Abstract
Research by Brady and his collaborators (1958) and by Davis and Berry (1963) has shown that the gastrointestinal system reacts quite differently to response-contingent aversive stimulation than it does when the stimulation is non-response-contingent. The present experiment was designed to analyze in greater detail the system's reactions to the first of these two stimulus conditions. Nineteen student volunteers served as Ss in a research design based upon the use of each S as his own control. Continuous electrophysiological recordings of gastrointestinal activity were taken from surface electrodes on the abdomen of each S during an initial 15-min. rest period and an immediately subsequent 25-min. task period. During the task period S could avoid an aversive auditory stimulus if he pressed a key at the proper time intervals; the task was sufficiently difficult that successful avoidances for different Ss ranged from an over-all 16% to 72% with a mean of 44% for the group as a whole. The resulting data made it possible to analyze the differential reactions of the gastrointestinal system on successful and unsuccessful trials when the occurence of the aversive stimulation was always response-contingent, i.e., under the potential control of S. Three parameters of the electrophysiological manifestations of gastrointestinal activity were studied: amplitude, displacement, and peak response time. Analyses of the results show that the mean amplitude of gastrointestinal activity increased significantly only when avoidance of the aversive stimulus was unsuccessful; during successful trials the amplitude remained at pre-task baseline levels. This differential reaction was strikingly apparent when the outcome of S's response differed on successive trials: when both trials of a pair involved the same response contingencies, i.e., either successful or unsuccessful avoidance, gastrointestinal reactions were not significantly different; but large and very significant changes occurred when pairs of trials involved different response contingencies. In contrast to the effects obtained by Davis and Berry (1963) under non-response-contingent conditions when very rapid adaptation occurred, our results show a significant trend toward increasing amplitudes of gastrointestinal activity as the task trials continued. Throughout the entire task period peak response times on unsuccessful trials were significantly shorter than on successful trials. Similar analyses of the displacement measure failed to show any significant effects. The results of the present experiment when considered in relation to those provided by earlier studies suggest that the differences in effects of response-contingent and of non-response-contingent conditions cannot be accounted for in terms of the physical characteristics of the aversive stimulus, of sensory processes per se, or of motor output. There is no support for the possibility that there may occur some interaction between level of performance of the response-contingent task and gastrointestinal activity or that the number of aversive reinforcements during a contingency period is a critical factor. There remains the possibility that the critical factors involved are central, rather than peripheral in nature.
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