186 ROBERT M. YERKES AND CHARLES A. COBURN 



certain constant relation or group of relations within the reac- 

 tion-mechanisms. For example, the mechanism to be operated 

 may, in the case of one problem, be the middle one of the group, 

 and the total number of mechanisms presented may vary from 

 three to nine. Only by perceiving and appropriately responding 

 to the relation which the experimenter designates as middleness, 

 can the subject solve the problem. 



It is necessary only, in the presentation of a varied series of 

 multiple choice problems to a given subject, for the experimenter 

 to devise a type of reaction-mechanism which is appropriate to 

 the action-system of the organism to be observed. We have 

 thus far made use of a simple keyboard for human subjects, 

 while for crows, ring-doves, and rats, we have employed a series 

 of similar boxes, each with entrance and exit doors which can 

 be operated at a distance by the experimenter. The form of 

 device which has proved suitable for the study of pigs will be 

 described in this report. 



It has proved very easy to develop suitable mechanisms and 

 we have every reason to suppose that this new method has great 

 advantages over most others for the comparative study of be- 

 havior in that essentially the same problems may be presented 

 to extremely different types of subject. 



The method has been employed in experiments with normal 

 and defective children, normal and insane adults, pigs, rats, 

 crows, and ring-doves. 4 To all of these subjects,. four problems 

 have been presented. They may be described briefly, by defini- 

 tion of the correct reaction-mechanism, as Problem 1, the first 

 mechanism at the subject's right; problem 2, the second mechan- 

 ism at the subject's left (that is, from the end of the series at 

 the subject's left) ; problem 3, alternately the first mechanism 

 at the subject's right and the first at its left; problem 4, the 

 middle mechanism of the series. 



It has become increasingly clear, as our investigations pro- 

 gressed, that the perfect solution of a problem by a given subject 

 is of much less importance as a matter of record than is detailed 

 information concerning the types of reaction and the appearance 

 and disappearance of reactive tendencies during the course of 

 experimentation. For the solution of a problem means simply 



4 The results of our experiments, except in the case of the crow, have not been 

 published. 



