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.