The Mental Life Of Monkeys And Apes Part 3

Following the series of control trials of problem 1 given to Skirrl on May 6, a period of four days was allowed during which the animal was merely fed in the boxes each day. This was done in order that he should partially lose the effects of his previous training to choose the first box at the left before being presented with the second problem, the second box from the right.

On May 11 regular experimentation was begun with problem 2. Naturally the situation presented unusual difficulties to the monkey because of his previously acquired habit, and on the first day it was possible to give only five trials, in all except the first of which Skirrl had to be aided by the experimenter to find the right box. He persistently, as appears in the first line of records of table 2, entered the first box at the left. The series was continued on May 13, but with very unsatisfactory results, since he apparently had been greatly discouraged by the unusual difficulties previously met. Only four trials could be given, and in these the showing made was very poor. It is noteworthy, however, that in trials 6, 7, and 8, May 13, there was no marked tendency to choose the first box at the left. Thus quickly had the force of the previous habit been broken.

For problem 2, the total number of open doors in the ten settings is fifty, as appears from the data on page 18, and as ten of these fifty open doors may be defined as right ones, the expected ratio of right to wrong first choices in the absence of previous training is 1 to 4. The actual ratio for the first series given in problem 2 is 1 to 8, while in the second series it is 0 to 10.

On the morning of May 13, work was interrupted in the ninth trial by what seemed at the moment a peculiarly unfortunate accident, but in the light of later developments, an incident most fruitful of valuable results.

Skirrl, in trial 9, directly entered box 1. Since this was not the right box, he was punished by being confined in it for ten seconds. While in the box he howled and when the entrance door was raised for him to retrace his steps, he came out with a rush, showing extreme excitement and either rage or fear, I could not be sure which. At intervals he uttered loud cries, which I am now able to identify as cries of alarm.

Repeatedly he went to the open door of box 1 and peered in, or peered down through the hole in the floor which received the staple on the door. He refused to enter any one of the open boxes and continued, at intervals of every half minute or so, his cries. For thirty minutes I waited, hoping to be able to induce him to complete the series of trials, but in vain. Although it was obvious that he was eager to escape from the apparatus, he would not enter any of the boxes even when the exit doors were raised. Instead, he gnawed at the door (12 in fig. 17) to the alleyway D and attempted to force his way through, instead of taking the easy and clear route to the alleys, through one of the boxes.

His behavior was most surprising and puzzling. Finally, I gave up the attempt to complete the series and returned him to his cage by way of the entrance door to the response-compartment E.

I then entered the apparatus to seek some explanation of the animal's behavior, and my search was rewarded by the finding of two sharp pointed nails which protruded for an inch or more in the middle of the floor of box 1. My a.s.sistant, who had been charged with the task of installing the locks for the several doors, had used nails instead of screws for attaching staples underneath the floor and had neglected to clinch the nails. Skirrl, in the dim light of the box, doubtless stepped upon one of the nails and inflicted a painful, although not serious, injury upon himself. It was impossible for him to see clearly the source of his injury. He was greatly frightened and expressed the emotion most vigorously. His behavior strongly suggested a superst.i.tious dread of some unseen danger. It may be that the instinctive fear of snakes, so strong in monkeys, was partly responsible for his response.

The first result of this accident was that more than two weeks were lost, for it was impossible, during the next few days, to induce the animal to enter any of the multiple-choice boxes voluntarily. From May 14 to May 24, I labored daily to overcome his newly acquired fear. The usual procedure was to coax him through one box after another by standing at the exit door with some tempting morsel of food. After several days of this treatment, he again trusted himself to the boxes, although very circ.u.mspectly and only when both entrance and exit doors were raised. Not until May 24 was it possible to resume regular experimentation, and on that day it was found necessary to indicate the right box by raising the exit door slightly and then immediately lowering it. Trials in which this form of aid was given are indicated in table 2 by a star following the last choice.

Gradually, Skirrl regained his confidence in the apparatus and began to work more naturally. For a long time he would not stand punishment, and it was necessary for the experimenter to be very careful in locking the doors, since the sound of the bar sliding beneath the floor often frightened and caused him to quit work. Day after day the tendency to peer through the holes in the floor at the entrance to the boxes rendered it clear that the animal feared some danger from beneath the floor. This behavior was so persistent that much time was wasted in the experiments.

