The Mental Life of Monkeys and Apes

Introductory material (continued 2)

Reading edition

On July 16, the period of confinement in wrong boxes was increased to sixty seconds, and it was so continued for a number of days. But in the end, it became clear that the period of thirty seconds, combined with a liberal reward in the shape of desired food and a single series of ten trials per day, was most satisfactory. The detailed data of table 2 indicate that at this time Skirrl was making his choices by memory of the particular setting.

Skirrl, on July 17 was evidently hungry and eager to locate food, but seemingly unable to select the right box. In trial 5 (765th) of the series, he was punished by confinement in box 8. When the doors were unlocked in order that the entrance door might be raised to release him, the lock-bar, sliding under the floor, made a slight grating noise, and the instant the entrance door was opened, he jumped out excitedly. He made no outcry, but as soon as he was out of the box, sat down, and taking up his right hind foot, examined it for a few seconds. Having apparently assured himself that nothing serious had happened, he went on unconcernedly about his task. The presumption is that the sound of the lock-bar, associated as it was with his painful experience in box 1, revived the strongly affective experience of stepping on the nail. Psychologically described, the sound induced an imaginal complex equivalent to the earlier painful experience. The behavior seems to the writer a most important bit of evidence of imagery in the monkey. Finally, on August 9, after ten hundred and seventy trials, Skirrl succeeded in choosing correctly in the ten trials of a series, and he was therefore considered to have solved the problem of the second door from the right end of the group.

On the following day, he was given a control series with the settings which are presented on page 19 and also at the bottom of table 2. In this series he chose correctly five times,—in other words, as often correctly as incorrectly. An analysis of the choices indicates, however, that two of the five correct choices were made in box 8, which, as it happened, had proved a peculiarly easy one for him throughout the training, since from the first he tended to avoid door 9. Consequently, it is only fair to conclude, from the results for this control series and for those given on August 11 and 12, that the animal chose not on the basis of anything remotely resembling a general idea of secondness from the right end, but instead on the basis of gradually acquired modes of reaction to the particular settings. This conclusion is strengthened by the fact that he had failed to learn to react appropriately and readily to most of the settings of the regular series.

The curve which represents the course of the learning process in this problem is presented in figure 19. For this and all other curves which involve more than a single series of observations a day, the method of construction was as follows: The first series for each day of training is indicated on the curve by a dot, while the second or third series on a given day, although space is allowed for them, are not so indicated. Consequently, the form of the curve is determined chiefly by the first series per day. The extreme irregularities of this curve are most interesting and puzzling, as are also the variations in the daily ratios of right to wrong first choices. Three times in the course of the training, this ratio rose to 1 to 9, or higher. The causes for such extreme variations are not easily enumerated, but a few of the most obvious contributory causes are variations in the weather, especially cloudiness or fogginess, which rendered the apparatus dark; variations in the degree of hunger or eagerness for food; differences in the activities of the animals in the cages outside of the laboratory (sometimes they were noisy and distracted the subject), and finally, differences in the physical fitness and attitude of the animal from day to day.

The more or less incidental behavior in connection with this experiment more strongly than the statistical results of the work on problem 2 indicate the existence of imagery. That ideas played a part in the solution of the problem is probable, but at best they functioned very ineffectively. The small number of methods used in the selection of the right box, and the slight variations from the chief method, that of choosing the first box at the right end and then the one next to it, apparently justify Doctor Hamilton's characterization of this monkey as defective.

[Illustration: FIGURE 19.—Error curves of learning for the solution of problem 2 (second box from right end).]

Problem 3. Alternately First at Left and First at Right

Following the control series given in connection with problem 1, an interval of rest lasting from August 12 to August 19 was allowed in order that Skirrl might in part at least lose the effects of his training and regain his customary interest in the apparatus by being allowed to obtain food easily instead of by dint of hard labor,—labor which was harder by far, apparently, than physical activity because it demanded of the animal certain mental processes which were either lacking or but imperfectly functional. The difficultness of the daily tasks appears to be reliably indicated by the tendency to yawn.

Systematic work on problem 3, which has been defined as alternately the first door at the left and the first door at the right of the group, was begun August 19, and for nine days a single series of ten trials per day was given. Work then had to cease because of the experimenter's return to Cambridge.

The results of the work on this problem demand but brief analysis and comment. The expected ratio of one right to four wrong choices per series appears (see table 3) for the first series of trials, and this in spite of the fact that Skirrl had been trained for several weeks to choose the second door from the right end. One would ordinarily have predicted a much larger number of incorrect choices. The right choices were due to the monkey's strong tendency to go first to the first door at the right and thence to the one next to it. Indeed in the series given on August 24; this method was followed without variation. In other words, in every one of the ten trials Skirrl entered first the box at the extreme right end of the group. This necessarily resulted in as many right as wrong first choices. Consequently, the ratio reads 1 to 1. But the method was not adhered to, and at no time either before or after that date did he succeed in equalling this achievement. There was, as a matter of fact, no steady improvement, and so far as one may judge from the records which were obtained, the course of events in the solution of this problem would have been similar to those in problem 2.

TABLE 3

Results for Skirrl, P. irus, in Problem 3

[Footnote *: Aided by experimenter.]

2. Sobke, Pithecus rhesus

Problem 1. First at the Left End

Sobke was somewhat afraid of the experimenter when the investigation was undertaken, and instead of willingly coming out of his cage when the door was raised, he often had to be coaxed out and lured into the apparatus with food. Whereas Skirrl was frank and rather aggressive, Sobke was stealthy in his movements, furtive, and evidently suspicious of the experimenter as well as of the apparatus. He was perfectly safe to approach, but would not permit anyone to touch him. After a few days, he began to take food from the hands of the experimenter.

Preliminary work to acquaint this monkey with the routine of the experiment was begun on April 13. As in the case of Skirrl, he was lured into the apparatus and was taught the route through the boxes to the starting point by being allowed to obtain food once each day in each of the nine boxes. The procedure was simple. The entrance door and the exit door of a particular box were raised and the animal admitted to the reaction-compartment and permitted to pass through the box whose doors stood open, take its food, and return to the starting point. Sobke very quickly learned the route perfectly and came to work steadily and rapidly. After five days of preliminary work of this sort, he was so thoroughly accustomed to the apparatus that it was evidently desirable to begin with regular training experiments.

The first series of trials was given on April 19. Both punishment and reward were employed from the first. The punishment consisted of confinement for thirty seconds in each wrong box, and the reward of a small piece of banana, usually not more than a tenth of a medium sized banana for each correct choice. The total time for the first series of trials was fourteen minutes. This indicates that Sobke worked rapidly. My notes record that he worked quickly though shyly, wasted almost no time, made few errors of choice, and waited quietly during confinement in the boxes. In this, also, he differed radically from Skirrl who was restless and always tried to escape from confinement.

Throughout the work on problem 1, punishment and reward were kept constant. Everything progressed smoothly; there were no such irregularities of behavior as appeared in the case of Skirrl, and consequently the description of results is a relatively simple matter. Sobke invariably chose the end boxes. His performance was in every way superior to that of Skirrl.

As previously, the detailed results are presented in tabular form (table 4). From this table it appears that, whereas the expected ratio of right to wrong first choices for this problem is 1 to 2.5, the actual ratio for Sobke's first series was 1 to .67. This surprisingly good showing is unquestionably due to his marked tendency to choose the end box of a group; and this tendency, in turn, may in part be the result of the preliminary training, for during that only one box was open each time. But, if the preliminary training were responsible for Sobke's tendency, it should be noted that it had very different effect upon Skirrl, and, as will be seen later, upon Julius.

The results for the ten different settings of the doors for problem 1 as they appear in table 4 are of interest for a number of reasons. In the first place, the setting 1. 2. 3 appearing twice,—at the beginning of the series and again at the end—yielded markedly different results in the two positions. For whereas no mistakes were made in the case of setting 1, there were fifty per cent of incorrect first choices for setting 10. Again, satisfactory explanation is impossible. It is conceivable that fatigue or approaching satiety may have had something to do with the failures at the end of the series, but as a rule, as is indicated by settings 1, 2, and 6, if correct choices were made at the beginning, they continued throughout the day's work.

In this problem, Sobke's improvement was steady and fairly rapid, and in the eighth series, trials 71 to 80, only correct first choices appear. Consequently, seventy trials were required for the solution of the problem. This number is in marked contrast with Skirrl's one hundred and thirty-two trials.

Immediately following the first perfect series, Sobke was given two series of control tests on April 28. Conditions were unfavorable, since the day was stormy and the rain pattering on the sheet-iron roof made a great din. Nevertheless, he worked steadily and well up to the sixth trial, which was preceded by a slight delay because of the necessity of refilling some of the food boxes. After this interruption, wrong choices occurred in trial 6. And again after trial 9, there was brief interruption, followed by wrong choices in trial 10. The ratio of right to wrong choices for this first control series was therefore 1 to .25.

