ゴキブリにおける電撃の自発的交替現象え及ぼす効果

IWAHARA (4) failed to find any difference in spontaneous alternation betghween subjects which were given massed (20″ interval) trials and those given spaced (120″ interval) using a simple Y-maze (see Fig. 1), in the cockroach. Moreover the average percentage of alternation was 43 %, slightly below the 50% chance level assuming no position habits. This result seemed to contradict with IWAHARA'S similar rat study (5) in which the percentage of alternation was 72% for a massed group and 61% for a spaced group.<BR>The observed difference could be due to motivational factors, because the drive for the cockroaches was negative photo-tropism, while that for the rats was evidently positive hunger drive. If this was the case, a further decrease in alternation was expected when electric shock was administered in place of a slightly negative drive of the tropism.<BR>Three groups (NS-S, S-NS, & S-S) of cockroaches were used. NS-S, for example, reads that the group was given no shock on day 1 but was given electric shock (20V, D.C.) on day 2. The subject was run in a Y-maze (Fig. 1) 11 trials a day with an inter-trial interval of 20″ for two consecutive days. The results on day 1 indicated that electric shock reduced spontaneous alternation in comparison with no shock but with mild negative photo-tropism. The negative effect of shock increased with trials (Tables 1 & 2). On the other hand the opposite result was shown for no-shock groups including IWAHARA'S previous group. As a fairly high negative correlation (-.663) was observed between the percentage of alternation and the position habit on day 1, it may be concluded that electric shock fixated cockroaches' responses.<BR>This phenomenon seemed to correspond with MAIER'S study of fixation in the rat where the dominant drive was frustration which is clearly a negative drive as is electric shock. However no consistent results were obtained on day 2 probably because of after-effects of the previous day training.