On the last day of May, punishment by confinement for ten seconds in wrong boxes was introduced, but since this tended to discourage the monkey, there was subst.i.tuted for it on June 1 the punishment of forcing him to work his way out of each wrong box by raising the entrance door which had been closed behind him. This he could fairly readily do, and his stay in a box rarely measured more than ten seconds.

As a variation in the mode of procedure, confinement for thirty seconds was tried on June 5, but it worked unsatisfactorily and had to be abandoned. During this series, the animal was startled by the sound from one of the sliding bars under the floor, and in the sixth trial he refused to work.

As improvement was very slow, varied modes of rewarding and punishing the animal were tried in the hope of discovering a means of facilitating the work. Among the former are the use of banana, grapes, peanuts, and other eagerly sought foods in varying quant.i.ties, and in the latter are included periods of confinement ranging from ten seconds to sixty seconds. In the end, confinement of about thirty seconds, combined with a small quant.i.ty of food which was much to the monkey's taste, gave most favorable results.

All this time Skirrl's attention to the task in hand was seldom good. He was easily diverted and even when extremely hungry, often stopped work in the middle of an early trial, yawned repeatedly and finally sat down to wait for release from the apparatus.

The results obtained during the long continued trials with this animal in problem 2 are presented in table 2, which differs from the previously described table, first, in that several of the trials are followed by an asterisk to indicate that aid was given by the experimenter, and second, in that two additional columns, headed, respectively, R and W, are presented. These give the right and wrong first choices for each day, whereas the two columns preceding them give the same data for each series of ten trials. Similarly, the ratio of right to wrong choices is presented for each day in table 2, instead of for each series of ten trials as in table 1.

From the results of table 2, several peculiarly interesting facts appear. In the first place the influence of the habit of choosing the first box at the left disappears with surprising suddenness, and in the second place, there are remarkable contrasts in the results for different settings as they appear in their respective vertical columns.

Thus, in the case of setting 1, after the first trial mistakes became relatively infrequent, whereas in setting 6, which involved the same number of doors, mistakes continued to be the rule until nearly a thousand trials had been given. The most likely explanation of this difference is that for some reason the animal avoided box 9.

The _reactive tendencies_, or better, the _methods of reaction_ which manifested themselves during this long series of observations may be described as follows: (a) choice of the first box at the left; (b) random choice with tendency to choose first, a box near the middle of the group; (c) choice of first box at the right followed by the one next to it on the left; (d) direct choice of the right box.