TABLE 4

Results for Sobke, P. rhesus, in Problem 1

Six minutes after completion of the first control series, a second was given under slightly more favorable conditions, and in this only a single wrong choice occurred, in that box 2 was first chosen in trial 6 instead of box 1. From the results of these two control series, it is evident that Sobke's solution of problem 1 is reasonably adequate. He is easily diverted or disturbed in his work by any unusual circumstances, but so long as everything goes smoothly, he chooses with ease and certainty. Whether it is fair to describe the behavior as involving an idea of the relation of the right box to the other members of the group would be difficult to decide. I hesitate to infer definite ideation from the available evidence, but I strongly suspect the presence of images and relatively ineffective or inadequate ideation.

It is perfectly evident that Sobke is much more intelligent than Skirrl. In practically every respect, he adapted himself more quickly to the experimental procedure and progressed more steadily toward the solution of the problem than did Skirrl. The contrast in the learning processes of the two monkeys could scarcely be better exhibited than by the curves of learning which are presented in figure 18. The first, that for Sobke, is surprisingly regular; the second, that for Skirrl, is quite as surprisingly irregular. These results correlate perfectly with the steadiness and predictability of the former's responses and the irregularity and erraticness of the latter's.

Problem 2. Second from the Right End

On the completion of problem 1 Sobke was in perfect condition, as to health and training, for experimental work. He had come to work quietly, fairly deliberately, and very steadily. His timidity had diminished and he would readily come to the experimenter for food, although still he was somewhat distrustful at times and became timid when anything unusual occurred in the apparatus.

As preparation for problem 2, a break in regular experimentation covering four days followed the control series of problem 1. On each of these four days the monkey was allowed to get food once from each of the nine boxes, both doors of a given box being open for the trial and all other doors closed. For this feeding experiment, the doors were opened in irregular order, and this order was changed from day to day.

Systematic work with problem 2 began on May 3, with punishment of thirty seconds for mistakes and a liberal reward of food for each success. Early in the series of trials it was discovered that Sobke was likely to become discouraged and waste a great deal of time unless certain aid were given by the experimenter. On this account, after the first two trials, the method was adopted of punishing the animal by confinement for the first ten mistakes in a trial, and of then, if need be, indicating the right box by slightly and momentarily raising the exit door. Every trial in which aid was thus given by the experimenter is indicated in table 5 by an asterisk following the last choice. In the first series of trials for this problem, aid had to be given in seven of the ten trials, and even so the series occupied seventy-one minutes. It is possible that had no aid been given, the work might have been continued successfully with a smaller number of trials than ten per day. But under the circumstances it seemed wiser to avoid the risk of discouraging and thus spoiling the animal for use in the experiment. It should be stated, also, that it proved impossible to adhere to the period of thirty seconds as punishment in this series. For the majority of the wrong choices confinement of not more than ten seconds was used.

For the second series, given on May 4, the conditions were unfavorable in that it was dark and rainy, and the noise of the rain on the roof frightened Sobke. He refused to work after the fourth trial, and the series had to be completed on the following day. The total time required for this series was seventy-eight minutes.

The work on May 6 was distinctly better, and the animal's behavior indicated, in a number of trials, definite recognition of the right door. He might, for example, make a number of incorrect choices, then pause for a few seconds to look steadily at the doors, and having apparently found some cue, run directly to the right box. No aid from the experimenter was needed in this series.

On the following day improvement continued and the animal's method of choosing became definite and fairly precise. He was deliberate, quiet, and extremely business-like. The time for the series was thirty-one minutes.

The period of punishment was increased on May 12 to thirty seconds. Previously, for the greater number of the trials, it had been ten to fifteen seconds. This increase apparently did not disturb the monkey, for he continued to work perfectly throughout the series, although making many mistakes in spite of deliberate choices and the refusal of certain boxes in each trial.

An interesting and significant incident occurred on May 13 when at the conclusion of trial 5, Doctor Hamilton came into the experiment room for a few minutes. Sobke immediately stopped working, and he could not be induced to make any choices until Doctor Hamilton had left the room. This well indicates his sensitiveness to his surroundings, and his inclination to timidity or nervousness even in the presence of conditions not in themselves startling.

Work was continued thus steadily until May 28 when, because of the failure of the animal to improve, it seemed wise to increase the period of confinement as punishment to sixty seconds. In the meantime, it had sometimes been evident that Sobke was near to the solution of his problem. He would often make correct choices in three or four trials in succession and then apparently lose his cue and fail utterly for a number of trials.

After June 1, in order to hasten the solution of the problem, two series per day were given. In some instances the second series was given almost immediately after the first, while in others an interval of an hour or more intervened. It was further found desirable to give Sobke all of his food in the apparatus. When the rewards obtained in the several trials did not satisfy his hunger, additional food was presented, on the completion of the series of experiments, in one or more of the food cups. On days marked by unwillingness or refusal to work, very little food was given. Thus, the eagerness of the monkey to locate the right box was increased and, as a matter of observation, his deliberateness and care in choice increased correspondingly. Sixty seconds punishment was found satisfactory, and it was therefore continued throughout the work on this problem.

It was evident, on June 9, from the behavior of the monkey as well as from the score, that the perfect solution of the problem was near at hand. This fact the experimenter recorded in his daily notes, and sure enough, on the following day Sobke chose correctly throughout the series of ten trials. The time for this series was only ten minutes. The choices were made deliberately and readily.

An analysis of the data of table 5 reveals five methods or reactive tendencies which appeared more or less definitely in the following order: (a) Choice of first box at the left, because of experience in problem 1. This tendency was very quickly suppressed by the requirements in connection with problem 2. Indeed one of the most significant differences which I have discovered between the behavior of the primates and that of other mammals is the time required for the suppression of such an acquired tendency. The monkey seems to learn almost immediately that it is not worth while to persist in a tendency which although previously profitable no longer yields satisfaction, whereas in the crow, pig, rat, and ring dove, the unprofitable mode of response tends to persist during a relatively large number of trials. (b) The tendency to choose, first, a box near the left end of the group, to go from that to the box at the extreme right end of the group, thence to the one next in order, which was, of course, the right box. This tendency appears fairly clearly from May 7th on. (c) The box at the extreme right was first chosen and then the one next to it. For example, in setting 2, box 4 would be chosen first, then box 3. Or, if this did not occur, the method previously described under (b) was likely to be employed, as for example, in setting 8, where such choices as 7.6.5.1.8 appear. (d) In certain series there appeared a marked preference for a particular box, usually box 3 (see results for May 24). This was doubtless due in a measure, if not wholly, to the fact that box 3 was the right box twice in each series of ten settings. But it should be added that the same is true of box 7, for which no preference was manifested at any time. (e) Direct choice of the right box.

The five reactive methods or tendencies enumerated above roughly appeared in the order named, but there were certain irregularities and the order as well as the time of appearance varied somewhat from setting to setting. In general, method c was the most frequently used prior to the development of method e, the direct choice of the right box.

