Adaptation of the Original Response to a Conditioned Stimulus

Since the time of Pavlov, it has been a common observation that the conditioned stimulus (CS) in a classical conditioning situation is seldom, if ever, a completely neutral stimulus since, prior to learning, it usually elicits some response. However, in most conditioning studies only the change in the conditioned (learned) response has been studied, little systematic work having been conducted on the changes in the original (reflex) response to the CS. Hilgard and his students, mainly in the context of eyelid conditioning experiments (4, 5, 6), have reported some pertinent data, and there have also been some experiments, outside of a learning situation, concerned with the effects of repeated elicitation of a reflex (3, 7, 10). The results, generally speaking, have shown that the amplitude of the reflexes decreased as a function of the number of presentations of the stimulus and increased after rest periods. Little except observational data has been furnished with respect to the frequency measure, and little information has been provided concerning the variables affecting this measure. The purpose of this paper is to report evidence concerning changes in the frequency of the reflex blink to a tone used as a CS and to report the effects of instructions on this measure