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 20, and, on the
other hand movements in the rhythm of 200 almost as accurate as those
of 140 to the minute.
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