TABLE 5

Results for Sobke, P. rhesus, in Problem 2

========+===========+==============+==============+==============+==============+==============+==============+==============+==============+==============+==============+===+===+===+===+======== | No. | S.1 | S.2 | S.3 | S.4 | S.5 | S.6 | S.7 | S.8 | S.9 | S.10 | | | | | Ratio Date | of | | | | | | | | 1.2.3.4.5 | | | R | W | R | W | of | trials | 7.8.9 | 1.2.3.4 | 2.3.4.5.6.7 | 1.2.3.4.5.6 | 4.5.6.7.8 | 1.2.3 | 2.3.4.5 | 6.7.8.9 | 1.2.3.4 | 3.4.5.6.7.8 | | | | | R to W ————+—————-+———————+———————+———————+———————+———————+———————+———————+———————+———————+———————+—-+—-+—-+—-+———— | | | | | | | | | | | | | | | | May | | {7.7.9.7.7 | {1.2.4.1 | {3.2.7.2 | {4.6.1.6 | | {3.1.3.3 | | | {4.1.4.1 | {3.8.3.3 | | | | | 3 | 1-10 | {9.7.9.7.9 | {1.4.1.1 | {7.7.7.5 | {1.6.1.1 | 5.8.6.7 | {3.3.1.1 | 3.5.4 | 9.1.8 | {4.1.4.2 | {3.8.6.3 | 0 |10 | 0 |10 | 0:10.00 | | {7.9.9.7.8* | {4.3* | {2.7.6* | {1.3.5* | | {1.1.2* | | | {1.4.3* | {8.3.7* | | | | | | | | | | | | | | | | | | | | | | | | | {4.7.2.7 | | (8.8.4.8 | | {5.5.5.5 | {9.5.5.9 | | | | | | | 4 and 5 | 11-20 | (7.9.7.9.9 | 1.4.1.3 | {2.7.3.2 | 1.6.5 | {8.8.4.8 | {3.3.1.1.3 | {5.5.5.3 | {7.1.6.6 | {4.4.4.4 | {8.8.6.8 | 0 |10 | 0 |10 | 0:10.00 | | {9.7.7.9.8 | | {7.2.6* | | {4.8.7* | {3.3.1.2 | {5.5.4* | {6.5.8* | {4.4.4.3 | {8.7 | | | | | | | | | | | | | | | | | | | | | 6 | 21-30 | 9.7.9.7.8 | 4.3 | 7.2.3.7.6 | {6.3.1.6 | 6.8.7 | 3.1.2 | {5.3.5.3 | {6.9.4.6.1 | {4.1.2.4 | {3.4.5.3 | 0 |10 | 0 |10 | 0:10.00 | | | | | {6.2.6.5 | | | {2.4 | {7.9.7.8 | {4.2.3 | {8.6.7 | | | | | | | | | | | | | | | | | | | | | 7 | 31-40 | 7.9.7.8 | 1.4.3 | 2.7.6 | 3.5 | 4.8.7 | 3.1.2 | 3.2.3.5.4 | 8 | 4.3 | 5.8.3.4.8.7 | 1 | 9 | 1 | 9 | 1: 9.00 8 | 41-50 | 7.9.7.8 | (4.2.4.1.4 | 6 | 5 | 6.5.4.8.7 | {3.1.3.1 | 5.3.5.4 | {7.4.2.1 | {4.2.4.1 | 5.3.8.7 | 2 | 8 | 2 | 8 | 1: 4.00 | | | {4.2.2.4.3 | | | | {3.1.3.2 | | {9.8 | {4.3 | | | | | | | | | | | | | | {5.3.5.3 | | | | | | | | 10 | 51-60 | 7.7.8 | 3 | 7.3.2.7.6 | 6.4.6.5 | (6.4.8.5 | 3.1.3.2 | {2.5.3.5 | 5.9.8 | 4.2.4.3 | {6.5.4 | 1 | 9 | 1 | 9 | 1: 9.00 | | | | | | {4.8.7 | | {2.5.4 | | | {3.8.7 | | | | | | | | | | | | | | | | | | | | | 11 | 61-70 | 7.9.7.8 | 1.4.3 | 4.3.2.7.6 | 6.5 | {5.4.8.6 | 3.2 | 5.4 | 6.5.2.3.1.8 | 3 | 6.5.3.8.7 | 1 | 9 | 1 | 9 | 1: 9.00 | | | | | | {5.4.8.7 | | | | | | | | | | | | | | | | | | | | | | | | | | 12 | 71-80 | 7.9.8 | 3 | 7.3.2.7.6 | 6.5 | 5.4.8.7 | 1.2 | 5.4 | 8 | 4.3 | 5.4.3.8.7 | 2 | 8 | 2 | 8 | 1: 4.00 13 | 81-90 | 7.8 | 4.3 | 3.7.6 | 6.5 | 8.7 | 1.3.2 | 2.5.2.5.4 | 7.6.5.9.8 | 3 | 8.7 | 1 | 9 | 1 | 9 | 1: 9.00 | | | | | | | | | | | | | | | | | | | | | | | | | | {1.2.1.2.2 | | | | | | 14 | 91-100 | 7.8 | 3 | 6 | 5 | 6.5.4.7 | 1.3.2 | 5.4 | 9.8 | {1.4.2.2.1 | 7 | 4 | 6 | 4 | 6 | 1: 1.50 | | | | | | | | | | {4.1.4.3 | | | | | | | | | | | | | | | | | | | | | | 15 | 101-110 | 7.8 | 3 | 7.6 | 5 | 5.4.5.7 | 3.2 | 5.4 | 8 | 2.1.3 | 8.8.7 | 3 | 7 | 3 | 7 | 1: 2.33 | | | | | | | | | | | | | | | | 17 | 111-120 | 7.8 | 4.3 | 7.6 | {2.1.2.1.2 | 8.7 | 3.2 | 5.4 | 7.6.5.1.8 | 3 | 8.7 | 1 | 9 | 1 | 9 | 1: 9.00 | | | | | {1.3.2.6.5 | | | | | | | | | | | | | | | | | | | | | | | | | | | 18 | 121-130 | 8 | 4.3 | 7.6 | 6.5 | 7 | 3.2 | 5.4 | 7.6.5.2.8 | 3 | 8.7 | 3 | 7 | 3 | 7 | 1: 2.33 | | | | | | | | | | | | | | | | | | | | | | | | {5.3.2.5.3 | | | | | | | | | | | | | | | | {2.5.2.5.3 | | | | | | | | 19 | 131-140 | 8 | 3 | 3.2.6 | 5 | 7 | 3.2 | {5.5.2.5.5 | 7.6.9.8 | 3 | 7 | 6 | 4 | 6 | 4 | 1: 0.67 | | | | | | | | {3.2.5.5.3 | | | | | | | | | | | | | | | | {2.5.5.4 | | | | | | | | | | | | | | | | | | | | | | | | 20 | 141-150 | 7.8 | 3 | 3.2.7.6 | 6.5 | 5.4.7 | 3.2 | 3.2.5.4 | 6.5.4.3.8 | 3 | 7 | 3 | 7 | 3 | 7 | 1: 2.33 21 | 151-160 | 7.8 | 3 | 5.7.5.3.7.6 | 5 | 7 | 3.2 | 5.3.5.2.5.4 | 7.6.5.9.8 | 3 | 6.4.3.8.7 | 4 | 6 | 4 | 6 | 1: 1.50 | | | | | | | | | | | | | | | | 22 | 161-170 | 7.8 | 3 | 7.6 | 3.2.6.5 | 7 | 3.2 | {5.2.5.3 | 7.6.5.8 | 3 | 7 | 4 | 6 | 4 | 6 | 1: 1.50 | | | | | | | | {2.5.4 | | | | | | | | | | | | | | | {3.1.3 | | | | | | | | | 24 | 171-180 | 8 | 3 | {3.2.7.5 | {3.6.4 | 8.7 | {1.3.3 | {3.5.4 | 8 | {4.4.2.1 | 7 | 4 | 6 | 4 | 6 | 1: 1.50 | | | | {7.3.6 | {3.6.5 | | {3.2 | | | {4.3 | | | | | | | | | | | | | | | | | | | | | | 25 | 181-190 | 7.9.7.9.8 | 3 | 3.7.6 | 5 | 8.7 | 3.2 | 5.4 | 4.3.8 | 4.3 | 8.7 | 2 | 8 | 2 | 8 | 1: 4.00 26 | 191-200 | 8 | 3 | 6 | 5 | 8.7 | 3.2 | 5.4 | 8 | 4.3 | 8.7 | 5 | 5 | 5 | 5 | 1: 1.00 27 | 201-210 | 7.9.8 | 3 | 3.2.7.6 | 5 | 8.7 | 3.2 | 5.4 | 8 | 3 | 8.7 | 4 | 6 | 4 | 6 | 1: 1.50 28 | 211-220 | 8 | 3 | 3.7.6 | 4.3.2.6.5 | 8.7 | 3.2 | 5.4 | 7.6.5.9.8 | 3 | 7 | 4 | 6 | 4 | 6 | 1: 1.50 29 | 221-230 | 7.8 | 3 | 5.4.3.7.6 | 6.5 | 7 | 2 | 3.2.5.4 | 7.6.5.8 | 3 | 3.8.7 | 4 | 6 | 4 | 6 | 1: 1.50 31 | 231-240 | 7.7.8 | 3 | 3.7.6 | 6.5 | 8.7 | 3.2 | 5.4 | 9.8 | 3 | 3.7 | 2 | 8 | 2 | 8 | 1: 4.00 June | | | | | | | | | | | | | | | | 1 | 241-250 | 8 | 3 | 5.4.7.6 | 3.2.6.5 | 8.7 | 3.2 | 5.4 | 8 | 3 | 8.7 | 4 | 6 | | | | | | | | | | | | | | | | | | | " | 251-260 | 7.9.8 | 3 | 3.7.6 | 5 | 6.5.4.8.7 | 3.2 | 4 | 5.4.3.8 | {4.2.1.4 | 7 | 4 | 6 | 8 |12 | 1: 1.50 | | | | | | | | | | {2.4.4.3 | | | | | | | | | | | | | | | | | | | | | | 2 | 261-270 | 7.8 | 3 | 6 | 3.2.6.5 | 7 | 3.2 | 3.4 | 8 | 3 | 6.5.3.8.7 | 5 | 5 | | | " | 271-280 | 7.8 | 3 | 3.7.6 | 3.6.5 | 7 | 3.2 | 5.4 | 7.6.5.4.3.8 | 3 | 7 | 4 | 6 | 9 |11 | 1: 1.22 3 | 281-290 | 7.8 | 3 | 7.6 | 3.6.5 | 8.7 | 3.2 | 4 | 7.8 | 3 | 7 | 4 | 6 | | | " | 291-300 | 9.8 | 3 | 3.6 | 4.3.6.5 | 8.7 | 2 | 3.5.4 | 7.6.5.9.8 | 3 | 8.7 | 3 | 7 | 7 |13 | 1: 1.86 4 | 301-310 | 8 | 3 | 7.6 | 3.4.3.6.5 | 8.7 | 2 | 3.2.5.4 | 7.6.5.8 | 3 | 3.8.7 | 4 | 6 | | | " | 311-320 | 8 | 3 | 5.4.7.6 | 3.2.6.5 | 7 | 2 | 3.2.5.4 | 8 | 3 | 7 | 7 | 3 |11 | 9 | 1: 0.82 5 | 321-330 | 8 | 3 | 6 | 4.6.5 | 7 | 2 | 3.5.4 | 8 | 4.3 | 7 | 7 | 3 | | | " | 331-340 | 8 | 3 | 7.4.7.6 | 3.2.4.6.5 | 7 | 3.2 | 3.5.4 | 8 | 3 | 7 | 6 | 4 |13 | 7 | 1: 0.54 7 | 341-350 | 8 | 3 | 7.6 | 5 | 8.7 | 1.3.1.2 | 3.5.4 | 8 | 3 | 7 | 6 | 4 | | | " | 351-360 | 8 | 3 | 7.6 | 5 | 8.7 | 2 | 3.5.4 | 8 | 3 | 7 | 7 | 3 |13 | 7 | 1: 0.54 8 | 361-370 | 7.8 | 3 | 4.7.6 | 3.5 | 8.7 | 2 | 3.4 | 9.8 | 3 | 7 | 4 | 6 | | | | 371-380 | 8 | 3 | 7.6 | 3.4.4.3.5 | 8.7 | 3.2 | 3.4 | 8 | 3 | 7 | 5 | 5 | 9 |11 | 1: 1.22 9 | 381-390 | 8 | 3 | 6 | 4.2.1.5 | 7 | 2 | 3.4 | 8 | 3 | 8.7 | 7 | 3 | | | " | 391-400 | 8 | 3 | 6 | 5 | 7 | 2 | 3.4 | 8 | 3 | 7 | 9 | 1 |16 | 4 | 1: 0.25 10 | 401-410 | 8 | 3 | 6 | 5 | 7 | 2 | 4 | 8 | 3 | 7 |10 | 0 |10 | 0 | 1: 0.00 ————+—————-+———————+———————+———————+———————+———————+———————+———————+———————+———————+———————+—-+—-+—-+—-+———— | | | | 1.2.3.4.5 | | | | | | 1.2.3.4 | 2.3.4.5 | | | | | | | 5.6.7.8 | 2.3.4.5.6 | 6.7.8.9 | 5.6.7 | 1.2.3.4 | 4.5.6 | 2.3.4.5 | 1.2.3 | 5.6.7 | 6.7.8.9 | | | | | | +———————+———————+———————+———————+———————+———————+———————+———————+———————+———————+—-+—-+—-+—-+———— 11 | 1-10 | 6.7 | 3.5 | 8 | 6 | 3 | 5 | 3.4 | 3.2 | 7.7.2.6 | 8 | 5 | 5 | 5 | 5 | 1: 1.00 12 | 11-20 | 7 | 3.6.6.2.5 | 8 | 6 | 3 | 4.5 | 4 | 2 | 7.6 | 8 | 7 | 3 | 7 | 3 | 1: 0.43 ========+===========+==============+==============+==============+==============+==============+==============+==============+==============+==============+==============+===+===+===+===+========

