44 ROBERT M. YERKES 



were kept constant. Everything progressed smoothly; there were 

 no such irregularities of behavior as appeared in the case of 

 Skirrl, and consequently the description of results is a relatively 

 simple matter. Sobke invariably chose the end boxes. His 

 performance was in every way superior to that of Skirrl., 



As previously, the detailed results are presented in tabular 

 form (table 4). Prom this table it appears that, whereas the 

 expected ratio of right to wrong first choices for this problem 

 is 1 to 2.5, the actual ratio for Sobke's first series was 1 to .67. 

 This surprisingly good showing is unquestionably due to his 

 marked tendency to choose the end box of a group; and this 

 tendency, in turn, may in part be the result of the preliminary 

 training, for during that only one box was open each time. But, 

 if the preliminary training were responsible for Sobke's tendency, 

 it should be noted that it had very different effect upon Skirrl, 

 and, as will be seen later, upon Julius. 



The results for the ten different settings of the doors for prob- 

 lem 1 as they appear in table 4 are of interest for a number of 

 reasons. Inthefirstplace, the setting 1. 2. 3 appearing twice,^ — ■ 

 at the beginning of the series and again at the end — yielded 

 markedly different results in the two positions. For whereas 

 no mistakes were made in the case of setting 1, there were fifty 

 per cent of incorrect first choices for setting 10. Again, satis- 

 factory explanation is impossible. It is conceivable that fatigue 

 or approaching satiety may have had something to do with the 

 failures at the end of the series, but as a rule, as is indicated by 

 settings 1,2, and 6, if correct choices were made at the beginning, 

 they continued throughout the day's work. 



In this problem, Sobke's improvement was steady and fairly 

 rapid, and in the eighth series, trials 71 to 80, only correct first 

 choices appear. Consequently, seventy trials were required 

 for the solution of the problem. This number is in marked 

 contrast with Skirrl's one hundred and thirty-two trials. 



Immediately following the first perfect series, Sobke was given 

 two series of control tests on April 28. Conditions were un- 

 favorable, since the day was stormy and the rain pattering on 

 the sheet-iron roof made a great din. Nevertheless, he worked 

 steadily and well up to the sixth trial, which was preceded by 

 a slight delay because of the necessity of refilling some of the 

 food boxes. After this interruption, wrong choices occurred in 



