山雀に於ける明るさ選擇反應の移調に及ぼす背景の影響

抄録

The present study was conceived with the aim of obtaining such direct experimental data as to throw light upon the role of the immediate backgrounds in the selective responses for brightness in animals. It was concerned with four problems: (1) When varied tits, after learning to choose one side of a brightness-pair on an immediate background of medium gray, had to react to a new pair, consisting of the “right” object of the training period and a new object, which had the same relation to the “right” object as this had had to the “wrong” object during training, what would be the percentage of the frequency that the animals would choose the new object? (2) If the immediate background too was changed relatively with the “transposition” of the brightness-pair so as to take the same medium position between the two grays as in the original training period, what would be the effect upon the frequency of the choice of the new object? (3) If the background change was executed with the “transposition” of the brightness-pair otherwise than the relative way, what would be the effect? (4) How could we explain the change, if any, in the frequency of the choice which thus was attributable to the differences in the background change?
Six varied tits were trained to fly down from a cage and to seek. their food front under one of the two circular covers, which were placed apart from each other on a table, and to fly back to the cage with a grain to eat it up there. One of the covers was light gray, which was used as the positive stimulus for three of the subjects, and the other was dark gray, which was the positive stimulus for the other three, while the surface of the table was medium gray. The animals could get their food under the positive stimulus only, and no special punishment was used excepting the detour they had to make in order to get food when they went to the negative stimulus first. The training was considered to have been completed when the percentage of the choice of the positive stimulus, notwithstanding the position of it, surpassed 90 per cent consecutively for five days. The subjects showed large individual differences concerning the length of the training period.
After the completion of the training, four birds among the six were subjected to the critical experiments, which consisted of one ordinary “transposition” test without any change of the immediate background and three other kinds of “transposition” tests, in which the immediate background too was variously changed. The first of these background changes was executed in the same direction as the “transposition” of the stimuli and relative to it, the second was in the same direction and to a position that was one step further than the new neutral stimulus, and the third was in the opposite direction and to a position that was one step further than the negative stimulus of the original training period. In these critical experiments the animals could find their food under both stimuli.
The results of these experiments were as follows: the frequency of the choice of the new stimulus was the largest (77%) when the “transposition” of the stimuli was not accompanied by the change of the background, and it was the smallest (55%) when the background was changed with the “transposition” of the stimuli to the farthest position from the original. In the two cases where the degree of the changes of the background was smaller than this, the frequencies of the choice of the new stimulus were also of medium grade (66% and 66.3%), no matter whether the direction of the change was the same or the opposite.