[Footnote *: Aided by experimenter.]

Examination of table 5 indicates that some of the settings proved very easy for Sobke; others, extremely difficult. Consequently, the number of methods which were tried and rejected for a given setting varies from two to five. Setting 2 proved a fairly simple one, and after the inhibition of the tendency to choose the first box at the left, the only definite tendency to appear was that of choosing the first box at the right, and then the one next to it. After one hundred and thirty trials, this method suddenly gave place to direct choice of the right box, and during the following twenty-eight series, no error occurred for this setting. Setting 4, on the contrary, proved extremely difficult, and a variety of methods is more or less definitely indicated by the records.

It is needless to lengthen the description by analyzing the data for each setting, since the reader by carefully scanning the columns of data in table 5 may observe for himself the various tendencies and their mutual relations.

Sobke's curve of learning (figure 19) in problem 2, is extremely irregular, as was that of Skirrl. Similar irregularities appear in the daily ratios of right to wrong first choices presented in the last column of table 5. Most of these irregularities were due, I have discovered, to unfavorable external conditions. Thus, dark rainy days and disturbing noises outside the laboratory were obviously conditions of poor work.

On the day following the final and correct series for problem 2, a control series was given. In this Sobke seemed greatly surprised by the new situations which presented themselves. Repeatedly he exhibited impulses to enter the box which would have been the correct one in the regular series of settings. He frequently inhibited such impulses and chose correctly, but at other times he reacted quickly and made mistakes. It was evident from his behavior that he was not guided by anything like a definite idea of the relation of the right box to the other members of the group.

In a second control series given on the following day, June 12, confusion appeared, but less markedly. For the first setting, a correct choice was made with deliberation. For the second setting, box 3 was immediately chosen, as should have been the case in the regular series of settings. Sobke seemed confused when he emerged from this box and had difficulty in locating the right one. Then followed direct correct choices for settings 3, 4, and 5. For setting 6, there is recorded a deliberately made wrong choice, and so on throughout the series, the choices being characterized by deliberateness and definite search for the right box. Uncertainty was plainly indicated, and in this the behavior of the animal differed markedly from that in the concluding series of the regular experiment.

It seems safe to conclude from the results of these control series that Sobke has no free idea of the relation of secondness from the right and is chiefly dependent upon memory of the particular settings for cues which lead to correct choice.

Problem 3. Alternately First at Left and First at Right

For four successive days after the last control series in connection with problem 2, Sobke was merely fed in the apparatus according to previous description (p. 43). He exhibited a wonderfully keen appetite and was well fed during this interval between problems.

The method of experimentation chosen for problem 3 in the light of previous experience was that of confining the monkey for a short time, ten to fifteen seconds, in the wrong box, in each of the first ten mistakes for a given trial, and of then aiding him to find the right box by the slight and momentary raising of the exit door. Aid proved necessary in a few of the trials during the first four days. Then he worked independently. As work progressed it was found possible and also desirable to increase the period of confinement, and in the end, sixty seconds proved satisfactory. It was also thought desirable to increase the number of trials per day from a single series during the early days to two or even three series from June 29 on. Often three series could be given in succession without difficulty. During the early trials on this problem Sobke worked remarkably well, but later his willingness diminished, evidently because of his failure readily to solve the problem, and it became extremely difficult to coax him into the apparatus. On days when he entered only reluctantly and as it seemed against his will, he was likely to be nervous, erratic, and often slow in making his choices, but above all he tended to waste time by not returning to the starting point, preferring rather to loiter in the alleyways or run back and forth.