TABLE 2

Results for Skirrl, _P. irus_, 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 11&13 1- 9 7.7.9.7.8 {1.2.2.1.4.1 {2.3.2.3.2.5 {4.6.1.4.1.1 4.4.7 3.1.2 4 4.1.8 1 1 8 1 8 1: 8.00 {2.1.2.1.3 {2.3.2.5.6 {2.6.1.6.5 24 11- 20 8*[1] 2.4.3* 4.5.6* 2.2.5* 5.6.6.7* 3.1.2 {5.2.3.5.3.2 4.6.8* 4.4.3* 5.5.6.7* 0 10 0 10 0:10.00 {3.5.2.4* 25 21- 30 8* 4.4.3* 5.6 {6.6.2.3.4 6.7 2 4 5.6.3.8 4.4.3 6.4.6.8.7 2 8 2 8 1: 4.00 {6.6.5* 26 31- 40 8 4.3 6 4.5 6.7 3.2 5.4 5.8 4.3 5.3.8.7 2 8 2 8 1: 4.00 27 41- 50 8 4.4.3 6 5 6.8.6.8.7 3.3.3.2 5.4 {6.5.4.3 4.3 5.4.8.7 3 7 3 7 1: 2.33 {2.1.5.8 28 51- 60 8 4.4.3 7.6 5 5.6.7 3.3.3.2 4 {5.4.3 4.3 {5.4.3.3.4.5 3 7 3 7 1: 2.33 {3.6.8 {6.4.3.5.7 29 61- 70 8 4.3 6 6.6.5 7 3.3.3.2 5.4 7.6.4.7.6.8 4.3 7 4 6 4 6 1: 1.50 31 71- 80 8 4.4.4.3 6 6.5 6.8.7 3.2 5.4 {6.7.6.4.3 4.3 6.7 2 8 2 8 1: 4.00 June {2.6.3.7.8 {6.8.6.5.4 1 81- 90 8 4.3 6 5 {6.5.6.5.8 3.1.3.2 5.4 8 4.3 7 5 5 {5.4.6.4.7 " 91- 100 9.7.8 4.2.4.3 7.5.6 5 6.8.7 3.3.1.2 5.3.4 8 4.3 6.8.7 2 8 7 13 1: 1.86 2 101- 110 8 4.3 6 5 7 3.2 5.4 7.8 4.3 6.8.6.5.7 4 6 " 111- 120 8 4.3 7.3.5.7.6 {6.2.3.6.4 7 3.2 {5.2.3.5.3.2 9.6.4.7.8 {4.1.2 6.8.7 2 8 6 14 1: 2.33 {3.6.2.5 {3.5.2.3.4 {4.2.3 {6.8.6.3 3 121- 130 8 4.4.3 6 5 6.7 3.2 {5.3.2.3 8 4.2.3 {5.4.5.8.8 4 6 {5.2.5.4 {6.3.8.7 " 131- 140 8 4.3 5.7.3.2.6 4.5 5.7 1.3.2 5.3.4 6.7.8 4.2.1.3 7 2 8 6 14 1: 2.33 4 141- 150 8 4.3 7.6 6.5 7 2 {5.3.2.3 6.8 4.1.3 5.6.7 3 7 {5.5.4 " 151- 160 8 4.3 6 5 6.7 2 4 5.6.7.8 4.3 5.6.8.7 5 5 8 12 1: 1.50 5 161- 170 8 4.3 7.6 6.5 6.8.7 3.2 5.3.2.3.5.4 8 4.3 6.7 2 8 " 171- 176 8 2.4.3 7.6 6.5* 8.7 3.2* 1 5 3 13 1: 4.33 7 177- 180 5.4 8 4.4.3 8.7 1 3 " 181- 190 8 4.3 7.6 6.5 7 3.2 5.3.2.5.4 8 4.3 7 4 6 5 9 1: 1.80 8 191- 200 8 4.3 7.6 6.5 8.7 3.2 5.4 8 4.3 8.7 2 8 " 201- 210 8 4.3 6 6.4.6.5 8.7 3.2 5.4 8 4.3 7 4 6 6 14 1: 2.33 9 211- 220 8 4.3 7.6 6.5 8.7 3.2 5.4 8 4.3 8.6.7 2 8 " 221- 230 9.8 4.3 7.6 6.5 6.7 3.2 5.4 7.6.8 4.3 7 1 9 3 17 