it ti it ii it u ii gen. ilium. ti it . ilium. . . . tt ■ 18 3 4 3 4 3 4 5 6 6 6 5 5 5 4 3 6 4 6 6 5 4 5 5 5 3 6 3 7 5 1 4 1 5 4 n " 19 " 20 " 21 elect, stim. a it it ti it ti it it ti ti ti ti it ti " 23 " 24 " 25 " 26 " 27 " 28 " 30 " 31 lect. it it stim. tt it it it ii Apr. 1 ii " 2 it " 3 it it " 4 it it " 6 it u " 8 ti a " 9 it u " 10 it u " 11 u u " 13 ti it « 14 it it " 17 it u " 18 it ti " 20 u ti " 21 it it " 23 ii it " 24 it ti " 25 u it " 27 ti it " 28 it a " 29 u u " 30 ti ti May 9 ti ii " 11 ii it " 14 ti ii a it l u 2 it 5 34 ROBERT M. YERKES or not, and it is indicated that in a few series of observations the conditions of illumination were mixed, that is, for some of the reactions general illumination was employed, whereas in others it was lacking. Throughout the regular experiments the electric stimulus was employed. On April 17th, as is indicated, the intensity of the visual stimulus was lessened, thus dimin- ishing the difference in the stimuli to be distinguished. Table 3 presents the comparable results for doves number 1 and number 2. The chief difference in the conditions for these results and those obtained with doves numbers 3 and 4 is the absence of the electric stimulus in the case of the former. With the exception of one week, March 23rd to March 28th, Mr. Eisenberg trained number 1 and number 2 to achromatic dis- crimination on the basis of food as a reward without the use of the electric shock as punishment for mistakes. His results, therefore, may be compared with those of the writer, with a view to discovering the value of punishment as contrasted with reward in this experiment with ring-doves. Such comparison indicates, in the first place, that it is pos- sible to make a larger number of observations per series with punishment than without it. Thus, the writer by the aid of the electric stimulus was able to make ten, fifteen or even twenty observations per series. Whereas, Mr. Eisenberg, without the electric stimulus, could not satisfactorily make more than ten observations, and during a considerable portion of the training he made only five. Second, the time required for the work varied much more widely when punishment was not used than when it was used. As appears from tables 2 and 3, all of the doves acquired the ability to discriminate with a reasonable degree of certainty, and to react appropriately. The course of habit formation in case of each of the four subjects is surprising. Instead of being steady, regular, and fairly rapid, as the writer had anticipated, it proved to be irregular and extremely slow. One day the experimenter would feel confident that his subjects were acquiring the habit, and the next day he would find them utterly unable to react properly. In table 4 the choices are presented by groups of fifty, and the course of habit formation is indicated with the daily varia- tions eliminated. This table shows that as the result of three hundred trials, no one of the four doves had acquired the ability A STUDY OF COLOR VISION IN THE RING-DOVE 35 TABLE 4 Reactions in Light-dark Training Grouped in Fifties to Show Slowness of Improvement and Irregularities Dove 1, J 1 Dove 2, c? Dove 3, 9 Dove 4, tf Right Wrong Right Wrong Right Wrong Right Wrong 1 -50 18 32 18 32 32 18 27 23 51-100 18 32 20 30 23 27 29 21 101-150 22 28 21 29 23 27 35 15 151-200 23 27 28 22 25 25 25 25 201-250 20 30 25 25 27 23 22 28 251-300 25 25 26 24 30 20 29 21 301-350 37 13 36 14 34 16 34 16 351-400 36 9 41 9 41 9 46 4 401-450 27 8 38 12 47 3 451-500 30 5 33 2 to react properly. Between the three hundredth and the four hundredth trials, all of them, however, showed marked im- provement. Were it not that two experimenters were involved and the conditions of observation thoroughly controlled, it might fairly be suspected that the doves finally discovered some other basis for reaction than the difference in the intensity of illumi- nation. We are convinced, however, that this was not the case and that the results satisfactorily prove that the ring-dove is extremely slow, under the conditions described, in learning to react appropriately to achromatic stimuli, even though they differ very markedly. It must be admitted, however, that there are certain features in table 3 which are puzzling. Number 1 discriminated perfectly on April 23rd, and number 2 on April 24th, whereas on both the preceding and the following days they did poorly. This suggests to the writer that they had happened upon some means of choosing other than that intended by the experimenter. From a careful comparison of the data of tables 2, 3, and 4, it is clear that by the use of the electric stimulus, it is possible to develop a visual discrimination habit in the dove much more quickly, and consequently with less labor, than by the employ- ment of the food getting desire alone. All of the foregoing observations are merely preparatory to the work with chromatic stimuli. It therefore seems unneces- 36 ROBERT M. YERKES sary to burden the reader with further details of conditions or results, except possibly with respect to the general illumination and its relation to the reactions. In some of the series, general illumination was not employed, and it was naturally apparent that the doves could distinguish the stimuli much more easily than when the surroundings were illuminated. It was deemed desirable to use general illumination in order to guard against choice on the basis of the visibility of the sides and floor of the stimulus chambers, for naturally enough, this differed greatly in the light and the dark chambers in the absence of general illumination. On the whole, it seemed very much more satis- factory to conduct experiments in the general illumination pro- duced by a two candle power frosted carbon incandescent lamp, at a distance of 110 cm. above the center of the partition be ween the stimulus chambers. As an aid to rapid reaction, the alleys of the experiment-box were kept dark except at the moment of entrance of the dove. In each alley was placed a low-power lamp which could be turned on the instant the door F was raised, and turned off the instant the door H was opened. This served to induce the dove to enter the alley- way and to hasten through it to the food-box. After a few daily series, the birds made the trip quickly and volun- tarily, seldom loitering in the passageways and usually passing from entrance chamber to discrimination chamber rapidly. The food placed in the entrance chamber as a motive for return to that portion of the experiment-box was milk-soaked bread, with a small quantity of cracked corn added. During a large portion of the series, the birds ate little, unless they were practically deprived of food while in the living-cage. It is thus fair to say that the process of habit formation in the case of doves 3 and 4 depended almost solely upon punishment, whereas the process in the case of birds 1 and 2 depended solely upon reward. As in the writer's previous use of punishment, the induced current was used by means of a Porter inductorium with a number 6 Columbia dry cell as source of current. In the early experiments, no attempt was made to keep the feet of the birds moist, and as a consequence, the secondary coil had to be placed well over the primary. Its position was varied somewhat from A STUDY OF COLOR VISION IN THE RING-DOVE 37 day to day, but in general it was placed at 1 cm. for the female and at 3 cm. for the male. This, of course, means that the male responded to a very much weaker electric stimulus than did the female, but it is probable that this indicates not so much a difference in sensitiveness to the stimulus as the result of differ- ence in weight, for the male bird was much heavier than the female. During March it was found difficult to get satisfactory responses, even when the maximum current was used, and the experimenter finally hit upon the device of placing a square piece of moist blotting paper before the food-box in the entrance chamber. This was found to yield very satisfactory results. The secondary now had to be set at 2 cm. for the female and 2\ for the male. The settings proved satisfactory throughout the remainder of the work, and whereas previously the responses to the electric stimulus had varied extremely, they subsequently were very constant. RESULTS WITH CHROMATIC STIMULI Doves 3 and 4, having been trained to practically perfect discrimination of a bright area from a dark area of the same size, were tested for preference of spectral red and green. The value of the red stimulus was 626 to 640/*/^, while that of the green was 498 to 510/*/*. In energy, as measured by the selenium cell, the red stood slightly above the green, but they were so nearly the same that it seemed needless to attempt to equate them more closely for these preliminary experiments. Table 5 presents in summary the results of the chromatic reactions of doves 3 and 4. From this table it appears that on April 21st, when given an opportunity to choose either the red or the green chamber, without punishment, number 3 chose the one as often as the other, whereas number 4 chose the red eight times, the green twice. On April 22nd, in the absence of general illumination and with a period of two minutes for darkness adaptation before the series was commenced, the results were entirely different, for number 3 selected the green nine times out of ten, while number 4 chose it five times out of ten. On the following day, the original conditions of April 21st were reinstated and the responses were similar to those of that 38 ROBERT M. YERKES date. On April 28th, by the elimination of general illumination, darkness adaptation was effected, and the results again, as on April 22nd, favored the green. TABLE 5 Results of Experiments with Chromatic Stimuli Dove Number 3, 9 Dove Number 4, tf Date Conditions T3 4J Date Conditions 13 c « o « 6 Apr. 21 Preference for Apr. 21 Preference for a 22 red or u u green 5 1 5 9 u 22 red or ii a green ii 8 5 2 5 a 23 (darkness a it 3 adaptation) a 3 7 a 23 (darkness adaptation) ii ii ii 7 3 u 28 (gen. ilium.) 11 11 It (no gen. ilium.) 4 6 a 28 (gen. ilium.) ii ii ii (no gen. ilium.) 5 5 Apr. a 29 30 Red-black training. . . II u 11 16 9 4 Apr. 29 30 Red-black training. . . ii ii 18 12 2 8 May 1 a u 13 7 May 1 ii ii 18 2 u 2 a a 13 7 i< 2 ii ii 19 1 u 3 a u 10 10 it 3 ii ii 20 tt 4 it a 17 3 it 4 a ii 20 tt 5 a u 18 2 it 5 ii ii 17 3 u 6 a a 17 3 H 6 ii it 19 1 tt 7 a u 19 1 ii 7 a ii 19 1 a 8 a u 18 2 a 8 ii it 17 3 May « 9 Red-green training. . . 10 14 10 6 10 May 9 Red-green training . . . 10 16 20 4 it 11 it a 10 10 ii 11 a u 15 5 U 12 a a 13 7 « 12 a II 16 4 a 13 11 a 15 5 u 13 ii II 15 5 a 14 a it 13 7 tt 14 ii 11 13 7 a 15 it a 14 6 II 15 ii 11 17 3 u 16 u tt 14 6 II 16 it II 13 7 a 17 u tt 14 6 II 17 !! II 16 4 a 18 a tt 13 7 II 18 11 II 15 5 tt 19 a it 16 4 II 19 II II 18 2 u 20 a tt 16 4 II 20 11 II 18 2 tt 21 a u 15 5 II 21 II II 19 1 a 22 a tt 17 3 II 22 Ii II 19 1 tt 23 u tt 14 6 II 23 11 II 14 6 tt 24 u tt 14 6 II 24 11 II 16 4 a 25 u n 18 2 II 25 II II 17 3 11 26 a it 18 2 II 26 II II 18 2 u 27 » u 20 II 27 II II 18 2 tt 28 a tt 20 II 28 II II 20 From these four series of ten reactions with doves numbers 3 and 4, it may be inferred that under the condition of general illumination in which these doves had been trained to distin- guish the light stimulus patch from the dark and to react posi- A STUDY OF COLOR VISION IN THE RING-DOVE 39 tively to the lighter of the two, the spectral red and green stimuli appeared of about the same intensity to the female dove, whereas to the male, the red appeared the more intense. One naturally infers that both birds, as a result of their previous training, would go to the stimulus patch which appeared the lighter of the two, supposing that an appreciable difference existed. The series of observations on April 22nd and 28th with darkness adaptation indicate that green appeared considerably lighter for both birds than without adaptation. Green was chosen more frequently by number 3 than by number 4, apparently because the two stimuli were of more nearly the same value in general illumination for this bird than for the male. From these few observations, and naturally only a few obser- vations could be made of preference, we may conclude that spectral red and green stimuli of approximately the same energy values did not appear markedly different to the female dove in general illumination, whereas without general illumination the green seemed the more intense. For the male, on the contrary, the red seemed somewhat more intense than the green, and darkness adaptation rendered the two of practically the same intensity. Hess 4 has already demonstrated the Purkinje phenomenon in chickens and doves, by a method radically different from that of the writer, while Lashley 5 has more recently demonstrated it in the game bantam by the method of this investigation. There seems to be no reason for doubting that the observations described above also constitute a satisfactory demonstration of the modification of stimulating value by adaptation. A series of observations was now instituted, beginning on April 29th, on the development of the ability to distinguish red from black and of the habit of reacting positively to red and negatively to black. Supposing that red appeared light and black dark, it would seem that both doves, merely as the result of their light-dark training with colorless stimuli, should select red uniformly and avoid the black. The results, however, as they appear in table 5, do not wholly justify this expectation. 4 Hess, C. Untersuchungen iiber das Sehen und uber die Pupillenreaction von Tag- und Nachtvogeln. Archiv. fur Augenheilkunde, 1908, Bd. 59, S. 143. . Vergleichende Physiologie des Gesichtssinnes. Jena, 1912, Bd. 4, S. 9. 5 Watson, J. B. Behavior. New York, 1914, p. 350. 40 ROBERT M. YERKES Instead, they seem to indicate that for the female dove, the red was so dark that it tended to be confused with the black, or at least was not accepted as the equivalent of the light area which the bird had previously learned to choose. In this red-black training, it was possible to give each dove twenty trials in succession. As a result of one hundred and forty trials, number 3 was reacting properly ninety per cent of the time. Curiously enough, the male, number 4, chose the red eighteen times out of twenty in his first series, and showed throughout his reactions, in the red-black training, ability to respond to these two stimuli much as he had to the light and dark achromatic stimuli. This is, of course, wholly in agree- ment with the results of the preference tests, which clearly indi- cated that the red stimulus for some reason possessed a higher stimulating value for the male than for the female. It is, of course, impossible to say, on the basis of the red- black results, that either bird responded to the chromatic differ- ence instead of to the intensity difference of the stimuli. It is doubtless safer to assume that the latter alone was the basis of choice. Beginning on May 9th both doves were presented with the red and green stimuli which on April 21st had been offered as a basis for preference reactions, with the difference that now they were required to choose the red and to avoid the green on penalty of electric stimulation. Again, each daily series con- sisted of twenty successive trials. The female exhibited, at first, slight ability to distinguish the two stimuli and to respond appropriately, but after three hundred and eighty trials, she was reacting perfectly. The male, on the contrary, reacted perfectly even from the first, his second series of twenty trials including no mistakes. It is thus fairly clear that he responded to the intensity difference of the two chromatic stimuli, and it seems wholly probable, in view of the gradual development of the habit, that she also acquired the ability to respond to the same difference. From these preliminary observations, it seems safe to con- clude that for the ring-dove a red and a green from the spec- trum of the carbon arc, of the wave lengths designated above, and of approximately the same energy, as measured by the selenium cell, are sufficiently unlike in stimulating value to be A STUDY OF COLOR VISION IN THE RING-DOVE 41 readily distinguished by certain individuals and with difficulty by others. The particular results in hand suggest that the red has a higher stimulating value for the male than for the female. The next step in the experiment would naturally enough have been observation of the responses of the subjects to varied energy values (intensities) of the two chromatic stimuli. Un- fortunately, the investigation had to terminate at the end of May and the laborious preparation for these final observations was unavoidably wasted. The writer had fully expected and hoped, within the period of six months at his disposal when the investigation was undertaken, to ascertain whether the ring- dove can distinguish a red from a green stimulus throughout a wide range of energy or intensity values. This he did not suc- ceed in doing, and consequently this report must be entitled ' Preliminaries to a study of color vision in the ring-dove." The principal conclusions w T hich may safely be drawn from these observations have been suggested in the course of the presentation, but by way of summary and review, they may be enumerated here. 1. It is fairly obvious that the ring-dove is not sufficiently docile to be an ideal subject for the study of color vision by means of the method which Watson and I have developed. 2. It is indicated that the value of a certain red and a certain green may be very different for two ring-doves, and it is pos- sible that this difference is correlated with sex, the red having a higher stimulating value for the male than for the female. 3. As has already been demonstrated by the writer in the case of a number of animals, the use of the electric stimulus as a means of compelling attention to an experimental situation and of promoting habit formation is desirable in work with the ring-dove. 4. Ring-doves differ markedly in temperament. The pair used by the writer throughout this work presented differences which must be considered if one is to understand the results. To begin with, the ♦male was somewhat wild, but at the same time fairly bold, whereas the female was tamer but more timid. Be- cause of this contrast in timidity, the male almost from the start proved the better subject. He was not so easily disturbed or distracted, reacted therefore more steadily, and chose more certainly. With constant handling he became quite as tame as 42 ROBERT M. YERKES the female and lost almost entirely his timidity in the apparatus. She, however, continued to be rather timid throughout the sev- eral months of work, although she was perfectly tame. The differences in the nature of the reactions, as recorded in the experimenter's record-book, can be appreciated only in the light of these temperamental facts. The sex contrasts indicated in the above paragraphs one dare not emphasize very strongly on the basis of observations on two individuals, but they at least suggest the desirability of further study of the sexes. It is the writer's opinion that they agree sufficiently closely with the results obtained in the case of other animals to justify their provisional acceptance. As has been repeatedly noted with other animals, there are good and bad days in experimental work with ring-doves, — days which are good or bad, not, so far as one may tell, because of variation in the experimenter or his manipulation of the appa- ratus, but chiefly because of variations in the condition of the subjects. The experiments described in this paper were made at about the same hour each morning, and it was quite impos- sible for the experimenter to predict the outcome of a series in the light of previous series, for the attention of the doves to the situation seemed to vary independently of any conditions or group of conditions which the experimenter could take into account. There are animals which can be relied upon to work steadily and fairly predictably. The ring-dove is not one of them. The writer has been led to reflect, because of the outcome of this series of observations, on the possible relation of the sim- plicity of the experimental situation to the results. He was compelled to devote several weeks to the establishment of a simple habit in two ring-doves, a habit which was next to value- less except as a preparation for further observations. It is natural that during this long period of preparation he should frequently wonder whether the desired end might not be gained more quickly by a different method. It seems probable that a complex situation would have proved more favorable, and that had the two stimuli varied in other respects than in intensity, the animal's attention would more readily have been directed to them and more steadily held upon them. The matter is men- tioned here because it is obviously of extreme importance to A STUDY OF COLOR VISION IN THE RING-DOVE 43 students of behavior to discover the most efficient means of developing preparatory habits in animals. In concluding this paper, the writer can not refrain from calling attention to the waste of time which results from the sacrificing of trained animals at the end of an investigation. It should be possible, through exchange, to make the same subject serve in various experiments. And different experi- menters, supposing our methods to be reasonably standardized, might study quite different problems on the basis of similar preparatory habits. Thus, for example, the doves which in this investigation have been trained to certain visual reactions, might perfectly well be employed for other forms of visual response, or even to greater advantage for studies of the relation of the central nervous system to the acquired responses. It is sug- gested, therefore, that American investigators who are actively engaged in studies in animal behavior keep in close touch and develop a system of reporting their experiments while in pro- gress, which may serve as a basis for the serviceable exchange of trained subjects. The writer happens to have on hand at the moment of writing three tame crows which are highly trained in certain modes of response. The labor of taming and training them would have to be valued at several hundred dollars. It is impossible, under present conditions, to make use of these birds, and unless some other investigator can be found who can take advantage of this preparation, they will have to be either set at liberty or otherwise sacrificed. THE BEHAVIOR OF BROOK TROUT EMBRYOS FROM THE TIME OF HATCHING TO THE ABSORPTION OF THE YOLK SAC GERTRUDE M. WHITE Zoological Laboratories, University of Wisconsin WITH FOUR FIGURES CONTENTS PAGE a. INTRODUCTION 44 b. EXPERIMENTS AND OBSERVATIONS 46 1. Hatching 46 2. Swimming movements 48 3. Reactions to mechanical jars 49 4. Reactions to touch 49 5. Reactions to current 49 6. Reactions to light 52 7. Reactions to current and light 53 8. Carbon dioxide and light 54 9. Reactions to shadows ' 55 10. Feeding reactions 55 c. GENERAL DESCRIPTION OF THE EARLY LIFE OF THE BROOK TROUT 56 d. SUMMARY 59 e. BIBLIOGRAPHY 60 A. INTRODUCTION Although certain senses of mature fishes have been carefully studied, little work has been done upon the reactions of embryos. The investigations of the adult fish have been made chiefly with reference to the senses of smell, taste, sight, and hearing. Her- rick ('03) found that some fishes possess taste buds located in the skin, by which they habitually discover their food, while other fishes have the sense of taste confined to the mouth. That the catfish has a true olfactory sense, which is distinct from gustatory, was shown by Parker ('10). The sense of hearing has also been studied by Parker ('05, '08, '11), who believes that some fishes are stimulated by sounds of slow vibration. Bernoulli ('10), on the other hand, maintains that the fishes with which he worked do not hear, but respond through tactual 44 THE BEHAVIOR OF BROOK TROUT EMBRYOS 45 and visual stimulation, when at all, to the mechanical motion of the water. The work of Paton ('07), who describes some of the reactions of fish embryos, is of particular interest. He believes that the early attempts of fish embryos to lie upon the ventral side are not due to the influence of the nervous system, but rather to the position in which they lie in the egg, and the shape of the body, combined with the propulsion of the water. Even embryos of thirteen and fourteen millimeters show a tendency to right themselves when they swim. This author found that trout embryos of fifteen millimeters often swam once or twice around a dish five centimeters in diameter, but in all fishes progression was possible long before this, even at nine or ten millimeters. Squeezing or pricking the yolk sac of the trout caused exaggerated movements in the young fish. The head was found to be less sensitive to touch than the body;* the eye in all stages examined was rather insensitive to touch. Prompt and unmistakable responses to thermal stimuli appeared at an early age. The rate of the heart beat at ten millimeters was twenty-five or twenty-eight, and at fifteen millimeters was seventy-five or eighty. Since the information concerning the reactions of fish embryos is so meagre, it seems desirable that the kinds of stimulation to which various types of fish react, and the age at which such reactions begin, should be ascertained and possible applications to economic problems considered. The present paper is an attempt to give a connected account of the life activities of the Brook Trout, Salvelinus fontinalis, from the time of hatching to the absorption of the yolk sac. The Brook Trout is usually found in clear, cold spring water, and prefers brooks or streams flowing over gravelly bottoms. It pushes from the rivers into the smaller streams, seeking the head-waters, where it rests in the deep pools and eddies. Under natural conditions it is seldom found in water over 60° F. to 65° F. The Brook Trout spawns in autumn as the temperature of the water falls. The season, which usually lasts about two months, begins earlier in the northern latitudes, in the Lake Superior region in September, or even in August, while in New York, New England, and Lower Michigan, it commences about the middle of October. The time necessary for developing the 46 GERTRUDE M. WHITE eggs is dependent upon the temperature of the water, varying from about 125 days at 37° F. to about 50 days at 50° F. The experiments here described were performed in the Zo- ological Laboratories of the University of Wisconsin. About five hundred embryos were used, eggs being obtained at the Madison Fish Hatchery, and brought to the laboratory in four different batches, so that embryos of various stages could be observed at the same time. The youngest stages were kept in a wire tray in a trough of running water (from Lake Mendota) while the older individuals were placed in glass dishes and set in running water to keep them cool. About one hundred Rain- bow Trout, Salmo irideus, of two different stages and a number of young German Brown Trout, Salmo fario, which swam freely in the trough, were kept under observation. During the experiments the temperature of the water ranged from 5° C. to 10° C. Most of the experiments were performed in a dark room, the temperature of which was usually about 19° to 20° C. The fish were handled with a feather or with a spoon made of bent wire with netting stretched across it. Al- though theie was a high rate of mortality (due to gas-bubble disease, fungi, algae which crept into the gills, and persistent handling), several of the Brook Trout survived during the whole period. All experimental data refer to the Brook Trout unless otherwise stated. This work was accomplished under the direction of Professor A. S. Pearse, for whose helpful suggestions and encouragement it gives me great pleasure to express my appreciation. B. EXPERIMENTS AND OBSERVATIONS 1. Hatching The egg of the Brook Trout is small and nearly colorless, measuring about four millimeters in diameter. The embryo, which is about three times as long as the diameter of the egg, lies curled around its yolk sac with the tip of the tail beside the head. The eyes and head are visible through the thin shell. The hatching is initiated by movements starting at the head and later extending through the whole length of the body, so that the position of the embryo in the egg is somewhat changed. Such movements continue at intervals, varying from a quarter of a minute to an hour or more, until the shell is so strained THE BEHAVIOR OF BROOK TROUT EMBRYOS 47 that a slit appears. There does not seem to be any distinction as to which part of the embryo comes out first, for in the twenty- three cases observed, eight embryos appeared head first, one tail first, and in fourteen cases the yolk sac broke through before the body. The final shedding of the egg case is sometimes brought Fig. 1. Egg of a Brook Trout shortly before hatching. Magnified six and two-third times. (Drawn by Miss Wakeman) Fig 2. Embryo hatching head first. Magnified six and two-third times about by a violent movement of the body, but in nearly all the instances observed it was a gradual process lasting from three- quarters of an hour to five or six hours, during which the initial slit was slowly enlarged by the rhythmical motions of the body and the respiratory movements. If the anterior end is to be ^Z^ Fig. 3. Dorsal view of an embryo three weeks old (15 mm.). Magnified six and two-thirds times the first to appear, the violent contraction of the embryo raises the head until the strain splits the shell far enough to free the region bearing the pectoral fins, which immediately begin to move. The front of the head soon follows. Whether the tail or the yolk sac comes out first, the length of time required is 48 GERTRUDE M. WHITE nearly the same, and the details of the process differ very little. Unless the animal is disturbed, it may lie quiet for hours while the egg case slips off, but if the fish is jarred, a violent contrac- tion almost invariably results, thus hastening the loss of the egg case. In nature, where there are great numbers of fish hatching simultaneously, they undoubtedly touch one another continually, shortening the time required for hatching. The Brook Trout makes its appearance as a pretty, delicate, translucent creature about twelve centimeters long. Its most conspicuous features are its enormous eyes, which occupy almost the whole head, its huge yolk sac covered with a fine network of bloodvessels leading to the heart, the beating of which can plainly be seen. Along the back is a strip of pigment extending from the head to the tip of the slender tail. Fig. 4. Lateral view of an embryo three weeks old. Magnified six and two-thirds times 2. Swimming Movements Although the Brook Trout spends most of the first six weeks of its larval life lying quietly on its side, it is perfectly capable of swimming as soon as the egg case is lost. In fact, Paton ('07), who worked on trout among other varieties of fish, states that definite progression is possible when the embryo is nine or ten millimeters long. In the present experiments, if a fish which had just hatched was suddenly touched, it would whirl round and round as if its cumbersome yolk sac formed a movable pivot. By the fourth day the movements are still rotatory, but the fish swim in larger circles and can go straight ahead for a greater distance. There is also more darting about, the tail being always the most active part of the body. The trout which is one week old (14-15 millimeters) swims in a spiral course. As the yolk sac diminishes in size, the fish is better able to control its movements. It lies upon its ventral side like an adult at the age of six weeks in most cases, and in swimming, continually darts about, turning first one way, then the other. THE BEHAVIOR OF BROOK TROUT EMBRYOS 49 3. Reaction to Mechanical Jars Possibly the first stimulus to which a developing trout reacts is that of mechanical jars. Often before the embryo has com- pletely left the shell, the shaking of the dish or currents in the water cause it to contract, and if the tail is free, to swim about with the head still encased. This sensitiveness to mechanical vibrations continues throughout the larval life. Even so slight a vibration as that caused by blowing on the water makes the fish dart about. 4. Reactions to Touch The sense of touch is well developed when the trout hatches* but it is impossible to predict what response will be given to a stimulus in any particular part of the body. Embryos in nearly all stages of development from the time of hatching until the yolk sac was lost, were touched systematically with a slender, pointed stick, and with bristles to determine whether one part of the body was more sensitive than another. I found, as Paton ('07) did, that although it is very difficult to localize the tactile areas, the head is much less sensitive than the body, and the eye is quite insensitive. Judged by such responses, the tail seems to be the most sensitive part of the body. It was found that the trout avoided a brush much more vigorously than they did a pointed stick or a single bristle. This is probably because the brush stimulates them at more points. If touched persistently the embryos swim about, turning rapidly in all directions. When they are eventually fatigued, the responses become less marked, the trout may then merely move its tail or increase the rate of movement of its fins. It may even become absolutely quiet for a time, after which the reactions take place as before. The young trout show some measure of adaptability, for they grow somewhat accustomed to being handled, and particularly in the case of the oldest fish (three months old), those which had been repeatedly picked up were slightly easier to catch than those which had never been touched. 