Does a backward-conditioning CS initially acquire excitatory properties?

Includes bibliographical references (pages [29]-31)The present study sought to evaluate two opposing explanations of the development of inhibition to a CS which is unpaired with an aversive UCS. The contingency theory, developed by Rescorla, considers inhibition to be merely the result of such a negative contingency, while the second-order conditioning theory, which is based on the traditional conception of conditioning, holds that a CS must first be excitatory before it can become inhibitory. By employing a backward-conditioning paradigm and a small number of conditioning trials, the present study provided an experimental contrast of these two theories. Contingency theory would predict an inhibitory influence of the backward ­conditioning CS following this training while the second-order conditioning theory would predict an excitatory influence of this CS. Sixty-four rats were randomly divided into experimental groups (n=8). Following an initial day of handling and exploration, Ss received either 8 or 18 backward-conditioning trials (shock followed after 15 sec. by light) while confined in one half of a two-compartment apparatus. Approximately 23 hours after conditioning, Ss were returned to the conditioning apparatus and underwent escape-from-fear training (hurdle-jumping). Over the first 25 hurdle-jumping trials, Ss were presented with either of two stimulus complexes; (l) static apparatus cues alone (CS1) or (2) static apparatus cues plus the backward-conditioning stimulus (CS1+CS2). Immediately following the 25th trial, half the Ss in each group received 10 additional trials in the presence of the same stimulus complex experienced over the first 25 trials (Control-Ss) while the remaining Ss experienced a shift in the stimulus complex for these trials (Shift-Ss). Although a trend over the first 25 trials towards superior escape learning was found in the groups trained in the presence of the "backward-conditioning CS, the effect of this variable on performance was not significant. In addition, the shift in stimulus complex after the 25th trial failed to affect performance in any systematic manner. A second trend was found with the number-of-conditioning-trials variable. Superior performance, although not significant, was apparent for those Ss administered 18 as compared to 8 conditioning trials. The major conclusion offered on the basis of the present findings was that the contingency theory was incapable of accounting for the neutral influence demonstrated (statistically) by the backward­ conditioning CS, while the trend in performance stood as a direct contradiction of this theory. Through recourse to the possibility that the present study had erred in the selection of the number of conditioning trials, the second-order conditioning theory was deemed capable of assimilating the present results. The supportive trends found in the data suggest the wisdom of further attempts to validate the second-order conditioning theory of the development of inhibition.M.A. (Master of Arts