1: 5.67 10 231- 240 8 4.3 7.6 6.5 6.7 3.2 5.4 {3.2.3.2.4.3 4.3 7 2 8 2 8 1: 4.00 {2.5.4.7.8 11 241- 250 8 4.3 7.6 6.6.5 8.7 3.2 5.4 8 4.3 8.7 2 8 2 8 1: 4.00 12 251- 260 8 4.3 6 6.5 6.7 3.3.2 5.4 {7.6.7.7 3 3.7* 3 7 3 7 1: 2.33 {6.9.8* 14 261- 270 8 3 6 6.5 7 3.2 5.4 {5.3.4.3 3 {3.3.3.3.4 5 5 5 5 1: 1.00 {9.8* {4.6.4.7* 15 271- 280 7.9.8 4.2.3 3.4.3.7.6 6.5 8.7 3.2 5.4 8 4.3 8.7 1 9 " 281- 290 8 4.3 7.6 6.5 7 3.2 5.4 7.8 4.3 7 3 7 4 16 1: 4.00 {4.3.2.3 16 291- 300 7.8 {4.4.4 6 6.5 7 3.3.2 5.4 {6.5.4.3 4.3 6.7 2 8 {4.4.3 {5.6.7.8 " 301- 310 8 4.4.3 7.6 6.5 7 3.3.2 5.5.4 {7.6.5.4.6 4.3 7 3 7 5 15 1: 3.00 {5.7.9.8 17 311- 320 7.8 4.3 7.6 6.6.5 7 3.2 5.4 7.6.7.6.7.8 4.3 7 2 8 " 321- 330 8 4.3 7.6 6.5 8.7 3.2 5.4 8 4.3 6.7 2 8 4 16 1: 4.00 18 331- 340 7.7.8 4.3 6 6.5 7 3.2 5.4 8 4.3 7 4 6 " 341- 350 8 4.3 7.6 6.6.5 8.7 3.2 5.4 8 4.3 7 3 7 7 13 1: 1.86 19 351- 360 8 4.3 7.6 6.5 6.5.6.5.7 3.2 5.4 8 4.3 7 3 7 " 361- 370 8 4.3 7.6 6.4.3.6.5 7 3.2 5.4 9.8 4.3 7 3 7 6 14 1: 2.33 21 371- 380 8 4.3 7.6 6.5 7 3.2 5.4 7.8 4.3 8.7 2 8 " 381- 390 8 4.3 7.6 6.5 7 3.2 5.4 8 4.3 7 4 6 6 14 1: 2.33 22 391- 400 8 4.3 7.6 6.5 6.5.4.6.7 3.3.3.2 5.4 6.7.8 4.4.3 7 2 8 " 401- 410 8 3 7.6 6.5 8.7 2 5.4 6.7.7.8 3 7 5 5 7 13 1: 1.86 23 411- 420 8 4.4.3 7.6 6.5 8.7 3.2 5.4 {7.6.7.6 4.3 7 2 8 2 8 1: 4.00 {6.7.8 24 421- 430 8 4.3 6 6.5 7 3.2 5.4 8 3 7 6 4 " 431- 440 8 3 7.6 6.5 7 3.3.2 5.4 8 4.3 7 5 5 11 9 1: 0.82 25 441- 450 7.8 4.4.3 7.6 6.5 6.5.7 3.3.2 5.5.4 7.8 4.3 7 1 9 1 9 1: 9.00 26 451- 460 7.8 4.3 7.6 6.5 7 3.2 5.4 8 4.3 7 3 7 " 461- 470 8 4.3 7.6 6.5 7 3.2 5.4 8 4.3 8.7 3 7 6 14 1: 2.33 28 471- 480 8 4.4.3 7.6 6.5 7 3.2 5.4 9.8 3 8.7 3 7 3 7 1: 2.33 29 481- 490 8 4.3 7.7.6 6.5 7 3.2 5.4 8 4.3 8.7 3 7 3 7 1: 2.33 30 491- 500 7.9.8 4.3 7.6 6.5 7 3.2 5.4 8 4.3 7 3 7 " 501- 510 8 4.3 7.6 6.5 8.7 3.2 5.4 8 4.4.3 8.7 2 8 5 15 1: 3.00 July 1 511- 520 8 4.3 7.6 6.5 7 3.2 5.4 8 4.3 7 4 6 4 6 1: 1.50 2 521- 530 8 4.3 7.6 