The Mental Life of Monkeys and Apes | Page 4

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.
As no adequate description of the method has yet been published 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 problems, however, are
completely soluble by an organism of excellent ideational ability. For
the human subject, the solution of the easiest problem of all requires
almost no effort, whereas even moderately difficult problems may
require many repetitions of effort and hours or days of application to
the task. In each case, the solution of the problem depends upon the
perception of a certain constant relation among a series of objects to
which the subject is required to attend and respond. Such relations are,
for example, secondness from one end of the group, middleness, simple
alternation of ends, or progressive movement by constant steps from
one end of a group to the other.
It is possible to present such relational problems by means of relatively
simple reaction-mechanisms. In their essential features, all of the
several types of multiple-choice apparatus designed by the writer and
used either by him or by his students and assistants are the same. They
consist of a series of precisely similar reaction-devices, any one or all
of which may be used in connection with a given observation. These
reaction-mechanisms are so chosen as to be suited to the structure and
action-system of the animal to be studied. For the human being the
mechanism consists of a simple key and the total apparatus is a bank of
keys, with such electrical connections as are necessary to enable the
observer to obtain satisfactory records of the subject's behavior. Let us
suppose the bank of keys, as was actually the case in my first form of
apparatus, to consist of twelve separate reaction-mechanisms; and let us
suppose, further, the constant relation (problem) on the basis of which
the subject is required to react to be that of middleness. It is evident
that in successive trials or experiments the keys must be presented to
the subject in odd groups, the possibilities being groups of 3, 5, 7, 9, or
11. If for a particular observation the experimenter wishes to present
the first three keys at the left end of the keyboard, he pushes back the
remaining nine keys so that they cannot be operated and requires the
subject to select from the group of three keys the one which on being
pressed causes a signal to appear. It is of course the clearly understood

task of the subject to learn to select the correct key in the group on first
trial. This becomes possible only as the subject observes the relation of
the key which produces the desired effect to the other keys in the group.
On the completion of a subject's reaction to the group of three keys, a
group of seven keys at the opposite end of the keyboard may, for
example, be presented. Similarly,