The Mental Life Of Monkeys And Apes Part 4

_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 pa.s.s 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

========+===========+==============+==============+==============+==============+==============+==============+==============+==============+==============+==============+===+===+===+===+======== No. S.1 S.2 S.3 S.4 S.5 S.6 S.7 S.8 S.9 S.10 Ratio Date of R W R W of trials 1.2.3 8.9 3.4.5.6.7 7.8.9 2.3.4.5.6 6.7.8 5.6.7 4.5.6.7.8 7.8.9 1.2.3 R to W --------+-----------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+---+---+---+---+-------- April 19 1-10 1 8 3 9.7 6.2 6 7.5 4 9.7 1 6 4 6 4 1:0.67 20 11-20 1 8 3 7 2 6 7.5 8.4 9.9.7 1 7 3 7 3 1:0.43 21 21-30 1 8 4.3 9.7 2 6 5 8.4 7 1 7 3 7 3 1:0.43 22 31-40 1 8 3 7 6.2 6 6.5 4 7 3.1 7 3 7 3 1:0.43 23 41-50 1 8 3 7 2 6 5 4 9.7 3.1 8 2 8 2 1:0.25 24 51-60 1 8 3 9.7 2 6 5 4 7 2.1 8 2 8 2 1:0.25 26 61-70 1 8 3 7 2 6 5 4 7 3.1 9 1 9 1 1:0.11 27 71-80 1 8 3 7 2 6 5 4 7 1 10 0 10 0 1:0.00 --------+-----------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+---+---+---+---+-------- 2.3.4 1.2.3.4.5 2.3.4 6.7.8.9 3.4.5 4.5.6.7.8.9 6.7.8.9 1.2.3.4.5 5.6.7.8 3.4.5.6.7.8 5.6.7 6.7.8.9 +--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+ 28 1-10 2 6 3 4 6 5.4.1 2 3 5 5.4.2.1 8 2 " 11-20 2 6 3 4 6 2.1 2 3 5 1 9 1 17 3 1:0.18 ========+===========+==============+==============+==============+==============+==============+==============+==============+==============+==============+==============+===+===+===+===+========

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 circ.u.mstances, 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 punis.h.i.+ng 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 circ.u.mstances 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 a.n.a.lysis 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 a.n.a.lyzing 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_