6.5 7 3.2 5.4 {7.6.5.6.5 4.4.3 7 3 7 {6.5.6.8 " 531- 540 8 4.3 7.6 6.5 7 3.2 5.4 8 4.3 7 4 6 7 13 1: 1.86 3 541- 550 7.8 4.4.3 6 6.5 7 3.2 5.4 8 4.3 5.5.7 3 7 " 551- 560 7.8 4.3 6 6.5 7 3.2 5.4 8 3 7 5 5 8 12 1: 1.50 5 561- 570 7.7.8 4.3 6 6.5 6.7 3.3.2 5.4 8 4.3 7 3 7 " 571- 580 8 4.3 6 6.5 7 3.2 5.4 7.8 4.3 7 4 6 7 13 1: 1.86 {6.5.4.6.5 6 581- 590 7.8 4.3 7.6 6.6.5 {5.4.5.4.4 2 3.4 6.5.4.3.7.8 3 7 3 7 3 7 1: 2.33 {6.5.6.5.8.7 7 591- 600 8 4.3 6 6.5 7 3.2 5.4 7.8 4.3 8.7 3 7 " 601- 610 7.8 4.3 7.6 6.5 8.7 3.2 5.4 8 4.3 8.7 1 9 4 16 1: 4.00 8 611- 620 8 4.3 7.6 6.5 8.7 3.2 5.4 8 4.3 8.7 2 8 " 621- 630 8 4.3 7.6 6.5 8.7 3.2 5.4 9.8 4.3 8.7 1 9 " 631- 640 8 4.4.3 7.7.6 6.5 8.7 3.2 4 8 4.3 8.7 3 7 6 24 1: 4.00 9 641- 650 7.8 4.3 7.6 6.5 6.7 3.2 {3.2.5.3 7.6.5.4.8 3 8.7 1 9 1 9 1: 9.00 {2.5.4 {6.5.4.3.7 10 651- 660 7.8 4.3 6 6.5 7 3.2 5.4 {6.5.4.7.6 4.3 7 3 7 {5.4.8 10 661- 670 8 3 7.6 5 7 3.2 5.4 8 3 8.7 6 4 9 11 1: 1.22 12 671- 680 7.8 3 6 6.5 7 3.2 5.4 6.5.4.7.8 4.3 8.7 3 7 3 7 1: 2.33 13 681- 690 8 3 7.6 6.5 {6.5.4 3.2 4 6.7.8 3 {6.5.4.5 4 6 {6.5.7 {6.5.8.7 " 691- 700 8 3 6 5 7 3.2 5.4 8 3 7 8 2 12 8 1: 0.67 14 701- 710 8 3 7.6 6.5 {6.5.4.5 2 3.5.4 8 3 7 6 4 {4.6.8.7 " 711- 720 8 3 6 5 7 2 5.4 6.5.4.8 3 6.5.7 7 3 13 7 1: 0.54 15 721- 730 7.8 3 6 6.5 7 3.2 5.4 8 4.3 7 5 5 " 731- 740 8 3 7.6 6.5 7 3.2 5.4 8 3 7 6 4 11 9 1: 0.82 16 741- 750 7.8 3 6 6.5 7 3.2 4 8 3 7 7 3 " 751- 760 7.8 3 7.6 6.5 7 2 4 7.8 4.3 7 5 5 12 8 1: 0.67 17 761- 770 8 4.3 6 5 8.7 3.2 5.4 8 4 7 6 4 " 771- 780 8 2.2.3 7.6 6.5 7 3.2 5.4 7.8 4.3 7 3 7 9 11 1: 1.22 19 781- 790 8 3 7.6 5 7 3.2 3.4 7.6.5.8 3 7 6 4 " 791- 800 7.8 3 6 5 7 2 5.4 8 3 6.5.6.7 7 3 " 801- 810 8 2.3 6 5 6.5.7 2 5.4 8 3 7 7 3 20 10 1: 0.50 20 811- 820 7.8 3 7.6 5 7 3.3.2 5.4 8 2.2.3 7 5 5 " 821- 830 8 3 6 6.5 7 3.2 4 8 2.3 8.7 6 4 11 9 1: 0.82 21 831- 840 8 3 5.4.5.6 5 7 2 4 6.7.8 3 8.7 7 3 " 841- 850 8 3 7.6 5 7 3.2 3.2.4 8 3 7 7 3 14 6 1: 0.43 22 