MENTAL LIFE OF MONKEYS AND APES ' 25 



tunity, he chose box 8, which was the right one. The record 

 therefore reads 9.8. In trial 3, setting 3, he chose incorrectly 

 twice before finally selecting the right box. The record reads 

 6.7.3, and so on throughout the ten trials which constitute a 

 series. The summary for this series indicates three right and 

 seven wrong first choices, that is, three cases in which the right 

 box was entered first. The ratio of right to wrong first choices 

 is therefore 1 to 2.33. Since the total number of doors open 

 in the ten settings is thirty-five, and since in each of the ten 

 settings one door is describable as the right door, the probable 

 ratio, apart from the effects of training, of right to wrong first 

 choices is 1 to 2.50. It is evident, therefore, that Skirrl in his 

 first series of trials closely approximated expectation in the num- 

 ber of mistakes. 



By reading downward in any particular column of results, 

 one obtains a description of the changes in the animal's reaction 

 to a particular setting of the doors. Thus, for instance, in the 

 case of setting 1, which was presented to the animal in trials 

 numbered 1, 11, 21, and so on to 141, it is clear from the records 

 that no definite improvement occurred. But oddly enough, 

 in the case of setting 10, which presented the same group of 

 open doors, almost all of the reactions are right in the lower half 

 of the column. For setting 2, it is evident that mistakes soon 

 disappeared. 



Comparison of the data of table 1 indicates that the number 

 of correct first choices is inversely proportional to the number 

 of doors in use, while the number of choices made in a given 

 trial is directly proportional to the number of doors in use. 



During the first week of work on this problem, Skirrl im- 

 proved markedly. His performance was somewhat irregular 

 and unpredictable, but on the whole the experiment seemed 

 fairly satisfactory. Cold, cloudy, or rainy days tended to dimin- 

 ish steadiness and to increase the number of mistakes. Simi- 

 larly, absence of hunger was unfavorable to continuous effort to 

 find the right box. 



The period of confinement, as punishment for wrong choices, 

 was increased from thirty seconds to sixty seconds on April 26. 

 But there is no satisfactory evidence that this favored the solu- 

 tion of the problem. Work on May 4 was interrupted by a 

 severe storm, the noise of which so distracted the n|(Onkey ' that 



