METHODS OF EXHIBITING REACTIVE TENDENCIES 27 



Yerkes Method 



For use by the method of multiple choices, the apparatus 

 demands neither modification nor special adaptation. The chief 

 features of the method have already been described several 

 times, and it is needless here to do more than formulate a set 

 of problems with wider range of difncultness than those hereto- 

 fore used in reported experiments on lower animals. Those 

 proposed problems, ten in number, are presented in brief form 

 below, with a series of ten settings for each. Thus, in case of 

 problem 1, for which the correct mechanism is always box 

 number 5, that is the fifth from the left end of the apparatus, 

 the first setting involves the use of boxes 1 to 6, the second 

 setting, of boxes 3 to 12, and so on. It is understood* that, if 

 possible, this series of ten settings (ten trials) shall be presented 

 to a subject once a day until the problem has been solved. If 

 for any reason the series of ten trials cannot be completed on 

 a given day, it should be resumed from the point of interrup- 

 tion on the following day. If more than one series per day can 

 be given, either the ten trials may be divided into two groups 

 of five each or the total series may be repeated. 



In each of the series of ten settings, a total of sixty boxes is 

 presented. The average number of boxes open in each trial 

 is, therefore, six. Of these sixty boxes, ten are definable as 

 correct boxes. The probability of correct first choice prior to 

 experience is for any series of ten trials, one to five. In order 

 that this ratio of probable right to wrong first choices shall not 

 be disturbed, it is desirable that the experimenter make use of 

 the proposed settings. 



Proposed Problems and Settings for Multiple-Choice 



Method 



Problem 1. Same box (box 5). 



1-6 (5) ; 3-12 (5) ; 4-6 (5) ; 5-9 (5) ; 2-10 (5) ; 



4-5 (5) ; 4-10 (5) ; 3-6 (5) ; 1-8 (5) ; 5-10 (5). 

 Problem 2. First at left end. 



6-12 (6); 11-12 (11); 3-11 (3); 1-5 (1) ; 4-11 (4); 



10-12 (10); 5-9 (5); 2-12 (2); 8-11 (8); 7-12 (7). 

 Problem 3. Middle. 



1-7 (4); 10-12 (11); 6-10 (8); 1-11 (6) ; 1-3 (2); 



4-10 (7); 1-9 (5); 9-11 (10); 1-5 (3); 6-12 (9). 



