ly that the mistakes which
are made in reproducing a movement may spring from two different
sources. They result partly from an erroneous perception or memory of
the movement carried out, and partly from the inability to realize the
movement intention. One series of investigations was accordingly
devoted to the studies of those sensations and perceptions by which we
become aware of the actual movement. Everything which accentuates
these sensations must lead to an overestimation of the motion, and the
outcome is that the movement is made too small. The concentration of
attention, therefore, has the effect of reducing the actual motion,
and the same influence must result from any resistance which is not
recognized as such and hence is not subtracted in the judgment of the
perceiver. Another series of researches was concerned with the inner
attitude which causes a certain external movement effect and which may
lead to an unintended amount of movement as soon as the weight to be
lifted is erroneously judged upon. Closely related studies, finally,
deal with a mistake which enters when the movement is reproduced from
memory after a certain time. The exactitude of a simple arm movement
seems to increase in the first ten seconds, then rapidly to decrease.
The emotional attitude, too, is of importance for the reproduction of
a movement. I trained myself in making definite extensor and flexor
movements of the arm until I was able to reproduce them under normal
conditions with great exactitude. In experiments extending over many
months, which were carried on through the changing emotional attitudes
of daily life, the exact measurement showed that both groups of
movements became too large in states of excitement and too small in
states of fatigue. But in a state of satisfaction and joy the extensor
movement became too large, the flexor movement too small, and _vice
versa_, in unpleasant emotional states the flexor movement was too
strong and the extensor movement too weak.[34]

We have a very careful investigation into the relations between
rapidity of movement and exactitude.[35] The subjects had to perform a
hand movement simultaneously with the beat of a metronome, the beats
of which varied between 20 and 200 in the minute. In general the
accuracy of the movement decreases as the rapidity increases, but the
descent is not uniform. Motions in the rhythm of 40 to the minute were
on the whole just as exact as those in the rhythm of