Perceptual learning in flavor aversion: Evidence for learned changes in stimulus effectiveness

Rats were exposed to the compound flavors AX and BX, presented in alternation, and to CX on a separate block of trials. Generalization to BX after aversion conditioning with AX was less than to CX. An equivalent effect was found when the nature of the common element was changed after preexposure but not when the common element was omitted during preexposure, during conditioning and test, or both. Rats conditioned with X alone again showed less aversion to BX than to CX; similarly, rats conditioned with a novel flavor (Y) showed less aversion to BY than to CY. These effects support the proposal that intermixed preexposure to AX and BX enhances the perceptual effectiveness of their unique features, A and B. Our standard theories of classical conditioning concern them-selves principally with the conditions under which associations are formed between the central representations of external events. They say little about how such representations are activated. They assume the existence of a representational node for each of the stimuli that can be demonstrated to be effective as a conditioned stimulus (CS) or unconditioned stimulus (US) and then simpl