5. Reactions to Current Since Brook Trout live in swift flowing streams, one would expect them to react to currents. In order to test this matter. a trough was constructed in which they could be tested. The apparatus was fifty inches long by two and one-fourth inches 50 GERTRUDE M. WHITE wide and three inches deep with straight sides. A piece of rubber tubing connecting with a faucet was attached to the center of one end, in such a way that a current of uniform in- tensity flowed through the whole length of the trough; at the other end, was an outlet covered with netting to prevent the loss of the fish. After testing various strengths of current, the one which brought about the greatest number of reactions was found to be that which carried carmine solution the length of the trough in half a minute. Therefore, this strength of current was used in most of the experiments. Since all tests were made in a dark room, it was a simple matter to turn on the faucet a cer- tain distance with the room in total darkness, in that way elim- inating all reactions to light. Nevertheless, since it was found that the daylight had little effect on the results, the room was not darkened for all the experiments. Nearly all stages of young Brook Trout from the time of hatch- ing to the absorption of the yolk sac were tested. Table 1 shows some of the results. TABLE 1 Showing the Reactions of Brook Trout to Current Number of ex- periment Number of fish used Age of fish Condition of light Number of fish positive Number of fish negative Number of fish indifferent Per cent of fish positive 1 2 3 4 25 25 20 20 4 days 4 days 34 days 42 days day dark day day Trout rea( 22 21 17 16 3 4 3 4 88% 84% 85% 80% Total np.rr.p.ntacfp of Rronk 'ting positi velv 84.25% The fish were placed in the trough one at a time in most cases, with right and left sides alternately toward the current before the water was turned on. The fact that the older trout showed a slightly smaller percentage of positive reactions is probably not significant, as there appears to be no difference in their reactions, except such as would be caused by their greater activity and strength. Although it is not recorded in table 1, embryos which had just been hatched were found to react posi- THE BEHAVIOR OF BROOK TROUT EMBRYOS 51 tively to current. But they were usually unable to swim more than a few centimeters, or able merely to orient themselves, owing to the size of the yolk sac. While none of the Brook Trout were persistently negative in their reactions to current, there were always a few which did not give a definite positive response. Since it was noted that a fish was sometimes carried backward farther than it was able to advance, the four embryos in experiment number two which did not react definitely- were tested later in the light, where they could be watched. One fish did not swim at all. Three fish were carried backward, but oriented toward the source of the current. They struggled to advance, but were unable to do so. Therefore, these were actually positive. Of the twenty-one which are marked positive, five were evi- dently weak; their condition somewhat resembling the three just mentioned. Since these were found on being tested in the light to be clearly positive, and on the third trial in the dark progressed decidedly toward the current, they were included with the trout which had just been observed to move definitely against the current. In order to discover whether surrounding objects affect the reaction to current, a striped paper was passed back and forth, beneath and at the sides of the glass dish containing Brook Trout about three weeks old. No reaction resulted. Brook Trout were also placed in a round glass dish set within another dish and a current of water made to run between the dishes. To this also the fish failed to react. Hence during the first few months, the sense of sight appears to have little or no rela- tion to the reaction of Brook Trout to current. This does not agree with what Lyon ('04) believed to be true regarding the fishes with which he worked. Positive rheotropism was also exhibited by a school of German Brown Trout two or three months old, that were almost invari- ably found resting or swimming about near the source of the current in the trough where they were kept. On testing Rain- bow Trout three days old, when the yolk sac is enormously large, forty or fifty per cent were observed to be positive to current, while sixty per cent were indifferent, the latter either lying quiet or whirling about without orienting themselves when stimulated. 52 GERTRUDE M. WHITE 6. Reactions to Light That young Brook Trout are negatively phototropic has been recognized by the fish-hatchers who, finding that the trout seek the dark corners, keep the troughs covered. Their phototropism, however, was tested more accurately in the following manner: A Nernst lamp was placed within a large box (75 cm. wide x 120 cm. long x 120 cm. high) blackened inside and out, and having an opening (6 cm. x 9 cm.) at one end. A narrow glass dish, 4 cm. through, containing water was placed before the hole to absorb the heat rays; at right angles to this was an oblong glass dish with rectangular sides (38 cm. long x 10 cm. wide x 8 cm. high) in which the fish were placed. Brook Trout of nearly every age, from those which had just hatched to those two months old, were placed in the dish singly or in groups and left for varying lengths of time. Table 2 shows the results. TABLE 2 Showing the Light Reactions of Brook Trout Age of trout Number of trout Strength of light Number of trout negative Number of trout positive 2 days 2 days 2 days 21 days 21 days 21 days 25 25 5 10 10 10 1.5 candle meters 2.3 candle meters 7.7 candle meters 2.3 candle meters 7.7 candle meters 16 candle meters 14 21 4 7 8 8 2 2 2 Totals 85 62 6 Totals. Number of trout indifferent 11 2 1 1 2 17 Per cent of trout negative 56% 84% 80% 70% 80% 80% 75% Per cent of trout positive 8% 20% 20% 8% Per cent of trout indifferent 44% 8% 20% 10% 20% 17% THE BEHAVIOR OF BROOK TROUT EMBRYOS 53 In the experiments tabulated the trout were placed in the center of the dish with right and left sides alternately toward the light, so as to eliminate complication from a propensity to turn toward a particular side of the body. Each fish was ob- served for five minutes. The strengths of the lights given are approximately what the fish actually encountered in the center of the dish. It may be noted that a somewhat greater percentage reacted negatively to a light 2.3 candlemeters than to a light 1.5 candlemeters. Above 2.3 candlemeters, however, the in- crease in the strength of light seems to make little difference. Brook Trout less than a week old in general react more strongly to a weak light (2.3 candlemeters) than to a strong one (16 candlemeters). With the older fish this does not seem to be true. The conclusion that young Brook Trout larvae are negatively phototropic was corroborated by other incidental observations. When a dish containing fish was placed before a window, they almost invariably sought the side of the dish away from the light. The same was true of the Rainbow Trout. In order to discover whether a Brook Trout is photokinetic, a Nernst lamp was suspended about eighteen inches above a dish containing them. When the light was first turned on, the trout darted about vigorously, many seeking the corners of the dish. After a few minutes' exposure, however, they came to rest quietly as before. The same experiment was tried with Rain- bow Trout with like results. It was observed that the raising of a window curtain suddenly allowing the sunlight to fall on a dish of Rainbow Trout, stimulated them to unusual activity for several minutes. From these experiments it is evident that Brook Trout are photokinetic and negatively phototropic. 7. Light and Current It has been shown that Brook Trout are negative to light and positive to current. It is desirable to know how they react when the two stimuli conflict. Fish-hatchers claim that when a light is placed at the head of the current, the trout go away from the light, thus reversing the usual reaction to current. In order to study this matter, the trough used for the current experiments was entirely covered except for an opening 3 cm. 54 GERTRUDE M. WHITE x 4 cm. at the end where the water entered. Opposite this open- ing was placed a Nernst lamp having an intensity of about ten candlemeters in the center of the trough. Trout about one week old were placed in the center of the trough, four at a time in most instances, since the trough was found to be large enough to hold that many without inter- ference. Their positions were noted just before the water was turned on and again five minutes later. Twenty-five Brook Trout were used. Of these twenty-three moved away from the light and two fish did not change their positions. This seems to show that Brook Trout become negative to current when a light is placed at the head of the stream. This probably means that in natural conditions, when they have to choose between shelter and cool water, they seek shelter. 8. Carbon Dioxide and Light Since an excess of Carbon Dioxide is a condition which a growing fish is likely to meet, the way in which a Brook Trout responds to it and the effect it has upon its light reactions is very important in determining whether or not the trout is to escape from the unfavorable conditions, and swim into purer water, where there is more oxygen. For the purpose of discovering the effect of an excess of carbon dioxide upon the response to light, fifty individuals were tested separately in the apparatus used for the light experiments in a five per cent solution of carbonated water. 1 The strength of the light for one-half the fish was two candlemeters, for the other half about eight candlemeters. The results of the two were similar. Almost immediately after a trout was placed in the carbo- nated water, the fins began to move more rapidly and the mouth to open and close with a gulping motion. Shelf ord ('14) de- scribes this same condition in the fish that he tested in an excess of carbon dioxide. In the present experiments, the trout were stimulated to great activity, swimming continually from one end of the dish to the other with no apparent reference to the light. They were as likely to stop at the end of the dish toward the light as at that away from it. Excess of carbon dioxide appar- ently causes the Brook Trout to be indifferent to light. 1 The solution of carbonated water was made by adding carbonated water from a siphon to the ordinary city water, which is taken from Lake Mendota. THE BEHAVIO OF BROOK TROUT EMBRYOS 55 A ten per cent solution of carbonated water was also tried, but this was found to partially anesthetize the Brook Trout in from three to five minutes, and therefore no reactions re- sulted. The young trout were able to endure a five per cent solution for two or three hours without apparent injury; at the end of such a period of time they seemed somewhat slug- gish. A two and a half per cent solution also had a stimulating effect. A twenty or twenty-five per cent solution caused all swimming movements to stop almost immediately, and made the heart beat of a trout three weeks old fall within about eight minutes from an average of eighty beats a minute to thirty-seven. Death ensued very soon after that. This was tried in several other cases with similar results. 9. Reaction to Shadows As was stated in the discussion of rheotropism, the Brook Trout three weeks old does not respond to moving objects out- side the water. This seems to be true of objects in the water also, provided they do not cause mechanical jars. This absence of reaction to shadows continues until the embryo is about six weeks old, when the greater part of the yolk sac is absorbed. At this time the trout suddenly begin to respond; the waving of a hand above the dish causes them to dart about in all direc- tions. If such a movement is made repeatedly, however, they soon become accustomed to it and cease to react for a time. The reaction to shadows is, therefore, not present at hatch- ing, but becomes apparent at the time when the yolk sac is greatly reduced in size and shortly before the feeding reactions begin. It would be interesting to know whether there is a change in the eye or the nerve connections at this period, which brings about this new response, or whether it is merely due to in- creased swimming power. 10. Feeding Reactions The feeding reactions begin when the Brook Trout are about two months old. At this time the larvae appear to develop a sudden curiosity concerning everything about them. They swim to the top more frequently and often explore the bottom. The fish studied were fed liver chopped very fine and put into the water with a dropper. For several days the trout did not appear 56 GERTRUDE M. WHITE to notice it, at least they were not observed to eat. A stream of meat juice directed against the body was avoided in the same manner as a jet of clean water. After a week or less, however, the trout began to take bits of food into their mouths as they chanced upon them and often to swallow them. From this time on they were observed to dart after pieces of meat floating about in the water, although they often rested directly upon meat lying on the bottom without appearing to pay any attention to it. They were also seen to chase bubbles and bits of filter paper, and to take them into their mouths, but they never swallowed them. The fish were fed in dishes with black or white bottoms. The trout were found to take food more eagerly from the dishes with black bottoms where the food was more plainly visible, although they would also eat pieces of meat over the white backgrounds. This fact is made use of by the fish-hatchers who feed the larvae in blackened troughs. In order to discover what part is played by the chemical sense in helping the Brook Trout to find its food, a bag con- taining meat was placed in the water; this was nosed by the trout and one fish bit at it. At other times two bags, one with food and one without it, were set in the dish. The trout inves- tigated both bags, but they bit at neither. They were appar- ently unable to discover meat hidden under a paper in the bottom of the dish. Although they wandered over it as they swam about, it was not noted that its presence had any effect upon the fish. The Brook Trout apparently first react through sight to the presence of food, since they were often observed to leave pieces of meat near them to dart after bits farther away, which would not be the case, were it the chemical sense which was most strongly stimulated. The gustatory sense appears to determine whether or not the food is swallowed. C. GENERAL DESCRIPTION OF THE EARLY LIFE OF THE BROOK TROUT Let us follow a developing Brook Trout on the pebbly bottom of a swift flowing stream. During the first six weeks of its existence it does not move far from the spot where it was hatched, but lies quietly in the shadows among the stones, out of sight of its enemies. It is not affected by objects passing over head. THE BEHAVIOR OF BROOK TROUT EMBRYOS 57 If someone throws a stone into the water the jar startles the little fish into swimming about rapidly for a few seconds, after which it sinks again into some shady nook. Here it rests, until a sudden eddy caused by an animal swimming through the water, makes it dart a few inches into the current. Other tiny fish touch and jostle it continually. If the water becomes filled with carbon dioxide, it becomes more active, and overcoming its impulse to avoid the light, swims about restlessly from place to place- until it comes into purer water, where it again sinks down beneath the stones. Thus far its responses have been largely avoiding reactions, serving to keep it from unfavorable conditions. When the trout is about six weeks old, it becomes more sen- sitive to objects outside itself. The sight of other animals pas- sing by sends it scurrying under the cover of moss and stones. Shortly after this it begins to be curious, nosing nearly every object which it sees. It swims to the top of the water in pursuit of a bubble. It explores the bottom of the stream, often swim- ming head downward, passing in and out among the rocks, stones, and algae. Many particles on the bottom or floating above are taken into the mouth. If found to be good to eat, they are swallowed; if not, they are expelled. As the fish eats, it takes food more and more eagerly until it is satisfied, when it ceases to react, and hides in the algae. Throughout its larval life the Brook Trout is reacting to external and internal stimuli, responding to nearly every cur- rent, object, or ray of light that strikes it. In general, the behavior suits the needs of the fish. As long as the trout are very young, and are encumbered with the large yolk sac, which renders them unable to swim any distance, their reactions are such as would naturally tend to keep them lying quietly out of the sight of their enemies. They exhibit no curiosity, but avoid the light, hiding beneath the rocks and stones, reacting to current just enough to keep them from being carried down stream. The trout appear not to notice external objects, except as their approach jars the fish, making them struggle to regain their equilibrium. As was previously stated, an excess of carbon dioxide renders them temporarily indifferent to light, so that they swim about restlessly until they reach a place where the water is purer. 58 GERTRUDE M. WHITE When the Brook Trout grow larger, lose the yolk sac, and become strong enough to escape their enemies by swimming away, they begin to notice moving objects inside and outside of the water. The approach of any object sends them darting about in all directions in search of a hiding place. Just before the trout are old enough to commence eating, they show great interest in every object in the water, and begin to try taking any small object from a bubble or a bit of alga to a piece of meat into their mouths, though they appear to swallow only such as are edible. From the consideration of the facts of behavior one is natur- ally led to ask what are the artificial conditions which best suit the needs and instincts of the young trout. In other words, what is the economic importance of the experiments discussed in this paper. One easily concludes from the observation of the natural conditions of Brook Trout and their reactions to current and carbon dioxide, that the first essential is cool run- ning water with plenty of oxygen. The water should be free from algae of a sort which is apt to get into the gills. If a fungus attacks the young trout, the disease spreads rapidly, unless the infected and dead fish are removed, since the fish knock against each other as they swim about. The fact that Brook Trout are so strongly negative to light seems to indicate that hatching troughs should be covered, or if the fish are in ponds or streams, that the trout should have natural covers, such as rocks, stones, or water plants, under which to hide. By living beneath these they may often escape predaceous animals which prey upon them. Since it requires nearly a week for Brook Trout to learn to eat, they should be carefully watched when they are near the feeding stage, for if they do not learn to take food before the yolk sac is entirely absorbed, they will die of starvation. Shortly before the trout are two months old, they commence to swim to the top frequently and to exhibit curiosity, which indicates that they will soon begin to eat. Meat ground or chopped very fine should then be introduced into the water, so that the fish may take particles of it into their mouths by chance, as they wander about, and thus become accustomed to it before it is necessary for them to eat. THE BEHAVIOR OF BROOK TROUT EMBRYOS 59 D. SUMMARY 1. The Brook Trout which has just hatched swims with a whirling movement. About the fourth day after hatching, the trout commences to swim in a spiral course, and from then on, the movements become gradually better co-ordinated, the trout swimming in larger circles and going straight ahead for greater distances. 2. The Brook Trout reacts to touch and mechanical jars immediately after hatching. The head is the least sensitive to touch of any part of the body, the eye being insensitive. The reaction is more marked when the trout is stimulated at a number of points, than when it is touched with a single bristle. 3. Positive rheotropism becomes apparent as soon as the trout has hatched. 4. The Brook Trout is photokinetic and negatively photo- tactic. 5. Directive light from a lamp at the source of the current reverses the usual rheotropic reaction, showing that Brook Trout are more strongly negative to light than they are posi- tive to current. 6. An excess of carbon dioxide up to a certain point stimu- lates Brook Trout; a very strong solution depresses them. A five per cent solution stimulates trout to move about continu- ally and makes them indifferent to light. Stimulation is also brought about by a two and a half per cent solution. A twenty or twenty-five per cent solution causes a rapid fall in the rate of the heart beat, then death. 7. Brook Trout begin to respond to shadows about the fifth week after hatching, when the yolk sac is greatly diminished in size. 8. Feeding reactions commence when Brook Trout are about two months old. The sense of sight seems to cause the trout to take small objects into the mouth, the gustatory sense to decide whether or not they are edible. 9. Before the yolk sac is absorbed the reactions of the young trout are protective, afterward they are exploratory and ag- gressive. 60 GERTRUDE M. WHITE BIBLIOGRAPHY Bernoulli, A. L. Zur Frage des Horvermogens der Fische. Arch. f. d. ges. 1910. Physiol, vol. 134, pp. 633-644. Clark, Frank N. The Brook Trout. U. S. Com. oj Fish and Fisheries. Revised 1900. edition, pp. 80-90. Herrick, C. J. The Organ and Sense of Taste in Fishes. U. S. Commission 1902. Bulletin for 1902, pp. 237-272. Lyon, E. P. On Rheotropism: I. Rheotropism in Fishes. Am. Jour. Physiol., 1904. vol. 12, pp. 149-170. Parker, G. H. Influence of the Eyes, Ears, and Other Allied Sense Organs on 1909. the Movements of the Dogfish Mustelus canis (Mitchill). Bull. U. S. Fisheries, vol. 29, pp. 45-47. 1910. Olfactory Reactions in Fishes. Jour. Exper. Zool., vol. 8, no. 4, pp. 535-542. Paton, S. The Reaction of the Vertebrate Embryo to Stimulation and the Asso- 1907. ciated Changes in the Nervous System. Mitteil. a. d. Zool. Stat. z. Neapel, Bd. 18. Heft 2 und 3, pp. 535-581, Taf. 23-25. Shelford, V. E., and Allee, W. C. Rapid Modification of the Behavior of Fishes 1914. by Contact with Modified Water. Jour. Animal Behav., vol. 4, no. 1, pp. 1-30. THE EARTHWORM AND THE METHOD OF TRIAL L. H. BITTNER, G. R. JOHNSON, AND H. B. TORREY Reed College, Portland, Oregon About ten years ago Jennings attempted to clarify existing conceptions of the behavior of the lower organisms by sub- stituting for what he believed to be an inadequate theory of tropisms a conception that rested on what has come to be known as the " method of trial." Tropism hypotheses have existed at various times that have differed in various respects. There is no doubt that in one respect or another, some of these hypotheses have been open to just criticism. That the method of trial affords an escape from such criticism, however, is becoming less and less apparent with the passage of time. Notwithstanding their differences, all tropism hypotheses agree in excluding the conception of orientation by trial reac- tions. Fundamental to them all is the conception of orienta- tion by means of movements that, with reference to a given source of stimulation, are predictable as to direction. However cogent, then, the criticism of a particular variety of tropism hypothesis in other respects, it can hardly affect the funda- mental characteristic which they all possess in common. Some months ago, an analysis of the behavior of Porcellio scaber showed that the method of trial was incompetent to inter- pret the orientation of this organism under photic stimulation. 1 In the present paper we shall consider the orientation, under similar stimulation, of the earthworm (Allolobophora sp.), an organism of some complexity -of structure, whose behavior has seemed to some observers to lend support to the method of trial. These critics have based their conclusions in part on observations, 2 in part on the identification of "random" with 1 Torrey and Hays. The Role of Random Movements in the Orientation of Porcellio scaber to Light. Jour. Animal Behav., 1914, 4, p. 110. 2 See especially Holmes. The Selection of Random Movements as a Factor in Phototaxis. Jour. Comp. Neur. Psych., 1905, 15, p. 98. 61 62 L. H. BITTNER, G. R. JOHNSON, AND H. B. TORREY "trial" movements, a source of confusion that has already been discussed in the paper on Porcellio to which we have just referred. The earthworm comes midway between the sow bug (Porcel- lio) and the leech in the freedom with which it bends its body when reacting to light. It has been shown 3 that the first move- ments of Porcellio after stimulation are away from the source of light. The body moves stiffly as a whole. The photoreceptors are anteriorly placed paired eyes. Holmes cites observations on the leech Glossosiphonia that show a wide range of mobility in its response to light, dependent upon its characteristic locomotion. The earthworm does not react stiffly, like Porcellio, nor are more than a very few anterior segments concerned in what- ever random movements may be observable under photic stim- ulation. Holmes was led to believe that the method or orienta- tion of the leech is, in principle, the same as that of the earth- worm. He calls especial attention to the characteristic waving of the body, preliminary to fixation of the anterior end. Our observations, however, encourage us to place emphasis on the resemblance of the reactions of the earthworm to the behavior rather of Porcellio than of Glossosiphonia. The random move- ments of the earthworm have thus appeared to us to be less significant elements in its orientation to light than the obser- vations of Holmes indicated. It is characteristic of the earthworm when advancing in dif- fused light, to protrude its anterior end first on one side and then on the other, with successive extensions, in fairly regular alternation. A distinct tendency thus exists for this end, when bent to one side, to bend to the opposite side at the next exten- sion. Mechanical causes, such as tensions in muscles and skin, are probably responsible for it. It is natural to expect evidence of this tendency in experiments on earthworms where relatively low intensities of light are employed unilaterally. Mast, indeed, asserts that in active worms, " the anterior end is simply turned sharply in the direction opposite to that in which it is when it receives the stimulus. . . . Thus it is turned toward the light about as often as from it, regardless of the light inten- sity." 4 Sluggish individuals, however, reacted quite differently. 3 Torrey and Hays, 1914. 4 Light and the Behavior of Organisms. 1910, p. 200. THE EARTHWORM AND THE METHOD OF TRIAL 63 From what we judge to have been a neutral position, six slug- gish individuals, in one hundred and fifty trials, turned toward the light in but ten of them. In certain other cases there " was no evidence of even the slightest preliminary turning toward the source of light." (P. 201.) From this evidence ours differs in that our active individuals behaved in the low intensities of light used very much like the sluggish individuals of Mast. Whatever the ultimate signifi- cance of this distinction, we have been forced to conclude, as Mast appears to have concluded, that under some conditions, earthworms respond to photic stimulation by orienting reactions that are in no sense trial or random movements. Nevertheless, in our figures, there was unmistakable evidence of that tendency which has been mentioned of the anterior end to swing from side to side. This did not appear, however, in our first series of experiments. In our first series, sixteen active individuals, taken from darkness, were each subjected to one hundred exposures in quick succession to a very low light intensity. The worm under observation crawled over a moist slate. When, in very weak diffused light, the anterior end was pointed straight forward, the light of a small pocket lamp was flashed upon it from a distance of 50 mm. at an angle of ninety degrees with the body axis. The results are shown in the accompanying table. From these figures it appears that our earthworms exhibited a marked disposition to react without trial negatively to the light used. Our second series of observations was taken under somewhat different conditions, and shows very clearly the tendency to which we have alluded above. Each of ten worms was sub- jected to a total of but thirty trials, in groups of ten. In the first ten trials, the anterior end was bent toward the light at the instant the light was flashed; in the second ten it was in a neutral position, that is, directed forward; in the third ten, it was bent away from the light. Each worm was rested for about seven minutes in darkness after each group of ten trials. A light of slightly greater intensity was used, namely, a 25 w. Mazda lamp, 160 mm. distant, so screened that the ray falling on the worm was about 8 mm. wide. In other respects, the conditions were essentially the same as in the first series. 64 L. H. BITTNER, G. R. JOHNSON, AND H. B. TORREY TABLE 1 No. of trials Direction of first movement Toward light Away from light Earthworm No. 1 100 100 . 100 100 100 100 100 100 100 100 100 100 100 100 100 100 18 22 18 28 16 26 34 14 24 28 12 32 20 21 43 34 82 2 78 3 82 4 72 5 84 " 6 74 7 66 8 9 10 86 76 72 11 12 13 88 68 80 " 14 79 " 15 57 16 66 Totals 1600 390 1210 Percentages 24.4% 75.6% TABLE 2 No. of trials Position of anterior end with reference to light Toward Neutral Away Sense of response — + + — + Earthworm No. 1 30 .. 30 9 1 8 2 8 2 10 10 10 10 10 10 10 8 2 9 1 9 1 10 1 9 1 8 2 8 2 9 1 8 2 9 1 9 1 2 9 1 3 4 5 30 32 30 30 30 30 30 30 7 3 8 3 7 3 6.. 9 1 " 1 ... 8 2 8 9 9 1 10 " 10 9 1 Totals 302 95 5 87 14 85 16 Percentages of first movements away from light 95% 86.13% 83.16% THE EARTHWORM AND THE METHOD OF TRIAL 65 Assuming now, the observed tendency of the anterior end to swing in fairly regular alternation from side to side in succes- sive extensions; and assuming, further, the tendency brought out by the figures just given, for the anterior end to swing directly away from the light; one should expect to find the anterior end swinging away from the light most frequently, in this second series, when it was turned toward the light at the instant the latter was flashed, and least frequently when it was turned away from the light at the moment of flashing. This expectation is, in fact, realized in the following figures. The light was flashed on the right of the first seven individuals, on the left of the others. The third double column of figures is especially significant, as it shows a very marked negative reaction of the worms ob- served, under the conditions of the experiment, in spite of the conflicting tendency manifested in diffused light to swing the anterior end in the opposite direction. Holmes has pointed out the danger of failing to notice certain very inconspicuous movements that might be started toward the light but not followed up. We have tried to guard against this opportunity for error. At the same time, it may be worth while to remark that a certain degree of extension of the anterior segments appears to be necessary to expose the photoreceptors to effective light intensities. Our figures seem to us to show clearly that photic stimulation, far from inducing random move- ments, immediately calls forth reactions in a definitely predict- able direction. In the face of the facts, a view based upon minute random movements that are not referable to photic stimulation can hardly affect the conclusion that the earth- worm must be placed, with Porcellio, in that group of organisms whose orientation to light is determined essentially by move- ments that are predictable as to direction and hence neither random movements nor " trials." ELIMINATION OF ERRORS IN THE MAZE* HELEN B. HUBBERT While engaged in a research problem on the learning ability of white rats at different ages, my attention was directed to the question of the elimination of useless movements in the learning of the maze. I decided to test whether or not such eliminations occur progressively, i.e., whether useless movements most closely connected with satisfaction (food) are the first to drop out, while the useless movements most remote from the source of satisfaction (food) persist the longest. The observations recorded in this paper were made on four groups of rats of different ages during their learning of the Watson maze which, with its camera lucida attachment, is described at length in a previous number of this journal. 2 The process of training and the criteria of learning were the same as those set forth in a previous paper. 3 As has been pointed out by Watson, 4 according to the pleas- ure-pain hypothesis, the inference of progressive elimination is plain.' Food (the "satisfier") is at the center of the maze. Errors in the alley nearest the food should be the first eliminated ; those in the alley next nearest, second, and so on until we reach those in the first alley (the one farthest from the food). Errors in this alley should be the ones last eliminated. An examination of the plan of the maze will show that in every alley except VI there are three possibilities of error, viz. : 1. Taking the wrong turn at the alley entrance. 2. Going too far in the alley, i.e., past the entrance to the next alley. 3. Taking the correct turn, but returning ("doubling" on the pathway) . In VI the first error is impossible because there is no stop, and either turn leads to the food box. The second error re- solves itself into a circling of the food box, which, however, 1 From the Psychological Laboratory of The Johns Hopkins University. 2 Watson, J. B. Journal Animal Behavior, vol. IV, p. 56. 3 Hubbert, H. B. Ibid, pp. 60-62. 4 Watson, John B. Behavior. Holt & Co., p. 268. 66 ELIMINATION OF ERRORS IN THE MAZE 67 rarely occurs. 