851- 860 8 4.3 6 5 7 3.2 3.5.4 8 3 8.7 6 4 " 861- 870 7.8 4.3 7.6 6.5 8.7 3.2 4 8 3 8.7 3 7 " 871- 880 8 4.3 7.6 6.5 8.7 3.2 5.4 8 4.3 8.7 2 8 11 19 1: 1.73 23 881- 890 8 3 7.6 6.5 8.7 3.2 5.4 8 3 8.7 4 6 " 891- 900 8 3 7.6 6.5 7 3.3.2 5.4 8 4.3 7 5 5 9 11 1: 1.22 24 901- 910 8 4.3 7.6 6.5 7 3.2 5.4 8 3 8.7 4 6 " 911- 920 8 3 7.6 5 7 3.2 5.4 8 3 7 7 3 11 9 1: 0.82 26 921- 930 7.8 3 7.6 5 7 3.2 5.4 8 2.2.3 8.7 4 6 " 931- 940 8 3 7.6 6.5 8.7 3.2 5.5.4 8 4.3 8.7 3 7 7 13 1: 1.86 27 941- 950 8 3 6 6.5 7 3.2 5.4 8 3 7 7 3 7 3 1: 0.43 28 951- 960 8 3 7.6 6.5 5.4.7 2 5.5.4 8 3 7 6 4 6 4 1: 0.67 29 961- 970 8 3 7.6 5 8.7 2 4 8 3 7 8 2 8 2 1: 0.25 30 971- 980 8 3 4.3.2.6 5 {6.5.4.6 2 5.5.4 8 3 7 7 3 7 3 1: 0.43 {6.5.7 31 981- 990 8 3 6 6.5 8.7 2 4 8 3 7 8 2 8 2 1: 0.25 August 2 991-1000 8 3 7.6 5 7 2 {2.3.5.3 7.6.8 3 7 7 3 7 3 1: 0.43 {2.3.3.4 3 1001-1010 8 3 7.6 5 7 2 4 7.6.5.6.7.8 3 5.4.3.4.3.7 7 3 " 1011-1020 8 2.3 5.6 3.2.3.6.5 7 2 5.4 9.8 2.1.3 7 4 6 11 9 1: 0.82 4 1021-1030 7.8 3 5.4.3.7.6 6.5 {6.5.6 3.2 5.4 8 {2.2.4.2 8.7 2 8 {5.6.7 {4.2.3 " 1031-1040 7.8 3 6 6.4.3.6.5 7 2 3.5.4 8 2.3 8.7 5 5 7 13 1: 1.86 5 1041-1050 8 3 6 2.3.2.6.5 8.7 2 4 8 2.2.4.3 {8.8.6.8.4 6 4 6 4 1: 0.67 {6.5.8.7 6 1051-1060 8 3 6 4.2.6.5 7 3.2 5.4 8 3 8.7 6 4 6 4 1: 0.67 7 1061-1070 8 3 5.4.3.6 4.5 {6.5.6.5 2 4 8 3 7 7 3 7 3 1: 0.43 {4.8.7 9 1071-1080 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 --------+-----------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--------------+---+---+---+---+-------- 10 1- 10 6.5.7 3.2.6.5 8 6 2.4.3 5 5.4 2 7.5.2.7.6 8 5 5 5 5 1: 1.00 11 11- 20 7 3.6.5 8 6 3 6.5 4 3.2 7.6 8 6 4 6 4 1: 0.67 {3.2.3.5.3 12 21- 30 7 2.2.6.5 7.8 6 3 5 {2.5.3.2 2 6 8 7 3 7 3 1: 0.43 {5.3.2.5 {2.5.5.4 ========+===========+==============+==============+==============+==============+==============+==============+==============+==============+==============+==============+===+===+===+===+========

