t this is
psychologically the clue which leads to the final tap, will readily
appear from the following remarkable fact: I was able to bring about at
will either the back-step with the right foot, or the additional extra
tap with the left foot by concentrating the mind either upon the last
unit or upon the one just preceding it. In either case the movement
which served as stimulus to the horse followed naturally upon
concentration on the number. I could of course also control the response
by direct voluntary control of the movements involved. Hans thus solved
for me the same ten problems first with the back-step, then with the
extra final tap.

Finally we will indicate the one true inner cause of the difficulty in
getting the number 1 as a response. It is not easy to relax attention
immediately after having just begun to concentrate. Relaxation,
therefore, often occurs with a certain retardation, and the result is a
belated jerk of the head.

Briefly, I would also mention a few of the more interesting
introspective observations which were made in situations in which the
horse responded with movements of the head for answers such as "yes" and
"no", "up" and "down", etc. From the very beginning I put questions to
Hans which would have to be answered by a shake of the head. It often
happened that instead of indicating "0", Hans would begin tapping some
number. But the wonder of it was that, in many cases, he responded
properly. I knew only that I inwardly pronounced the word "null" (zero),
and that I looked expectantly at the horse's head. In the case of
questions to which I expected the answer "yes" or "no", I imagined
myself enunciating the answer, i. e., I used motor imagery. The tests
failed, the moment I employed only visual or auditory imagery, whereas,
motor imagery was always effective in calling forth correct
reactions.[M] When the proper response was "up" and "down" I would
think of those directions in space, and likewise with "left" and "right"
in which case also I would put myself in the horse's place.

[Footnote M: Thus it is possible to think of the word "no" in three
different ways. I may get a visual image of the written or printed
word, or the auditory image of the word as spoken by another person,
or finally I might think of it in terms of images of the sensations
of movement which would arise if I myself were to enunciate or write
the word. And so, in like manner, I could think