5 The third error is the most common one. Start- ing to the right, the rat retraces its path and goes to the left, or vice versa. Clearly then, the sixth alley is not strictly com- parable with the others, and should not be considered. It is therefore set off from the rest in the accompanying tables. In the first alley the emotional disturbance of the animal is very great. Whether he will turn to the right or to the left is a matter of pure chance. Watson has shown that the learn- ing of the maze is due largely to the kinaesthetic and organic impulses which cannot begin to play their role very effectively until some distance has been run in the maze. 6 As stated above, the start in the first alley is as likely to be in the wrong as in the right direction. If the start is wrong increasing dis- turbance ensues, and is often carried over into alley II. 7 Aside from this fact, there is the very strong tendency to back-track to the point of entrance (E), which has a different stimulating value from any other part of the maze. It is for these reasons that the first alley as well as the sixth is judged incomparable with the rest and hence is set off from them in the tables. This leaves for consideration four alleys, II, III, IV and V. Whether the process in question is spoken of as the elimination of errors, the "stamping in" of useful movements and the "stamping out" of useless ones, or simply as the elimination of alleys matters little; the facts remain the same. The writer has chosen for convenience to speak of the elimination of super- fluous movements in an alley as the elimination of the alley itself, and the results are so tabulated. For example, Rat 4 of Group A made its last error in alley II at the 11th trial, running the alley perfectly in all succeeding trials. The alley is therefore spoken of as eliminated at the 12th trial. Likewise III was eliminated at the 8th trial, IV at the 3rd and V at the 7th trial, no errors being made in those alleys after the 7th, 2nd, and 6th trials respectively. The first column gives the laboratory number of the animal, while column 2 gives the total number of trials the animal required to learn the maze. 5 This error seldom occurs, because in passing the entrance to the food box the smell and sight of the food become directive. 6 Watson, J. B. Kinaesthetic and Organic Sensations — Their Role in the Reac- tion of the White Rat to the Maze. Psychological Monographs, Series No. 33. 7 It is not unlikely that the deviation of the results in alley II from those in III, IV and V may be explained in this way. 68 HELEN B. HUBBERT In the tables, cases which undoubtedly show uniform pro- gressive elimination, i.e., a 5-4-3-2 order, are doubly starred (**). Cases which might possibly be considered progressive are singly starred (*). Cases clearly not progressive are unmarked. TABLE I Group A— 25 Days Trials Alleys Rat I II III IV V VI 4 18 10 12 8 3 7 3 5 14 7 6 9 9 8 5 6 45 40 32 29 10 37 10 7 66 60 35 43 49 15 1 8 32 25 26 25 17 11 1 9 38 33 22 27 31 24 1 10** 28 21 22 14 8 5 9 11 18 13 12 7 2 10 5 12 32 19 27 16 17 13 1 13 46 39 38 41 13 26 1 14 24 17 17 4 3 12 2 15 34 25 13 11 1 28 4 16 27 17 14 22 5 6 1 17 26 21 13 11 6 7 19 19 40 30 33 34 30 19 5 20** 34 28 28 15 10 9 1 21 36 31 18 25 13 14 2 22 32 27 23 23 18 23 7 23 34 15 19 29 22 23 1 24 24 11 18 9 6 19 10 25 36 19 29 19 19 30 3 Totals. . 21 rats 508 457 421 293 346 92 Averages 24 22 20 14 16 4 2 cases (**) uniformly progressive or 10%, vs. 90% not progressive. 9 cases where IV and V are eliminated before II and III, or 43%. DISCUSSION OF THE TABLES Group A— 21 Rats These rats began the problem when twenty-five days old. Two of the twenty-one showed uniform progressive elimina- tion, i.e., alley V was eliminated first, alley IV second, alley III third and alley II fourth and last. We find then two cases of uniform progression and nineteen cases clearly not uniformly ELIMINATION OF ERRORS IN THE MAZE 69 progressive, i.e., ten per cent progressive versus ninety per cent not progressive. If we now count the cases where IV and V are eliminated before II and III but not in a 5-4-3-2 order, e.g., Rats 4 and 16, we find them to be nine, or forty per cent of the group, which is less than would be expected on a chance basis. If, however, instead of considering individual cases, we look at the averages, we still find no uniform progression. But here again IV and V are eliminated before II and III. TABLE II Group B— 65 Days Alleys Rat Trials I II III IV V VI 11 18 13 8 8 9 3 1 12 34 25 28 20 29 25 1 13** 22 9 17 10 3 1 7 14 22 16 15 15 3 7 1 15 28 19 12 22 9 9 3 16 36 30 17 9 31 16 8 17 36 30 25 16 2 26 7 18 66 61 47 24 54 33 5 19 32 26 18 4 2 8 3 20 36 31 20 9 12 9 4 21 46 41 36 37 8 8 6 22 21 15 13 6 6 8 2 23 38 31 22 33 29 26 1 24 38 33 30 15 24 28 1 25 14 9 4 5 9 3 1 27 40 35 29 12 9 25 3 28 20 15 9 10 5 4 1 Totals — 17 rats 439 350 255 244 239 55 Averages 26 21 15 14 14 3 1 case (**) uniformly progressive or 6%, vs. 16 cases not uniformly progressive or 94%. 5 cases where IV and V were eliminated before II and III, or 29%. Group B— 17 Rats These animals began the problem when sixty-five days old. Of the seventeen, one rat showed uniformly progressive elim- ination while sixteen did not, i.e., six per cent progressive and ninety-four per cent not progressive. 70 HELEN B. HUBBERT TABLE III Group C— 200 Days Alleys Rat Trials I II III IV V VI 6 18 12 9 4 7 9 3 7 54 48 46 40 42 35 16 8 44 39 36 33 38 24 21 9 26 13 19 5 21 5 5 10 20 15 5 4 3 4 1 11 20 13 14 4 13 11 11 15 32 27 23 23 7 20 4 17 56 50 35 22 45 19 11 18 79 71 66 30 74 29 12 19 49 44 44 18 9 15 11 20* 27 22 9 8 8 8 8 21 32 26 18 7 13 12 2 23 30 25 17 25 4 22 3 24 30 25 15 13 14 9 1 25 35 26 30 9 30 8 8 27 22 11 17 9 14 6 6 29 104 99 95 74 88 88 5 30* 108 101 98 87 87 38 22 31 64 58 45 55 23 12 1 33 32 27 15 27 24 19 5 34 22 13 15 5 13 17 17 35** 37 30 30 16 13 10 2 36 32 21 8 2 8 15 26 38 14 9 7 4 4 6 1 Totals. . 24 rats 825 716 524 602 441 202 Averages 34 29 22 25 18 1 8 1 case (**) or 4% uniformly progressive. 2 cases (*) or 8% doubtful. 21 cases or 88% not progressive. 3 cases or 13% in which IV and V were eliminated before II and III. Here we find five rats eliminating IV and V before II and III, or twenty-nine per cent. The averages show possible uniform progression, although the values for III, IV and V are too nearly identical to warrant such an interpretation. Group C— 24 Rats These rats began the problem when two hundred days old. Of them, one rat showed uniform progressive elimination, two possible progressive elimination, while twenty-one did not show ELIMINATION OF ERRORS IN THE MAZE 71 such progression. Stated in percentages, four per cent were progressive, eight per cent possibly progressive and eighty-eight per cent non-progressive. Here we find only three cases or thirteen per cent where IV and V were eliminated before II and III. The averages showed no progression; IV and V were not even eliminated before II and III. TABLE IV Group D— 300 Days Alleys Rat Trials I II III IV V VI 15 78 67 72 35 39 35 3 16 20 14 11 9 10 8 1 17 48 43 28 15 36 14 3 18 40 31 35 9 32 34 7 19 14 9 9 4 9 5 1 20** 58 45 52 35 28 27 5 21 30 25 12 6 9 9 13 22 82 77 67 47 64 66 66 24 42 37 33 26 25 28 34 25 54 49 27 37 49 49 37 26* 19 14 10 7 7 7 4 27* 70 65 61 24 24 22 24 28 38 33 24 20 6 24 5 30 27 22 16 15 8 13 6 31 84 78 32 53 72 69 69 33 16 11 8 5 2 11 3 34 66 60 60 25 26 48 27 35 38 32 20 19 20 17 9 36 26 15 15 5 15 11 21 37 44 39 29 17 13 30 5 38** 34 28 23 15 8 6 1 39** 35 5 29 23 21 11 4 Totals . . 22 rats 799 673 451 523 544 128 Averages 32 30 20 24 25 16 3 cases (**) or 14% uniformly progressive. 2 cases (*) or 9% doubtful. 17 cases or 77% not progressive. 3 cases or 14% where IV and V were eliminated before II and III. Group D— 22 Rats These rats began the problem when three hundred days old. Three of the twenty showed uniformly progressive elimina- tion, two showed possible progressive elimination, while seven- 72 HELEN B. HUBBERT teen did not show uniform elimination, i.e., fourteen per cent were progressive, nine per cent possibly progressive and seventy- seven per cent not progressive. There were three cases where IV and V were eliminated before II and III or fourteen per cent. The averages do not show progressive elimination nor were IV and V eliminated before II and III. We do find, however, in every group that alley II is nearly always the last to be eliminated. A possible explanation of this has already been offered on page 67. The results in alleys III, IV and V are so nearly identical that the three may be con- sidered as eliminated at practically the same time. From these experiments it seems fairly probable that the rapid- ity with which a given co-ordination in a complex habit is formed is not proportional to the distance from the point at which the co-ordination takes place to the point at which food is to be obtained. NOTES NOTE ON THE REACTION OF THE HOUSE-FLY TO AIR CURRENTS F. ALEX. McDERMOTT Mellon Institute, University of Pittsburgh, Pittsburgh, Pa. While making some experiments on the drying of certain vege- table materials in a current of air, the following observation was made, which may be of interest. The material had a strong attraction for flies, of which there were several in the room, and as their presence did not interfere with the work, no precautions were taken to screen them off. The apparatus consisted of a flat bottomed aluminum dish, 20 cm. in diameter, with vertical sides 8 cm. high; into this dish was blown a current of air having a volume of about one-fourth to one-half cubic meter per minute, by means of an electric hair-drier (speed equals about 100 meters per minute). The air was slightly heated, showing 29 to 30° C, when the room tempera- ture was 26 to 27° C. The air current struck the center of the bottom of the dish at an angle of 60°, passing over two 5 cm. aluminum dishes, in which the material being dried was contained. Flies alighting on the material in these dishes soon turned toward the direction from which the air was coming, walked down over the edge of the dish, on to the bottom of the large dish, and toward the point where the air current struck the bottom, usually stop- ping two or three centimeters from the center; here they would remain, with their axes parallel to the direction of the air current, and their heads facing to windward for half an hour or longer, if not disturbed. They appeared to be pressed down against the bottom of the dish by the force of the air current, quivering slightly with variations in the pressure, and they were observed not to be feeding. New comers, alighting in any other than the position above described, moved about in short jerks, until they had assumed this position. Sometimes chains of two or three, immediately back of one another, would be formed, with spaces 73 74 F. ALEX. McDERMOTT of only a few millimeters between them, though more usually they placed themselves so as to have the head in the direct air current. Those in other portions of the dish assumed posi- tions with the axis parallel to the stream lines, with the head to windward, even though they happened to be in a slight eddy current. A thermometer was placed in the dish, inclined toward the fan; a few insects climbed up this toward the fan, but the current appeared to be too strong for them. Increasing the tem- perature of the air current to 40° C. caused scattering and finally flight, though the flies seemed reluctant to go, rather attempting to back away slowly, before taking to flight. Sudden stopping of the current .of air caused immediate dispersal. While most of the insects took to flight at once on being disturbed mechani- cally, as with the bulb of the thermometer, a few of them would allow themselves to be pushed about and even pressed down tightly on the bottom of the dish, with the thermometer bulb, without taking flight. The writer believes that the observation has been made that flies lighting on moving vehicles usually turn with the axis parallel to the direction of motion, and with the head forward, but he is not aware of any observation of the kind here recorded. Unfortunately, means were not at hand to try the effect of wider and lower variations of the temperature of the air. FINANCIAL STATEMENT For the information of its subscribers, contributors, and bene- factors, the Journal of Animal Behavior proposes hereafter to publish, in the first number of each volume, a brief statement of its financial condition. Financial Statement for the Journal of Animal Behavior, December 30, 1913 to December 1, 1914 (Volume 4) receipts Balance from 1913 $154.67 Receipts from sales of complete volumes and odd numbers 786.30 Receipts from advertising 50.00 Gifts and contributions toward the cost of illustrations and tabular material 222.13 Interest 27.26 $1,240.36 EXPENDITURES Cost of manufacturing and distributing vol- ume 4 (this does not include cost of paper, paid in 1913) $868.48 Office expenses, including postal and express items 180.00 1,048.48 Balance on hand $191.88 JOURNAL OF ANIMAL BEHAVIOR Vol. 5 MARCH-APRIL 1915 No. 2 A STUDY OF THE BEHAVIOR OF THE CROW CORVUS AMERICANUS AUD. BY THE MULTIPLE CHOICE METHOD CHARLES A. COBURN AND ROBERT M. YERKES 1 The Harvard Psychological Laboratory and the Franklin Field-Station We have previously reported in this Journal 2 observations on the behavior of crows in certain forms of visual discrim- ination. The subjects of that investigation were transferred from the Franklin Field-Station in September, 1913, to the Laboratory of Animal Psychology in Cambridge, and were there kept until June, 1914, in a cage approximately six feet in its several dimensions. Despite their close confinement and the lack of an out-of-door fly, the birds continued in excellent health and proved themselves able to withstand wholly satisfactorily the conditions of laboratory life. When returned to the Field- Station, they were considerably less tame than during the previous summer. For this reason they were not used further for exper- imental purposes, but were kept for general observations. Young crows were captured for the experiments which are reported in this paper. Instead of following up the study of visual discrimination, we devoted our attention, during the summer of 1914, to an attempt to analzye ideatiqnal and allied forms of behavior in the crow by means of the Yerkes multiple choice method, and 1 The observations reported were made chiefly by Mr. Coburn and the paper was written by Mr. Yerkes. 2 Coburn, C. A. The behavior of the crow Corvus Americanus, Aud. Journal of Animal Behavior, 1914, 4, 185-201. 76 CHARLES A. COBURN AND ROBERT M. YERKES to the accumulation of additional facts concerning the natural history, instincts, and general habits of the birds. On June 7th, 1914, three young crows were captured near the Station. These birds were about ready to leave the nest. One, indeed, was taken from a limb beside the nest. This indi- vidual from the first exhibited fear and was so troublesome that after two days it was discarded and the remaining two birds w T ere kept for observation. They were placed in a box which was frequently passed by human beings, and were several times a day fed by hand, being allowed to come out of the box at will and become thoroughly accustomed to the experimenters. From the time of capture they were perfectly tame, ate readily, and the characteristic fear reactions never appeared. When taken from the nest, they were probably at least six weeks old. Throughout this report, these birds will be referred to as number 3 and number 4. Number 3 was from the first the larger of the two and the less timid. It, during the several months of observation, always came to us, perching on arms, shoulder, or head, as it had opportunity, and showing a friendly interest which was apparently somewhat independent of its desire foi food. It evidently liked to be petted. Our assumption is that this bird is a male. 3 Number 4, by contrast, was smaller, shyer, more wary, and after a few weeks ceased to come to either of us, except as drawn by hunger, and even then it often hesi- tated to perch upon the hand or arm. In all probability, it is a female. It has eaten less than number 3, and has been considerably more difficult to experiment with. Usually, in the course of an experiment, if the birds were in competition, number 4 would stand aside for number 3. Our additional experience with crows during the present season but emphasizes our conviction that they are among the most interesting of birds, and that their behavior is in every respect worthy of careful analytic study. With respect to what we shall term "ideational behavior," they have fallen short of our expectations, for in the light of their varied interests, ingenuity, curiosity, ceaseless activity, and apparent insight into simple situations, we had assumed that they possess an intelligence equal to that of many of the more intelligent mammals. The 3 Since this was written, dissection has definitely established our surmise in the case of both birds. A STUDY OF THE BEHAVIOR OF THE CROW 77 experiments now to be reported were conducted for the special purpose of obtaining definite and reliable information concerning the nature and limitations of their ability to adjust themselves to certain fairly simple, although novel, situations. We sought to make our measurements of intelligence by a method recently devised at the Psychopathic Hospital, Boston, by R. M. Yerkes, for the comparative study of ideational and allied forms of behavior in man and other animals. This method has been named the soluble-problem multiple-choice method. It was devised primarily for the purpose of enabling the comparative psychologist to present to any human or infra-human subject, no matter what the age, degree of intelligence, or condition of normality or abnormality, a series of situations increasing in complexity from an extremely simple one to one so intricate that even the most intelligent human subject might spend hours or days in adjusting himself to it. By means of this multiple choice method, it is hoped and confidently expected that the materials of comparative psychology may be rapidly increased and the analyses of animal behavior be made invaluable to the psy chopathologist . A general description of the method should preface this account of the special form in which it was applied to the crow, inasmuch as only a very brief account of it has been published. 4 In brief, the essentials of the method are these. A series of reaction mechanisms, appropriate to the subject, are presented. From this series one mechanism must be selected which, when properly approached, will yield the subject the satisfaction of success and, possibly, the reward of food. With each presenta- tion of the reaction mechanisms, they are varied in number and in position. The subject is therefore forced to select the proper mechanism on the basis of some particular relationship of that mechanism to its fellows, this relationship having been determined upon in advance by the experimenter. It may be, for example, such a simple relation as first at the left of the series as the subject approaches, or first at the right of the series, or second at the left, or alternately the first at the left and the first at the right, or the middle of the series. Imagine, then a series of piano keys which may be presented to a human subject. They 4 Yerkes, Robert M. The study of human behavior. Science, 1914, 39, 625-633. In this paper the writer describes his method in contrast with the Hamilton quad- ruple choice method. 78 CHARLES A. COBURN AND ROBERT M. YERKES may vary in number from two to twelve (this was the original form of apparatus). Some one key, in any group of keys pre- sented, when pressed will cause a bell to ring, thus indicating, success. Without other aid than his own observation, the subject is expected, from repeated presentations of the keys, to discover the essential relation and to acquire the ability to select the right key with certainty. This method has the advantage of enabling the experimenter to present increasingly difficult problems to his subjects. It has further the advantage of enabling him conveniently to record the essential features of reaction, and later to analyze the reactions at his leisure. But most important of all, it yields strictly comparable results when applied to widely differing organisms. Naturally, although the same problems may be presented to diverse types of organism, the reaction mechanisms must be suited to the subject in question. Without further general comment or discussion of the multiple choice method, we shall describe the form of apparatus and procedure employed with the crow. APPARATUS AND METHOD In the accompanying plate, designated as figure 1, and in the ground plan of the observation-room and apparatus, shown in figure 2, the general experimental situation is represented. Figure 1 shows in the background the building which was used both as a shelter for the crows and as an observation place for the experimenter. To this building is attached a fly which appears in C, D, and E of Figure 1. In figure 2, the ground plan of the building, are seen the experimenter's room, A, and the crow room, B, the latter containing a perch, P. All coarsely dotted lines in this figure indicate walls or partitions made of poultry wire. The large fly was, for the purposes of our ex- periment, divided into two parts by a wire partition. In the smaller of these portions, shown at the right of figure 2, the multiple choice apparatus was located. The crows could enter this portion of the fly only at the will of the experimenter, where- as they were allowed the freedom of the larger portion, which we have labelled C. As figure 2 is drawn to scale (one inch to forty-eight) it is unnecessary to give the measurements of the *■■■*_ V I i'ii J ■HBH Figure 1. Views of crows and apparatus for multiple choice experiments. A and B, crows, number 3, d\ on shoulder of experimenter, and number 4, 9 , on arm; C, the multiple choice box seen from the observer's room and from the direction of approach by the crow, the compartments are numbered 1 to 9 and below each number is an entrance door. D, the same seen from the oppo- site side or rear, with the nine exit doors closed. E, the box seen from the observer's room, with entrance doors 1 to 6 and exit door 2 open. At the extreme left, above the entrance door to the experiment compartment of the fly, one of the crows is visible. F, the observer's table, showing curtain before window (partially drawn aside to admit light for the camera) and the weighted cords with pull buttons for opening and closing doors. \ 't lii i I i i\ i ii if i / I l \ \ | \ i I i / 1 ;i j if 1 1 \\ i \ v wi n n ~ r~ jn H i I mj i» i i / i/ i rh-r \ I \ j > iUi ii i if r -tr -<-t-H -H-H-f/l / (/ ) Figure 2. Ground plan of crow house, fly, and apparatus. Scale, T V- A, obser- vation room; B, bird room; C, main portion of fly; D, passageway for experi- menter; E, multiple choice box; F, entrance door between main fly, C, and alley to reaction chamber, H; G, exit door between alley S and main fly; H, reaction chamber, the floor boards of which are separated somewhat; I, L, approaches to the doors F and G; J, observer's table and key-board; K, observ- er's stool; N, doors for experimenter's use; P, perches; R, alley leading to middle of reaction chamber H; S, alley leading from exits to main fly; W, water tub for crows. Numerals 1 to 9, compartments of multiple choice box; a, attachment of cord to entrance door, t, of compartment 9; b, screw eye for cord; c, screw eye at entrance to observer's room; d, wooden button on cord; under d is a small brass pulley for cord; h, i, j, k, indicate course of cord from exit door of com- partment 9 to key-board; x, metal cover for food receptacle of compartment 9; z, food receptacle of compartment 4. 80 CHARLES A. COBURN AND ROBERT M. YERKES building and fly. We shall give a more detailed description of the experimental device. The latter is shown fairly well from different points of view in the parts of figure 1. Figure 1 C is a view of the multiple choice box from the front, that is, the side of approach by the subject. All the entrance doors are closed. Figure 1 E shows the apparatus from the same point of view, with the entrance doors 1 to 6 and the exit door 2 open. Figure 1 D, instead, shows the apparatus from the opposite side, with the several exit doors closed. By referring now to both figures 1 and 2, we should be able to obtain a clear idea of the construction of the experimental mechanism and its use. The multiple choice box, as we shall call it, appears in ground plan as E of figure 2. It is divided into nine like compartments, each with a door at both ends, opening outward. The outside measurements of the multiple choice box are 81 inches long by 20 inches wide by 15 inches high. The frame of the box is made of 2 by 2 inch stock, and the floor, ends, partitions, and doors, of half -inch stock. The top, which is hinged for convenience of access, consists of wire netting, If inch mesh, on a wooden frame. On the inside, each of the nine compartments is 19 inches long by 8 inches wide by 13 inches high. The entrance and exit doors are 9| inches high by 7f inches wide. All of the doors are mounted with spring hinges which hold them shut. On the lower inner edge of each exit door is a piece of tin (x) which, when the door is closed, projects 2 inches into the compartment and covers a hole (z) in the floor of the compartment 1^ inches in diameter by f inches deep. These metal covers, as well as the holes, are represented in the ground plan of the apparatus, figure 1, x and z. The use of these holes is to contain food which serves as a reward for the bird when the exit doors are opened. The system of entrance and exit doors, nine of each, and also the main entrance door, labelled F in figure 2, and shown in the extreme lower left corner of figure 1 E, and the main exit door, labelled G in figure 2, and shown at the right end of the multiple choice box in figure 1 D, are controlled from the experiment room A by a system of cords passing through screw eyes and pulleys. A STUDY OF THE BEHAVIOR OF THE CROW 81 These cords are indicated by dotted lines where they pass under the floor of the multiple choice box or under the boards which serve as an approach to the box : Elsewhere they appear as solid lines. The arrangement of the cord-system within the experi- ment room is rather unsatisfactorily shown in figure 1 F. On a table, J, before which the observer sits on the stool, K, are two groups of cords, each with a wooden button attached in a convenient position. The group at the experimenter's left consists of the cords connected with the ten entrance doors, and the group at the right, similarly, of those connected with the ten exit doors. We may now trace the course of the cords from the doors of compartment 9. A cord is fastened at a to the lower outer corner of the entrance door t. It thence passes through the screw eye b in the edge of the approach board. From this point it extends, under the interrupted floor of the reaction chamber H, to a screw eye, c, in a block across the aperture leading to the experiment room. Thence the cord passes over a small brass pulley at d and through a hole in the table J. (In figure 2 the pulley is hidden by the wooden button on cord.) It is kept taut by a lead weight under J. Similarly, the cord for the exit door of compartment 9 is attached to the lower outer corner of the door at h, passes through the screw eyes, i and j, to the pulley k, and is kept taut by a leaden weight. The cords for the main entrance and exit doors, F and G, run to the extreme left and right respectively of the experimenter's table. The experimenter operates a door by grasping the wooden button shown on each cord in figure 1 F and pulling it toward him. When he has pulled as far as the button will come, the door to which the cord is attached stands wide open, and the leaden weight under the table serves to hold it in this position as long as the experimenter desires. When he wishes it closed, he simply pushes the button back to its former position, and the strength of the spring hinges suffices to overcome the pull of the weight. In order that the bird should not see and be influenced by the movements of the experimenter, a black curtain was hung before the opening into the experiment room, and through small holes cut in it, the experimenter was able to observe the movements 82 CHARLES A. COBURN AND ROBERT M. YERKES of his subject. At no time during the investigation did the crows give evidence of noticing the experimenter when they were reacting. The remaining features of the apparatus will be mentioned in connection with the following brief description of the exper- imental procedure. In preparation for a series of trials, the experimenter opens each of the exit doors and places in each food container a small bit of milk-soaked bread. He then closes the exit doors, thus covering the food, and takes his place at K. He next opens a group of entrance doors. Let us suppose, as is shown in figure 1 E, that the doors numbered 1 to 6 are opened, and, further, that the compartment which may be designated as the correct one is the first at the subject's left, that is number 1. Having made these preparations, the experimenter, by means of the proper cord, opens the main entrance door F, and the bird, either by walking up the approach board I or by alighting on the approach board L, on a level with the entrance door, is immediately able to enter the reaction chamber H, by way of the alley R. By two wire partitions which appear as dotted lines in figure 2, it is forced to walk straight ahead until it reaches the center of compartment H. It may then face and, if it so chooses, directly approach the central compartment of the mul- tiple choice box. But under the circumstances, with entrance doors 1 to 6 open, it would naturally swerve toward the left. In case it enters compartment 1, the experimenter quickly and noiselessly closes the entrance door after it, by releasing the appropriate cord, and immediately thereafter, opens the exit door of the compartment by pulling on the appropriate cord. He, thus, with one hand prevents the retreat of the bird from the compartment and with the other uncovers the food, so that the bird may obtain the reward for a correct reaction. As soon as the food has been swallowed, the crow steps out of the compart- ment, the exit door is closed by the experimenter, and the bird either immediately, or at the experimenter's pleasure, is allowed to return to the fly C by way of the main exit door G. If, instead of choosing the right compartment, the crow enters some other one, the procedure is different. Immediately upon its entrance, the experimenter closes the entrance door. He then, with a stop-watch, measures a definite period during which the bird is confined in the compartment. This period was varied A STUDY OF THE BEHAVIOR OF THE CROW 83 during our experiments from 15 to 60 seconds, in an attempt to discover the most satisfactory length of confinement. At the proper moment, the experimenter opens the entrance door and the crow is allowed to retrace its steps. It may then immedi- ately make another choice. But not until it enters the right compartment, is it awarded with food and allowed to return to the fly. Thus punishment for incorrect choices is combined with reward for correct choices. In further description of the apparatus, it should be said that wire partitions at each side of the multiple choice box, and extending from the lid of the same to the roof of the fly, prevented the crow from walking or flying over the box, while boards both in front of the box and behind it and on a level with its floor form a floor which prevented the bird from getting under the box. The only possible course for the subject from main entrance to main exit door is by way of one of the compartments. Experience shortly indicated that the crows could be used most satisfactorily if given their trials alternately, and the method finally settled upon was that of admitting one crow to the appar- atus, allowing it to make its choice, and then holding it in the passageway beyond the exit doors until the other crow had passed through the main entrance door into the reaction chamber. Thus, as one subject emerged from a compartment of the box E, the other bird entered the reaction chamber. When, as some- times happened, the one or the other bird failed to respond immediately and appropriately and both were in the fly, it was fairly easy for the experimenter to admit the proper bird by carefully manipulating the entrance door. PRELIMINARY TRAINING The crows obtained almost all of their food in the multiple choice box. In order that they should work steadily and indus- triously, it was necessary to have the pieces of bread or mouse meat, which was sometimes used instead of bread, very small. It proved possible to obtain as many as twenty reactions per day from each bird, in series usually of five each. We shall now consider the course of experimentation and its results. One June 21st, the crows having attained ability to feed themselves, preliminary training was undertaken, and from that time they were fed in the multiple choice box. They 84 CHARLES A. COBURN AND ROBERT M. YERKES exhibited no fear, rapidly became familiar with the apparatus, and acquired skill in making the trip from the main fly, through the experiment compartment, back to the fly. For several days, both the entrance and the exit doors of the compartments were kept open. Then the situation was changed by the closing of the exit doors, and the crows were trained to enter a compart- ment and wait for their food. On June 27th, the first series of trials worthy of special mention was given. The apparatus was in perfect working condition. Food was placed on the floors of the several compartments ; the exit doors were closed and the entrance doors were open. The main entrance door was opened, and both birds were allowed to enter the reaction chamber and go to the compartments for food. As they entered the compartments, the exit doors were opened and the entrance doors closed. Thus, by a series of trials they were habituated to the opening