MENTAL LIFE OF MONKEYS AND APES 9 



The light which I have obtained on the general problem of 

 ideation has come, first, through a method which I have rather 

 inaptly named the multiple-choice method, and second, and 

 more incidentally, through a variety of supplementary methods 

 which are described in Section IV of this report. These supple- 

 mentary methods are simple tests of ideation rather than sys- 

 tematic modes of research. They differ from my chief method, 

 among other respects, in that they have been used by various 

 investigators during the past ten or fifteen years. It was not 

 my aim to repeat precisely the observations made by others, 

 but instead to verify some of them, and more especially, to throw 

 additional light on my main problem and to further the analysis 

 of complex behavior. 



What has been referred to as the multiple-choice method was 

 devised by me three years ago as a means of obtaining strictly 

 comparable objective data concerning the problem-solving abil- 

 ity of various types and conditions of animals. The method 

 was first tried with human subjects in the Psychopathic Hos- 

 pital, Boston, with a crude keyboard apparatus which, how- 

 ever, proved wholly satisfactory as a means of demonstrating 

 its value. It has since been applied by means of mechanisms 

 especially adapted to the structure and activities of the organ- 

 isms, to the study of the behavior of the crow, pig, rat, and ring- 

 dove (Yerkes, 1914; Coburn and Yerkes, 1915; Yerkes and Co- 

 burn, 1915). The method has also been applied with most 

 gratifying results to the study of the characteristics of idea- 

 tional behavior in human defectives, — children, and adults, — 

 and in subjects afflicted with various forms of mental disease. 

 It is at present being tried out as a practical test in connection 

 with vocational guidance and various forms of institutional ex- 

 amination, such as psychopathic hospital and court examinations. 



As no adequate description of the method has yet been pub- 

 lished to which I can here refer, it will be necessary to present 

 its salient characteristics along with a description of the special 

 form of apparatus which was found suitable for use with monkeys 

 and apes. 



The method is so planned as to enable the observer to present 

 to any type or condition of organism which he wishes to study 

 any one or all of a series of problems ranging from the extremely 

 simple to the complex and difficultly soluble. All of the prob- 