[Footnote 1: First choices correct by reason of aid from the experimenter are not counted as correct (R) in the summary.]

[Footnote *: Aided by experimenter.]

The method of choosing the first box at the right end and then the one next to it developed in the case of all except two of the ten settings.

The time of appearance is worth noting. In setting 1, it failed to appear; in setting 2, it developed early,--after about one hundred trials; in setting 3, after about one hundred and fifty trials; in setting 4, after about one hundred and fifty trials; in setting 5, after about one hundred and seventy trials; in setting 6, after about one hundred trials; in setting 7, after about fifty trials; in setting 8, it never developed; in setting 9, after about fifty trials; and in setting 10, it developed very late,--after about four hundred and seventy trials.

This method of reaction, although inadequate, proved remarkably persistent, and it is doubtful whether it had been wholly overcome at the conclusion of the experiment. In the case of the series of trials given on June 8, numbered 191 to 200, the method used was either that of the first at the right and then the next, or direct choice of the right box.

Throughout the trials with this problem, the end boxes, numbers 1 and 9, were avoided. This is at least partially explained by the fact that they never existed, and obviously never could appear, in problem 2, as right boxes. In trials 601 to 610, given on July 7, there occurred partial return to the formerly established method of choosing the first door at the right. This relapse was characteristic of what happened during the many days which intervened between the definite appearance of this habit and the final solution of the problem.

Especially in connection with such relapses, Skirrl showed extreme fatigue or ennui and often would refuse to work and simply sit before the open doors yawning. This happened even when he was extremely hungry and evidently eager enough for food.

From July 12 on the hunger motive was increased by feeding the monkey only in the apparatus and by so regulating the amount of food given in each trial that he should obtain barely enough to keep him in good physical condition. An increase in the number of correct choices promptly resulted, and continued until on July 14 the ratio of choices was 1 to .54. It appeared from these data that a relatively small number of choices, say not more than ten a day, the rewards in connection with which supplied the only food received by the animal, yielded most favorable results.

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 a.s.sured himself that nothing serious had happened, he went on unconcernedly about his task. The presumption is that the sound of the lock-bar, a.s.sociated 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 a.n.a.lysis 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 s.p.a.ce 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 att.i.tude 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.

[Ill.u.s.tration: 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 a.n.a.lysis 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

========+===========+==============+==============+==============+==============+==============+==============+==============+==============+==============+==============+===+===+===+===+======== Date No. of S.1 S.2 S.3 S.4 S.5 S.6 S.7 S.8 S.9 S.10 R W R W Ratio 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 3.4.5.6.7.8.9 3.4.5.6.7.8.9 R to W ________ ___________ ______________ ______________ ______________ ______________ ______________ ______________ ______________ ______________ ______________ ______________ ___ ___ ___ ___ ________ August {6.5.4.6 {8.7.6.5 19 1- 10 7.5 6.7 {3.2.6.4 5.3.6 {7.8.7.6 8 4.3.5.4.5.2 5 9.8.7.6.4.3 {4.5.8.7 2 8 2 8 1:4.00 {3.6.1* {8.6.4 {6.5.9* {5.4.6.5 {8.7.6.7 20 11- 20 7.6.5 {6.5.6.5 {4.6.5.3 5.3.2.4.6 {7.5.8.8 8 5.4.3.2 4.5 8.7.6.5.4.3 {8.7.6.8.3 1 9 1 9 1:9.00 {7 {2.5.1* {7.6.4* {7.6.4.3.9 {6.2.5.6 {5.3.5.4 21 21- 30 7.6.7.6.5 7 {5.3.6.5 2.5.5.6 8.6.5.4 8 {3.5.3.5 5 {9.8.7.6 8.9 3 7 3 7 1:2.33 {4.3.1* {4.3.2* {5.4.3 23 31- 40 7.6.5 6.5.7 {6.4.3.2 3.2.6 8.7.6.4 8 5.4.5.3.2 5.2 8.7.3 9 2 8 2 8 1:4.00 {5.6.2.1 24 41- 50 7.6.5 7 {6.2.5 6 {8.7.8.7 8 5.3.2 5 {9.8.7.6 9 5 5 5 5 1:1.00 {4.3.1 {5.7.5.4 {5.4.3 {8.7.3.6 25 51- 60 7.6.5 6.5.7 5.2.1 6 8.5.4 8 2 2.5 9.8.7.4.3 {8.7.5.3 3 7 3 7 1:2.33 {8.7.9* 26 61- 70 7.6.5 6.5.7 1 2.1.6 8.7.6.4 8 2 3.2.5 9.8.7.5.3 {3.6.8.3 3 7 3 7 1:2.33 {4.7.9 {8.6.3.3 27 71- 80 7.6.5 7 2.1 1.5.6 8.7.6.4 8 2 5 9.8.7.6.3 {7.5.3.8 4 6 4 6 1:1.50 {3.6.9* 28 81- 90 7.6.7.5 7 3.1 6 8.6.4 4.8 2 2.4.5 8.7.4.3 3.8.9 3 7 3 7 1:2.33 ========+===========+==============+==============+==============+==============+==============+==============+==============+==============+==============+==============+===+===+===+===+========

[Footnote *: Aided by experimenter.]

2. Sobke, _Pithecus rhesus_