The effect of electric shock on spontaneous alternation in the cockroach

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.