TABLE 6

Results for Sobke, P. rhesus, in Problem 3

========+===========+==============+==============+==============+==============+==============+==============+==============+==============+==============+==============+===+===+===+===+======== | No. | S.1 | S.2 | S.3 | S.4 | S.5 | S.6 | S.7 | S.8 | S.9 | S.10 | | | | | Ratio Date | of | | | | | | | | | 3.4.5.6 | 3.4.5.6 | R | W | R | W | of | trials | 5.6.7 | 5.6.7 | 1.2.3.4.5.6 | 1.2.3.4.5.6 | 4.5.6.7.8 | 4.5.6.7.8 | 2.3.4.5 | 2.3.4.5 | 7.8.9 | 7.8.9 | | | | | R to W ————+—————-+———————+———————+———————+———————+———————+———————+———————+———————+———————+———————+—-+—-+—-+—-+———— | | | | | | | | | | | | | | | | June | | | | | {3.1.2.1 | {7.8.7.8 | | | | {9.8.7.9 | | | | | | 17 | 1—10 | {6.6.7.6 | 5.7 | {4.4.3.5.4 | {4.4.2.1 | {8.8.7.8 | 8 | 2 | 3.2.5 | {8.7.6.9 | 3.8.9 | 2 | 8 | 2 | 8 | 1:4.00 | | {6.5 | | {5.4.2.1 | {5.4.6* | {7.7.4* | | | | {8.7.3* | | | | | | | | | | | | | | | | | | | | | | | | | | {3.4.2.5 | | {8.7.7.5 | | | | | | | | | | 18 | 11—20 | 6.6.6.5 | 5.7 | {4.5.6.4 | 3.1.4.3.6 | {8.8.7.8 | 8 | 3.2 | (3.4.2.4 | 9.8.8.7.3 | 8.6.9 | 1 | 9 | 1 | 9 | 1:9.00 | | | | {2.3.1* | | {7.8.4* | | | {4.5 | | | | | | | | | | | | | | | | | | | | | | | | | | | {3.6.5.4 | | {8.8.7.7 | | | | | | | | | | 19 | 21—30 | 6.5 | 7 | {2.5.2.6 | 3.6 | {7.8.8.8 | 8 | 4.3.2 | {3.2.4.2 | {9.8.7.9.7 | 9 | 3 | 7 | 3 | 7 | 1:2.33 | | | | {3.5.1* | | {8.4 | | | {2.5 | {6.5.4.3 | | | | | | | | | | | | | | | | | | | | | | | | | | | | (8.8.8.8 | | | | {9.9.8.9 | | | | | | 21 | 31—40 | 6.5 | 5.6.5.7 | {3.5.4.6 | 2.5.3.6 | {7.8.3.8 | 8 | 4.2 | 2.5 | {9.5.9.9 | 9 | 2 | 8 | 2 | 8 | 1:4.00 | | | | {4.3.5.1 | | {8.7.4* | | | | {9.9.3* | | | | | | | | | | | | | | | | | | | | | | 22 | 41—50 | 7.6.5 | 6.5.5.7 | 1 | 2.1.3.6 | {8.8.8.8 | 8 | 2 | 2.3.2.2.5 | {9.8.9.8.7 | 9 | 4 | 6 | 4 | 6 | 1:1.50 | | | | | | {7.8.4 | | | | {6.5.9.3 | | | | | | | | | | | | | | | | | | | | | | 23 | 51—60 | 5 | 6.5.7 | 1 | {1.2.1.1 | 8.5.4 | 8 | 5.4.2 | 2.4.2.5 | {9.8.4.9 | 9 | 4 | 6 | 4 | 6 | 1:1.50 | | | | | {3.2.6 | | | | | {7.3 | | | | | | | | | | | | | | | | | | | | | | 24 | 61—70 | 7.6.5 | 7 | 2.3.1 | 2.1.5.4.2.6 | 8.7.8.4 | 8 | 4.5.4.3.2 | 2.2.4.5 | 9.7.6.8.3 | 9 | 3 | 7 | 3 | 7 | 1:2.33 25 | 71—80 | 6.5 | 5.7 | 3.1 | 6 | 8.5.4 | 8 | 2 | 3.2.5 | 9.8.7.3 | 3.9 | 3 | 7 | 3 | 7 | 1:2.33 | | | | | | | | | | | | | | | | 26 | 81—90 | 7.7.6.5 | 6.5.7 | 3.1 | {1.4.1.1 | 8.4 | 8 | 5.4.2 | 2.5 | 9.8.9.6.3 | 9 | 2 | 8 | 2 | 8 | 1:4.00 | | | | | {5.1.6 | | | | | | | | | | | | | | | | | | | | | | | | | | | 28 | 91—100 | 7.6.5 | 7 | 1 | 1.2.4.6 | 8.4 | 8 | 2 | 3.2.2.2.5 | 9.8.8.7.9.3 | 9 | 5 | 5 | 5 | 5 | 1:1.00 | | | | | | | | | | | | | | | | 29 | 101—110 | 7.6.5 | 5.7 | 1 | {1.1.5.3 | 8.4 | 8 | 2 | 4.2.5 | {9.9.8.9.4 | 9 | 4 | 6 | | | | | | | | {2.1.6 | | | | | {9.7.6.3 | | | | | | | | | | | | | | | | | | | | | | " | 111—120 | 6.5 | 6.5.7 | 1 | 2.1.1.3.6 | 8.5.4 | 8 | 2 | 3.2.5 | 9.8.7.6.4.3 | 9 | 4 | 6 | 8 |12 | 1:1.50 30 | 121—130 | 5 | 6.5.6.5.5.7 | 1 | 3.1.6 | 8.7.6.8.5.4 | 8 | 2 | 4.2.4.2.5 | 9.3 | 9 | 5 | 5 | | | " | 131—140 | 5 | 7 | 1 | 2.3.6 | 8.5.6.4 | 8 | 2 | 5 | 9.8.3 | 3.9 | 6 | 4 |11 | 9 | 1:0.82 July | | | | | | | | | | | | | | | | 1 | 141—150 | 5 | 7 | 1 | 1.6 | 8.7.4 | 8 | 2 | 3.2.5 | 9.8.6.9.3 | 9 | 6 | 4 | | | " | 151—160 | 5 | 7 | 1 | 2.5.3.6 | 8.4 | 8 | 2 | 2.5 | 9.3 | 8.8.7.5.4.9 | 5 | 5 |11 | 9 | 1:0.82 2 | 161—170 | 6.5 | 7 | 1 | 2.6 | 8.4 | 8 | 2 | 3.5 | 9.3 | 9 | 5 | 5 | 5 | 5 | 1:1.00 3 | 171—180 | 6.5 | 7 | 1 | 1.5.6 | 8.4 | 8 | 2 | 3.5 | 9.3 | 9 | 5 | 5 | | | " | 181—190 | 5 | 7 | 1 | 4.6 | 8.6.4 | 8 | 2 | 5 | 9.8.4.8.5.3 | 9 | 7 | 3 |12 | 8 | 1:0.67 5 | 191—200 | 6.5 | 5.7 | 1 | 6 | 8.4 | 8 | 2 | 5 | 9.5.3 | 9 | 6 | 4 | | | " | 201—210 | 5 | 7 | 6.1 | 2.6 | 8.6.4 | 8 | 5.3.5.4.3.2 | 4.3.5 | 9.7.3 | 9 | 4 | 6 |10 |10 | 1:1.00 | | | | | | | | | | | | | | | | 6 | 211—220 | 5 | 5.7 | 1 | 2.6 | 8.6.4 | 8 | 2 | 4.3.5 | 9.3 | {5.4.8.3 | 4 | 6 | | | | | | | | | | | | | | {8.5.4.9 | | | | | | | | | | | | | | | | | | | | | " | 221—230 | 5 | 7 | 1 | 5.3.6 | 8.6.8.4 | 8 | 4.2 | 3.2.5 | 9.3 | 9 | 5 | 5 | 9 |11 | 1:1.22 7 | 231—240 | 5 | 7 | 1 | 2.6 | 8.4 | 7.4.8 | 2 | 4.3.5 | 8.3 | 9 | 5 | 5 | | | " | 241—250 | 5 | 7 | 2.6.3.5.1 | 6 | 8.4 | 8 | 2 | 5 | 9.3 | 9 | 7 | 3 | | | | | | | | | | | | | | | | | | | | | | | {2.6.2.6.4 | | | | | | | | | | | | " | 251—260 | 5 | 7 | {6.3.2.6 | 6 | 8.4 | 8 | 2 | 5 | 9.5.3 | 9 | 7 | 3 |19 |11 | 1:0.58 | | | | {5.4.3.1 | | | | | | | | | | | | | | | | | | | | | | | | | | | | 8 | 261—270 | 7.5 | 7 | 1 | 6 | 8.4 | 8 | 5.2 | 5 | 8.3 | 8.5.4.9 | 5 | 5 | | | " | 271—280 | 5 | 7 | 2.6.4.6.1 | 6 | 8.5.8.4 | 7.4.8 | 5.5.3.5.2 | 5 | 9.3 | 9 | 5 | 5 |10 |10 | 1:1.00 | | | | | | | | | | | | | | | | 9 | 281—290 | 5 | 5.7 | 1 | 6 | 8.4 | 8 | 2 | 2.5 | 8.3 | {7.3.8.6.8 | 5 | 5 | | | | | | | | | | | | | | {4.7.3.9 | | | | | | | | | | | | | | | | | | | | | " | 291—300 | 5 | 7 | 1 | 6 | 8.4 | 8 | 2 | 5 | 9.3 | 9 | 8 | 2 | | | " | 301—310 | 5 | 7 | 1 | 6 | 8.4 | 8 | 5.2 | 5 | 9.5.3 | 9 | 7 | 3 |20 |10 | 1:0.50 10 | 311—320 | 5 | 7 | 1 | 6 | 8.4 | 7.4.8 | 2 | 5 | 9.3 | 9 | 7 | 3 | | | " | 321—330 | 5 | 7 | 1 | 5.2.6 | 8.7.4 | 8 | 2 | 5 | 9.3 | 9 | 7 | 3 |14 | 6 | 1:0.43 12 | 331—340 | 5 | 7 | 1 | 6 | 8.4 | 8 | 2 | 5 | 8.3 | 9 | 8 | 2 | | | " | 341—350 | 5 | 7 | 1 | 6 | 8.4 | 8 | 5.2 | 5 | 9.3 | 9 | 7 | 3 |15 | 5 | 1:0.33 13 | 351—360 | 5 | 5.7 | 1 | 6 | 8.4 | 8 | 5.2 | 5 | 3 | 9 | 7 | 3 | | | " | 361—370 | 5 | 7 | 6.1 | 6 | 4 | 8 | 5.2 | 3.2.5 | 9.3 | 9 | 6 | 4 |13 | 7 | 1:0.54 14 | 371—380 | 5 | 7 | 1 | 6 | 8.4 | 8 | 2 | 5 | 3 | 7.4.3.9 | 8 | 2 | | | " | 381—390 | 5 | 7 | 1 | 6 | 8.4 | 8 | 2 | 5 | 9.3 | 4.7.3.9 | 7 | 3 |15 | 5 | 1:0.33 15 | 391—400 | 5 | 5.5.7 | 1 | 3.6 | 8.4 | 8 | 3.2 | 5 | 8.3 | 9 | 5 | 5 | | | " | 401—410 | 5 | 7 | 1 | 6 | 8.4 | 8 | 2 | 5 | 7.3 | 6.5.3.9 | 7 | 3 |12 | 8 | 1:0.67 16 | 411—420 | 5 | 7 | 1 | 6 | 8.4 | 8 | 2 | 5 | 3 | 9 | 9 | 1 | | | " | 421—430 | 5 | 7 | 1 | 6 | 4 | 8 | 2 | 5 | 3 | 4.7.4.9 | 9 | 1 | | | " | 431—440 | 5 | 7 | 1 | 6 | 8.4 | 8 | 2 | 5 | 3 | 5.7.3.9 | 8 | 2 |26 | 4 | 1:0.15 17 | 441—450 | 5 | 7 | 1 | 6 | 4 | 4.8 | 2 | 5 | 4.3 | 3.5.9 | 7 | 3 | | | " | 451—460 | 5 | 7 | 1 | 3.6 | 4 | 5.4.8 | 2 | 5 | 9.3 | 9 | 7 | 3 | | | " | 461—470 | 5 | 7 | 1 | 6 | 4 | 8 | 2 | 5 | 3 | 9 |10 | 0 |24 | 6 | 1:0.25 19 | 471—480 | 5 | 7 | 1 | 6 | 8.4 | 8 | 2 | 5 | 3 | 9 | 9 | 1 | 9 | 1 | 1:0.11 ————+—————-+———————+———————+———————+———————+———————+———————+———————+———————+———————+———————+—-+—-+—-+—-+———— | | | | | | | | | | | | | | | | | | 5.6 | 5.6 | 4.5.6.7.8.9 | 4.5.6.7.8.9 | 1.2.3.4.5 | 1.2.3.4.5 | 2.3.4.5.6.7 | 2.3.4.5.6.7 | 3.4.5.6.7.8 | 3.4.5.6.7.8 | | | | | | +———————+———————+———————+———————+———————+———————+———————+———————+———————+———————+—-+—-+—-+—-+———— 19 | 1—10 | 5 | 6 | 4 | 9 | 1 | 5 | 3.7.2 | 7 | 3 | 8 | 9 | 1 | 9 | 1 | 1:0.11 ========+===========+==============+==============+==============+==============+==============+==============+==============+==============+==============+==============+===+===+===+===+========

