56 ROBERT M. YERKES 



The data of table 6 indicate for this problem only three pro- 

 nounced reactive tendencies: (a) As the initial tendency, the 

 choice of the second box from the right end. This proved sur- 

 prisingly 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. 



Trials 



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 adecjuately solved than the second. This is not surpris- 

 ing when the nature of the two problems is considered, for 

 whereas problem 2 requires choice by perception of the rela- 

 tionship 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 mon- 

 key, 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 ex- 



