Evidence for an involvement of associative conditioning in reflex modification of the acoustic startle response with gaps in background noise

Abstract The experiments reported here were designed to determine the role of associative conditioning in reflex modification of the acoustic startle response, using gaps in background noise. The first experiment was done to characterize the effects of repeated testing for 9 days with 20-msec gaps in white noise as the preliminary stimulus (SI) and a 120-dB, 40-msec 13-kHz tone as the eliciting stimulus (S2). The second experiment was a test of associative conditioning. Three groups of rats were tested daily for 6 days under one of the following conditions: SI and S2 paired in a contingent manner, S2 only, or SI only. All groups then received the contingent pairing of SI and S2 for an additional 9 days of testing. In the third experiment, a separate group of rats was tested with either contingent or noncontingent presentation of the SI and S2 for 6 days, and then, on the 7th day, both groups received the stimuli in a contingent fashion. Results indicate that the amount of inhibition increases with repeated, daily testing, and that it achieves asymptotic levels of inhibition after 5-6 daily sessions. The presentation of SI and S2 together is a necessary, but not sufficient, condition for normal development of inhibition. Alternatively, the contingency that exists between the two stimuli is likely to be the determining factor necessary for development of the inhibition. These data imply that an associative learning process may be a major factor in the gap-inhibition phenomenon.