[Footnote *: Aided by experimenter.]

The data of table 6 indicate for this problem only three pronounced reactive tendencies: (a) As the initial tendency, the choice of the second box from the right end. This proved surprisingly weak, in view of the animal's long training on problem 2, and it disappeared quickly. (b) Choice of the end boxes, and (c) direct choice of the right box.

For this, as for the other problems, extreme differences in method and in time and degree of success appear for the different settings. Thus, while settings 1, 2, 3, 6, 7, and 10 proved to be easy, settings 4, 5, 8, and 9 were evidently more difficult.

[Illustration: FIGURE 20.—Error curve of learning for the solution of problem 3 (alternately the first box at the left end and the first at the right end) by Sobke.]

From the first this problem promised to be much easier for Sobke than problem 2, and although the actual number of trials necessary for the solution is greater by sixty for problem 3 than for problem 2, comparison of the data of the tables justifies the statement that the third problem was both easier and more nearly adequately solved than the second. This is not surprising when the nature of the two problems is considered, for whereas problem 2 requires choice by perception of the relationship of secondness from the right end of the group, problem 3 requires, instead, the choice of the end member of the group each time, with the additional variation of alternation of ends. Now as it happens, the end member is easily selected by the monkey, and it appears further that alternation was relatively easy for Sobke to acquire. Consequently, the combination of end and alternation proved easier than the choice of the second from the right end of the group.

The above statements are supported by comparison of the curves of learning. The curve for problem 2, figure 19, is extremely irregular; that for problem 3, figure 20, much more regular. Similarly, the daily ratios of right to wrong choices as exhibited in tables 5 and 6 indicate smaller variations for the third problem than for the second.

Sobke made ten correct first choices in the third series for July 17, but he was working very uncertainly and it seemed rather a matter of good luck than good management that he succeeded in presenting this perfect series: For this reason and also because it did not seem feasible to have Sunday intervene between the final and perfect regular series and the control series, an additional regular series was given on July 19, in which, as the table indicates, a single mistake occurred, in trial 5. The monkey was working perfectly. The series of trials required only ten minutes, and it was evident that carelessness and eagerness to obtain food were chiefly responsible for the mistake.

The control series given on July 19 immediately after the series just described resulted similarly in one failure and nine successes. The choices were made easily and with certainty, and the only mistake, that of setting 7, was apparently due to carelessness.

This excellent showing for the control series wholly justifies the comparison of problems 2 and 3 as to difficultness, made above. Whereas in both problems 1 and 2 the control trials caused confusion, in the case of problem 3, they did not essentially alter the behavior of the animal. The fact seems to be that for this problem the particular setting is of relatively little importance; while turning alternately to the extreme left and the extreme right is of prime importance. That Sobke had the idea of alternation or of the end box, there seems no more reason for insisting than that he had the idea of secondness from the right end in problem 2. It is possible, even probable, that these ideas existed rather vaguely in his consciousness, but there is obviously no necessity for insisting that the solution of the problems depended upon them.

Problem 4. Middle

As the available time for the continuation of the experiment was limited, it was decided to proceed with work on problem 4 immediately upon the completion of problem 3, and on July 20, the problem of the middle door was presented to Sobke. Since it was anticipated that this sudden change would confuse and discourage him greatly, the only form of punishment administered was the momentary lowering of the entrance door of the wrong box. As in the previous problem, he was aided after ten successive wrong choices. As might have been anticipated, he persistently entered the end boxes of the groups, and this in some instances probably would have been kept up for many minutes had not the experimenter lured him into the right box by slightly raising the exit door. In the first series, he had to be aided in five of the ten trials. The total time for the series was forty-five minutes, the total number of choices, eighty-eight. In the second series, he was aided in four of the trials. The total time required was seventy-two minutes, and the total number of choices was seventy-six.

Throughout the first series, Sobke worked hard, but with evidently increasing dissatisfaction. He clung persistently to his acquired tendency to choose the end boxes, and after each trial he returned less willingly to the starting point. Up to this time his attitude toward the experimenter had been perfectly friendly, if not wholly trustful. But when on July 21 he was brought into the apparatus for the second series, he exhibited a wholly new form of behavior, for instead of attending diligently to the open doors and devoting his energies to trying to find the right box, he instead, after gazing at them for a few seconds, turned toward the experimenter and jumped for him savagely, throwing himself against the wire netting with great force. This was repeated a number of times during the first two or three trials, and it occurred less frequently later in the series. Since nothing unusual had happened outside of the experiment room, the suggested explanation of this sudden change in attitude and behavior is that the monkey resented and blamed on the experimenter the difficulty which he was having in obtaining food.

From this time on until the end of my work, Sobke was always savage and both in and out of the apparatus he was constantly on the watch for an opportunity to spring upon me. Previously, it had been possible for me to coax him into the apparatus by offering him food and to return him to his cage by walking after him. But on and after the twenty-first of July, it was impossible for me to approach him without extreme risk of being bitten.

Doctor Hamilton when told of this behavior, reported that several times monkeys have shown resentment toward him when they were having trouble in the experiment. I therefore feel fairly confident that I have not misinterpreted Sobke's behavior. When on July 22 I gave Sobke an opportunity to enter the apparatus, he refused, and it was impossible to lure him in with food. Two hours later, having waited meantime for his breakfast, he entered readily and worked steadily and persistently through his third series of trials, but in no one of these trials did he choose correctly. Neither on this day nor the following did he exhibit resentment while at work. He apparently had regained his affective poise and was able to attend as formerly to the task of locating his rewards.

During these first three series, although the ratio of right to wrong choices stood 0 to 10, there occurred a marked reduction in the number of trials in which aid was necessary as well as in the total number of choices, and on July 23 correct reactions began to appear. Improvement during the next hundred trials was steady and fairly rapid, and on July 31, a record of seven right to three wrong trials was obtained. This was surprising to the experimenter, as well as gratifying, since he was eager to have the animal complete this problem before work should have to be discontinued.

Everything went smoothly until August 2, when my assistant, who had been left in charge of the experimental work for a week, attempted to increase the number of trials per day to two series. Sobke apparently was not quite ready for this increase in the amount of his day's labor and refused to work at the end of the first series. In this series he did less well than on the previous day. The following day, August 3, unfortunately and contrary to the wishes of the experimenter, the laboratory was painted and there was necessarily considerable disturbance because of the presence of the workmen, and in addition, the pervasive odor of fresh paint. Sobke chose still less successfully on this date, and on August 4, he refused to work after the eighth trial. It is true that during these bad days the total number of choices steadily diminished while the successes, also, diminished, or at best, failed to increase. When on August 9, I returned to the laboratory to take charge, I found that Sobke was no longer trying to solve the problem as when I had gone away. His attitude had changed in that he had become indifferent, careless, and obviously discouraged with his task.

