My work, although obviously preliminary and incomplete, differs from most of the previous studies of the complex behavior of the infrahuman primates in that I relied chiefly upon a specially devised method and applied it systematically over a period of several months.  The work was intensive and quantitative instead of more or less incidental, casual, and qualitative as has usually been the case.  Naturally, during the course of my special study of ideational behavior observations were made relative to various other aspects of the life of my subjects.  Such, for example, are my notes on the use of the hands, the instincts, the emotions, and the natural aptitudes of individuals.  It is, indeed, impossible to observe any of the primates without noting most interesting and illuminating activities.  And although the major portion of my time was spent in hard and monotonous work with my experimental apparatus, I found time each day to get into intimate touch with the free activities of my subjects and to observe their social relations and varied expressions of individuality.  As a result of my close acquaintance with this band of primates, I feel more keenly than ever before the necessity of taking into account, in connection with all experimental analyses of behavior, the temperamental characteristics, experience, and affective peculiarities of individuals.

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 supplementary methods are simple tests of ideation rather than systematic 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 ability of various types and conditions of animals.  The method was first tried with human subjects in the Psychopathic Hospital, Boston, with a crude keyboard apparatus which, however, 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 organisms, to the study of the behavior of the crow, pig, rat, and ringdove (Yerkes, 1914; Coburn and Yerkes, 1915; Yerkes and Coburn, 1915).  The method has also been applied with most gratifying results to the study of the characteristics of ideational 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 examination, such as psychopathic hospital and court examinations.