and closing of the doors and were taught to make the circuit promptly from the main fly back to the same by way of the multiple choice box. On the following day, June 28th, the food was placed in the food containers and the exit doors were closed. Number 3 entered the compartments rapidly and made the circuit usually without delay, but number 4 at first refused to enter the compart- ments. Within two days, it, however, was readily entering, in its search for food. On June 28th, only three or four of the entrance doors to the compartments were opened at any one time. In the previous preliminary training all of the doors had been opened. Neither bird showed any marked preference for a particular compartment in the multiple choice box. On June 30th, the method was tried of confining one of the crows in the crow room B, of figure 2, while the other was given its trials. Later in the day, the birds were given another series of trials alternately, the one being kept in the exit alley as described on page 83, until the other had entered the reaction chamber. This method proved satisfactory and was later employed to the exclusion of the former. Up to this point, the two subjects adapted themselves to the different situations with almost equal rapidity. Number 4 was somewhat less willing to try new things than number 3, and seemed to be hampered by its shyness. A STUDY OF THE BEHAVIOR OF THE CROW 85 A significant incident is the following. In one of the trials* number 4 accidentally fell through a five inch space which had been left before the entrance doors in order that the crow should not too closely approach a compartment unless it intended to enter it. The bird fell to the ground beneath the apparatus, finding there some pieces of bread which had been dropped earlier in the day. Naturally enough, it ate them before it could be induced to return to the fly. Ever thereafter, until this crack had been closed, this bird, as it approached the com- partments, would look through the crack to the ground. Several times it flew down in search of food. RESULTS, PROBLEM 1 With the final series of trials given on June 30th, regular experiments were initiated. The problem which the birds were required to solve was that of learning to select the first open door at the right. Ten settings as we shall call them, were chosen by the exper- imenters. These are given below, numbered 1 to 10. After each number appears the series of open doors ; in the next column, the total number of doors open; and finally in the last column, the number of the right compartment in which the reward of food might be obtained. Problem 1. First door at the subject's right to be chosen Settings Doors open No. of doors open No. of right door 1 7.8.9 3 9 2 2.3.4 3 4 3 3.4.5.6.7 5 7 4 1.2 2 2 5 2.3.4.5.6 5 6 6 6.7.8 3 8 7 3.4.5 3 5 8 2.3.4.5.6 5 6 9 1.2.3 3 3 10 7.8.9 3 9 In this series of ten settings, a total of thirty-five doors were open, of which number, ten were of course "right doors." Con- sequently, the chance of a selection of the right door, without previous experience or trial, is one to two and one-half. In general, it was the purpose of the experimenter, as far as possible, to follow through this series of settings from 1 to 10, and then to return to the beginning and repeat the series. No matter how many trials in succession could be given, the exper- 86 CHARLES A. COBURN AND ROBERT M. YERKES iments were resumed at the point of interruption of the regular series of settings. Thus, if five trials were given, beginning with setting 1 and extending through setting 5, the next series would begin with setting 6 and continue through setting 10. As a matter of convenience, it was also decided to have the two crows work on different settings. For example, while crow 3 was presented with the settings 1 to 5, crow 4 would be presented with settings 6 to 10. This enabled the experimenter to avoid the necessity of refilling the food containers after . each trial, and it also prevented the crows from developing the tendency to follow one another by sensory cues. After a very few days of experimentation, both birds reacted with remarkable alacrity and facility. They were, as a rule, prompt to enter the reaction area and almost as prompt to leave the exit area. In the initial regular experiments, thirty seconds confinement in the wrong compartment was used as punishment for mistakes. But it shortly appeared that this was too long an interval, for the birds hesitated to enter any of the compartments after a half minute confinement in one of them. It was therefore decided to use the period of fifteen seconds as punishment for incorrect choices. Especially during the early experiments, the crows often exhibited considerable fear and excitement when shut in the small compartments. This diminished toward the end of our work, and it was then possible to confine them for a half minute or even a minute without causing disturbing excitement. The experimenter kept, as a matter of routine, a record of the time from admission to the reaction chamber to entrance into the right compartment. There is no special reason to consider these records significant, and we shall omit them from this report. Careful record was also kept of the chief features of the behavior of the bird during this interval. The simple system of symbols, which appears below, was adopted for this purpose. O, to center of the reaction area r, to left hand far corner of the area -|, to right hand far corner of the area L, to left hand near corner of the area _j, to right hand near corner of the area U, to center of the near side of the area C, to center of the left side of the area 3, to center of the right side of the area A STUDY OF THE BEHAVIOR OF THE CROW 87 If the crow merely looked into one of the compartments with- out entering, the number of the compartment was recorded. If it, instead, entered a compartment, the number was under- scored. In case the compartment entered happened to be a "wrong one", the time of entrance was placed in parenthesis immediately after the number of the compartment. When the time exceeded a minute, the number indicating the minutes was placed in a circle. For less frequent forms of behavior, other provisions were found convenient, and by the use of symbols and other abbreviations it was found easy to obtain a fairly complete description of the subject's behavior. To illustrate the use of the above symbols, the following record of a trial (trial 32 of number 3 on July 23), setting 1.2, is presented. 4, 3, i_, J, l_> ®, L, o. L, 1, L, ©, (trying to get out of area), L, _l, ®, J, L, J, (pkd. at hole in floor), ®, 1, o, L, 9, ©, ©, ©, O, n L, 2, ®, 1, 2, 8' 13". In this trial, crow number 3 did not enter the wrong compartment at all. The time between the fifth and the seventh minutes was spent before compartment 9. It was decided by the experimenters that when a crow had made ten correct choices in succession, its training should be considered complete, or in other words, it should be said to have solved the problem. In the case of the problem in question, crow number 3 at the end of thirty-two trials had entered the right compartment twelve times in succession, but in several of these trials it had been aided by the experimenter, who moved the exit door slightly in order to attract the attention of the bird after it had for several minutes refused to enter any compartment. In the accompanying table 1, a summary of the trials for each of the birds in problem 1 appears. At the head of the several columns are the settings numbered 1 to 10, with the right number in bold faced type. In the first column -at the left, under each of the several settings, appears the number of the trial and the series of compartments entered. Thus, for example, referring to the results for crow number 3, in trial number 5, which was the first trial in the regular series, the bird entered compartment 8 and then compartment 9. In trial 6, it immediately entered compartment 4, the right one. The 88 CHARLES A. COBURN AND ROBERT M. YERKES letter a, following a number, indicates that the bird was aided in its choice by the experimenter. It is possible by careful study of this and succeeding tables to discover the reactive tendencies of the organism, and to note both the appearance and the disappearance of the same. Problem 1, the first door at the right, proved a very easy one for both crows. It was mastered by number 3 after fifty-five trials, and by number 4 after fifty-one trials. Table 2 presents the results of the various series of trials, ranging in number from three to five for each subject. The number of successes and failures in each series and the ratio of successes to failures for each day appear. The letter R in this table indicates correct first choices, the letter W, incorrect first choices. The table has to do only with first choices. In contrast with the above results in problem 1, the first door at the right, we present in table 3 a summary of the results for problem la, the first door at the left, the trials for which were given not immediately after those just described but at the end of the season, and after the crows had for several weeks worked on problem 2, the second door at the left. Naturally the influence of their training to go to the second door retarded the formation of the habit of choosing the first door at the left. For the satis- factory solution of the problem, one hundred trials were required by each bird. Doubtless a change of experimenters after trial 75 somewhat delayed progress. The results which appear in tables 3 and 4 demand no further comment. Recurring now to problem 1 , it is obvious that from the human point of view this is a very simple problem. The crows solved it readily, but in the course of their work they frequently exper- ienced discouragement and were aided in a considerable number of their early trials by the experimenter. Doubtless our results would be more significant had this aid been withheld, but at the outset of our work we hesitated to run the risk of spoiling our subjects by over-discouraging them. In problem la, no aid was needed. Varied reactive tendencies do not appear in connection with this problem. Very few wrong choices were made. Conse- quently, all that can be gleaned from the results is a general knowledge of the behavior of the crow in the face of a certain fairly simple experimental situation. A STUDY OF THE BEHAVIOR OF THE CROW 89 w C fa CO « w pa 5 2 o U « o fa (A w Pi S. 10 7.8.9 CCJ ex 00 CX CX CX H LO co CM 00 CO LO S.9 1.2.3 co CO CO CO H -* LO CM co LO S. 8 2.3.4.5.6 co co CO CO CO H co co CM CM CO co CX S. 7 3.4.5 LO 03 LO LO LO H CM CM CM LO CO oo S. 6 6.7.8 00 c3 00 oo OO I h ■ — 1 r— 1 .—1 CM CO S. 5 2.3.4.5.6 CD * * CO LO CO co H o I— I o CM CO co co CO LO CO '-' CM CM CM CM CM T— 1 CM H oo CX CX r— i CM CO LO LO LO S. 3 3.4.5.6.7 cci t> t- t> CO t> H t> 00 ■— 1 I— 1 CO I— 1 LO S. 2 2.3.4 ■* 00 coco ^_^ flj CO Z u c/2 & o «nri° -^ i_ a> +j - _ u ~ 3 — . "^: OCM CC! <*-. — <_ *J ■i cfl iC*0 CJ u^^o - t 5'- 1 r. .^H 'j~. rn T3 ,« - PQ 90 CHARLES A. COBURN AND ROBERT M. YERKES w O « U m s D o U H CO w S. 10 7.8.9 Oi CT) en CTl H O r— 1 »— 1 CM co CO co S.9 1.2.3 ! CO CO co CO CO H 00 O o CM CM CO 1—1 ■5* LO S.8 2.3.4.5.6 CO co CM CO CO co H CD i-H CO o <** S. 7 3.4.5 LO LO LO LO LO CO LO H CO 00 1—1 00 CM o CO en CO CO S.6 6.7.8 cd 00 t> co 00 00 t> oo co 00 h lo t> CM G5 CM CM S. 5 T. 2.3.4.5.6 CO CO i-H CO CO CM CO CO CO i-H LO CO -< CM CM CM CM H 1—1 LO i-H LO CM o LO S.3 3.4.5.6.7 t- t> c^ o co 1— I CM CO CO Oi S. 2 2.3.4 03 "tf CO ■^ H CM i— i CO CM LO CO CO S. 1 7.8.9 en od 00 05 00 CO en H * r— 4 CM CM CO 00 CO t> LO ^jjco CO CM -tf ca cor- "Ilo LO CO CO rtoo OCM CCPO .Oh TJ v. ■ Z ■ CJ u X A STUDY OF THE BEHAVIOR OF THE CROW 91 TABLE 2 Daily Series and Averages with Ratios of Correct to Incorrect First Choices Crow Number 3 Problem 1 Crow Number 4 No. Ratio No. Ratio Date of trials R W R W of R to W Date of trials R W R W of R to W June 30 4 2 2 2 2 1: 1 June 30 4 3 1 3 1 1:.33 July 3 2 1 July 3 1 2 < » 1 1 t a 1 1 < « 3 2 1 ( a 3 2 1 ( « 3 3 8 2 1:.25 i « 3 2 1 5 5 1: 1 ' 2 2 2 2 2 2 i « 4 4 6 0:6 ( u 4 3 1 5 1 1:.20 3 3 1 2 3 3 2 1 < « 5 5 i « 5 3 2 ( « 4 3 1 ( « 4 3 1 i a 4 2 2 11 5 1:.45 ( u 4 2 2 10 6 1:.60 4 5 4 1 ' 4 5 4 1 < « 5 3 2 i u 5 5 i u 5 5 12 3 1:.25 i a 5 5 14 1 1:.07 5 5 5 5 1:0 92 CHARLES A. COBURN AND ROBERT M. YERKES w O OS Oh CO CO « t i w W ca J S « D s z H £ O OS o PS o CD H s w Pi S. 10 1.2.3 (3.2.3.2 \2.2.1 3.2.2.2.1 2.1 2.3.3.1 2.3.1 2.1 2.1 LO CO CM CO CM 1— 1 H o ooo ooo r-t CMCO ■>* LOCO l>- LOCO oooo o o I— I S.9 7.8.9 oo t> oo oo t>oooo c^- 00 00000000 1> 00 00 00 00 00 00 c^ c^ CJ CO CO t^ H O CD CT; * LOCO CO t^ oooo 00 S. 7 5.6.7 LO LO LO LO LO LO LO fl.2.3.4 \5.6.7.8.9 CM— i LO H •-ICMCO ■* LOCD CMO CO C; OS S.6 6.7.8 CD CD CD CD CD CD CO 00 CO iftO LO CO H co cococo cococo •— i CMCO ^f LOCO 00 CO C3 S. 5 2.3.4.5.6 CO CM # cvjCO CO CMCMCM CMCMCM CM -H LO »— < CM H LO LO LO LO LO LO LO LO ■— i CMCO -^ LOCD t> o CO LO "^ CX co c£J 0O MO) LO CI OC500 000000 oo^t CO H r-* CMCO " e Cs S. 3 3.4.5.6.7 LO 00 <> CO COCOCO COCOCO COfSCO CM CO H CO COCOCO COCOCO CO ■—i CMCO ^ LO CO t>- 00 CO S. 2 7.8.9 8.9.8.7 8.7 8.7 8.7 8.8.7 7. 6.7.8.9 CO coco t> H CM CMCMCM CMCMCM CM ■—i CMCO TfLO CD O C--C. t^oo CM OS S. 1 1.2.3 CO i— i CM CO CO CM ^h qs CM CMCMCM CM —i CO CM — i oo CO COCOCO CM CM CM CM CM 1> 00 t> .— 1 H ^ CM CO ^f LO CO C **» coco t^00 1 — 1 Ci A STUDY OF THE BEHAVIOR OF THE CROW 93 w m o OS OS w oa O OS U OS o h en H -J en W o CO CM CO- *— 1 f— 1 --HCOCM LO CO ^H CM CM CM CM •— i i-H * CO CO CO CO CO CM ^h CM >-H (N CM CM 1— 1 H ID ID ID LO ID LO LO LO —I CM CO -tf LO CO t>- LOOi coco 8 I — 1 co oq l> CO t> c~- c^ tr^ t> c— t^ co t> t> t^ H ■<* ""^ ^* ^* *^ T^ ^^ ^f •— I CM CO "sF LO CO t^ CO CJ) ID CO CO CO CO t> ^f ■<* CDCDCO C-- -3< CO LO CO LO t> ID CD CD CD ^'00 CO ■* COt^C^Tf-^Tf-^LD-^tUD fCt^ CO "* v H CO CO CO CO CO CO CO CO >— I CM CO Tf LO CO c^ CO CO CO CO CD 2.3.4 6.7.8.9 LO LO LO LO LO LO LO LO ~4 LO *-H LO H CM CM CM CM CM CM CM CM — i CM CO ■<* LO CO t> CM 00 CD CO CO CD CO CO CO co co LO t^ CO t> CD CO CD CD CO mot t>LO CO H - — i CM CO ^ LO CO C^ -HCO COCO CO LO CD ID CM co CO CM CO CO CO CMLO-^ CM CM^O (N CM -* -* CO CM CO CM ^H LO T— 1 i-H CM H ooooooo •— i CM CO Tt LO CO O- ot- oooo LO co "* ^^t CO H C7s CJ> C7> C; C7) CX, Oi t— i 0) CO •■* ID CO Ol CD t^OO PC co lo co n< co -<# co * LO CD co o CO CM co <7> CO co CD CO NCONNNNN sO COCD t> H o t> r~ t^ t> c^ t>- ^HCM CO^LOCO CM i— 1 CO co CM CM CO CM i— I CO ■— i •— i 03 co t> CO CM CO CO CM CO CM • t> co ^ h CD CO CO CO CO CO CO rH CM CO ■* LO CO 82 05 en bO c CD /. co CD CD co c. ]3) 'C o CD .c » — i CX) !s bC C "c c 'Sb CD C3Q -a CD CJ c CO 03 TJ CD bo C ca CD o co RJ CD CD CO bfl C CD CO CD H •a CD Ih CJ CJ O U) i- F.E to AT io *r 3e ar v° Figure 3 the group the brightness value of the gray with which the stimulus color was confused. The gray values are then represented, Figure 4, by the straight horizontal lines, whose positions prob- ably indicate the "brightness equivalents" of the several colors for the cats, in the sense in which Miss Washburn uses that term (pp. 145 and 146). The deviations of the curves from the horizontal then indicate how much the several colors may vary, for the human eye, from that gray and yet be indistinguishable from it for the animals. These deviations are large for red and blue, slight for green, and *ff °£ ~R. 134 J. C. DeVOSS and rose ganson very slight for yellow, as if there the animals approximated the brightness-difference-threshold of the human eye. The deviations probably show much more the defects of colored papers. They are complex colors and while one factor, say the tint, may presumably brighten the paper, another, say the red or violet, darkens by at least an equal amount. Thus RT1 is very much brighter than R for the human eye, yet the influence of the tint is slight in comparison with the influence of the red W naJUtxJ %**£* jo sr Figure 4 for the animal. Hence it is still confused with red. RT2, how- ever, is discriminated from R after many trials, but darkened orange-red is confused. The relations are shown in the following tabulation. Red Correct No. of Verdict* with Errors Choices Trials F.E. RT1 238 342 600 10 Confusion RT2 156 444 600 7 Diff. Dis. ORS2 258 342 600 30 Confusion ORS1 240 360 600 30 Diff. Dis. OR 6 24 30 15 Discrimination * Based on our standard of twenty-four correct choices out of thirty-trials, as the test for discrimination. COLOR BLINDNESS OF CATS 135 This low stimulating effect of red has been shown for the dancing mouse, the rabbit, and "possibly" 9 for the monkey. Apparently the cat is no exception to the rule. Yet even in the case of red the cat appears to need no such enormous differences in brightness as does the dancing mouse, in order to discriminate promptly. Nevertheless it would be quite unfair to base an opinion of the cat's discriminating ability on his reactions to red. DISCRIMINATIONS Our account of the confusions made by the cats is complete. Only matters of minor importance are shown by the discrim- inations. To our surprise no trace of individual variations ap- peared in the confusions. This is more apparent because of our determination to employ so many trials that the results would not be vitiated by improvement due to training. 10 Individual differences did come to light in what we have called difficult discriminations, i. e., those which required at least two hundred forty trials for the animal to learn to discriminate. The greatest difference between any two animals appears in certain colors presented with yellow as the stimulus color. It is indicated by the number of trials required for discrimination by each animal and is shown in the following table. TABLE XIV Yellow No. of Trials No. of Trials with for Cat 2 for Cat 4 G 240 30 GT1 330 30 GT2 360 60 YG 330 30 OYS1 60 330 630 630 ROS1 240 240 RO 480 480 VRT2 210 150 There are four prompt discriminations by one cat, only one by the other. The great difficulty of discriminating orange from yellow shown by both animals indicates that it must appear to them very much like the yellow. In this case stopping after five hundred seventy trials would have resulted in a decision 9 Watson, J. B. Some experiments bearing on the color vision of monkeys* Jour. Comp. Neur. and Psych., vol. 19, 1909, p. 19. 10 See Yerkes, The Dancing Mouse, pp. 127 and 128. 136 J. C. DeVOSS AND ROSE GANSON that orange is confused with yellow. The per cent of right choices of orange was but 66.2, of VRT2 by Cat 4, only 60.7. There were six cases of difficult discrimination with blue, four with red none with green. It remains to present the colors which, in experiments with yellow as a stimulus color, were promptly discriminated from it and yet were of nearly the same flicker value as the yellow. It will be interesting to set down in parallel series the colors confused with yellow, those discriminated from it with difficulty, and those easily discriminated from it but of similar flicker value, and underneath each color the number denoting its flicker equivalent. Stimulus Color, Yellow. F.E.— 1-2 1. Confused GYT1, GYT2, YT1, YT2, OY, OYT1, OYT2, YO, YOT1, YOT2, OT1, OT2 2 1-2 1-2 1-2 2 2 1-2421-23 2 2. Discriminated with Difficulty G, GT1, GT2, YG, OYS1, O, ROS1, RO, VRT2 6 3 1-2 3 5 6 15 9 5 3. Discriminated Easily RVT2, VT2, BT2, GBT2, BGT1, BGT2, YGT1, YGT2, GY, ROT2, ORT2, 2 332 3 2 3 1-2 32 3 The first two series of flicker-equivalents show that flicker values were a factor in producing confusions and in causing difficulty of discrimination. In the second series the presence of orange, which we have already seen to be almost as bright as yellow for the cat, is a factor which produces difficulty in four cases. In the case of GT2 the extreme brightness of the tint is overcome by the darkening effect of the green, though they come near balancing each other. In the third series of flicker values the effect of red, violet, blue, green, and orange in darkening the tints for the cat is very evident. This would indicate that those colors have great dark- ening effect and that fact confirms to a great degree the brightness position we have given them in Figure 2, which is drawn from the results of grays. If further evidence of 'the opposite effects of antagonistic factors is needed, we may take the case of GY. Though the COLOR BLINDNESS OF CATS 137 flicker value differs slightly from yellow the presence of green enables discrimination. Add a "tint" and confusion takes place. Brighten the color to the next brighter tint and the result is still confusion. Thus, Color F.E. Result GY 3 Discrimination GYT1 2 Confusion GYT2 1-2 Confusion Here the effect of the tints overbalances the effect of the green and produces confusion. Elsewhere the darkening effect of the colors is so enormous that the tints and shades have relatively slight effect on the cat. This was to be expected, of course, if the curve derived ' from experiments with grays is approximately correct. Altogether the results derived from experiments with grays and with colors are surprisingly consistent. USEFULNESS OF FLICKER EQUIVALENTS The great drawback of our experiments was the time they consumed in trying so long a list of colors. Could this, by any means have been shortened ? In our work with colors had we tested for yellow only those of its flicker equivalent, we should have discovered five of the twelve confusions. Had we explored one-half of a flicker unit on each side the yellow, we should have discovered five more confusions, and had we explored for two and one-half units on either side, we should have found them all. To have done the same thing with blue we should have had to explore a range of fourteen units, but using only the exact flicker equivalent would have found for us one of the four confusions with blue. Exploring a range of three flicker units on either side the green would have discovered all the confusions. Using the exact flicker value of the green would have revealed one confusion. Using the exact flicker-equivalent of red would not have yielded any one of the confusions, (It is true only of red.) but using one half of a flicker unit on either side of the red would have brought out one confusion. Two flicker units would have shown three of the nine confusions, five units would have shown six, fifteen flicker units would have shown them all. Even exploring a range of fifteen flicker units on each side of 138 J. C. DeVOSS and rose ganson every stimulus color would be a very different affair from pairing each stimulus color with each of the eighty-nine other Bradley colors. Such procedure in the experiments with these cats would probably have reduced the time required from twenty-eight months to eight. An animal which discriminates the stimulus colors from all those of the same and nearly the same flicker values has a very different type of vision from that of the cat. Though the colors have vastly different brightness values for the cat and for the human eye, the brightness equivalents and the flicker-equivalents have intersected many times. A claim that the use of flicker values would not save time must assume that four broad bands of flicker-equivalents on either side of yellow, blue, red, and green respectively might none of them meet, at any point, the brightness values of the animals. Such an assumption is so improbable that in work with colors the neighborhood of the flicker-values of the stimulus colors should be explored first, provided the animal has already made a number of discriminations to become accustomed to the experiment. In the experiments with grays, yellow was confused with a gray of the same flicker value. To find the confusion gray for green, we should have had to use a range of four flicker units. With red, blue, and violet flicker values would have been useless for discovering the grays, and "systematic groping" such as we have used in our experiments would be necessary in finding the gray values of those colors for the cats. GENERAL REMARKS We frequently tried the cats with two glasses lined with the same colored paper, e. g., two yellows, two blues, etc. They failed, so that the assumption that they distinguished by wrinkles or spots on the paper is gratuitous. Our records show practically a dead level of uniformity in the responses of each pair of cats. It seems hardly necessary to confirm the work of one cat by giving the same tests to another. It adds a trifle of reliability, but it has added but one new fact to our results, and that of slight importance. This uniformity of behavior suggests also a dead level of stupidity. A glimmer of intelligence was observed, for, as already stated, one cat gave good evidence of selecting the food-glass by the position of the thumb-button at the rear of the apparatus, COLOR BLINDNESS OF CATS 139 and as good evidence of failing to do so when the buttons were concealed by shields. Our experiments show that the cat has very defective day- light vision as compared with that of human beings. Is it possible that this defective vision accounts for the behavior of Thorndike's cats which clawed at the place where the loop had been when the loop was no longer there ? For such vision as the cat possesses, a mad scramble would conceivably be a much quicker way to lay hold of a loop than an attempt to see it. An accident of similarity of brightness between the loop and the background might render it well nigh invisible to the animal. Is it possible that the poorer the vision an animal possesses the more he becomes dependent on kinaesthetic sensations, which Watson has shown to play a fundamental role in the life of some animals. Our records show that an animal may make more than fifty per cent of right choices throughout a large number of trials and yet not learn to discriminate between the two objects. Our experience shows that the possibility of the texture error should be guarded against, as well as the error due to improvement by training. In some cases discrimination occurred only after eight hundred trials. So many criticisms have been made of the use of colored papers that one advantage in using them, no matter how trifling it be, should be welcome. All the confusions made by these cats can be exhibited to the eye by pasting the papers on gray cardboard. The result of viewing the papers will be a better conception of the nature of the cats' vision than can be got from reading pages of description of their behavior in the experiments. Finally we asked two persons of dichromatic vision to sort these colored papers as Holmgren worsteds are sorted. Each of the dichromates made five confusions which had been made by the cats. Both of the dichromates and the cats agreed in the matches (confusions) of two pairs of colors, and for each of these pairs the flicker-equivalents were identical. Our account of our exploratory tests of the cats' vision is finished. We hope that feline vision may now be studied quanti- tatively, by means of apparatus which permits of accurate measurement of the wave-lengths and intensities of the lights, as they reach the eye of the animal. THE WHITE RAT AND THE MAZE PROBLEM II. THE INTRODUCTION OF AN OLFACTORY CONTROL* STELLA B. VINCENT Chicago Normal College What part has olfaction in the life of a rat ? The answer to this query would have to be based upon what we know of brain structure and from our casual observation of rat behavior, since, there has been very little direct experimentation published that has as its main concern this form of sensitivity. The rat has well defined olfactory lobes and tracts. But these parts are relatively smaller than those of some other rodents and decidedly smaller than those of some other mammals. The olfactory paths in the brain of the rat have not had much study and we are thrown back, therefore, upon what we know of the life and habits of the animal for the answer to our question. It might be thought, from watching the reactions of the rats in the maze, that smell was a very important sense. The frequent sight of a rat lifting itself on its hind feet and sniffing vigorously, the constant use which it makes of its nose on the floor and sides of the maze, would lend credence to such a supposition. Yet it has been shown that anosmic animals are under no serious disadvantage in learning the maze and that much of this sniffing and apparent smelling has an important tactual function. What the world of odor is to a rat we have little power of conceiving but how it affects the behavior we may somewhat discover. The odors which are vital in the animal world are, presumably, food odors, sex odors and body odors. By the term body odor is meant those olfactory qualities which perhaps are peculiar to individual animals but which certainly characterize the animals of a single cage or group. By differentiation from this familiar 1 This work was done in the Psychological Laboratory of the University of Chicago. I am greatly indebted to the department for the opportunity to do it and to pro- fessor Carr for suggestive help and criticism of both experimentation and paper. 140 THE WHITE RAT AND THE MAZE PROBLEM 141 odor it serves to mark off a strange animal or give warning of an enemy. Rats are omnivorous and hence there can be slight necessity for any fine discrimination in the way of foods. A generalized response to food odor will be all sufficient. I have, indeed, never seen in white rats any clear discrimination of foods which might be said to depend upon smell and have failed to find any mention of such power by others. If food be introduced into a cage unobtrusively, a rat usually stumbles over it before dis- covering it. It might be supposed that blind and normal rats would show different behavior in food seeking, yet in some preliminary experiments covering several weeks, the food in every instance, by both normal and blind rats, was apparently found accidentally. The animals were very tame and were very hungry. The food used was nuts, cheese and milk soaked bread. The experiments, although significant, were too brief to be conclusive. The instances which Small 2 cites of the reactions of very young animals to different odors may clearly depend upon the chemical sensitivity of the mucus membrane of the nostrils and must be sharply distinguished from olfaction proper. Pro- fessor Watson, 3 however, found that blind animals, otherwise normal, were affected by odors to which anosmic animals failed to respond. To repeat, smell is more closely associated with food getting than is any other sense; yet it may be safely assumed, and we should expect to find, that the sense is less refined in animals which do not pick and choose their food than in those which do. If a rat from another group is introduced into a cage containing other rats they "nose" the whole body of the stranger. The rats do not appear to get the odor across the cage for the excite- ment and characteristic actions begin only with contact. Rats also respond by different behavior to strange handling. No doubt a large part of the excitement is due to different methods of lifting, etc. ; but after the emotional disturbance is allayed the "nosing" of the hand seems to indicate an odor stimulation also. The power to follow a trail is usually supposed to depend upon slight traces of body odor which remain upon the path which 2 Small, W. S. Notes on the psychic development of the young white rat. Am. Jour, of Psych., 11,89. 3 Watson, J. B. Kinaesthetic and organic sensations, etc. Psych. Rev. Mon. Sup., 8, no. 2, p. 65. 142 STELLA B. VINCENT an animal has taken. Animals which do not prey upon others for food have little need for tracking. Experimentation has failed to show such ability in these animals. Sex odor calls forth specific behavior. This odor, however, does not seem to carry from cage to cage even though the cages are placed side by side. Efforts to establish the tracking of one sex by the other have been made 4 . Watson said he found no good evidence of tracking but that adult rats showed preferences for entrances that contained the odor of the opposite sex. 5 Small insists that he had no evidence to show that the males followed their own tracks or those of other males or that females followed the tracks of the males. 6 Possibly these attempts have not been made at the right periods; at least the results are inconclusive. How well rats or other animals can localize odors is still an open experimental field as is also the possibility of olfaction functioning in giving distance values. The object of this work was to see whether an olfactory control could be introduced into the learning of the maze, and, if it could be, to discover how it would affect the learning process as compared with other forms of control. The modified Hampton Court maze was used, the same one which served for the experiments with vision. 7 Before beginning the work, the inside of the maze was heavily coated with white enamel paint to cover and to destroy any previous odors, and upon the floor of all of the runways were laid long strips of heavy white paper. The paper was cut 4 in. in width and where the strips overlapped they were fastened with gummed paper. Upon this papered floor was rubbed in, down the center of the runways, a narrow trail of alternating beef extract and cream cheese. It was thought better to use two substances in order to guard against a possible olfactory fatigue. The trail was laid upon paper because of the ease with which such a covering could be removed in varying the experiment and because of a desire to avoid a permanent odor in the maze. The rats used in this work were young, untrained rats about 4 Watson, J. B. Animal Education, p. 51. Small, W. S. Experimental study of the mental processes of the rat. Am. Jour, of Psych., 12, 232. 6 Op. cit., p. 53. 6 Op. cit., p. 213. 