Expectancy for Airpuff and Conditioned Eyeblinks in Humans *

Three experiments were designed to test the hypothesis that expectancy for an unconditioned stimulus (US) serves as an intervening variable in the well-documented empirical relationship between the awareness of stimulus contingencies and the occurrence of conditioned reactions (CR) in human classical conditioning. Experiment 1 showed that, when subjects are instructed to respond by keypressing to US in a conditioning-like procedure, reaction time (RT) provides the same kind of information as a direct rating of expectancy. In experiment 2, the RT task was superimposed on an otherwise standard eyeblink conditioning procedure. Reliable discriminative conditioning failed to occur, although changes in RT give evidence of increasing expectancy for US. Experiment 3 aimed to repeat experiment 2 with several modifications in procedure, intended to facilitate conditioning. The between-subjects correlation between RT to US and frequency of eyeblink CRs was reasonably high (0.52). However, when consecutive trials were considered, a shift was apparent between the two variables: RT changes occurred earlier than CR development. The implications of these results with respect to the expectancy theory of conditioning are discussed.