TABLE 7

Results for Sobke, P. rhesus, in Problem 4

========+===========+==============+==============+==============+==============+==============+==============+==============+==============+==============+==============+===+===+===+===+======== | No. | S.1 | S.2 | S.3 | S.4 | S.5 | S.6 | S.7 | S.8 | S.9 | S.10 | | | | | Ratio Date | of | | | 1.2.3.4 | | | 1.2.3.4.5 | | | 3.4.5.6 | | R | W | R | W | of | trials | 2.3.4 | 5.6.7.8.9 | 5.6.7 | 7.8.9 | 4.5.6.7.8 | 6.7.8.9 | 1.2.3 | 2.3.4.5.6 | 7.8.9 | 6.7.8 | | | | | R to W ————+—————-+———————+———————+———————+———————+———————+———————+———————+———————+———————+———————+—-+—-+—-+—-+———— | | | | | | | | | | | | | | | | July | | | {5.9.5.5 | {1.7.1.3 | {9.7.9.7 | | {1.9.3.1 | | {6.3.2.6 | | | | | | | 20 | 1- 10 | 2.4.2.4.3 | {5.9.5.6 | {1.7.1.7 | {7.9.7.9 | {8.4.8.4 | {9.2.9.3 | 3.1.3.2 | {3.6.3.2 | {9.3.4.3 | {8.6.6.8.6 | 0 |10 | 0 |10 | 0:10.00 | | | {5.8.7* | {1.7.4* | {7.7.8 | {4.6 | {9.1.5* | | {6.3.4* | {3.9.3.6 | {8.6.8.6.7 | | | | | | | | | | | | | | | | | | | | | | | | | | {7.9.7.7 | {4.8.5.5 | {1.4.3.2 | | | {3.9.3.8 | | | | | | 21 | 11- 20 | 2.3 | {5.6.5.5 | {1.2.7.1 | {7.9.7.7 | {8.4.8.4 | {8.9.1.9 | 3.1.2 | {6.2.3.2.6 | {4.3.3.5 | 6.7 | 0 |10 | 0 |10 | 0:10.00 | | | {9.5.5.7 | {7.3.7.4 | {9.7.8* | {5.4.6* | {1.9.5* | | {3.5.2.4 | {3.4.6* | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | {3.7.4.8 | | | | | | 22 | 21- 30 | 2.3 | 5.6.5.6.7 | 1.7.4 | {7.9.7 | 4.7.4.6 | {1.4.6.3 | 3.1.2 | 5.2.6.4 | {4.3.5.8 | 6.6.7 | 0 |10 | 0 |10 | 0:10.00 | | | | | {7.7.8 | | {2.7.5 | | | {3.7.6* | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | {5.4.7.4 | | | | | | 23 | 31- 40 | 2.4.3 | 5.6.8.7 | 1.7.4 | {7.7.7.7 | 4.7.6 | 2.7.5 | 3.1.2 | 6.4 | {7.5.4.3 | 7 | 1 | 9 | 1 | 9 | 1: 9.00 | | | | | {7.7.8 | | | | | {7.3.6 | | | | | | | | | | | | | | | | | | | | | | 24 | 41- 50 | 3 | 5.6.7 | 1.6.4 | 7.7.7.8 | 4.7.6 | {2.7.6.4 | 3.2 | 6.5.4 | 5.3.8.6.6 | 7 | 1 | 9 | 1 | 9 | 1: 9.00 | | | | | | | {2.7.3.8 | | | | | | | | | | | | | | | | {9.6.5* | | | | | | | | | | | | | | | | | | | | | | | | | 26 | 51- 60 | 4.3 | 6.5.7 | 2.7.4 | 7.8 | 6 | {6.4.2.7 | 3.2 | {6.5.3.5.2 | 7.6 | 7 | 2 | 8 | 2 | 8 | 1: 4.00 | | | | | | | {4.8.6.5 | | {6.5.6.4 | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | {4.7.3.7 | | | | | | | | | 27 | 61- 70 | 3 | 6.5.7 | 2.5.4 | 7.7.8 | 5.7.6 | {4.6.1.4 | 2 | 6.5.4 | 5.7.6 | 6.7 | 2 | 8 | 2 | 8 | 1: 4.00 | | | | | | | {7.3.5 | | | | | | | | | | | | | | | | | | | | | | | | | 28 | 71- 80 | 3 | 7 | 6.5.4 | 7.8 | 5.4.7.6 | 2.7.6.5 | 2 | 5.5.4 | 7.6 | 7 | 4 | 6 | 4 | 6 | 1: 1.50 | | | | | | | | | | | | | | | | 29 | 81- 90 | 3 | 6.5.7 | 2.4 | 7.7.8 | 5.4.6 | {2.7.7.6 | 2 | 4 | 5.4.7.6 | 7 | 4 | 6 | 4 | 6 | 1: 1.50 | | | | | | | {2.7.6.5 | | | | | | | | | | | | | | | | | | | | | | | | | 30 | 91-100 | 3 | 7 | 2.6.5.4 | 7.8 | 6 | 5 | 2 | 5.4 | 5.4.6 | 7 | 6 | 4 | 6 | 4 | 1: 0.67 31 | 101-110 | 3 | 7 | 2.4 | 7.8 | 6 | 5 | 2 | 4 | 7.6 | 7 | 7 | 3 | 7 | 3 | 1: 0.43 August | | | | | | | | | | | | | | | | 2 | 111-120 | 3 | 7 | 6.5.7.6.4 | 7.8 | 6 | 4.2.7.6.5 | 2 | 6.5.4 | 7.6 | 7 | 5 | 5 | 5 | 5 | 1: 1.00 3 | 121-130 | 3 | 6.5.7 | 7.6.5.4 | 7.8 | 7.6 | 5 | 2 | 6.5.4 | 7.6 | 7 | 4 | 6 | 4 | 6 | 1: 1.50 | | | | | | | | | | | | | | | | 4 | 131-140 | 3 | 7 | 6.5.7.6.4 | 7.8 | 6 | {2.7.6.4 | 2 | 6.4 | 3.5.4.6 | 7 | 5 | 5 | 5 | 5 | 1: 1.00 | | | | | | | {8.7.6.5 | | | | | | | | | | | {2.4.4.4 | | | | | | | | | | | | | | 5 | 141-150 | {2.4.4.2 | 6.5.7 | {2.7.6.7 | 8 | 7.6 | {2.8.7.6 | 3.2 | 6.4 | 7.6 | 8.7 | 1 | 9 | 1 | 9 | 1: 9.00 | | {4.3* | | {5.4 | | | {8.6.5 | | | | | | | | | | | | | | | | | | | | | | | | | 6 | 151-160 | 2.4.4.3 | 7 | 2.6.5.4 | 7.8 | 7.6 | 7.6.5 | 2 | 6.4 | 6 | 7 | 4 | 6 | | | | | | | | | | | | | | | | | | | | | {4.4.2.4 | | | | | | | | | | | | | | " | 161-170 | {4.2.4.2 | 7 | 6.5.4 | 7.8 | 7.6 | 7.6.5 | 3.2 | 5.4 | 7.6 | 7 | 2 | 8 | 6 |14 | 1: 2.33 | | {4.4.3 | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 7 | 171-180 | 4.3 | 7 | 6.5.4 | 8 | 7.6 | 5 | 2 | 6.5.4 | 7.6 | 7 | 5 | 5 | | | | | | | | | | | | | | | | | | | " | 181-190 | {4.2.4.4 | 7 | 7.6.5.4 | 7.8 | 6 | 6.5 | 2 | 6.5.4 | 7.6 | 7 | 4 | 6 | 9 |11 | 1: 1.22 | | {2.4.3 | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 9 | 191-200 | 3 | 7 | 5.4 | 8 | 8.7.6 | 6.5 | 2 | 6.5.4 | 7.6 | 8.7 | 4 | 6 | 4 | 6 | 1: 1.50 | | | | | | | | | | | | | | | | 10 | 201-210 | 3 | 7 | 2.5.4 | 7.8 | 7.6 | {2.8.7.6 | 2 | 6.5.4 | 7.6 | 7 | 4 | 6 | 4 | 6 | 1: 1.50 | | | | | | | {8.7.6.5 | | | | | | | | | | | | | | | | | | | | | | | | | 11 | 211-220 | 3 | 7 | 6.5.4 | 7.8 | 6 | {7.6.4.3 | 2 | 6.5.4 | 7.6 | 7 | 5 | 5 | 5 | 5 | 1: 1.00 | | | | | | | {2.7.6.5 | | | | | | | | | | | | | | | | | | | | | | | | | 12 | 221-230 | 3 | 7 | 2.4 | 7.8 | 6 | 7.6.5 | 2 | 6.5.4 | 8.7.6 | 7 | 5 | 5 | 5 | 5 | 1: 1.00 19 | 231-240 | 3 | 7 | 2.4 | 7.8 | 6 | 5 | 2 | 6.4 | 8.7.6 | 7 | 6 | 4 | 6 | 4 | 1: 0.67 | | | | | | | | | | | | | | | | 20 | 241-250 | 3 | 7 | 5.4 | 8 | 7.6 | {2.4.1.2.7 | 3.2 | 6.4 | 7.6 | 7 | 4 | 6 | 4 | 6 | 1: 1.50 | | | | | | | {8.7.6.5 | | | | | | | | | | | | | | | | | | | | | | | | | 21 | 251-260 | 3 | 7 | 6.5.4 | 7.8 | {7.4.5.4 | {6.4.3.2 | 2 | 6.5.4 | 8.7.6 | 7 | 4 | 6 | 4 | 6 | 1: 1.50 | | | | | | {8.7.6 | {7.6.5 | | | | | | | | | | | | | | | | | | | | | | | | | 23 | 261-270 | 3 | 7 | 6.5.4 | 7.8 | 6 | 6.5 | 2 | 6.5.4 | 7.6 | 7 | 5 | 5 | 5 | 5 | 1: 1.00 24 | 271-280 | 3 | 7 | 6.4 | 7.8 | 7.6 | 2.5 | 2 | 4 | 7.4.3.8.7.6 | 7 | 5 | 5 | 5 | 5 | 1: 1.00 25 | 281-290 | 3 | 7 | 2.5.4 | 8 | 7.6 | 5 | 2 | 6.4 | 7.6 | 7 | 6 | 4 | 6 | 4 | 1: 0.67 26 | 291-300 | 3 | 7 | 6.5.4 | 8 | 7.6 | 7.6.5 | 2 | 6.5.4 | 7.6 | 7 | 5 | 5 | 5 | 5 | 1: 1.00 27 | 301-310 | 3 | 7 | 2.6.5.4 | 8 | 7.6 | 5 | 2 | 6.5.4 | 7.5.4.9.8.6 | 7 | 6 | 4 | 6 | 4 | 1: 0.67 28 | 311-320 | 3 | 7 | 2.5.4 | 8 | 6 | 9.8.7.5 | 2 | 3.4 | 8.6 | 7 | 6 | 4 | 6 | 4 | 1: 0.67 ========+===========+==============+==============+==============+==============+==============+==============+==============+==============+==============+==============+===+===+===+===+========