7 Vincent, S. B. Vision in the maze. Jour. Animal Behav., 5, t. THE WHITE RAT AND THE MAZE PROBLEM 143 90 days old. They were fed in the -maze and handled for a week preceding the beginning of the real work. During the experi- mentation they ran the maze three times a day under the stimulus of hunger and were amply fed at the conclusion of each day's work. The first experiment was one in which the trail was laid in the true path in the maze and not in the cul de sacs. EXPERIMENT I. Olfactory Trail in True Path 1. Behavior The behavior in this experiment will be described somewhat in detail since it is significant. There was none of the wild running seen in the usual maze reaction. When put in the box the rats were at once attracted by the odor. Their little noses went down to the trail and they began to follow it immediately. They moved along in a jerky fashion stopping occasionally to smell and to lap the trail with their tongues. This manner of running made their progress an exceedingly slow one. Both the cheese and the beef extract which were used were diluted with water so that there was but a very slight trace of the food on the paper. Still the animals may have obtained some satisfaction in lapping, but such gratification must have been very limited. In general the rats lingered longer over the cheese than over the beef extract trail. The odor was probably stronger. They often hesitated at the places where the trail changed from one substance to another and sometimes struck the "back" or "home trail" here. These returns only now and then resulted in an entrance into a blind alley. They usually ended where the trail changed again. The maze is so constructed that the food box is in the center. When in use, there is always food in this box which the animals are encouraged to smell before the beginning of the experiment and which furnishes their reward when they reach the box at the end of their run. The true path passes directly by the side of this box. (See "Vision in the Maze," Fig. 1.) In the normal maze the early runs are always broken at the food box which the animals have to pass in the center of the maze. The food odor is stronger here and they bite and claw and scratch in a futile endeavor to end the quest at this spot. But notwith- standing the marked early influence of the odor of the food box this behavior, in the normal maze, is very quickly abandoned. 144 STELLA B. VINCENT Long before the rats cease to enter the cut de sacs, before any of these errors are entirely cut out, the loitering at the food box is no longer to be seen. It only thereafter occurs in exceptional cases where an animal is entirely lost and as a consequence is in a disturbed and emotional condition in which all the old errors reappear. The behavior of the animals following the odor trail, on the contrary, although similar at the food box was more persistent than any "off trail," blind alley error. The odor, it will be remembered, was that of the food with which they were accustomed to be fed. Perhaps the previous stimulation of the olfactory trail had made the animals more susceptible to this influence. But whether, as a result of following a food odor trail, all food odors attracted the attention more, or whether this stronger food odor represented the natural instinctive ending of a food trail and thus called a halt, these are questions for thought. Either or both positions are plausible. Whatever the cause of this behavior, as a result of it, the speed in all of the early trials was slower than that in the normal maze; but by following the trail the animals were kept in the true path so that the errors were greatly decreased in both the initial and in the succeeding trials. 2. The Tables Table 1 shows, side by side, the records for the first twenty- five trials in the normal and the olfactory mazes. Figs. 1, 2, and 3, show the curves plotted from these records. These curves are not made like those shown in "Vision in the Maze" because in the olfactory maze the learning period covered less than ten trials and was practically uniform. The units used in plotting were one trial, one minute and one error. Since it was the following of the trail in which we were interested, the error consisted in leaving the track. Returns were not counted and this fact makes these curves comparable with those made for the black- white maze where the returns could not be counted. The results of this experiment show an increase in accuracy, both initial and total, over the normal maze and an increased final speed. We will consider first the facts which bear out these assertions as to accuracy. Jo <0 5 THE WHITE RAT AND THE MAZE PROBLEM 145 3. Comparative Accuracy As the table shows, in the first trial, these animals in the olfactory maze averaged only 4.5 errors as compared with 14.7 made in the normal maze. Thus the initial accuracy was three times as great. The final accuracy was greater also. The olfactory maze shows .04 average errors per trial for the last five trials while the normal maze has an average error of .1 per trial for the same five runs. The total number of errors per animal in the olfactory maze is only one-third that of the animals 5" (0 iS 30 3,5 io Figure 1. Time and error curves for Experiment I. Olfactory trail in the true path. Full line time, dotted line errors. in the normal maze. The error curve, seen in Fig. 1, bears out all of the above statements. Its chief features are the low begin- ning height, and hence slight fall, and the almost complete low level which it maintains after the twelfth trial. A comparison of the error curve of the normal maze with this will emphasize these facts better than words. 4. Speed The time per run for the early trials was less than in the normal maze as may be seen from the table but this was entirely owing to the fact that there were so few errors. The actual speed was much slower. In the first trial they averaged only 4.5 errors per 146 STELLA B. VINCENT animal yet the time average is 13.5 minutes. The record for the second trial is practically the same. Almost the same average number of errors, 4.1, was made by the normal animals in the fifth trial in an astonishingly shorter time. For the first trip without error these rats had an average time of 160 sec. The time record for fifteen rats in the normal maze for the first perfect trip is less than one-fifth of this — 30 sec. In final speed, however, these animals excel. This maze has an average record of .28 min. for the last five trials as against .31 min. for the normal maze. This is a difference of nearly two seconds — an appreciable difference when one remembers that the maze can be run in ten seconds. The time curve (Fig. 1) is very unlike the usual time curve. Compare it with Fig. 3. It is not the beginning height which is remarkable but the persistence with which it maintains this level — the slow rate of elimination of the surplus time. Forty- seven per cent of the surplus time was eliminated in the normal maze in the second trial, in the olfactory maze only 2.5% was eliminated at this time; 80% was eliminated in the first four trials in the normal maze, but it took the rats in the olfactory maze nine trials to reach this point. By the tenth trial the animals in the normal maze had only 2% surplus time left to eliminate, but the rats in the olfactory maze did not fall per- manently below this 2% point until the twenty-fifth run. It must be clearly evident that this olfactory trail was affecting the learning process but before any definite conclusions were drawn it was necessary to put the trail in the cut de sacs, instead of the true path and to see what would happen then. EXPERIMENT II. TRAIL IN CUL DE SACS 1. Behavior This experiment was conducted exactly like Experiment 1, with animals of the same age, etc. The only difference was in the trail which was laid from the entrance of each cut de sac to its extreme end. There was a noticeable difference in the numer- ical results as well as in the behavior under these conditions. The animals in this maze also made fewer errors from the beginning than the animals in the normal maze and the speed was greater also. When put in the maze the rat ran, as in the usual maze, headlong down the runways. Soon he blundered THE WHITE RAT AND THE MAZE PROBLEM 147 TABLE I Records of the First 25 Trials, Time and Errors, of Rats in Normal and Olfactory Mazes Average Time in Seconds per Trial Average Errors per Trial Trial Olfactory Olfactory Olfactory Olfactory Normal trail in trail in Normal trail in trail in true path errors true path errors 1 1804 820 991 14.7 4.5 9.6 2 966 800 463 11.9 4. 5.6 3 1043 224 598 10.4 1.1 7.3 4 847 609 331 7.4 1.6 5.3 5 231 175 49 4.1 2. 2. 6 192 165 54 3.5 1.5 1.8 7 64 376 30 1.6 .6 1.1 8 49 295 27 1.4 .8 .5 9 37 178 37 1.5 .3 .5 10 32 52 22 1.1 .3 .1 11 26 155 30 .7 .6 .1 12 25 29 36 .4 .3 .3 13 31 35 32 1. .1 .1 14 20 52 21 .3 .8 0. 15 32 27 45 .6 .3 0. 16 46 26 83 .7 .1 1.1 17 44 24 97 .5 0. .3 18 51 25 173 .6 0. 2.1 19 40 23 150 .1 0. .8 20 32 39 177 .2 .1 1.1 21 31 29 94 .2 .1 .7 22 26 32 262 0. .3 1.7 23 17 32 117 0. .3 .8 24 19 37 107 .1 0. .8 25 22 76 147 0. 0. .7 TABLE II Tabulated Statement of the Results in the Three Mazes Normal Maze Average time of learning. . 12.1 ±3.6 trials Average time of the first five trials J16.3 ±6.7 min. Average speed of the last five trials I .31 ± .05 min. Total surplus time 93.9 min. Average errors first trial. . . 14.7 ±7.7 Average errors in the last' five trials | .1 ± .14 Total average errors per animal 66.6 ± 16 First run without error. ... 8.3 ±3.1 Olfactory trail in true path 8.1 ±2.4 trials 8.7 ±3.9 min. .28 ± .08 min. 64.98 min. 4.5 ±3 .04 ± .04 20.5 ±5.6 6.3 ±2.8 Olfactory trail in errors 7.3 ±3.8 trials 8.1 ±5.2 min. .47 ±.08 min. 66.45 min. 9.6 ±6.8 .44 ± .21 52.1 ±12 7.5 ±1.8 148 STELLA B. VINCENT THE WHITE RAT AND THE MAZE PROBLEM 149 into a cul de sac and down went his nose to the trail which he followed for its entire course, to the end of the alley. He moved along by jerks, as described before, and when he reached the end, he turned and in the same irregular, slow, halting way returned to the entrance of the alley. Between the cul de sacs, he ran; but when in them, slow movements were the rule. As a result more time was spent in a single cul de sac than had been the case in any of the other experiments. Still, from the first, these excursions from the true path were lessened in number as compared with the normal maze. The blind alleys seemed to be marked for the animal in some way. He began to go less and less deeply into them and finally, as he was running more and more confidently in the true path, I have seen him, time and again, actually thrown back on his haunches if chance running flung him into the entrance of a cul de sac. Or, he might be running quickly, swerve into an entrance, and there would be seen an instant decisive turning the minute he struck the trail. It looked like a real discrimination. Surprisingly enough, however, after the problem was learned, and the animal was making 90% correct trials, these errors began to reappear and it took almost as long to get rid of them the second time as it did the first. The meaning of this will be discussed later. There were many more returns in this experiment than there were in the one where the trail was laid in the true path — five times as many in the first trial, It was a long time before the rats learned to pass the food-box without lingering. The numer- ical results for accuracy confirmed the conclusions drawn from the observed behavior. 2. Comparative Accuracy Under the conditions of this experiment, the accuracy was decidedly greater than in the normal maze in the first fifteen trials. If we now make a comparison with the other olfactory experiment, we find that more errors were made in the first nine trials than were made by the animals which followed the trail in the true path but that the next six trials were more perfect. From the fifteenth trial on, the accuracy was far less than in Experiment 1, or in the normal maze, and it was only toward the end of the experiment, that it again approached their standard. The curve (Fig. 2) shows this variation exactly. The total 150 STELLA B. VINCENT average number of errors per animal was 20% less than in the normal maze but the animals made two and one-half times as many errors as their brothers in the experiment where the trail was in the true path. The learning time was actually shorter than in Experiment 1. There is so little difference, however, that it may be a matter of chance. The conditions, as a whole, were very favorable for learning as compared with the normal Figure 3. Time and error curves for normal maze. Full line time, dotted line errors. maze and scarcely less so than those in Experiment 1, where the trail was in the true path. It seems fair to conclude, there- fore, that these conditions did affect the accuracy, and in general favorably, but that there was a variableness in the final reactions which will require explanation. 3. Comparative Speed The speed in this maze was quite comparable with that in the normal maze except when the rats were in the cul de sacs and, THE WHITE RAT AND THE MAZE PROBLEM 151 because the errors were so few, the slowness in these places placed the animals under only a slight disadvantage. The running was much more rapid than that reported in Experiment 1. The figures in Table 1, giving the time per trial, do not show this since the data for the total distance is lacking. In the first trial in Experiment 1, there was an average of 4.5 errors and 1 return. The animals did not go to the end of each cul de sac and the returns were only partial. In this experiment, with trail in cul de sacs in the first trial, there was an average of 9.6 errors and 5 returns per animal. The larger proportion of these returns were home returns and the cul de sacs were explored to their farthest limits. According to these figures the time should have been three times as long in the latter case had the speed been comparable, instead of which it is practically the same (See Table 1). From this we should conclude that the speed was three times as great in the first trial in Experiment II as it was in the same trial in Experiment 1 where the trail was in the true path. There was a variability of speed in the middle part of the experiment which clearly depends upon the increase in errors. (See the curves Fig. 2). The average speed of the first trial without error may be taken as a point of comparison as we do not possess the figures for the total distance. The normal maze gives us an average of 30 sec. for this trial, the maze with the trail in the true path 160 sec, and this one 28 sec. At this point, then, in this experiment, we have a speed which is quite as fast as that in the normal maze. The final speed, however, within the limits of the experiment, was less — .47 min. (See Table 2 ) . Whether longer experimentation would have developed a speed equal to that in the normal maze, or whether the condi- tions would always have mediated against it is a question for discussion. EXPERIMENT III. TRANSFER OF TRAINING This experiment was the crucial one. The conduct of the rats had been affected by the olfactory trail in the maze, the learning had been aided, but had the animals really gained anything which they could carry over to another problem ? Was an olfactory control so well established that it could be utilized in another situation ? It was determined to take the animals, at the conclusion of Experiment 1 on the maze, over to a problem 152 STELLA B. VINCENT box. This box had three runways, leading from a common entrance, and they terminated in a food-box. The paper trail, some of the original paper from the runways, could be laid along these runways, changed in irregular order, and the rats tested here. Before taking them to the box, however, after the con- clusion of Experiment 1, the paper was entirely removed from the maze and the rats given one trial each on the maze itself. They made perfect runs showing no hesitation whatever. They did not seem to miss the paper at all and even incorporated in the runs a slight "slowing up," as had always been the case at the places where the trail changed from beef extract to cheese. Evidently the control had become kinaesthetic. The question we had to face now was this: Had the olfactory experience persisted notwithstanding the change of control. The rats were now taken over to the box. The first trials here gave entirely negative evidence. The olfactory trail might as well have been absent for all the attention which the rats gave to it. The path with the trail was only taken on an average of six times out of twenty trials. The next morning the animals were tried again and then it was seen what they were doing. No matter where the trail was laid, they were always making a straight run to the left and down the runway on the left side. Now this was just their first run in the maze. Clearly kinaesthesis was at the helm and olfaction had retired from the engagement. It was necessary, therefore, to arrange conditions such that the opportunity to make this run to the right or to the left should be done away with — a condition in which position so far as possible should be eliminated. A long rose box, about three feet in length was procured from a florist and in its end were inserted long, heavy, pasteboard mailing tubes. These tubes just filled one end of the box. They were lined with paper taken from the maze and one tube contained paper on which was the trail. In the experiment the tubes were alternated according to an irregular schedule. For the next few days the rats were tried out in this box. When they were put in at the end farthest from the tubes they immediately ran down to these exits. The two openings were side by side, there was no chance to turn, and in fifty trials they made 90% correct choices: i. e., they followed the trail nine-tenths of the time. While sitting in front of the tubes the rats could smell THE WHITE RAT AND THE MAZE PROBLEM 153 either one indifferently so there was usually a momentary hesi- tation at the entrances and then a dash into one or the other. Sometimes the head was put in tentatively and then came the sudden run through or the withdrawal. The experiment showed, conclusively, that the olfactory experience had been retained and that it could be utilized again. It also showed that the reaction to the original problem had become a matter of habit and that so strong and powerful was kinaesthesis that the removal of the sensory factors which helped to establish it had no effect upon its control. When later the animals were confronted with a problem where turning to the right or to the left was possible the response was in kinaesthetic, or tactual-motor terms. But when the possibility of runs and turns were cut out the effects of the olfactory learning and experience were asserted in a per- fectly effectual way. That this was not due to any attractiveness of the trail in itself is shown by Experiment IV. EXPERIMENT IV. ANOTHER TRANSFER This was the discrimination test for Experiment II. The same box and the same method was used as in Experiment III. Under these conditions the animals had to choose the path where there was no trail. They did this just as consistently as the others making just as good a record and confirmed in all points the conclusions drawn from Experiment III. The details are not needed here. DISCUSSION AND CONCLUSIONS Whatever may be true of rats in their native environment, we agree with Small, 8 that these animals do not usually follow a path in the maze by means of scent; yet, as these results show, they can do so. The evidence here is also against Professor Watson's statement that. "Olfactory sensations have no role in the selection of the proper turns in the maze. 9 " This assertion may be quite true of work on the maze as he used it, but certainly olfaction, in the experiments reported in this paper, helped to cut out the errors. Although we have seen no signs of instinctive tracking, these animals will follow an odor trail on first trial and can learn to follow an olfactory trail or to avoid such a trail. If a maze problem presents such a trail the result is an initial 8 Op. cit., p. 232. 9 Kinaesthetic and organic sensations, etc., p. 91. 154 STELLA B. VINCENT and total accuracy which is greater than normal although the final accuracy, when the trail is in the cul de sacs, is less. The learning time is also shortened. We should therefore say that such an olfactory control distinctly favors accuracy. How shall we explain this increased accuracy ? Was it a result of real sensory discrimination ? It can be explained, as the results in the black-white maze were explained, as being due to the dominance of some particular stimulus. A path, out upon which an animal first runs in a maze, if not alarming, becomes a familiar place — a home place. There may afterward be other such places in the maze, but this is the first one. He runs out from here, returns, goes a little farther, etc., but always with the possibility of the home return. In Experiment 1, the path was associated with a strong odor trail. Departure from this was to go into the unfamiliar and strange. Thus from the first the animal had more of this stimulus and it became in- creasingly familiar and increasingly dominant. Dominance, as a term here, may be explained in one way as the power of the familiar. It may have other explanations. Rats are seemingly possessed with an instinctive curiosity or tendency to explore; but fighting against this is an innate tendency to keep in familiar or known situations. The familiar or known situation in Exper- iment 1, was near the odor trail; in Experiment II, it was away from it. If we accept this view the odor stimulus would be powerful enough to keep an animal in the true path if it arose from this path or to keep it from the blind alleys if it lay there. It would work both ways. It w r ould do so by holding the atten- tion to the true path or by catching the attention and so serving as a warning when the animal strayed from the path. The errors would be lessened in either case. There were actions, however, which seemed to show that this behavior was more than a mere passive affair. I take it that an instant response to a stimulus, w T hen not instinctive, — a response which can be learned and which can be varied, now positively and now negatively — involves discrimination. There was none of this seen in the black-white maze. There was such behavior here. If this be the case, while the first explanation may be a true and a reasonable one, the increased accuracy here was partly, at least, a result of discriminative ability. There was an increase of errors in the middle of the learning THE WHITE RAT AND THE MAZE PROBLEM 155 period in Experiment II, and some slight evidence of the same thing in Experiment I. (See curves Fig. 1 and 2). The only interpretation 1 can offer is this: It was the result of the changing sensory control. The initial control was dom- inantly olfactory: but with repeated trials the kinaesthetic experience grew and strengthened and finally began to come into its own. The running became easy and rapid and the accuracy was becoming habitual. Attention, now being released from the control of the movement, was free to be attracted by the olfactory trail in the cut de sacs and errors became more frequent. The final elimination may have been, and probably was, a relearning with kinaesthesis more firmly established. But besides accuracy there is also speed to consider. The conditions of the two experiments give results which differ radically here. As compared with the normal maze, Experiment 1 showed slow initial speed and quick final. Ex- periment II showed quick initial speed and slow final. Let us first discuss Experiment II. There is no need to take much time here to discuss the speed in Experiment II. The true path resembled that of the normal maze and the beginning speed was comparable. The slower final speed was a result of the increase of errors. The variable curve seen in Fig. 3 has the same explanation. But let us turn to Experiment 1, where the facts are better seen. Olfaction has two uses. First it functions as a distance sense. The reaction in this case is always running — toward food, away from danger. The second function is associated with food- taking. Olfaction is so intimately associated with food-taking that, in man, taste and smell are difficult to disassociate. The point which is here to be emphasized is that when the second of these functions is set up in animals in connection with food it inhibits the first. It seems probable that olfaction furnishes animals with a more accurate criterion of distance than it fur- nishes man and that the nearness of food, with the consequent increased intensity, is the stimulus for the food-taking reaction and the running ceases or slows up. The one response is antici- patory, as Sherrington says, 10 the other consummatory. The one is a somatic reaction, involving the whole body, the other is visceral and confined to certain organs and segments. 10 Sherrington, C. S. Integrative action of the nervous system. 156 STELLA B. VINCENT If we now attempt to explain the slowness of the reactions of the rats in the maze in Experiment 1 , there are several possible interpretations: First, the slowness may be due to the fact that the odor of the food box which served to initiate the reaction is swamped, overpowered, by the nearer, more potent odor of the trail; or, second, that attention is divided between the two and hence we have the characteristic behavior; third, it may be that the pleasurable feeling set up by the odor of the trail is in itself a deterrent and results in loitering; or fourth, it may be that the nearness and strength of this stimulus does initiate the preliminary instinctive food-taking reactions which of them- selves end or modify the distance reactions of running. As one observed the behavior in the initial trial, there did not seem to be any emotional excitement which would suggest the inhibition of running through conflicting motor tendencies and hence the second explanation is discredited. That the trail odor was the predominating one in the first trial seems probable and that it was also pleasurable. The satisfaction of hunger at the end of this trial, however, must, in all succeeding trials, have played a large part and made the original trail a different more intense, more stimulating trail, a somewhat else, viz., a trail which ended with this satisfaction. Yet still there was the loitering and slow movement through all of the early trials which would lead us to think that the fourth supposition may be a reasonable one. Why, then, did this behavior alter in the later trials ? Because of the organization of the whole response into an habitual motor series which only required the odor for the initiation and possible reinforcement of the act. The more rapid final speed, which exceeded the normal, may have been caused by the reinforcement of the kinaesthetic control, now established, by the olfaction of the trail. Miss Richardson says, 11 "Olfaction may accelerate or retard the learning process; accelerate when the odor is a part of the stimulus connected with the problem — otherwise be disadvan- tageous." It is easy to conceive that it may have the same effect upon the actual rate of running — that it may result here in a genuine acceleration of speed. While the main purpose of this work was to establish and to 11 Richardson, F. R. A study of sensory control in the rat. Psych. Rev. Mon. Sup., 12, no. 1, p. 68. THE WHITE RAT AND THE MAZE PROBLEM 157 study the effects of an olfactory control in the maze, one of the most interesting features of the results was the proof of a transfer of training. So far as the writer knows there has not been shown before in the animal world, at least in such a graphic way, this change of sensory control from one form to another within a single learning process. THE CHICAGO EXPERIMENTS WITH RACCOONS L. W. COLE University of Colorado At the University of Chicago, three of Professor Carr's gradu- ate students, Dr. W. S. Hunter, 1 and Messrs. F. M. Gregg and C. A. McPheeters 2 have been engaged in repeating experiments similar to mine on raccoons, with results which are most grati- fying to me. Hunter (p. 46 and beyond) found the behavior of the raccoons as different from that of his dogs and rats as I found it different from the behavior of cats. He was compelled, as a result of his experiments, to give up the mere sensori-motor explanation of the behavior of these animals, nor could he attribute it to the association of motor impulses with a whole situation. Motor attitudes could, he thought, account for the behavior of the rats and dogs. It would not serve for an explanation of the reactions of the raccoons. At the close of my experiments, I, too, was compelled to regard those explanations as inadequate. He found that children and raccoons could respond successfully to a stimulus after a much longer delay than could the rats and dogs. He found for the raccoons a maximum delay of twenty- five seconds. The longest delay that I used was at least six seconds, or possibly nine seconds, if we consider only positive reactions of the animals. He compares the behavior of the raccoon favorably with that of a two-and-a-half -year-old child. Moreover, he admits an idea as a "possible cue" used by the raccoons and the children, as against purely motor or sensory cues, used by the other animals tested, though he prefers to attribute the reactions of the raccoons and those of, at least, the youngest child to "imageless thought." Now that my experiments have been confirmed so fully I must 1 Hunter, Walter. S The delayed reaction in animals and children. Behavior Monographs, vol. 1, no. 1, 1913. 2 Gregg, F. M. and McPheeters, C. A. Behavior of raccoons to a temporal series of stimuli. Jour. Animal Behavior, 1913, 3, 241-259. 158 THE CHICAGO EXPERIMENTS WITH RACCOONS 159 regard them as established. This seems to me to be an item of progress. The psychology of mammals must now cease to be a mere generalization of the psychology of cats. And two of my former students, Professor DeVoss and Miss Rose Ganson, have recently shown what I believe to be an excellent reason why cats may not be expected to behave the same as animals with less defective vision. We have, then, been driven from the cover Of accounting for all mammalian behavior by the sensori-motor hypothesis alone, and psychologists are free at last to try to learn how animals differ in their behavior, instead of denying all differences. This will help enormously, for it may enable us finally to discover a psychology of the higher animals which can explain as well as deny, which can be taken out of the laboratory and yet bear the light of day and the scrutiny of intelligent persons who observe animals. This we have not had. When you meet an observer of horses, who thinks his horse remembers its home, you do not convince him by denying his statements and the evidence he gives, or by calling him "naively anthropomorphic," or by telling him that he did not record the date of the occurrence, or by hurling at him the anathema of "anecdotal psychologist" with opinions "too trivial for serious analysis or notice". A science which can only deny everything and explain nothing is no science and will never receive nor deserve confidence. It certainly was legitimate in 1898 to start by denying the worth of anecdotes of animals for comparative psychology, but only if by denying them we should eventually find a way to explain them, or at least to explain observations of animal behavior which are made almost every day. Experimental animal psychology is now sixteen years old. Consequently it must soon cease to be a generalization of the behavior of cats and take some step which promises eventually to explain animal behavior. Otherwise it must confess bankruptcy and its inferi- ority to common sense, and remain a sort of science which cannot emerge from the laboratory and which cannot be believed by the psychologist himself the moment he emerges from it. I am in no hurry for this science to make progress but I should like to see it take a direction which promises something. I do not think that a devoted effort to adhere to an objective nomen- clature, or to hang the fate of progress on some word, as behavior, 160 L. W. COLE or behaviorism, or forever to deny what many observers affirm. is taking a promising direction. It is true that the professors at the University of Pisa saw Galileo drop the weights, and saw them reach the ground at the same moment, and yet refused to believe the evidence of their senses. Animal psychology which merely denies has had an influence in university circles similar to the influence of Aristotle on the professors at Pisa, but it has gained no such influence upon intelligent observers elsewhere. Instead of denying all psychic traits to animals would it not be better to deny our competence to explain more than the merest trifle of animal behavior ? I believe that Hunter's confirmation of my results should give a new stimulus to investigators to devise ingenious new experiments suited to find new facts. That avenue seems more hopeful than a denial that there are new facts to be found, and affirming that animal psychology must become a sort of "organic physics." It is of interest to observe also that while current mammalian psychology cannot come out of the laboratory, common sense observations continually find their way into it. In this paper of Hunter's, for example, one animal is a "stranger" to another and so pays close "attention" to the latter's movements. Pre- liminary experiments make his animals "acquainted" with the place and apparatus. The raccoons display a directness and "sureness" in their behavior which defies the mathematics of chance. Their "attention" was "distracted" by "yelling at them at the top of my voice" (P. 71). (A procedure likely to make them fierce beyond recall, and which, perhaps, explains the last statement of Dr. Hunter's paper. It is gratifying to learn that this method of distraction was used only infrequently.) Attention and association are everywhere ascribed to the animals and not the association so accurately described by Thorndike, but association pure and undefined. Surely these are greater and more gratuitous assumptions to make than that a horse remembers his stable, even when distant from it, or that a raccoon remembers the box from which it is difficult for him to escape. I realize that these remarks will expose me to the charge of being as completely deceived as was Herr von Osten, but his is not my position. My view is that "imageless thought," if Hunter's hypothesis is deemed correct, or, at least sporadic, images if my own explanation is accepted as the simpler one, THE CHICAGO EXPERIMENTS WITH RACCOONS 161 are perhaps so rare in animal experience that the most refined experiments will be required to discover and identify them; experiments beside which Hunter's experiments, and mine, will pale into insignificance, because of their simplicity. There is still another reason for hoping that the study of animal intelligence may sometime get beyond the stage of dispute and denial. Dispute and denial are poor material to occupy the time of college students. Long ago I had to give up that kind of teaching ,and occupy myself with the more solid infor- mation which we possess, of animal sense organs, because dialectic should be taught in philosophy and not in science. Note the extensive work of Kafka 3 , the first volume of which has just appeared. Dr. Hunter's agreement with me does not end with the facts noted above. He is almost persuaded to credit my experiments in putting the animals through the act to be learned, because he has observed the same sort of behavior in rats. At least he admits my apparent credibility relative to my four raccoons. It would be unfair to him, however, not to state his qualifications. On page fourteen he says: "Now with reference to that type of experiment in which the problem learned is that of working latches rather than climbing into boxes, I believe the data presented by Cole are conclusive, as far as the facts are concerned. Some raccoons at least appear to learn by being "put through." Whether all raccoons would do so is, of course, quite another matter/' (Italics mine.) The reader may reply, "You can surely get but cold comfort from this admission." It gives you the merest semblance or 'appearance' of credibility with regard to your report on your four animals alone. I at least have not charged you with having invented your records." True enough, but the admission means that Hunter's rats, if they have not made a breach, have at least made a weak place in the blank wall of opposition and denial. The latter is definitely given up. How wonderful is the rat at undermining ! The cold comfort comes from the facts that those experiments of mine have not been repeated at Chicago University. I fear, because their raccoons would not permit it (Hunter p. 86). Now should the Chicago laboratory secure a toothless raccoon 3 Kafka, Gustav. Einfuhrung in die Tierpsychologie. Leipzig, 1914. 