46 ROBERT M. YERKES 



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. 



Six minutes after completion of the first control series, a sec- 

 ond 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 every- 

 thing 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 sur- 

 prisingly regular; the second, that for Skirrl, is quite as sur- 

 prisingly 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 condi- 

 tion, 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 experimen- 

 tation covering four days followed the control series of problem 

 1. On each of these four days the monkey was allowed to get 