[Footnote *: Aided by experimenter.]

I immediately set about reinstating the former attitude by lessening the number of trials and the punishment, and by increasing the value of the reward, but my best efforts, continuing up to August 28, failed markedly to improve the condition. The number of correct choices did somewhat increase, but at no time did the animal attain the degree of success which he had achieved as early as July 31 in the eleventh series of trials.

During the last two weeks of experimentation, all possible efforts were put forth to discover the best combination of rewards and punishments. Punishment was varied from 0 to confinement of sixty seconds, and many kinds of food in different amounts were tried as rewards, but in spite of everything Sobke failed to improve markedly. From time to time, notably on August 12 and 21, he exhibited peculiarly strong resentment toward me and repeatedly attempted to attack me.

The outcome of my experiments with problem 4 is peculiarly interesting in that it indicates the importance of a favorable attitude toward the work and the extreme risk from disturbing or discouraging conditions. It seems not improbable that had the work progressed without change in experimenter, or method of procedure, and above all without the disturbance of the painting, Sobke might have solved problem 4 within a few days. This is by no means certain, however, for in problems 2 and 3 the ratio of right to wrong choices instead of increasing steadily increased very irregularly.

The detailed results for this problem are given in table 7. Reactive tendencies which appear are: (a) persistent choice of the end boxes followed, subsequently, by (b) the tendency to locate the middle box directly. This proved fairly easy when the number of boxes involved was only three as in settings 1, 4, 7, and 10. Setting 4 was most difficult of all, because box 9 was avoided or ignored. When the number of open boxes was as great as five, as in settings 2 and 8, the task was obviously more difficult, but whereas success in setting 2 appeared early, in setting 8 it failed to appear during the course of experimentation. For the settings 3, 6, and 9, involving either seven or nine open boxes, the direct choice of the middle box was next to impossible, and Sobke tended to choose, first of all, a particular box toward one end of the series, for example, box 2, in setting 3, and box 7 in setting 9. To the experimenter, as he watched the animal's behavior, it looked as though effort each time were being made to locate the middle member of the group. This appeared relatively easy for groups of three boxes, extremely difficult for as many as five boxes, and almost impossible for seven or nine.

3. Julius, Pongo pygmaeus

Problem 1. First at the Left End

The orang utan, Julius, was gentle, docile, and friendly with the experimenter throughout the period of investigation. He at no time showed inclination to bite and could be handled safely. As contrasted with Skirrl and even with Sobke, he adapted himself to the multiple-choice apparatus very promptly, and only slight effort on the part of the observer was necessary to prepare him, by preliminary trials, for the regular experiments. But in order to facilitate work, he was familiarized with the apparatus by means of regular route training and feeding in the several boxes from April 5 to April 9.

On April 10 the apparatus was painted white as has been stated previously, and on the following Monday, April 12, Julius when again introduced to it gave no indications of fear, uneasiness, or dislike, but worked as formerly, making his round trips quickly and eagerly entering any box which happened to be open, in order to obtain the reward of food.

The regular experimentation was undertaken on April 13, and the results of the first series of trials with Julius are sharply contrasted with those obtained with the monkeys in that fewer choices were necessary. Instead of the expected ratio of right to wrong first choices, 1 to 2.5, the orang utan gave a ratio of 1 to 1. An additional markedly different result from that obtained with the monkeys is indicated below in the total time required for a series of trials. As examples, the data for the first, second, fifth, and tenth series are presented.

TIME FOR SERIES OF TRIALS

1st series 2nd series 5th series 10th series Skirrl 35 min. 20 min. 14 min. 10 min. Sobke 14 " 17 " 10 " 9 " (8th series) Julius 12 " 11 " 14 " 9 "

It is also noteworthy that Julius in the presence of visitors or under other unusual conditions worked steadily and well, whereas the monkeys, and especially Sobke, tended to be distracted and often refused to work at all.

Almost from the beginning of his work on problem l, Julius began to develop the tendency to enter immediately the open door nearest the starting point. In case the group of open doors lay to the right of the middle of the apparatus, this method naturally yielded success; whereas if the group included doors to the left of the middle, it resulted in failure. Obviously it was a most unsatisfactory method, and although it enabled him to make more right than wrong first choices, it prevented him from increasing the number of right choices, and as table 1 indicates, it maintained the ratio of 1 right to .67 wrong first choices for eight successive days.

On April 23 a break occurred in which the number of correct choices was reduced from six to five. Julius worked very rapidly and with almost no hesitation in choosing. My notes record "he seems to miss the point wholly. It is doubtful whether the punishment is sufficiently severe." At this time he was being punished by thirty seconds confinement in each wrong box, the interval having been held fairly steadily from the first series of experiments. On April 26 it was increased to sixty seconds, in an effort to break him of the habit of choosing the "nearest" door. But he became extremely restless under the longer confinement and tried his best to raise the entrance and exit doors. Since there was at this time no mechanism for locking them when closed, it was difficult for the experimenter to prevent him from escaping by way of the entrance door or from raising the exit door sufficiently to obtain the food. Indeed, the longer confinement worked so unsatisfactorily that on the following day I substituted for it the punishment of forcing him to raise the entrance door of the wrong box in order to escape for a new choice. He was rewarded with food in the alleyway H, beside door 15 (figure 17), only when he chose correctly on first attempt.

This method discouraged him extremely and proved wasteful of time. Consequently, in a second series on the same date return was made to the former method, and he was rewarded with food whenever he found the right box. But on April 28, the two methods were again employed, the first in the initial series and the second in a final series of trials. The animal's persistent attempts to raise the doors gave the experimenter so much trouble that on April 29 barbed wire was nailed over the windows of the entrance doors with the hope that it might prevent him from working at them. But he quickly learned to place his fingers between the barbs and raise the doors as effectively as ever.

On April 30 the reward of food was given only when the first choice was that of the right box and in that event it was placed in the alleyway H as stated above.

As it seemed absolutely essential to break the unprofitable habit of choosing the nearest door, on May 3 a new series of settings was presented, in which only the doors to the left of the middle of the row of nine boxes were used as right doors. That is, in this new series, doors 1 to 4 occur as right doors; 5 to 9 do not. As punishment for wrong choices on this date, Julius was confined in the wrong box from one to five minutes. It was difficult to keep him in, but by means of cords which had been attached to the doors, this was successfully accomplished. Yet another and slightly different series of settings was employed on May 4, and this, proving satisfactory, was continued in use until the end of the experiment, with punishment ranging from sixty to one hundred and twenty seconds for each mistake.

Naturally the modification of settings introduced May 3 greatly increased the proportion of wrong first choices. Indeed, as appears in table 8, the ratio of right to wrong immediately changed from 1:0.67 to 1:4.00. Between May 3 and May 10, no steady and consistent improvement in method or in the number of correct first choices occurred, and on the last named date, Julius chose correctly only three times in his ten trials. At this time there was, as my notes record, no satisfactory indication of progress, and the status of the experiment seemed extremely unsatisfactory in as much as in spite of the experimenter's best efforts to break up the habit of choosing the nearest door, the orang utan still persisted, to a considerable extent, in the use of this method. The only encouraging feature of the results was an evident tendency to choose somewhat nearer the left end of a group than previously.