162 L. W. COLE what may not become of the credibility, temporarily and with qualifications, accorded me ? But what disposition, pray, will then be made of the behavior of Hunter's rats ? With many misgivings, therefore, I await the report of experiments which may even now be in progress. In instinctive behavior the Chicago raccoons confirmed my observations rather than those of Davis. Yet I am sure Davis's report is correct, despite the authorities quoted against him, for I saw occasional cases of what he observed regularly. We must not be too cocksure in these matters. Remember that Audubon never saw his pet raccoon wash its food in the water beside it (Davis p. 45 1 ) . 4 Yet that behavior gives to the raccoon both the name "lotor," and the name "Waschbar". 5 Interpretations: The reader who is familiar with Dr. Hunter's thesis will recognize the agreements I have mentioned between the behavior of my raccoons and those of the Chicago laboratory. Our interpretations of this behavior are entirely different, of course, except that we were both forced to give up the sensori- motor explanation. Forced from that position, I thought the animal might have memory, or at least a few memory images carried in visual terms, hence a visual image. I still believe that this is the simplest, or as some prefer to say, the most "parsimonious hypothesis." Hunter prefers the assumption of "imageless thought" or "sensory thought" to account for the raccoons behavior, and for that of at least the youngest child. This "imageless thought" must be, at least partly, visual, for he says (p. 74), "In the present case there seems to be no room for doubt that the object reacted to was the light." The reader must remember that this light had been turned off for twenty- five seconds before the animal was permitted to react to it, in the maximal delays with raccoons, hence the "representative functions," next mentioned. For he continues thus: "Now if a representative function were involved in the behavior of the reagents, as seems to have been the case with the raccoons and children, it must in part at least, have been representative of the lighted box, because all else — including the three possibilities 4 Davis, H. B. The raccoon : a study in animal intelligence. Amer. Jour, of Psychology, 1907, 18, 5 1 have to thank Mrs. R. M. Yerkes for calling my attention to this splendidly appropriate German name for the raccoon, and its superiority to the American name, whose source is not certain. THE CHICAGO EXPERIMENTS WITH RACCOONS 163 of movement — was constant from trial to trial, whereas a selective response must needs have an alternating cue". (Italics mine). I know of no way in which light can stimulate these animals except visually. And when the animals were permitted to react, it was by means of a function representative (at least partly) of the lighted box. One would think that the simplest escape from this dilemma would be by means of a visual image. But no, it is visual in source or cause, yet imageless in content. We have often been led to believe that sensation gives a rather fundamental content to thought. Perhaps we may now teach that Helen Keller, for example, has both the content of visual experience as well as a knowledge of its relations. Loeb 6 has recently given evidence to show that a retinal image produces a brain image, which corresponds with the former point for point. "Diese Tatsachen enthalten aber, wie mir scheint, auch den Nachweiss, dass in Gehirn ein Bild der gesehenen Gegen- staende entsehen muss" (p. 1016). By Hunter's hypothesis all of this image forming apparatus is rather useless, for no mental image arises in the raccoon, nor perhaps in the youngest child, under the conditions of the experiment. Doubtless it will occur to the reader of Hunter's paper that this explanation of the raccoons' behavior, by means of imageless thought, was in no way suggested to him by his experiments and seems to be a rather foreign addition to his thesis, forced upon him by the milieu or suggested by current discussions of the topic in human psychology. In order to use the concept to account for the results of his experiments he must make the claim (p. 77) that imageless thought is genetically prior to thoughts with images, and he must dismiss the opposite teaching as having "no factual basis" but seeming to be "the result of prejudice or of temperamental leaning." Then the point of origin of imageless thought is placed "at least as low as the raccoon" (p. 77). All this seems a trifle complex to me but the actual advance made is, now that the old explanation has been given up, that the reader may choose what hypothesis he will under the law of parsimony. Doubtless psychologists will be more interested in Hunter's immediate explanation than in his final one, which I have already 6 Loeb, J. Die Bedeutung der Anpassung der Fische an den Untergrund fuer die Auffassung des Mechanismus des Sehens. Zeit.f. Physiol., 1911, 25, 1015-1017. 164 L. W. COLE outlined. When the conditions of his experiment demanded that the animals go to an electric bulb, whose light had been extin- guished some seconds before, in order to execute a successful reaction, the rats and the dogs oriented toward the light, either with the whole body, or at least faced in its direction. They kept this orientation during the period of delay in so many of their correct responses that this "motor attitude" evidently served to bridge the time gap between the disappearance of the light and the release of the animal. Consequently their "motor- attitude" accounts for the success of the rats and dogs. The raccoons and the children did not even face the light in so great a proportion of their successful responses that the "motor- attitudes" hypothesis breaks down completely, as an explanation of their behavior. As a result of this outcome of the experiments, Hunter (p. 80) decides that, "Some intra-organic (non-orientation) factor not visible to the experimenter must be assumed in order to explain a significant number of the correct reactions of the raccoons and all of the successful reactions of the children. These cues fulfilled an ideational function." (Italics mine.) And again (p. 72), "As we have indicated, such a mechanism would apply only to the non-orientation cues used by the raccoons and children. The type of function here involved is ideational in character. By applying the term "ideas" to these cues, I mean that they are similar to the memory idea of human experience so far as function and mechanism are concerned. They are the residual effects of sensory stimuli which are retained and which may be subsequently reexcited. The revival, moreover, is selective and adaptive to the solution of a definite problem, and when aroused, they function successfully as a necessary substitute for a definite component of the objective stimulus aspect of the problem." He has already said that the effective component of the stimulus was the light. Unless he denies, then, a visual content to this "factor," it is a visual, imageless thought. But since he does deny it a representative content, though it has a representative function, he terms it "sensory thought," though the stimulus has been absent twenty-five seconds in the longest delays of the raccoons. This "sensory thought" then becomes the image- less thought of current discussion, by the genetic reversal of current opinion on that subject that I have mentioned above. THE CHICAGO EXPERIMENTS WITH RACCOONS 165 It is interesting to observe how very "similar to the memory idea" is this "intra-organic factor." It is a residual effect of a sensory stimulus. It may be retained and revived, is selective, etc. Elsewhere (p. 69), he describes this factor as "Some unknown intra-organic cue non-observable by the experimenter. Our data prove conclusively that some such cue was utilized by the raccoons and the children, the nature of such a factor must necessarily be defined at present in negative terms." When this statement was written it evidently had not occurred to Hunter to place this negative thing in the positive category of imageless thought. His experiments were completely described before reaching this point. Hence, it seems to me that imageless thought was an afterthought, as an explanation. On the second page of the paper we find this significant state- ment. "In the interpretative discussion at the close of the present monograph, we shall be confronted with the possibility that images or ideas may have guided the reactions of the subjects. In discussion, we shall assume that there is no necessity that psychology postulate such a representative factor save where successful reactions occur in the absence of the stimulus (object) or movement represented." So images may have been present. Yet throughout his references to my paper Hunter complains that I did not reach a proof of the presence of images. When his experiments were completed, he seems to be in much the same position. Just how an experimenter can give proof that animals remember or think, even in imageless thought, I am quite unable to guess. I thought that my animals gave evidence of possessing visual memory. Hunter's experiments strengthen this opinion of mine very much. Like Brehm and all subsequent observers of the raccoon, Hunter has noted the fly-catching activities of this animal. He consequently accords to the "Waschbar" the possession of acute vision. In this he agrees with my report. 7 Errors: On page eighteen, in re-describing some of my experiments, Hunter says, "a block with a steeple was placed in a hole," etc. With absolute confidence I must assure the psychological public that I used no "steeple" in my apparatus. 7 Cole, Lawrence W. Observations of the senses and instincts of the raccoon. Jour, of Animal Behavior, 1912, 2, 302. 166 L. W. COLE I have, very rarely, heard the word "steeple" used for "staple," but never before have I seen it so used in a scientific monograph. Again, I am regarded as having been "misleading" (p. 86) in my statement that "the year-old raccoons apparently are not quite full grown," for Dr. Hornaday and Mr. DeVry say "that raccoons reach maturity at three years of age." But do Dr. Hornaday and Mr. DeVry mean, therefore, that the raccoon accomplishes but one third of his growth each year, as Hunter seems to interpret them ? I cannot believe it. I kept my animals three years and I wish now to re-affirm the statement above. They grew but little after the first year. Work and confinement may have stunted them, though they were fed each day to satiety. In parks I have now seen many raccoons of about the same size which mine attained. They had been in confinement for a long time so they must have been full grown. I have also seen a number of much larger specimens. Criticisms of my Work: The introduction to Dr. Hunter's thesis takes the form of a fearful arraignment of both my experi- ments and my arguments. To use his own phrase, most of the latter "can be dismissed summarily" (p. 16). They are in turn dismissed summarily in favor of the sensori-motor explan- ation, so his theory of raccoon behavior at the beginning of his paper differs entirely from that at its close. I suppose that I ought to make some reply to these criticisms, but I shall be as brief as possible and at that I shall select only the most important ones. It seems better to omit any answer at all to such remarks as, "To some it may seem too trivial either for serious analysis or notice" (p. 10), a criticism which I seem to share with Lloyd Morgan and others, save that I have persisted in their trivialities. Criticism 1. "Hence assuming the facts that Thorndike and Cole assume to be unquestionable, it need only follow that the raccoon exhibits more complex sensori-motor behavior than the dog and the cat, and not that it shows a new type of behavior, i. e., a type of behavior involving the functional presence of a representative factor." (P. 15.) Reply. Yet he later found just such a factor functionally present in raccoons. Criticism 2 . 'To argue that this means image of apple is certainly naive at least. Could the raccoon not sense the apple when his nose was within a foot of it ?" (P. 18.) THE CHICAGO EXPERIMENTS WITH RACCOONS 167 Reply. Hardly probable, since the floor between him and the piece was carefully rubbed with another piece of the same apple, and his forepaws were still moist with the pieces of apple he had already eaten. But note Hunter's argument (p. 27) that smell was eliminated in his experiments because the rat was given only a bite, "so almost no food fell on the floor." Food was used with the raccoons in the same way. Criticism 3 . Varying means to the same end. My data under this head are just as inconclusive as that presented above. (P. 17.) Reply. Curious then that Professor James thought this "the mark and criterion of the presence of mentality in a phenomenon." "We all use this test," says James, "to discriminate between an intelligent and a mechanical performance." Criticism 4 "The criticisms on Cole's entire work reduce to these: (1) The facts are either inconclusive or irrelevant. And (2) there is no evidence of adequate controls." (P. 20.) Reply (a) Why then are the same facts, namely, responses to an absent stimulus, so satisfyingly conclusive of imageless thought ? This recalls the remark of Hodgson, "What you know least about, assert to be the explanation of everything else." (I quote from memory.) (b) "No controls." This is the repeated cry in these papers. It seems probable from the statements of the papers that their authors did not read my account and that they misunderstood the few pages they did read. I shall show this in detail in showing that Gregg and McPheeters (and their experiment was planned by Hunter) have entirely misunderstood what I did. In concluding the discussion of Hunter's report alone the points of similarity between his experiments and mine may be enumerated. He extinguished lamps which were used as stimuli, while I put a series of objects in view of the animal, then out of view again, and he must discriminate, under these conditions, between absent stimuli. Hunter secured delay by caging the animal, while I secured it by not feeding the animal until every member of the series had been put in view and (except the last member) out of view again. Sometimes six objects were used by me (i. e., each of three cards was shown twice). Hunter found it inapplicable to use the third light in many cases. 168 L. W. COLE The second paper, that of Gregg and McPheeters, had no other object than "to demonstrate the inadequacy of Cole's experiment." (P. 258.) They reconstructed my " card-display er," except that the levers were not screened from the view or touch of the animal and a system of strings and pulleys was added which the animal could also see. Then they gave the two raccoons two days training on the levers alone without any cards attached to them. (P. 245.) One of the two animals, Jack, failed utterly to discriminate. "Further training might have developed discriminative reactions in his case but time did not permit a continuance of the tests." (P. 246.) Jill discriminated between the two series on some basis, but Jill also "soon acquired the habit of standing close to the levers and touching her nose to them as they appeared." (P. 247.) Here, the reader will doubtless say that all analogy with my experiment ends. I should agree to this so far as the method and apparatus are concerned but it seems easier to change those than to change the nature of the raccoon, for there is a startling agreement between the behavior of their one successful animal and my four. Let us find this agreement. In the training series Gregg and McPheeters kept two constant factors. (1) A "normal" order of lever positions used, according to their respective distances from the animal. (2) They always presented the levers in series of three. Jill reacted to the order of lever positions chiefly, perhaps (p. 249), but she responded partly to the threes, for they say (p. 252), "Positive reactions of food getting may be stimulated successfully by any of the following groups, 1-2-3, 1-3-3, 1-2-2, 2-2-2, or 1-1-1. Likewise, inhibition, or negative responses may be stimulated by either group 3-3-3, or 2-2-2. The nature of the stimulus is relative to the character of the group with which it is alternated." One cannot help asking, why continue to alternate by threes only, unless they meant to teach the animal to respond to alternate threes ? Why not alternate by sixes as I did ? This was one of my "controls," which they have overlooked. Jill reacted to the two constant factors. In my experiments only the color (and brightness) of the cards was kept constant. My four animals responded to that. In both the Chicago THE CHICAGO EXPERIMENTS WITH RACCOONS 169 experiments and my own the raccoons responded to the constant factor. What more could they do, pray ? This seems to me to be an excellent example of the method of agreement. But this was the behavior of Jill, the single raccoon which succeeded in discriminating in their experiments. One would suppose that no very weighty conclusions would be drawn from the behavior of the animal which failed. But he is said to have responded to the sounds of the levers. Their "usual sound." (P. 248.) (Why not make the levers noiseless ?). This animal then responded to sound, perhaps partly to lever order and, I have no doubt, to any other element of the situation which was left constant, and which also enabled him to get food. "He seemed to watch the peep hole, although possibly he was merely listening for some sound upon which to base his reactions" (P. 246), so they set a metronome going to drown the noises made by movements of the experimenter! I confess I can see nothing in these experiments except a rather determined effort to divert the animal's attention from the cards and to get him to respond to the levers. The following items seem to show this: 1. Two days preliminary training on levers alone. 2. The board screen was reduced to "about five inches" in width (p. 244), thus showing apparently two thirds of the length of the levers, if Figures 2 and 4 (pp. 243 and 247) correctly represent the apparatus. 3. Putting the cards above the raccoon's line of vision, if Figure 4 is correct. 4. Converting my visual experiment into a tactual one by letting the raccoon touch the levers. 5. Adding the cue of noises in operating the levers, as well as noises due to the experimenter's movements. 6. Each of the three strings attached to the levers (Figure 4, p. 247) must have changed from slack to taut before the lever appeared, thus further directing the animal's attention to the levers' positions. I am unable to find "controls" against the animals having reacted to the strings. 7. Feeding the raccoon for having reacted to the levers. . 8. The colored cards were much smaller than mine. 9. Finally only one of their animals succeeded in discriminating as compared with four of mine. 170 L. W. COLE 'The essentials of Cole's apparatus and method were duplicated in our experiment." (P. 244.) Truly, with all these carefully arranged differences, I am quite unable to find that the "essen- tials" of the experiment were even similar to mine, but the reader may judge for himself. Any one who is familiar with my paper will remember that only a small part of the upper portion of the lever projected above the screen board. To be specific, my notes of Dec. 6, 1905, state that the lever "when upright" extended "one inch above the upper edge of the front piece." "Controls 1 ' 1 By the charge that I did not employ "adequate controls" is meant chiefly that I did not guard against discrimin- ation by position of cards and levers nor against discrimination by cues given by the experimenter. Let me call attention to two items which my critics have overlooked relative to the first precautions, and quote from notes of the experiments. On page 228, I say, "During one test red would be on the forward lever, one inch in front of the other, during the next test on the rear lever. The animal could not, therefore, react to the position of the cards." I did not re-state this precaution in the portion of my account on which the Chicago laboratory based its experi- ments, but one presumes that a critic reads completely the paper he criticises. To show that this precaution was kept up during* the three-color work I will quote my "daily plan" for one animal for three consecutive days. "April 23. Jack. Same as preceding. Blue middle, orange back, white front." "April 24. Jack. Three colors. Orange front, white middle, blue back." "Jack. April 25. Three colors. Blue front, orange middle, white back." It is evident that each card occupied every possible position in each three consecutive tests, and that no card occupied the same position for any two tests. Does this look as if I took no precautions against the animals reacting to the positions of the cards ? I find no such precautions as this, to leave only the colors constant, in the work of Gregg and McPheeters, so it seems that the animal was fed for depending on another cue. But the uninformed reader may ask, "But what of level position ?" At the beginning of each days work the levers THE CHICAGO EXPERIMENTS WITH RACCOONS 171 were "strung" on their supporting pivot in any order in which they were picked up. We did not remove them from the room in which the raccoons were kept and we generally found them scattered about the room. The levers were all alike so far as we could detect, until having split one, we replaced it with one having a "new" appearance. This should have brought a new type of result if the animals were responding to the appearance of the levers. It is true that this change of card position is mentioned briefly at the outset of the experiments instead of within the portion on which the Chicago experiments were based. But was no further precaution taken which was described on the final pages of report ? On page 259, Table 11,1 record that for two hundred trials the threes were "shown twice." Since this has been un- noticed or misunderstood let me explain it. It means that I would show red, red, red, red, red, red, and the animal must stay down through it all. Then came white, orange, red, and only then would the animal climb up on the high step to be fed. Thus nine movements were made, and all the levers were used. Then followed white, orange, red, and the animal reacted posi- tively and was fed. Thus he could hardly have been responding to alternate threes, or to lever position. Note also that there was an abrupt transition from showing the cards by threes to showing them by sixes. Yet the animal gradually learned to discriminate in this complicated experiment in which all factors were different, except the colors of the absent cards. I describe this showing the cards by sixes at the bottom of page 258, and refer to it as "while you raise three or even six colors, again on page 261." Perhaps tiiis detailed account of the precautions taken to guard against discrimination by threes, and against discrimination by position will serve to convince the reader that the experiments were not so careless or hasty as my critics have supposed. But it is further assumed that I mixed the experiments in which the experimenter manipulated the levers with those in which the animal was permitted to claw at them. The two types of experiment were separated by months. My paper states (p. 233) that no tendency to claw at the levers appeared for six weeks of the first type of experiment. After it did appear, clawing at the levers was not permitted until we had learned 172 L. W. COLE what we could by the experimenter's operating them. Nor did the raccoons attempt to claw at the levers, if the experimenter manipulated them rapidly. In fact we developed the habit by moving the levers slowly. This confusion on the part of Hunter, Gregg and McPheeters appears to be due to my giving a logical, instead of a chronological account of my experiments. The behavior of my raccoons was not, therefore due to touch. Consequently Hunter's experiments with lights is more similar to mine than that of Gregg and McPheeters, whose "card- displayer" had some points in common with mine. As to cues from the experimenter, I always extended my hand as if to feed the animal, at the negative as well as at the positive series. My notes contain many instances, at first, of this re- sponse to the hand. These were of course counted against the animal, and finally he ceased to be influenced by the movement. Different experimenters operated the levers and, in one case, it was found that the animals were responding to unconscious movements of the operator. This is mentioned in describing the vision of the raccoon. 8 This experience shows that if the mere presence of the experimenter, or his breathing, had been the cue to which the animals were responding the raccoons would have made far better records than they did, and the work of months would have been reduced to days. I should still prefer to have the experimenter present rather than to use the system of strings, which caused the noise, the peep hole, the opening for food, and to permit the noise of the experimenter's movements, which had to be overcome by a metronome, all of which were used by my critics. Conclusions: It is noticeable that, so far as Gregg and Mc- Pheeters draw a conclusion, they ascribe the raccoon's behavior to "motor attitudes," "sensory attitudes" and, if images were present in our animal, they must have been kinaesthetic, i.e., imaginal attitudes." (P. 258.) Thus they give the explanation of the raccoon's behavior which Hunter found was entirely inadequate to account for it, but which, he believes, does account for the behavior of the dogs and rats. Perhaps, at the time their experiments were made, Hunter's results were still in- complete and it was assumed that the raccoon's behavior would 8 Cole, Lawrence W. Observations of the senses and instincts of the raccoon. Jour, of Animal Behavior, 1912, 2, 302. THE CHICAGO EXPERIMENTS WITH RACCOONS 173 be found in nowise different from that of the dogs and rats. At any rate, we now have three different hypotheses to account for the behavior of raccoons. 1. Attitudes, motor, sensory or imaginal. Gregg and Mc- Pheeters. 2. Not attitudes, but imageless thought. Hunter. 3. Visual memory, at least sporadic. Cole. Truly, "Homines perfacile credunt id quod volunt." JOURNAL OF ANIMAL BEHAVIOR Vol. 5 MAY-JUNE 1915 No. 3 THE WHITE RAT AND THE MAZE PROBLEM: III. THE INTRODUCTION OF A TACTUAL CONTROL STELLA B. VINCENT Chicago Normal College In two papers, appearing in preceding numbers of this Jour- nal, I have attempted to show that vision and olfaction can be introduced as controls into the maze problem and to demon- strate some of the effects of such an introduction upon the learning process of the white rat. In this article I wish to re- view, briefly, in the light of the previous discussions, some work on the maze problem where the conditions for tactual and cutaneous control were emphasized and to add some experi- mentation not previously reported. For the full details of the earlier work see my monograph, : The Function of the Vibris- sae in the Behavior of the White Rat." 1 While this paper, the third of a series, attempts to show how tactual elements enter into and modify the maze reactions, it must be understood that the sensory experience is always a complex. Yerkes has sounded the warning clearly when he says: "An animal responds to a situation, not to any one inde- pendent and isolated stimulus. Every situation, to be sure, may be analyzed into its component simple stimuli, but the influence of each is conditioned by the situation." 2 The diffi- culty of isolating the tactual element is the chief reason why there has been so little work done with it in studies of labyrinth 1 Vincent, S. B. The Function of the Vibrissae in the Behavior of the White Rat. Behavior Mon., vol. 1, no. 5. 2 Yerkes, R. M. Relations of Stimuli in the Frog. Harvard Studies, vol. 2, p. 546. 176 STELLA B. VINCENT learning: The experimentation which has been undertaken up to this time has consisted mainly in moving the labyrinth to a different base, covering the floor path with different substances, interposing hurdles, and the use of anesthetics on the feet of the animals. Opinions as to the value of the sense in such problems have been based upon observation and voiced in general statements like this: " The longer one observes the behavior of the dancing mouse the more he comes to believe in the importance of touch and motor tendencies." 3 Or the assumption was perhaps a specific one and yet unsupported by any evidence, as: ' Tac- tual-motor sensations furnish the essential data for the recog- nition and discrimination involved in forming the special asso- ciations at critical points." 4 One investigator has made appar- ently contradictory statements, as : ; The indications point to the fact that the rat in no way uses his cutaneous sensations as a basis for 'sensing' the correct turns in the maze as distin- guished from the incorrect." 5 In this case the feet of the animal were anaesthetized with ethyl chloride. Reporting some experi- ments with blind animals he said: ' Runs squarely down the middle of the galleries, makes his turns into the various entries as boldly and with as much sureness as do the normal rats. The vibrissae undoubtedly play a large part (though not an indispensable one) in the early reactions of these rats to the maze." 6 Of normal animals he remarks: ' In all probability the rat does not discriminate his turns by means of any data contributed by the vibrissae." ' Vibrissae undoubtedly warn him of the presence of solid objects. . . . The function of the vibrissae to some extent at least may be dispensed with once the path is learned." 7 These seeming contradictions, however, are due to the confusion in the report of those activities involved in the formation of the habit and those essential to its control when established. The conclusions are those drawn from one type of maze and one form of motor habit and while possibly valid in this particular problem cannot be carried over to all such co-ordinations. 3 Ibid, Dancing Mouse, p. 178. 4 Small, W. S. Mental Processes of the Rat. Amer. Jour. Psy., vol. 12, p. 237. Watson, J. B. Kinaesthetic and Organic Sensations. Psy. Rev. Mon. Sup., vol. 8, no. 2, p. 78. 6 Ibid, p. 58. 7 Ibid, p. 69. THE WHITE RAT AND THE MAZE PROBLEM 177 Miss Richardson makes some definite statements though not in connection with labyrinth problems: " Slight contact (with plane) seemed to give her immediate orientation." 8 " The basis seemed to be that afforded by touch. Contact with the plane was doubtless evidence of its presence." . . . " It was only when they came in contact with the plane that some sen- sory impulse connected with its fall set off the old association and they would dash to the door of the box." 9 " There was no indication that any of the rats located the door by means of vision for each rat passed the door while 'searching' for it with- out reaching to it. Yet when the door was touched there fol- lowed the examination of the latch and the requisite movements to open the door." . . . Locating the door as before prob- ably with the snout." 10 " The normal rats like the blind rats seemed to discover the latch by contact." 