Effects of modulating tone frequency, intensity, and duration on the classically conditioned rabbit nictitating membrane response

Abstract

Theories of conditioning commonly assume that the conditioned stimulus (CS) activates a cascade of internal stimuli that govern the conditioned response (CR) on a moment-by-moment basis. As a means of manipulating the internal stimuli, in the present experiments we conducted delay conditioning using a tone CS of constant intensity and frequency. However, the subjects were tested with tones during which the frequency (Experiment 1) or intensity (Experiment 2) either increased or decreased in a continuous fashion over an 800-msec period. The experiments revealed that the test stimuli dramatically accelerated the recruitment of the CR. That is, both the initiation and peak of the CR occurred several hundred milliseconds earlier than that seen with the constant tone. CR likelihood and CR amplitude showed modest reductions. A third experiment entailed test manipulations of tone duration, which yielded only small changes in the CR’s time course. The results are discussed with respect to real-time mechanisms of classical conditioning and their neural substrates in the encoding of pure tones. © 1995, Psychonomic Society, Inc.. All rights reserved.