Abstract
Plasticity or the modifiability of behavior in the dancer has been studied by measurement of the rate of habit formation. The habit of choosing a white box instead of a black box was established by means of systematic training, on the basis of the association of an electric shock with the latter. Each animal was subjected to ten tests daily until it chose correctly on three consecutive days. The habit was then considered perfect and the training ceased. We may speak of the number of tests necessary for the establishment of a perfect habit as the index of plasticity. The index, then, may be defined as the number of tests up to the point at which errors of choice ceased for at least three days.
In order to discover the relation of sex and age to plasticity five pairs of mice were trained for each of the ages, one, four, and seven months. The investigation is unfinished, as older individuals are to be tested.
In this table each index for the males and the females is the average for five individuals. In the last column the results for the sexes are combined.
Sex differences which appear in the above table.
1. At the age of one month the males learn more quickly than do the females. The males require only 82 tests; the females require 106 for the establishing of a perfect habit. Consequently the index of plasticity for the one-month males is 82; that for the one-month females, 106.
2. At the age of four months the opposite is true. The females learn much more quickly than the males. As the table shows, the index for the males is 128; that for the females 106.
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