11 A layman would scarcely question the importance of the tactual experience in the life of animals, yet in experimental work its function had been called in question even in such prob- lems as Miss Richardson mentions and kinaesthesis had barred all rival contestants in labyrinth learning. It was in order to test the control in the maze that this work was undertaken. DESCRIPTION OF MAZE The method used in testing this tactual control was not quite the same as that employed in the work with vision and olfac- tion. In those experiments the stimulating values of the true path and the blind alleys were made to differ in as pronounced a manner as possible. In this case there was no attempt made either to accentuate the contact values of the floor or walls of the maze or to offer contrasting standards in the true path and the false. Another maze was built on a new plan where the conditions, it was hoped, were such that not only could the tactual functioning of feet and vibrissae be seen but also that such functioning would be a necessary part of the learning process. (Figure 1.) 8 Richardson, Florence. A Study of Sensory Control in the Rat. Psy. Rev. Mon. Sup., vol. 12, no. 1, p. 39. 9 Ibid, p. 40. 10 Ibid, p. 55. 11 Ibid, p. 56. 178 STELLA B. VINCENT The runways to this maze had sides which could be detached. When this was done there was left a maze pattern of open, elevated paths but these paths had sufficient space between them so that the animals did not try to jump from one to the other. It was found that on this open maze, w r here the whole pattern was exposed, the visual control was not sufficient to prevent there being just as real a problem as was seen in mazes with enclosed sides. The situation forced the use of the feet and the vibrissae in a way that the other mazes did not and this fact accounts for the title at the head of this paper. Other sensory elements contributed to the learning, without doubt, Fig. 1 — The maze as used with sides down but the tactual-cutaneous factors were the prominent ones and the ones which we wished to throw into relief. As it is desired to compare the results obtained in this w 7 ork with those secured where vision and olfaction were emphasized in the Hampton Court maze, let us compare the two labyrinths. COMPARISON OF HAMPTON COURT AND X MAZES The length of the true path in the Hampton Court maze is 40 feet, in this 17 feet. There is one more blind alley in the H.C. maze than in this. The cut de sacs have a total length THE WHITE RAT AND THE MAZE PROBLEM 179 of 30 feet in the one and 9 feet in the other. The paths, both true and false, of the H.C. maze are more complex in nature. The results obtained from the H.C. maze and those given by the smaller maze, which we will call the X maze, when the sides are on are very similar. In table 1 they are given in tabular form together with the dimensions of each maze. To make these results comparable it is necessary to multiply the errors of the X maze by 7/6, since the H.C. maze has 7 errors while the X maze has only 6. The time taken to run the maze should be directly proportional to the length of the path. In the first trial in any maze the cul de sacs are explored rather thoroughly; therefore the time of the first trial in the X maze should be multiplied by 40/17 x 30/9, the ratios between the lengths of the true paths and the cul de sacs in the two mazes. In the final trials, however, the errors are cut out and to get the comparative speed we multiply the figures for the X maze by 40/17 to correct the speed for the true path. By comparing the corrected results of the X maze with those of the H.C. maze we can see that the statement of similarity is substantiated. The X maze took an average of four more trials to learn than the H.C. maze. The slower learning time for the X maze is doubtless a result of the character of the cul de sacs. There are three pairs of blind alleys in this maze. One and three are exactly of the same length and character and so are two and six and likewise four and five. The two latter pairs differ only four inches in length while after the turns the distances in 1, 2, 3 and 5 are identical. (See figure 1.) The distances on the true path between the turns are also comparable. If, after the habit is formed, the running under these conditions is . carried on largely in kinaesthetic terms, as we believe, then differences between the kinaesthetic elements in the series should favor such an accomplishment. Such differences in kinaesthetic elements are differences in complexity, differences in the dis- tances between the turns as well as in the direction of the turns, and differences in the lengths of the cul de sacs, etc. Too great a similarity between such kinaesthetic units would hinder the learning. The plan of the H.C. maze, according to this con- ception, is more favorable for learning and hence the slower learning time of the X maze. The corrected figures for the X maze show a greater average number of errors in the first 180 STELLA B. VINCENT trial and in the last five trials but looking at the average number of errors for the first five trials and the total errors per animal we see that the balance is in favor of X maze. Thus the error balance in the figures of the two mazes now leans to one side and now to the other. These differences, also, probably spring from the form and character of the cut de sacs. The lower final speed in the X maze is caused by one slow animal. If we take the time for all of the runs in which there were no errors in both series and from these records compute the speed per foot for each maze we find it to be exactly the same, 2.5 feet per second. This is not the final speed, however. The object here is not to go over these details item by item but merely to show that, in general, these mazes are alike in type and the reactions made in them are therefore approximate. COMPARISON OF EXPERIMENTS ON X AND Y MAZES We will now turn to a consideration of the experimentation on the X maze, where the sides to the runways were on, and the same maze, which we will call the Y maze, the open maze, where the runways had no sides. The behavior in the X maze needs no description but that in the Y maze showed essential differences. When the sides were taken from the runways and the rats put on the maze they showed a marked tendency to follow the edges of the paths. They did this either by turning their vibrissae down against the sides or by curling their toes over the edges of the board. That this was a real control was shown by using rats whose vibrissae had been cut on one or both sides of the head, by using blind rats with and without vibrissae and rats in which the branch of the fifth nerve which innervates the upper lip and snout had been cut. The learning in all of these cases was made more difficult except in one instance. In this case the vibrissae were cut on one side only. As a result, the animals were forced to keep to one side of the maze and by following this side they made their way around the labyrinth almost imme- diately. It is impossible here to go into all of the evidence and readers are referred to the original monograph. 12 The work conclusively showed that the tactual-cutaneous experience had 12 Op. cit. THE WHITE RAT AND THE MAZE PROBLEM 181 a vital part in the solution of the problem. In the end the rats ran this maze with as much boldness and confidence as the other, with heads up, almost leaping corners, etc. The one exception was the group of blind rats without vibrissae. Let us compare the results of the two mazes as to accuracy and speed. We find that the time of learning was the same but in the Y maze the errors were less by one-half in the first trial and one-third in the first five trials, and the total number of errors was decreased about one-third although the final accuracy of the two mazes was practically the same. The beginning time was shorter because of the fewer errors but the average time of the first five trials was about the same in both. The final speed in the Y maze was slightly better. The most notice- able difference, then, was the decrease in errors. The open maze, from the beginning, favored accuracy and it should be noted that this accuracy was not attained at the expense of speed. In a maze, where the paths are enclosed by restraining walls, there is little need of fine bodily adjustments. The turns in the H.C. maze and in this maze are always 90 degrees but the place of the turn in the H.C. maze is always marked by some corner or projecting wall against which the body of the rat brushes or his vibrissae drag as he runs. A railway engineer does not have to keep his train on a straight course by the fraction of an inch, he has only to develop speed, his track is laid for him. The analogy is not perfect but in the enclosed maze the rat is comparatively ' safe." He does not have to control, as on the open maze, the finer postural and positional adjust- ments and as a result of this looseness of running he makes more errors. On the open maze the control of these finer adjust- ments is necessary in order to avoid slips and falls and hence there is greater initial and final accuracy. The nose, feet and vibrissae were constantly used at the different places of turning. The direction of the turn seemed a much easier thing to conquer than the exact place. The operated animals were at a great disadvantage. Vision aided these finer adjustments but the nose and feet and vibrissae seemed to be of greater help to the rat than sight. However, either sight or the touch of nose or vibrissae seemed to be a vital necessity to the learning. The animals could not well dispense with both in such a problem as was here presented. 182 STELLA B. VINCENT THE X MAZE RE-LEARNED AS THE Y MAZE That the habits set up in the two mazes were inherently of different type was shown by the following experiment: After the group of animals whose records are given for the X maze in table 1 had learned the maze the sides were removed and the rats were tried again. Kinaesthesis had apparently been firmly established during the first experiment and while some dis- turbance was to be expected, it was thought that it might affect the runs of but one day. The outcome shows the danger of supposing anything about animals. These rats had to relearn the maze almost as if it were a new problem. The old habits did not meet the situation. The animals went out upon the maze with flattened, crawling bodies; they clung to the edges with their toes, they followed these edges with their vibrissae; they used apparently every tactual-cutaneous help possible. While the fewer initial and total errors seem rather good evi- dence that something was carried over from one maze to the other, the fact that it took over eleven trials on an average for the relearning, as well as the evidence of the observed behavior, indicates that the habit had to be re-established through new sensory aids. A summary of the numerical data may be seen in the last column of table 1. The maze pattern was the same. The kinaesthetic series was the same: the distances, turns, all that goes to form what Pro- fessor Watson calls a kinaesthetic element, but the other sensory elements, always present in the kinaesthetic complex, light, possibly odor and sound but chiefly touch had greatly changed. Always, as the rat ran in the X maze, his sides and vibrissae brushed the walls, the projecting partitions and the angles of the box. All at once this part of the sensory experience was gone. It could be and it was replaced but with a tactual ex- perience of another sort requiring very different adjustments. In addition there was the necessity for the finer adjustments previously mentioned. Thus the problem became a new one. The position which I desire to maintain here and upon which I desire to lay emphasis is that, while in a fully formed habit kinaesthesis probably predominates as a control, the sensory experience is never purely kinaesthesis but always a complex and the finer are the adjustments which need to be made the more necessary the associated sense qualities of vision and touch become. THE WHITE RAT AND THE MAZE PROBLEM 183 en Q ca o o w K r/f Z c »— 1 (/) 2; w — 1 § u Q ►J CQ C/l < W H < o' z K < § o U E d C/3 "to >f— ( _d E . E Maze arned a 0) N 1-1 -t-> tM CO CO E CJ O CO Ih ^ C t-H CO t^i- a^ X% >< -H -H -H ■H-H -H 0) Oi "CO !h 00 C£5 Tf B s 3 1 — 1 ^-^ re x, o 2* X E CD T LO E E E -S g &CO N H -H -H -H +i CT; -H-H -H LO iO L.O o cr i- C2 "- I x o> cc a> ^~ c^u: t-H —iCO »— c- CO rH c *re C E • !— CD N re -t-j 4- +- 00 X r- X E c CU .3 S [^ C" 00 t^ CO 00 CM coco CM CM a^ X -H -H -H -H 00 -H-H -H -H ^4 00 IT. ■— ' CN 00 >— LOCO CC 00 ~ ^~ t> 1—1 Nlfl r— i—( :~. IT. rH p CD !s c E - N 5 CVJ Bt! 05 -t- >— c t-H +J CO 1 — 1 E IT. c cj CU w Ih CU ad re 3 "* re -H -H -H HH -H -H 2 *J1 — o t- 1— 1 <£ CO CO LOO; CM ^ X C£ CD CM CO rH i— i — tc ^H a •C CU > CU > Ih CU i£ i a cC G a •4-J re a CU 3 Ih C_ CO to CU Ih -4-> C/T C Si 3 -4-> bi Is +J C/3 l-i -4-> W Ih cC +j 1- tf 4. Uh C H +J S 5. s C '5 rH R 1- p t CU CU o u i-i CU o Ih Ih CU CU W a Ih cU CU £ a. > •a CU ak ■tH C/3 J3 C CU c o O a CU CU _ > ~ -I— E -2 CU — 10 ki 3 X CU CU c fctfl but Z MJ£ E tC bo bo "U en wmm ^ -*- « C3 K C3 C3 — t CU > 'C E - Ih CU > CU CU Js-! 3 re CU K H . > ° O h r— Z Z H < < < H H < c73 < E- 184 STELLA B. VINCENT CONCLUSIONS The conclusions from this study are that, given conditions which favor or necessitate the use of vibrissae or the tactual use of nose or feet, the maze habit is not more quickly established but that during the setting up of the habit fewer errors are made and because of this the time per trial is lessened and time is gained. The conclusion is also drawn that these conditions make, within the limits of the experiments, for greater final speed as well as for greater final accuracy. A STUDY OF THE BEHAVIOR OF THE PIG SUS SCROFA BY THE MULTIPLE CHOICE METHOD ROBERT M. YERKES AND CHARLES A. COBURN The Harvard Psychological Laboratory and the Franklin Field-Station INTRODUCTION The multiple choice method of studying ideational and allied forms of behavior was first briefly described in a lecture on the study of human behavior delivered at Cold Spring Harbor in 1913. x It has recently been more fully described in a paper which presents the results of its application in the study of the crow. 2 We shall, in the present report, assume knowledge of the previous descriptions and state only the essential features of the method and its adaptation to the organism observed. It was devised in the Psychopathic Hospital, Boston, as a means of obtaining comparable records of the ideational behavior of mentally deficient and deranged individuals. But it was also hoped that it might prove widely serviceable as a comparative method for the study of various types of organism. In many of its essential features, the Yerkes multiple choice method is similar to the Hamilton quadruple choice method, 3 but whereas in the latter four reaction-mechanisms are employed and only problems which, strictly speaking, are insoluble are presented to the subject, the present method involves the use of a variable number of reaction-mechanisms and the presenta- tion of soluble problems of a wide range of dimcultness. The experimenter seeks, in using the multiple choice method, to present to his subject, no matter what its type, age, or condi- tion, a problem which may be solved by the perception of a Yerkes, Robert M. The study of human behavior. Science, 1914, 39, pp. 625-633. 2 Coburn, Charles A. and Yerkes, Robert M. A study of the behavior of the crow Corvus Americanus Aud. by the multiple choice method. Journal of Animal Behavior, 1915, 5, pp. 75-114. 3 Hamilton, G. V. A study of trial and error reactions in mammals. Journal of Animal Behavior, 1911, 1, pp. 33-66. 185 186 ROBERT M. YERKES AND CHARLES A. COBURN certain constant relation or group of relations within the reac- tion-mechanisms. For example, the mechanism to be operated may, in the case of one problem, be the middle one of the group, and the total number of mechanisms presented may vary from three to nine. Only by perceiving and appropriately responding to the relation which the experimenter designates as middleness, can the subject solve the problem. It is necessary only, in the presentation of a varied series of multiple choice problems to a given subject, for the experimenter to devise a type of reaction-mechanism which is appropriate to the action-system of the organism to be observed. We have thus far made use of a simple keyboard for human subjects, while for crows, ring-doves, and rats, we have employed a series of similar boxes, each with entrance and exit doors which can be operated at a distance by the experimenter. The form of device which has proved suitable for the study of pigs will be described in this report. It has proved very easy to develop suitable mechanisms and we have every reason to suppose that this new method has great advantages over most others for the comparative study of be- havior in that essentially the same problems may be presented to extremely different types of subject. The method has been employed in experiments with normal and defective children, normal and insane adults, pigs, rats, crows, and ring-doves. 4 To all of these subjects,. four problems have been presented. They may be described briefly, by defini- tion of the correct reaction-mechanism, as Problem 1, the first mechanism at the subject's right; problem 2, the second mechan- ism at the subject's left (that is, from the end of the series at the subject's left) ; problem 3, alternately the first mechanism at the subject's right and the first at its left; problem 4, the middle mechanism of the series. It has become increasingly clear, as our investigations pro- gressed, that the perfect solution of a problem by a given subject is of much less importance as a matter of record than is detailed information concerning the types of reaction and the appearance and disappearance of reactive tendencies during the course of experimentation. For the solution of a problem means simply 4 The results of our experiments, except in the case of the crow, have not been published. A STUDY OF THE BEHAVIOR OF THE PIG 187 the termination of a series of observations. It is essential, therefore, that the experimenter fix his attention rather on the immediate response of his subject than on the attainment of the solution of problems. We especially call attention to this matter because many experimenters seem to feel dissatisfied with other than speedy and completely positive results. It seems fair to insist that by the multiple choice method positive results are obtained even if a subject cannot solve any of the problems which are presented to it. Since it is our intention to more fully discuss the essential features and the technique of the multiple choice method else- where, we shall here content ourselves with these brief intro- ductory statements and references. It should perhaps be added that only by reading the earlier article on the behavior of the crow can the reader hope to fully understand the present report. SUBJECTS The subjects of the experiments which constitute the obser- vational basis for this paper were two Chester white pigs. They were born April 1st, 1914, and they were therefore two months old when, on June 2nd, they were taken to the Field Station from an adjoining farm and placed in the experimental situa- tion. We shall refer to these individuals as the male and the female, since both sexes were represented. The male, however, had been castrated before we obtained the animals. From the first, individual differences were conspicuous. The male was considerably smaller and less active and energetic than the female; he ate less and showed less initiative. Through- out the period of observation, both animals were in perfect health and at no time was there reason to suppose that either environmental or physiological conditions were unfavorable to our experiments. From birth these pigs lived practically out of doors, having a yard to run in and a rather open shelter from storm. Although the experimenters had expected much of the pigs because of the indications from casual observation of their behavior, it may be said at once that they proved far more satisfactory subjects than we had dared to hope. Indeed, they worked so steadily and uniformly through the investigation that there was practically no loss of time. It is chiefly because of 188 ROBERT M. YERKES AND CHARLES A. COBURN this unexpectedly favorable relation of subject to method that we were enabled to obtain, during the summer of 1914, the numerous results reported below. APPARATUS Fortunately, it was possible at the Franklin Field- Station to locate our apparatus in an orchard convenient to the buildings. A rough shelter was built for the pigs under a large apple tree, and convenient yards were arranged by the appropriate use of wire fencing. The accompanying figures give a fairly good idea of the ex- perimental situation. In figure 1 A, the multiple ^choice appa- ratus appears in the foreground, behind a fence which com- pletely surrounds the enclosure. Immediately in front of the apparatus is a bench for the observer. Systems of weighted cords, conspicuous in 1 A, enable the experimenter to operate the slide doors of the multiple choice boxes. The arrangement of the yards is made clear by figure IB and figure 2. It was necessary to be able to isolate the pigs for observation as we 1 as to have the apparatus so arranged that an individual could readily be admitted for a trial and on the completion of its reaction, be returned to its appropriate yard. The multiple choice apparatus proper consists of nine similar boxes, shown in ground plan in figure 2. They were built of rough boards and numbered conspicuously 1 to 9. Each box is sixty inches long, by twenty inches wide, by forty-eight inches deep, with a slide door at each end. The distance between these doors on the inside of the box is forty-eight inches. From each of the entrance and exit doors a woven window- weight cord extends upward, through a pulley, then horizontally forward through another pulley, and downward, ending in a weight nearly over the observer's bench. To all of the cords from the entrance doors, white weights were attached; to all from exit doors, black weights. Each weight was sufficient to hold its door in position after the latter had been raised. It was found that this required about ten pounds, and iron window weights served our purpose. In front of the exit door of each box is a v-shaped food trough which is divided into nine like parts by the partitions between Figure 1. Multiple Choice Apparatus for Use with Pigs A. The reaction-mechanisms from the experimenter's position, cords for operating doors. Entrance doors 2 to 6 are raised. B. The same from the pig's point of view, showing one pig w trial. Entrance doors 2 to 6 raised as in figure A. C. The same view as that of figure B except that the pig has the reaction-space and is about to enter the middle box (no. 4) of are open. D. Here the pig is shown, after appropriate reaction, feeding box no. 4. The experimenter appears in the position necessary of cords and observation of response. E. The reaction-mechanisms seen from one end. showing weighted aiting in yard for been admitted to those whose doors in the trough of for manipulation B- , ■ m . m V A 1 2 3 4 5 6 7 8 9 ■ ! [ " f P 1 • ■ T D Figure 2. Ground Plan of Multiple Choice Apparatus Used for Pigs. Scale A, reaction mechanisms, nine similar boxes or stalls; V, stall number 4; 0, en- trance door of box; P, exit door of box; T, food trough of box; G, observer's stand and H, writing table; D, runway between trough, T, and stand, G; S, S, yards; B, reaction space; R, E, alleys or runways connecting D with S; I, observer's en- trance door to apparatus; J, observer's entrance door to reaction space B; L, M, slide doors between* yards and reaction space; K, N, slide doors between yards and alleys. The weighted cord systems for operating the entrance and exit doors (twenty in all) are not shown in this figure. They may be seen in figure 1, A, B, and C. 190 ROBERT M. YERKES AND CHARLES A. COBURN boxes. When the exit doors are down, the various parts of the food trough are covered by a horizontally placed sheet of metal which fits closely over them and thus prevents the subjects from obtaining food from the outside of the apparatus. The large enclosure is divided into four principal parts: (1) the part which contains the reaction-mechanisms with space for the observer's bench, G, and writing table, H, and a passageway for the subject from the exit doors of the apparatus to the yard, S; (2) second, the reaction space which is labelled B in figure 2, in which the subject responded to the multiple choice situation; (3) and finally, the two yards, S, S, from which the subjects started in the case of each trial and to which they returned on the completion of their reaction. K, L, M, and N, designate slide doors between the several portions of the large enclosure, while J and I represent doors which were used by the experimenter. The entire apparatus was constructed in sections, so that at the end of the season it might readily be taken down and stored. This brief and very incomplete description will be supple- mented somewhat in the section on experimental procedure. PROBLEMS AND GENERAL METHOD The four problems enumerated on page 186 were presented to each subject in the order named. For each of these problems, a series of ten settings of the doors was determined upon. These settings differ somewmat from those employed in our study of the crow. It is our intention, so far as possible, to use them with all types of subjects until our observations indicate desirable changes. We present below for each of the four problems (1) the num- bers of the settings, (2) the numbers of the doors open, (3) the total. number of doors open in each setting and for the series of ten settings, and (4) the number of the right door. It was our plan to give each subject an opportunity to respond to each of the ten settings for a given problem in order and to return then to setting 1 and repeat the series. It was found impossible, however, to give ten trials in succession in our early experiments, and in the case of both problems 1 and 2, as a rule a subject was given five trials in succession. For problems 3 and 4 it was found possible to give ten trials in succession. * A STUDY OF THE BEHAVIOR OF THE PIG 191 Problem 1. First Mechanism at the Subject's Right Settings Doors open No. of doors open No. of right door 1 1.2.3 3 1 2 8.9 2 8 3 3.4.5.6.7 5 3 4 7.8.9 3 7 5 2.3.4.5.6 5 2 6 6.7.8 3 6 7 5.6.7 3 5 8 4.5.6.7.8... 5 4 . 9 7.8.9 3 7 10 1.2.3 3 1 Total 35 Problem 2. Second Mechanism at the Subject's Left Settings Doors open No. of doors open No. of right door 1 7.8.9 3 8 2 1.2.3.4 4 3 3 2.3.4.5.6.7* 5 6 4 1.2.3.4.5.6 6 5 5 4.5.6.7.8 5 7 6 1.2.3 3 2 7 2 3 4.5 4 4 8." .'.'.'.'.'.'.'.'.'.'.'.'.' '. '. .1.2.3*. 4.5.6. 7.8.9! '.'.'. .9. '.'.'.'.'.'.'.'. '.'.'.'.'.'.'. '.'.8 9 1.2.3.4 4 3 10 3.4.5.6.7.8 6 7 Total 50 Changed from 3.4.5.6.7 to 2.3.4.5.6.7 after about one hundred trials. Problem 3. Setting 8 9 10 Alternately the First Mechanism at Subject's Right and the First at Its Left Doors open No. of doors open No. of right door 5.6 7 3 5 6 7.. . .3 . 1.2.3.4.5.6 1.2.3.4.5.6 . .4.5.6.7.8. .. 6 6 5 4.5.6.7.8 . .2.3.4 5. 5 . .4 . .2.3.4.5... . .4. . 3.4.5.6.7.8.9 7 3.4.5.6.7.8.9.... 7 Total 50 192 ROBERT M. YERKES AND CHARLES A. COBURN Problem 4. Middle Mechanism of the Series Setting Doors open No. of doors open No. of right door 1 2.3.4 3 3 2 5.6.7.8.9 5 7 3 1.2.3.4.5.6.7 7 4 4 7.8.9 3 8 5 4.5.6.7.8 5 6 6 1.2.3.4.5.6.7.8.9 9 5 7 1.2.3 3 2 8 2.3.4.5.6 5 4 9 3.4.5.6.7.8.9 7 6 10 6.7.8 3 7 Total 50 Both punishment and reward were used in these experiments. The punishment consisted of confinement for a definite interval, usually one minute, in each wrong box entered, while the reward consisted of food which could be obtained in the trough of the right box. EXPERIMENTAL PROCEDURE We shall now briefly enumerate, in order to supplement the descriptions of apparatus and methods which have been given, the steps in a regular series of observations. The experimenter having entered the enclosure with a supply of food, record-book, stop-watch, etc., first raises each of the nine exit doors and places in each section of the trough a quantity of food (sour milk, shelled corn, vegetables). He then lowers the exit doors, thus covering the food, and takes his position on the observation bench. In case both pigs are in the shelter yard, it is next necessary for him to drive one of them into the other yard. This having been done, he may proceed to set the entrance doors for the first trial. Let us suppose that the problem to be presented is problem -1 and that setting 1 is first to be used. In this case the experimenter raises entrance doors 1, 2, and 3. He is now ready to admit one of the pigs to the reaction space B of figure 2. This he does by raising momentarily the appropriate slide door between B and S. The instant the pig enters the reaction space, the experimenter starts his stop-watch and begins to record the important features of the behavior of the animal, noting especially its approach to the several doors, its tendency to enter boxes and the actual entrance and time of entrance into any one of the three acces- A STUDY OF THE BEHAVIOR OF THE PIG 193 sible boxes. Let us suppose that the animal enters directly box 3. Immediately the experimenter lowers the entrance door and thus confines the animal in the small compartment as punishment for an incorrect choice. At the expiration of one minute, the entrance door is raised and the pig is allowed to retreat from the box and make another choice. We may now suppose that the animal, after passing in front of boxes 2 and 1, returns to 1 and enters it. The experimenter immediately stops his stop-watch, lowers the entrance door, and, since this box is by definition the right one, he immediately raises the exit door and rewards the animal for correct choice by allowing it to eat for a few seconds. He then, either by speaking to the pig or by touching it with a whip, induces it to pass from the box by way of the passage, D, and the alley, R or E, back to the appro- priate yard, S. Having reset the apparatus, the experimenter now gives the other pig a trial with the same problem and either with the same or with a different setting of the doors. As a rule, the animals were fed only in the trough of the apparatus. They were almost always hungry, and although sufficiently well fed to keep them growing and in excellent health, they usually seemed fairly hungry at the end of a day's work. In no case was it necessary, in order to induce them to work steadily, to have them extremely hungry. The influence of visual and olfactory factors was to be ex- pected, and at various points in the investigation, precautions had to be taken against following. PRELIMINARY TRAINING On June 2nd the pigs were brought to the Field Station and placed in the shelter yard, and in the afternoon of the same day, they were fed in the trough of the apparatus, all of the doors of the boxes and the yards being raised. During the next six days they became thoroughly accustomed to the apparatus and learned both to feed in the trough and to make the trip readily from the yards, through the apparatus, and back to the starting point. They very quickly and satis- factorily adapted themselves to the situation, while at the same time becoming thoroughly tame and indifferent to the presence of the experimenter. 194 ROBERT M. YERKES AND CHARLES A. COBURN On June 9th it seemed fitting to attempt a series of prelim- inary trials. Each animal was given, in turn, opportunity to secure food in each of the nine boxes. When the subject entered the reaction space, B, the entrance door of a certain box stood open, and as soon as the animal had entered that box, the ex- perimenter closed the door behind it and opened the exit door in front of it, thus enabling it to obtain food. During these preliminary trials, the pigs were in separate yards and were given their trials alternately. We shall now' report the results of our regular experiments. RESULTS OF EXPERIMENTS As it is essential to present the data for each trial in the series of experiments, tables 1, 3, 4, 6, 7, 9, and 10 have been con- structed after the following manner. At the head of each table stand the several settings, the letter S serving as an abbreviation for setting and the number following it designating the place of the setting in the series. Immediately under the number of the setting appear the numbers of the doors open with the one to be chosen (correct one) printed in bold face type. Below this preliminary information concerning the particular problem in question, appear the results for each of the trials of each subject. The column headed T gives the number of a trial in the total series of trials for a given subject, in a given problem. Follow- ing the number of the trial are the numbers of the boxes entered, in the order of entrance. Referring to table 1, we discover that the female in her first trial under problem 1 selected, of the three boxes whose doors were open, first, number 3 She was, of course, punished by being confined in this box for one minute, and on release entered box 1, which was the correct box, and re- ceived the reward of food. Or again, in table 3 it may be noted that in trial 146, under problem 2, the female entered, in order, boxes 7, 9, 7, and 8, the group of open doors including 7, 8, and 9, and the box to be entered being number 8. These tables will enable the reader to obtain quickly definite information concerning the forms of response and the changes therein during the course of experimentation. We shall present the several tables under the problem numbers and reserve further comment for the section on the discussion of results. A STUDY OF THE BEHAVIOR OF THE PIG 195 DISCUSSION OF RESULTS The results will now be discussed under the headings of the four problems, and in connection with each a condensed tabular summary of the experiments will be offered, together with such comments as are necessary on the experimental procedure, the behavior of the subjects, and the significance of the various forms of response. PROBLEM 1 This problem, for which the definition of the correct mechan- ism is the first at the subject's right, proved extremely easy for the pigs. Incorrect choices were surprisingly few, and the number of trials necessary for the perfect solution of the prob- lem was also surprisingly few for both subjects, the female having chosen correctly throughout a series of ten settings at the end of forty trials and the male having similarly succeeded at the end of forty-five trials. As is indicated by tables 1 and 2, which contain all of the data for this problem, the experiments were not discontinued at this point, but each individual was given additional opportunity to work out the problem. In the light of our later experience, this was a mistake, but at the time we were unconvinced that the animals were depending upon the relation of the correct mechanism to the other members of the group, and we proceeded further with our observations in. order to settle certain points which were in doubt. From the first it was evident in connection with this problem that the female was more intelligent than the male, and that he tended to be markedly influenced by her. After observations were discontinued with her on June 14th, he reacted very poorly for a number of series, and then again improved and reacted perfectly in the last three series given on June 15th. In this problem the total number of doors open in the ten settings was, as may be seen by reference to the data presented on page 191, thirty-five. Of these, ten were of course correct. Hence the probability of a correct first choice apart from ex- perience would be 1 to 2.5. In table 2, it appears from the data of the last column for each individual that the ratio of correct to incorrect first choices was on the first day of training 1 to 1 for the female and 1 to 2.33 for the male. It should here be stated that in table 2, as well as in the like tables for the other 196 ROBERT M. YERKES AND CHARLES A. COBURN w j o o K Oh w S "J £ 04 O u. on H W o f— 1 co CO c-j i-H CO i— i •— ( i— i ?