The Mental Life Of Monkeys And Apes Part 5

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 appet.i.te 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 p.r.o.nounced 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.

[Ill.u.s.tration: 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 relations.h.i.+p 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 antic.i.p.ated 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 antic.i.p.ated, 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 att.i.tude 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 att.i.tude 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 a.s.sistant, 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 att.i.tude 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 att.i.tude 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 att.i.tude 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 subst.i.tuted 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.