— i «— i H O O LO LO LO LO ■— i rj co'?- loco en co 00 NN t^C^t^O H CD CD -^ ^f -^ "^ >— i CO TT LOCO 00 co X CO Tj< •>* -** -* Tj« LO H x oc co co coco .— i co ^r loco t> CO N- CD i LO LO t> LO LOCO LOLO H t> t>- CM CM CM CM .— 1 CO ^f LOCO co CO oo CO 00 N CD CD CD CO CD H CD CD <— 1 1—1 1— I t— i •—1 co •<* loco LO cd CD LO CO CM CM CM CM CO CM CM CM CO LO CD ^tx conj rsco CM H LO LO LO o o o o ^h cm co ^r lo co LO CO CD 00 N- N- t> t- LO t> N- N CD 00 N. H ■>* ^f* cd cd c. en r-i CM CM CO ■<* Lfi *tf co CO n- CO CO CO co-<* CO CO C> CO LO CO CO CO CD LO PC CO H co co co oc oo oo oo — C-J CM CO ^f LO CO CM CO °2 00 oo oo oo oo oo oo oo en oo CD in LO H CM CM CM t> N N N- ■— 1 CM CM CO -* lO CM iH co CO CM 1— 1 T- H CO i— i CM i-H i— 1 i— I i-H LO CO CM w4 1—1 H rH i— 1 i— I CO CD CO CO ^h cm cm co ^r lo 1— 1 1-H ^H COCM r-J CM CO 1— 1 r-H i-H CO i-H f-H O O LO LO LO LO ^h CM CO^fLOCO LOLO N- N- oo n- c^ c^ CD CD ■** t* tJ< -5j< ^ co ^t loco LO -* ^f CO •«*'* 00 •<* T#Tt 0000 cocococo *-i co^r loco coco c^x LO LO LO t> COLO CO LO t>LO LO COLO t>t> CMCMCMCM 1—1 i-H CO ** LO CO CMCM t^X W OS N-CO CO CD Ph oon t^coodco coco 4i CO CD i— i i— i i— ( i— I W i-H CO ^ LO CO »—3 i—i .— i t>x < 04 cvl O ^r cm cm fe CM CM CO CM CM CO LO 00 LOO) coc^ «NCO CMCM "*LO CMCM LOCD "^X CON (SCO CM H £^ LOLOLOOOOO J72 --H Ol CO ^ LO CD LOO 1 — 1 OO t^x LO i— i Cvi 00 t^ 00 I>- t^ t> CD oq CDCD DON CD 00 N- "<* "* ^f C7i CT; CD CD i—i CM CM CO -<* LO ■*CD CDCD COt> i— ( COCO coloco C^ t> CD CO CO CO CO CD LO ■<* COCO COCO CO LO PC CO co co co oo oo oo oo •— i CM CM CO -* LO COCO XX CON CO 00 00 00 00 00 X 00 CD od CO LOLO XX CD X co LO CM CM CM t> t> f~ t> -—I CM CM CO ^f LO CMO t>N CON- CM i-H CM CO CM -—I i—i -—I i—i CO CM coco CO i-H LO co CM »— I ■— i —I i— i <0 CO CO CO i—i CM CM CO ^C LO i— 1 CO CDCD CON- i— I A STUDY OF THE BEHAVIOR OF THE PIG 197 TABLE 2 Daily Series and Averages with Ratios of Correct to Incorrect First Choices Problem 1 Female Male No. Ratio No. Ratio Date of trials R W R W of R toW Date of trials R W R W of R toW June June 10 1- 5 3 2 10 1- 5 2 3 a 6-10 2 3 5 5 1:1 u 6-10 1 4 3 7 1:2.33 11 11-15 4 1 11 11-15 2 3 a 16-20 5 « 16-20 2 3 a 21-25 4 1 13 2 1: .15 a 21-25 2 3 6 9 1:1.50 12 26-30 4 1 1? 26-30 4 1 u 31-35 5 u 31-35 3 2 a 36-40 5 it 36-40 5 u 41-45 4 1 18 2 1: .11 a 41-45 5 17 3 1: .18 13 46-50 5 13 46-50 4 1 a 51-55 5 it 51-55 1 4 a 56-60 4 1 tt 56-60 4 1 a 61-65 4 1 18 2 1: .11 a 61-65 4 1 13 7 1: .54 14 1- 5 5 5 1:0 14 it 1- 5 6-10 2 3 9 "3 4 6 1:1.50 Z 15 66-70 3 2 it 71-75 4 1 u 76-80 5 it 81-85 5 17 3 1: .18 a 11-15 5 5 1:0 problems, the data refer only to first choices in each trial, the column headed R containing the number of correct first choices and that headed W the number of incorrect first choices for each series of trials or for the day. It further appears from this table that five trials constituted the regular series in problem 1, and it should here be stated that the experimenter always re- sumed experimentation at the point in the regular series of settings at which work had been interrupted. He therefore pro- ceeded in regular order from setting 1 to setting 10 and then returned to setting 1 and repeated the trials. Further comment on the behavior of the animals in problem 1 is needless, for the task is but slightly more difficult than the acquisition of a simple position habit, and it has already been satisfactorily demonstrated that many of the vertebrates acquire such habits with ease. 198 ROBERT. M. YERKES AND CHARLES A. COBURN PROBLEM 2 For this problem, which is definable as the second mechanism from the subject's left, all of the data for discussion will be found in tables 3, 4, and 5. Again, as in the case of problem 1, the regular series consisted, throughout the training, of five trials, but as many as six such series were given on a single day. Bracketed series appearing, for example, in table 5, under the dates June 23, 24, 25, and 28 and July 1, 2, 3 and 4, were continuous, that is, ten trials were given in succession instead of only five. For the ten settings of problem 2, the total number of open doors is fifty, and the expectation therefore is that prior to experience an animal will choose correctly once in five times, thus giving a ratio of right to wrong choices of 1 to 4. That this expected ratio does not appear on the first day of experimen- tation is due to the effect of the previous training in problem 1. The tendency to enter the first box at the left was persistent in both subjects and often that box was re-entered a number of times in spite of punishment. In tables 3 and 4 the data for these statements are presented, and in table 5 it may be noted that on the first day of work on problem 2 neither subject made a single correct first choice. The ratio of correct to incorrect first choices for the female rapidly, although somewhat irregularly, decreased with experi- ence until on July 4th it stood 1 to .19. On this date she suc- ceeded in choosing correctly in ten successive trials, and was therefore considered to have solved the problem perfectly. Similarly, the ratio for the male changed fairly rapidly until on July 11th it stood 1 to .11. At this time, although he had not succeeded in choosing correctly in each of the ten settings consecutively, his training was discontinued, for he had already delayed experimentation with the female for a week, and it was perfectly clear that although he made an occasional error, he was capable of perfectly solving the problem. Whereas the female finished this problem as a result of 390 trials, the male had made only nine out of ten correct choices at the end of 520 trials, when his training was discontinued. We are inclined to think that this is a reliable indication of the difference in docility between these two individuals. A STUDY OF THE BEHAVIOR OF THE PIG 199 We shall now turn to tables 3 and 4 for a further brief analysis of the reactions. For about 50 trials in problem 2, both pigs showed the effect of their experience in problem 1. Then the number of correct first choices rapidly increased for each of the ten settings. There were in the case of setting 1 few mistakes on the part of the female after 150 trials, whereas on the part of the male there were more than twice as many incorrect first choices. The same holds in general of each of the other settings, she proving herself much more steady and predictable in response than he. This was doubtless due in a measure to hunger, for it was much more difficult to keep him in the proper condition of eagerness for food than her. The data of these tables indicate no definite and persistent reactive tendencies during the course of experimentation other than the original acquired tendency to enter the first box at the right in the group and the subsequently acquired tendency to select the second box from the left in the group. Certain of the settings proved very much more difficult than others. Contrary to expectation, difncultness is not directly variable with the number of doors open. Setting 1, for example, as contrasted with setting 6, is much the easier, yet three doors are open in each case. In general, however, it is evidently true that the larger the group of open doors the more difficult it is for the animal to choose correctly and the larger the number of mistakes in a given trial, if the first choice is not correct. From the behavior of the two pigs in this problem, as con- trasted with the first, it is safe to conclude that they are per- fectly capable of selecting the proper reaction, mechanism by its relation in a group of similar mechanisms when the number in the group is as large as nine and when the constant relation of the correct mechanism is second from one end. It is further clear that this problem is a much more difficult one for the pigs than problem 1. But it is also certain that the difference in difncultness is not indicated by the difference in the number of experiences necessary for the solution of the problems, since the early days of work on problem 2 served merely to overcome the tendency acquired in connection with problem 1. It seems probable that should we subtract 100 trials from the totals under problem 2 we should have a fair basis of comparison 200 ROBERT M. YERKES AND CHARLES A. 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CO LO **' co co co CO CO LO' l> CO CO t> CO I> CO CO CO t>j LO CO CO t> "* CO t> CM* t>-' LO' CO CO LO* CO CO CO CO CO CO oo CM CO CMCM oo oo oo oo "* LOCO t- CM CM CM CM 00 00 00 OO BffiOH CM CM CO CO OOOOOOOOOOCOOOCOCO CMCO-*LOCOt^COOO COCOCOCOCOCOCOCO-* coco —i CM oooocooooocococococo CMCO"*LOCOt-~0000'— I "*-*-*"*"*"*^J*"*LOLO CO ^CO CO CO CO CM CO CO CO CO CO COCOCOCO CO cococO"*'"*'-*'"*'co-*' coco CO -*'cococococococococo CM CO CMCM C^ Cr— C — O- "* LOCO t>- CM CM CMCM ooooh cm cm co co NNNNNNISMC] r-]co-*LncDNcoc.o cocococococococo^t , CM CM —i CM t-t^t>t^t>CMCMCM^CM NCO*LOCDt>OOC7)Or- 1 "*-*"*"*-*-*"*"*LOLO 00 00 00 OOOOXN 00 t>-' 00 00 00 00 0000t>000000000000 00 t^oo 00 O00000000C00t>0000CO coco CM CO CMCM COCO CO CO ^•LOCDN CO CM CM CM co co co CO CCC.OrH CM CM CO CO co co co co co co co — i — < CMCO-*LOCOt>0000 COCOCOCOCOCOCOCO"* — iCM -* "J 1 CDCOCDCCCO'HiHiHfHiH CMCO"*LOCO^OOOO-— I -*-*"*-*-*"*-*-*LOLO a o o o o -a to o o • H u sO LO -<* CO CM o c LO ■«# CO o en -a c cd .a '£• o en Hi »o S c a> cu to "> is CJ^ co M CU C cu * co O o •X3 204 ROBERT M. YERKES AND CHARLES A. COBURN TABLE 5 Daily Series and Averages with Ratios of Correct to Incorrect First Choices Female Problem 2 Male No. Ratio No. Ratio Date of trials R W R W of R to W Date of trials R W R W of R to W June June 16 1- 5 5 16 1- 5 5 « 6-10 5 10 0:1 u 6-10 5 10 0:1 17 11-15 2 3 17 11-15 2 3 ii 16-20 5 ti 16-20 1 4 a 21-25 5 2 13 1:6.50 it 21-25 1 4 4 11 1:2.75 18 26-30 2 3 18 26-30 1 4 u 31-35 1 4 it 31-35 2 3 a 36-40 5 u 36-40 1 4 it 41-45 1 4 4 16 1:4.00 « 41-45 1 4 5 15 1:3.00 19 46-50 1 4 19 46-50 1 4 it 51-55 4 1 it 51-55 2 3 ii 56-60 2 3 it 56-60 1 4 a 61-65 1 4 8 12 1:1.50 tt 61-65 3 2 6 9 1:1.50 20 66-70 1 4 20 66-70 2 3 « 71-75 2 3 it 71-75 2 3 u 76-80 5 it 76-80 5 « 81-85 2 3 5 15 1:3.00 tt 81-85 2 3 6 14 1:2.33 21 86-90 5 21 86-90 3 2 » 91-95 5 it 91-95 3 2 u 96-100 2 3 tt 96-100 1 4 it 101- 1 4 3 17 1:5.67 it 101- 2 3 9 11 1:1.22 22 106- 5 22 106- 5 a 111- 2 3 tt 111- 2 3 ti 116- 5 a 116- 4 1 « 121- 1 4 3 17 1:5.67 it 121- 1 4 7 13 1:1.86 2 .?{ 126- 1 4 23 126- 2 3 131- 1 4 tt 131- 3 2 it 136- 2 3 ii 136- 2 3 a 141- 1 4 it 141- 3 2 a 146- 2 3 7 18 1:2.57 tt 146- 5 15 10 1: .67 24 151- 1 4 24 151- 2 3 '•{ 156- 1 4 tt 156- 4 1 161- 3 2 tt 161- 2 3 u 166- 3 2 tt 166- 5 ii 171- 4 1 12 13 1:1.08 tt 171- 2 3 15 10 1: .67 25 f 176- 2 3 25 f 176- 2 3 " \ 181- 3 2 * \ 181- 4 1 it 186- 3 2 it 186- 1 4 it 191- 3 2 11 9 1: .82 tt 191- 3 2 10 10 1:1 26 196- 1 4 26 196- 1 4 it 201- 3 2 tt 201- 3 2 it 206- 2 3 6 9 1:1.50 it 206- 3 2 7 8 1:1.14 27 211- 3 2 27 211- 2 3 ti 216- 2 3 tt 216- 2 3 it 221- 2 3 7 8 1:1.14 it 221- 3 2 7 8 1:1.14 ?{ 226- 2 3 28 / 226- 2 3 231- 3 2 " I 231- 3 2 tt 236- 2 3 ti 236- 4 1 ti 241- 5 ii 241- 2 3 it 246- 4 1 it 246- 4 1 it 251- 5 21 9 1: .43 u 251- 2 3 17 13 1: .76 29 I 256- 2 3 29 256- 3 2 A STUDY OF THE BEHAVIOR OF THE PIG 205 TABLE 5 — Continued Daily Series and Averages with Ratios of Correct to Incorrect First Choices Problem 2 Female Male No. Ratio No. Ratio Date of trials R W R W of R to W Date of trials R W R W of R to W June June 29 261- 3 2 29 261- 4 1 « 266- 4 1 u 266- 4 1 « 271- 3 2 a 271- 2 3 u 276- 2 3 a 276- 2 3 a 281- 4 1 18 12 1: .67 u 281- 4 1 19 11 1: .58 30 286- 4 1 30 286- 1 4 u 291- 2 3 u 291- 2 3 a 296- 5 a 296- 4 1 a 301- 2 3 13 7 1: .54 « 301- 3 2 10 10 1:1 July July 1 / 306- 3 2 M 306- 3 2 " I 311- 4 1 311- 3 2 1 u 316- 5 a 316- 3 2 u 321- 2 3 14 6 1: .43 a 321- 2 3 11 9 1: .82 M 326- 5 2 / 326- 4 1 331- 4 1 " I 331- 3 2 u 336- 4 1 a 336- 4 1 a 341- 4 1 17 3 1: .18 u 341- 2 2 13 7 1: .54 M 346- 5 M 346- 2 3 351- 2 3 351- 3 2 a 356- 4 1 a 356- 2 3 a 361- 3 2 14 6 1: .43 a 361- 3 2 10 10 1:1 4 / 366- 4 1 4 f 366- 4 1 " 1 371- 3 2 : 371- 3 2 " / 376- 4 1 376- 3 2 " \ 381- 5 " \ 381- 3 2 a 386- 5 21 4 1: .19 u 5 u 386- 391- 396- 3 5 2 2 3 16 9 1: .56 11 391 4 1 a 396 5 9 1 1: .11 a a 401- 406- 411- 3 1 3 2 4 2 it 14 11 1: .79 6 416- 5 u 421- 4 1 4 6 1:1.50 7 426- 2 o O a 431- 1 4 a 436- 3 2 l 00 CO 01 X CO X; 00 CO ID olcOOOOOC^^OO't^l^-' CO X X X X X X X t>^ 00 t> 00 X t>- X CO CO X CD xid' ": (X)' « ;t> o cm ooo CO "tf LO co t-^ oo x ^ ^ oooooooooo CM CO -* ID CO t^ 00 X C ^ i-H i— « . — 1 1 — i.— ti — i «— i ^h CM CM X t>t> CO COt^CO CO t>oq oqcqt> od id lo t> od CO CO CO t>C^LD XOOx" CO x co od x coco ex co co x x c-^ CX CO CO CO CO CX CO CX CO x ex oq xj oq cocooqcococo oo" t> t> od x co x od x x x x 00 CO in CO cm t> ID CO CO CO 00 CO ID 00 CO ID H ^co so .CMlO j^COCO .cm'ld 00X o rHCNCO^LncDNOOCT.O oo oq LD oo t>oo t> oOt^co 00 t>00 LD* ^ LD CO CO id i>:-^ c^ odod^ ■"# ID oq od^ ""* ^. t> "# LD oq oq OOLOOOodcb "D T^ T^ ^* t> -^o6t>Trod^rocod LD ID ID ID ID CMCO^f ID ID LD LD LD LOCO t^OOX LD O lOLOLOLDLOlOLOlDlDLD ^CMCO^flOCDl>OOXO ^h^h^h____^h_CM CO CO co co Tjj coco^ LD COCOCO CO CO LDCO CO -<* CO COCO co CO co co co co >-< co co -^ co »-h co cvj^'cocococococococo ■>* ■^ ^ ^ CMCO ^ ^* ^^ ^* ^^ *^ LD CO l> 00 X o "^f ^* ^ ^ ^ ^ "^* "^ ^ ^ ^CMCO-^LDCOt^OOXO rtrt rtrHrir-(rtrtrHN CO LDLD -^ CM CO ■># i— I i— i IDCOCO-— iCOCOf— iCMr- 1 COLD-^-rl'LDCMCM-^CM LD >~< <— i co ,— ' ^f •— ' co CO CM' CO i-h CO CO ID CM 00 X CO o cocococococococococo ^CMCO^LDCOt^OOXO LD co' co t>t>co LDLDLD LONNLOCD co'c^c-t>t^co't>i>c^c^ co C/) m CM CM CMCMCM CM CM CM CM CM CM —i cmco^ locoooox ^r; CM CM CM CM CM CM CM CM CM CM •"HCMCO^fLDCOC^OOXO LD LD ID LD t>- cd coco" LD LD co" t> t> ID LDLD CO LD ID LD ID LD t>^ t> ID ID C^t>CO'lDCOt>IDCOLDLO CMCOTf IDCOt^OOX ~i rHOKO^LOCDNOOOlO iC-J A STUDY OF THE BEHAVIOR OF THE PIG 209 05 Ci CTi O CT5 O CD CT1 CD CD CD CD 00 CD CD CD CD CD CD CD CD LO 00 CO to CO 05 lo ao cotd co O OOOOOOOOOOOOOOOOOOOO CM COTfLOtOt^OOCDO'— iCMCO'-fLOtOC^-COCDO'- ' 03 CM CMCMCMCMCMCMCMCOCOCOCOCOCOCOCOCOCO'3 , ^f , -* O co 1— 1 O CM COM CO CO CO CO CO CO oi ai co co co ai co co cji co co ai co ai co ai co a^ co co co CO LO00 COtO CO CO Cji Looq PC to CO LO ^h CMCO'3'LOtOC^COCDO'— tCMCO-<#LOtOt>-CCCDO^ CM CM CM CM CM CM CM CM CM CO CO CO CO CO CO CO CO CO CO •<* -^ CM CO r-i LO LO LO LO LO LO LO lo loco'locolo^'loloco'lo^cololololo'#°lololo LO CO to CMLO t> LO cotd CMLO t- 00 00 00 00 CO 00 00 00 00 00 CO 00 00 00 00 00 00 00 00 00 00 ^h CM CO ■>* LO tO t>- 00 CD O •— 1 CM CO ■>* LO tO C- 00 CD O <-t CM CMCMCMCMCMCMCMCMCOCOCOCOCOCOCOCOCOCO^f'^f 00 CM 00 CO CO 00 CM LO CO CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CO to fSLO CM CM co to (NLO CM t-, c^ t- C— t- t- t> O t- [*- C— t>- C~- t> t> C> t>- C-- t> t> t> ■— 1 CM CO rj< LO tO l> 00 CD O •— 1 CM CO ■"* LO tO t> 00 CD O •— 1 CM CM CM CM CM CM CM CM CM CO CO CO CO CO CO CO CO CO CO "# Tf CM tF t^ CO I— 1 00 LO 00 00 00 t> 00 00 00 00 00 00 C^ 00 00 00 00 00 00 00 00 00 CO 00 CO in CO CM LO 00 in CO CM •— 1 LO CO COCOCOCOCOCOCOCOtOtOCOCOCOCOtOtOCOCOCOCO •— 1 CM CO ^f LO CO f- 00 CD O ^h CM CO rf LO CO t— CO CD O 1— 1 CM CM CM CM CM CM CM CM CM CO CO CO CO CO CO CO CO CO CO ■<* ^p to CM to to CO to 1— I LOrj< CO CO . ■* -^ ■<* tJ< t* t>-'t^rt i ^t | T}- CO CD O >— 1 CM CO ^f LO CO t> CO CD O 1— 1 CM CM CM CM CM CM CM CM CM CO CO CO CO CO CO CO CO CO CO ■"* -* LO CM LO LO CO LO CO CO CO CO CO to tO tO tOtOtOCM'tOCOCOCO'tOtOLO'tOtOCO'tOtO"*tOtOtO to to ^ LOCO ai to to o^ LOCO CJi tJ* t^* ^J* "^* ^* ^* "^* ^* ^* "^J* ^^ *^* ^^ ^^ ^* ^rf* ^* ^t* ^^ ^^ ^* >— 1 CM CO ^F LO CO C^ CO CD O •— 1 CM CO 'tf LO CO t>- CO CD O ^h CM CM CM CM CM CM CM CM CM CO CO CO CO CO CO CO CO CO CO "# Tf 1# CM ^ CO I— 1 1— ( rH tD >-H 1— 1 1— 1 too lo'oo ■* 1— ( too LOCO LO CO CO CO CO CO CO CO CO CO CO CO CO CO CO CO CO CO CO CO CO CO ^H CM CO ^* LO to O CO CD O ■— 1 CM CO ■* LO to t~- CO CD O 1— 1 CM CM CM CM CM CM CM CM CM CO CO CO CO CO CO CO CO CO CO ^P Tf CO CM CO CO CO CO c- t>c^Lo'ot>c^Lo't>t>r>t^t>t>t^t^!>c^[>t>t— to LO CO to c^- LO CO to CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM >-H CM CO ■<* LO to t~- CO CD O >-H CM CO tF LO to t- CO CD O ■— 1 CM CM CM CM CM CM CM CM CM CO CO CO CO CO CO CO CO CO CO ■* ^ CM CM CM CM CO CM LO t> LO LO LO LO tO' LOLOLOLOLOLOLOLOLOLOt^LOtOLOLOtOLOLOtOLO LO to LO CO to LO to LO CO ^h CMCO'*LOtOC^aOCDO'— ICMCO^PLOCOC^COCDO^ CM CM CM CM CM CM CM CM CM CO CO CO CO CO CO CO CO CO CO tJ« tJ< CM rH 1— ( CO .—I 210 ROBERT M. YERKES AND CHARLES A. COBURN CO w J 03 O K Ph P-J -> 3 3 < 2 o c/i H ►J I o co 00 LO Oi LO Oi oo oo -*' oo" a> 6.3.8.7.9 7.9 9 9 6.9 Oi 00 Oi Oi Oi Oi OiOi O. Oi Oi Oi H o I— 1 oo CM CO o XT o LO ooooP, I — 1 oooo cm co ^r lo 00 cot^ oooo OOOiOH CO 00 coco oo i> oq-^co Oico Oi co Oi co co lo ^r co co oq oi t> co co c-~ t-j oq t> ro oq co lo co ■** oq" co co oo oo i> oo pi oi od x aid aid d ^f d co t>|a CO CO oi OJ Lf oi oi 00 -* 3 3 5 CO CO i^oioi coco COCOOioi h Oi a. a-. r-t cm Oi CO a> cs o> ai c- cji loco c- oo a> Oi i-H O. Oi Oi Oi " C-JCO -T O. Oi LOCO Oi O. Oi Oi t-oocr.o oo CO ITS ^* CO cm LO LO LOCO LO CM LO CM CO ■<* CM LO LO LO LO -^ CO CO COLO LO LO LOLO LOCO LO COLO LO LOLOLO CO CO CO CM H oo oooo i— i CM oo CO 00 00 00 00 00 00 LO CO t^ 00 c. oc oooo oooo ^h CM CO ^ oooo LOCO oc 00 00 00 N00OO CO LO ■<* CO CM CO LO CM LO CMCO CM CO CM LO CM O] LO CM CM LO CO^LOCMCO CM CO CM LOCM CO CO CM CM CM CMLO coco CM CM CM CM H t- i-H CM CO t^ [^ C^ t> t> LOCOOOOCTl t — 1 — 'CMCO-^ LOCO c — t^ c — c— t>oocr,o CO CO oo [^ CO LO 00 CO oo 00 CO oo 00 oooo 00 00 CO t> 00 00 LO oq oc 00 c^oo oooo oq t>^ 00 oooo H CO COCO r-H CM CO CO co CO CO CO CO CO lo co o oo Oi CO 1—1 co co co co — 1 OJCO^t< COCO LOCO CO CO CO CO NOOfJlO LO CO 00 c^ CO LO CO LO ■<* 00 t> t^co 00 CO CO co 00 ~rf t>- 00 CO 00 I>• , * oo t>-^< oooo 00-^ lo oq -^f -^ -^ odcoodcood-* "* LO oooo ■^LO ^tTi< h LO LOLO i— i CM LO CO LO LO LO LO LO LO mcDNMO LO •—I LO LO LO LO ^ CMCO -*f LO LO LOCO LOLO LO LO NOOOiO CO CO sO CMLO co LO LO CO I — 1 co coco •<* CM LOCO CO LO CO' LO CO r— t CM LO CO CM CO ^CO LOCO^ ^ CM CM CM CO CO CO co CM co c6 CO-H Tf "* loco co CO COCO LO CM CMCO co CM co LO oo Oi Tj* t^ t^ ^ •-h CM CO -7 1 LOCO Tj^ '^ ^^ ^3* C^OOOiO CO CO coco cmlo 1-5 Tf CM CM cocOLq— < c6r- "# LO CM LO i-J -* Lf LO CO ^* CO CM LO C£ CM ■'co >,LO CM CO LO 1— I T— 1 •—! T— 1 COCO LO>— ICO 1— 1 r— 1 1— I 1— 1 COCO CO <-H CMCO ■«j* ■"# *- CO CO ^H j i-H CM i-H CO H CO coco i-HCM CO CO CO co co co co co Locot^ooo CO r-4 CO CO CO CO ^h cmco ^r coco LOCO CO CO CO CO NOOOiO CM CO CO LO o CO c- [^ t>. t> C^LOI>-t> LO CO CO CO' t^ t~ COCO t^t> t>t> t^t>c^t> H CM CMCM — (CM CO CM CM CM CM CM CM LOCOt>00C^ CM CM CM CM CM ^h CM CO ■* C^JCM LOCO CM CM CM CM t> 00 0. I-H CO CO vri LO CO LOLO COCO LO co LO co" LO 0' LO LO LO LO coc^c^t>co LO LO IO t> LO LO t>cot>co LOLO t>CO LO LO o'lolo t-^ H i— 1 i-H CM 1 — I CO Tf T— 1 rHrH r^i 1 LO CO t> 00 Oi i-H ■-H c^j co ^r LOCO 1 — 1 »-H r-H 1 — 1 C^OOOiO A STUDY OF THE BEHAVIOR OF THE PIG 211 CD CD CD CD CD CD CD CD C5 CD CD CD CD CD CD CD CD CD CD CD CD 00 CD CD CD C^ CD CD LO 00 co co- 00 CD LO 00 COCD 00 OOOOOOOOOOOOOOOOOCiOOOOOOOO Nco'*m^ot^ooG'.o<-Dt> CMCMCMCMCMCMCMCMcococ^cococococococo^t , ^t , ^^t < ^r^Tt , '* o oo o I— I o CD o CM COCOCO CO COCOCO CO CO c^aiCTicocoo^cococoo^oic^cocococoaicococococococooico CO lo 00 COCD CO CO Looq Jco"coco"^co"LO^LOiOLOiOLOLOco"Loioioco"LOLo^"Lo^i ooooooooooooooooooooooooooooooodoooooooooooooooooooo i-hcmco^lococ^cocdO'— icMco- , *Locot'^oocD©>— < cm co ^f lo cd CMCMCMCMCMCMCMCMC^COCOCOCOCOMC^COCOCO"*-^^t , ^t<^t < ^t-[^t>L^-c^c^t^[— c — tr^c — t—c — c — t — t^c-~t^ t---c-- 1^ t— .-hcmco^locdi^oocdo^cmco-^locdc'^oocdO'— icMco^riocD CMCMCMCMCMCMCMC>]CMCOCOCV}COCOOOCOCOCOCOTt rH CCCCOOOOCOOOOOCCOOOOOOXCCOCOOCOOOaOOOOOOOOOOOOCOOOO 00 ■<# co" CM r— ( LO 00 CO- CM 1— J LO CDCDCOCOCOCDCDCDCDCDCDCDCOCOCD'.OCDCDCDCOCDCOCOCOCDCO i-hcmco^locdl^ooo^o^cmco^locdi^cx)cdo<— 'CMco^fLoco wcMCMCMCMCMCMCMCMcocococococococococo^^^^t'^'-tf'^ CD CD CD oo CD f—t CD ■>* -^od^^^^^^ooTt i ^^T}<^^Tt i ^Ti < o6'^t < iot>^ oo LO CO CM 1— 1 ^F LO ■<* CO- CM 1-H y—l LO CM LOLOLOLOLOLOLOLOLOLOLOLOLOLOLOLOlOLOLOLOLOLOLOLOLOLO r-*CMCO^LOCDL^C©a^O--HCMCO^LOCOt^OOCDO^CMCO^LOCO WCMCMCMC>3CMCMCMCMCOCOCOCOCOCOCOCOCOCO^^^^t<^t'*3 , '7 l LO LO LO oo LO CD CD CD CD CD CD CD ^h CM CM CD CD ■* (C!D CO CM COCMCM1XJCOCDCDCOCDCDCDCD)LO-CC^CM'C£)CDCD>^^CDCDCDCDCD CD CD CT> lo'oo CD CD 4.5.6 7.8.9 (J> ^* ^* ^* ^* *^t* "^* -^sf ^^ ^F ^^ ^^ "^ -^J* ^^t* "^t* -^* ^t* ^t* ^t* ^^ ^J* *^t* ■'^ **^ "^^i" 1 "^ i^C>JCO^LOCDL^COCDO'-HCMCO^LOCDt>OOCDO'-HCMCO^LOCO C>JCMCMCMCMCMCMCMCMCOCOCOCOCOCOCOCOCOCO"* l '*^t , ^» , -*^t'^t l ^ 00 ,— i i— i ^ i— i •—< CD i— i CO >— < CO CO CD LO COLO CD i— i ■** CD >— i CVJCMf^CM'^Co''^'^CM-'^C^>^i^CMi^>^rMC>JCM'^'^CMCD'— ir- ii— i 1 — I cdcd LO 00 x* CD- CM 4.5.6 7.8.9 lo- COCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCO r-iCMOO'sfLOCDO-rcCDO'— iCMCO^fLOCDt>OOaiO^CMCO^LOCD CMCMCMCMCMCMCMCMCMCOCOCOCOCOCOCOCOCOCO^t'^t'ri'^t'^^*'^ CO CO CO oo co t>tr^ot>-ir^C^C^t^c^ix>-[>t^t^t>LO-t>t>t>t>-c^t>t>CD-t>i> t> sO LO CO- CD o LO CO- CD CMCMCMCMCMCMCMCMCMCMCMCMCMCM03CMCMCMCMCMCMCMCMCMCMCM .-HCMCO^LOCDL^OOCDO^CMCO^t , LOCOt>-OOCDO^-'CMCO^f'LOCO WCM^CMCMCMCMCNCMCOCOCOCOCOCOCOCOCOCO^f'^^'^r 1 '*'*^ 1 CM t> CM CM 00 CM i-H LO_ LO LO LO LO LO LO LO LOLOLO LO ^l^CDC^CO"t>LOLOL^l^Cl5LOLOl^l^CO"LOl^LOLOLOLOLOLOLOLO LO CD LO CO LO CO CD LO CO LO i— iCMCO-^LOCDt^OOCDO'— iCMCOTfLOCOC'^OOCD'— '■— •CMCO-'S'LOCO CMCSICMCMCMCMC^CMCMCOCOCOCOCOCOCOCOCOCO^-^''*-^^}'-^"^' I— < 1— ( 00 ^-1 212 ROBERT M. YERKES AND CHARLES A. COBURN TABLE 8 Daily Series and Averages with Ratios of Correct to Incorrect First Choices Problem 3 Female Male No. Ratio No. Ratio Date of trials R W R W of R to W Date of trials R W R W of R to W July July 11 1- 5 5 5 5 1:1 11 1- 2 8 2 8 1:4.00 12 11- 10 12 11- 4 6 a 21- 3 7 3 17 1:5.66 « 21- 1 9 5 15 1:3.00 13 31- 1 9 13 31- 2 8 « 41- 3 7 4 16 1:4.00 U 41- 3 7 5 15 1:3.00 14 51- 4 6 14 51- 1 9 u 61- 3 7 7 13 1:1.86 a 61- 1 9 2 18 1:9.00 15 71- 4 6 15 71- 2 8 « 81- 2 8 6 14 1:2.33 U 81- 3 7 5 15 1:3.00 16 91- 2 8 16 91- 4 6 1! 101- 4 6 6 14 1:2.33 a 101- 4 6 8 12 1:1.50 17 111- 3 7 17 111- 3 7 a 121- 3 7 6 14 1:2.33 « 121- 3 7 6 14 1:2.33 18 131- 5 5 18 131- 5 5 a 141- 6 4 u 141- 6 4 a 151- 5 5 16 14 1: .88 u 151- 3 7 14 16 1:1.14 19 161- 4 6 19 161- 4 6 u 171- 6 4 10 10 1:1 a 171- 6 4 10 10 1:1 20 181- 4 6 20 181- 6 4 « 191- 3 7 7 13 1:1.86 a 191- 6 4 12 8 1: .67 21 201- 6 4 21 201- 6 4 (t 211- 5 5 11 9 1: .82 U 211- 5 5 11 9 1: .82 22 221- 8 2 22 221- 5 5 ii 231- 7 3 15 5 1: .33 ii 231- 5 5 10 10 1:1 23 241- 9 1 23 241- 5 5 a 251- 8 2 17 3 1: .18 ii 251- 6 4 11 9 1: .82 24 261- 9 1 24 261- 6 4 « 271- 8 2 a 271- 9 1 a 281- 7 3 24 6 1: .25 a 281- 9 1 24 6 1: .25 25 291- 7 3 25 291- 7 3 « 301- 7 3 u 301- 8 2 a 311- 9 1 23 7 1: .30 u 311- 7 3 22 8 1: .36 26 321- 6 | 4 26 321- 8 2 a 331- 9 1 15 5 1: .33 u 331- 9 1 17 3 1: .18 27 341- 6 4 27 341- 8 2 « 351- 9 1 15 5 1: .33 a 351- 7 3 15 5 1: .33 28 361- 9 1 28 361- 6 4 u 371- 9 1 18 2 1: .11 ii 371- 9 1 15 5 1: .33 29 381- 7 3 29 381- 8 2 a 391- 9 1 16 4 1: .25 ii 391- 9 1 17 3 1: .18 30 401- 8 2 30 401- 8 2 (( 411- 10 18 2 1: .11 ft 31 411- 421- 8 8 2 2 16 4 1: .25 \ Aug. 1 ii 431- 441- 451- 8 8 6 2 2 4 16 4 1: .25 " i 461- 10 24 6 1: .25 2 421 7 3 7 3 1: .43 ' 2 471 8 2 8 2 1: .25 3 1-10 7 3 7 3 1: .43 i 3 1-10 9 1 9 1 1: .11 3 431 7 3 7 3 1: .43 3 481 8 2 8 2 1: .25 3 11-20 8 2 8 2 1: .25 i 3 11-20 5 5 5 5 1:1 A STUDY OF THE BEHAVIOR OF THE PIG 213 Although these figures are far from conclusive, we are con- vinced from the behavior of the animals that neither was choos- ing by familiarity with the particular settings. She, as has been pointed out, did as well with the control series as with the regular series, and he did even better in the first control series than in the regular series, while showing extreme confusion in the second control series. This was doubtless due to insufficient hunger and the distracting influence of a mistake in the first trial of the series. His carelessness throughout the last control series was conspicuous. Comparison of the results for problems 2 and 3 indicate that for the female problem 3 was somewhat the more difficult, whereas for the male, problem 2 required a larger number of trials. We are by no means convinced by this comparison that the problems have not been used in the order of increasing diffi- cultness, for we consider the female subject a much more reliable individual than the male, and we suspect that his greater facility in the solution of the third problem was due in part, at least, to the experience of the experimenters in dealing with his tem- peramental and other peculiarities. PROBLEM 4 The data to be considered in this connection appear in tables 9, 10 and 11. The correct mechanism is definable simply as the middle one, and the expectation prior to experience is one correct to four incorrect first choices, since the total number of doors open in the series of ten settings is fifty. As is shown in table 11, precisely this ratio resulted from the first day's experi- mentation in the case of each individual. Ten trials per series were given regularly throughout the work on this problem. Unlike the preceding problems, this one proved insoluble. Consequently, the detailed results as they appear in tables 9 and 10 are especially important, since from them may be read the reactive tendencies and their relations to one another. It is, of course, easy to understand why the ratio of correct to incorrect first choices should change steadily in the direction of the solution of the problem, for each subject gradually learned to react appropriately to certain of the settings while failing to acquire the ability to react to the relation middleness. 214 ROBERT M. YERKES AM) CHARLES A. 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COCO *CO * *"*'cOCO *CO* CO**"*'cOCOCOCOCOCO "*COCOCOCOCOCOCOCOCO*"*COCOCO co-* mco t>- ooc?.o^ oaco-* m co t> oc o o -— cm co -* m co t> oo o o — mk-tlicnkc cmcm cmcm cm cm cm coco co ooco cococococo — — — — — -*"*-* -r -r m in m uo m uo uo m m m 216 ROBERT M. YERKES AND CHARLES A. COBURN -* a - W "W o <« '- s Ph -S y, s — w CQ O < fc p w COO cried c-c^ t^ t> t~~ CO c^ t> c — t — t>- t^c^ododt>-t>ododt>c-t^o6o6t>odt^i^ H oo r-l CM o co o S.9 4.5.6 LO LOCO LO LO LO LOLOLOLO LO LO LO LO LO CO LO LOCOCOCOCDLOCOLOcdcdcOCOLOLO^LOCO H » — i CM (35 co rr rn <-h n- C 1 . 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YERKES AND CHARLES A. 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CM CM co-* CM CM CMCMCMCMCMCMCMCM mcoNoomo-HO] CMCMCMCMCMCOCOCO CM CM CM CM CM CM CO ^tLOCOOOO co co co co coco CM CM CM CM CX O— 'CM CO "* "*"* CM CO ^p CM CM CM CM CM CM ■<* lo co t>- oc x ^^ '^* ^^* ^^ ^^ ^t 1 CMCMCMCMNCMCMCMCMCM O^HCMCO^PLOCOt>-OOX LOLOLOLOLOLOLOLOLOLO X cm COCO co COCOCMCOCOCOCOCO CO CO CM CO CO CO CO CO ■*CO CM CM CO CO CO coco ^p"* CM CM CO CO CO CO COCOCOCOCOCOCOCO COCO H CO-"* CM CM LOCOt^OQOlO'-lCM OO CM CM CM CM CO CO CO CO ^f LOCDOCO co co co co coco CO ■* ■>* rf CO "* ^P LO CD t> 00 X ^* ^* ^3* ^ "^ ^p O^^CMCO^PLOCOt>OOX LOLOLOLOLOLOLOLOLOLO A STUDY OF THE BEHAVIOR OF THE PIG 219 S w 3 S o a z I-H w ►J o < £ W K J O CQ - < cfi H 5 t/3 o I-H CO 00 CO t>od c— t>t> coc^coc^c^ododi>t^-c^i>-t^t>t>t^t^ K oo rt CM ooo CO "* LO 0000 OOOOClCl00 0000 S^SgO^CMCO^LOCOt-OOCXO^j co CO iri ■<* LO LOCO coco LO LO LO COCO'*' LOLOLO LO LO LO LOLO'*CO^'lOLOCOLOLOLOLOLOCOlOCO H r— ( CT) CJ5 C7i CM CO'* CT-. (?. a\ CT-j CM °~ J 0" 1 O 3 OJ CTi CX Ol Cl Ol Oi O Sgt5$go^cMco-*Loco^coc->o 00 co CO LO CO CM LO'* CO ">*■ ■"* tO -* CO-* L^ -*'*'*'*'t'a < COLOCO'*'*-*'*'*C£;^J< H 00 00 r— 1 00 00 00 CM CO ^ locc^ooo^S^S^S^S^SScm co CO CM CM CM CM CM CMCMCMCMCMCMCMCMCMCMCMCMCMCMCMCM H l-H CM CO ■* LOCDL^OOO r , "- |CV3C0 ^ ,L0 ^ l ^ 00<:r3 CO co LO CM i—l CO CO lo coc^i oj LO CO LO LO LO CO CO coco CO cocococococo ^^'*''*T^^'*LOCO^^COLOCOCMCMCMLO^^t<°cO CO OqCMCMCMcM^CM^'*CMCMTt'*CM'*'*'*'*CMCM'cM'cOCM H COCO 1 — 1 co co co CM CO ■* cotococoto^^^^^^^^^O^O^O LOcSt2ooS°^ r<1 2^ Ln ' X3I; " ooai S LO co 00 LO ■<* COCO CO CO CO co cq co LO LOCO LO CO COCO-^CO'*t>COCOCOCD'*COCOCOLOCO H LOLO i-H LOLOLO cMco^r gS^ggo^CMco^LOcoc-ooa-.O CO °5 00 t>00 oo 00I>00 oq oqoq oo 00t>00C^t>00000000000000CO00C^00 H 1—1 T^ ^ ^ CM CO ■* — +1 _~ __ — — "** "^ "■* ■** "** "^ "^ ■** ■** "** ^ loco^ooct. ^^ 00 ^ 10 ^ 1 ^ 0001 ^ CO CO* CO in "* CO LO ^fLO coco LO LO'* LO CO coco LO LO LO 'tf' LO LO LO LO -* LO ^ LO cO'*'*'*'*loloco"lolO'*lolococolo H coco i-H CO CO CO CM CO T M ^~ .^.— COCOCOCOCOCOCOCOCOCOCO loScSooS ^;^ 1 ^^ 10 ^^ 00 ^^ CM CO CI 00 l> CO LO' oc'c^- odt>od t- LO LO' t> [^ cDt^t>cdt>cdt>odt>t>odt^t>t^c^t— H CM CM-h CM CM CM CM CO'* LOcot-ocS ^ 1 ^ 00 ^^^ 1 ^ 00 ^^ i— I CO PC CM coco CO CO CO CO coco ^ ^3* "^ COCOCOOJCMCMCOCOCOCOCOCOCOCOCOCO H f— I 1— 1 i-H 1— 1 1— 1 1-H CM CO "* locc^ooS2^SSSSSSs2§ 220 ROBERT M. YERKES AND CHARLES A. COBURN TABLE 11 Daily Series and Averages with Ratios of Correct to Incorrect First Choices Female Problem 4 Male No. Ratio No. Ratio Date of trials R W R W of R to W Date of trials R W R W of R to W Aug. Aug. 4 1- 5 4 1 5 a 6- 5 a 6- 1 4 ti 11- 4 6 4 16 1:4.00 .a 11- 3 7 4 16 1:4.00 5 21- 2 8 5 21- 2 8 u 31- 3 7 5 15 1:3.00 a 31- 2 8 4 16 1:4.00 6 41- 3 7 6 41- 4 6 ti 51- 4 6 7 13 1:1.86 n 51- 4 6 8 12 1:1.50 7 61- 2 8 7 61- 2 8 a 71- 4 6 6 14 1:2.33 « 71- 3 7 5 15 1:3.00 8 81- 4 6 8 81- 4 6 « 91- 2 8 a 91- 5 5 ti 101- 2 8 8 22 1:2.75 a 101- 5 5 14 16 1:1.14 9 111- 3 7 9 111- 3 7 « 121- 4 6 u 121- 3 7 « 131- 8 2 15 15 1:1 ti 131- 4 6 10 20 1:2.00 10 141- 3 7 10 141- 4 6 a 151- 4 6 a 151- 3 7 it 161- 6 4 13 17 1:1.31 a 161- 3 7 10 20 1:2.00 11 171- 5 5 11 171- 5 5 « 181- 3 7 a 181- 4 6 ti 191- 4 6 12 18 1:1.50 u 191- 6 4 15 15 1:1 12 201- 5 5 12 201- 5 5 ti 211- 3 7 a 211- 3 7 « 221- 5 5 13 17 1:1.31 a 221- 4 6 12 18 1:1.50 13 231- 8 2 13 231- 4 6 u 241- 3 7 I! 241- 5 5 a 251- 4 6 15 15 1:1 a 251- 5 5 14 16 1:1.14 14 261- 8 2 14 261- 5 5 ti 271- 4 6 a 271- 3 7 u 281- 6 4 18 12 1: .67 it 281- 4 6 12 18 1:1.50 15 291- 3 7 15 291- 5 5 (i 301- 3 7 it 301- 5 5 « 311- 3 7 9 21 1:2.33 a 311- 3 7 13 17 1:1.31 16 321- 3 7 16 321- 3 7 a 331- 6 4 « 331- 6 4 ti 341- 4 6 13 17 1:1.31 it 341- 2 8 11 19 1:1.73 17 351- 4 6 17 351- 3 7 a 361- 4 6 u 361- 5 5 it 371- 4 6 12 18 1:1.50 a 371- 7 3 15 15 1:1 18 381- 5 5 18 381- 5 5 « 391- 5 5 « 391- 4 6 a 401- 7 3 17 13 1: .76 u 401- 3 7 12 18 1:1.50 19 411- 6 4 19 411- 6 1 4 A STUDY OF THE BEHAVIOR OF THE PIG 221 TABLE 11 — Continued Daily Series and Averages with Ratios of Correct to Incorrect First Choices Female Problem 4 Male No. Ratio No. Ratio Date of trials R W R W of R to W Date of trials R W R W of R to W Aug. Aug. H 421- 7 3 " 421- 6 4 (1 431- 4 6 17 13 1: .76 <( 431- 5 5 17 13 1: .76 20 441- 6 4 20 441- 4 6 a 451- 2 8 « 451- 4 6 a 461- 7 3 15 15 1:1 (i 461- 7 3 15 15 1:1 21 471- 6 4 21 471- 5 5 a 481- 6 4 12 8 1: .67 ft 481- 7 3 12 8 1: .67 22 491- 7 3 22 491- 5 5 a 501- 4 6 ft 501- 4 6 (( 511- 4 6 15 15 1:1 « 511- 7 3 16 14 1: .88 23 521- 6 4 23 521- 6 4 « 531- 7 3 it 531- 6 4 ft 541- 5 5 18 12 1: .67 « 541- 7 3 19 11 1: .58 24 551- 4 6 24 551- 5 5 (i 561- 6 4 « 561- 7 3 ft 571- 7 3 17 13 1: .76 ft 571- 8 2 20 10 1: .50 25 581- 5 5 25 581- 4 6 ft 591- 4 6 9 11 1:1.22 a 591- 7 3 11 9 1: .82 25 1- 7 3 7 3 1: .43 25 1- 4 6 4 6 1:1.50 26 11- 7 3 26 11- 6 4 ft 21- 7 3 < ft 21- 6 4 it 31- 6 4 20 10 1: .50 « 31- 5 5 17 13 1: .76 27 41- 6 4 27 41- 6 4 ft 51- 5 5 ft 51- 6 4 » 61- 5 5 16 14 1: .88 ft 61- 7 3 19 11 1:.58 28 71- 5 5 5 5 1:1 28 71- 5 5 5 5 1:1 30 81- 5 5 30 81- 4 6 « 91- 7 3 a 91- 4 6 «i 101- 5 5 17 13 1: .76 a 101- 5 5 13 17 1:1.31 31 111- 6 4 31 111- 7 3 it 121- 7 3 ft 121- 5 5 « 131- 5 5 18 12 1: .67 » 131- 8 2 20 10 1: .50 Sept. Sept. 1 141 5- 5 1 141- 9 1 it 151 5- 5 a 151- 6 4 it 161 5- 5 15 15 1:1 ft 161- 9 1 24 6 1: .25 2 171 9- 1 2 171- 9 1 « 181 6- 4 it 181- 7 3 « 191 7- 3 22 8 1: .36 it 191- 6 4 22 8 1: .36 3 201 5- 5 5 5 ^ 3 201- 8 2 8 2 1: .25 222 ROBERT. M. YERKES AND CHARLES A. COBURN After six hundred trials had been given to each individual by use of the series of settings presented on page 192, under problem 4, it was apparent that the animals could succeed in solving the problem only by acquiring a definite habit for each particular setting, and it was further evident that the settings including seven and