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

Abstract

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.

Overshadowing and associability change.

“…To explain the results of a number of perceptual learning studies (e.g., Blair & Hall, 2003a, 2003b, Hall proposed an antihabituation mechanism which opposes the normal habituation mechanism that is assumed to operate whenever any stimulus is frequently presented. According to this idea, the perceptual effectiveness of a stimulus declines whenever it is presented (habituation).…”

Modulation of the Effective Salience of a Stimulus by Direct and Associative Activation of Its Representation.

“…In studies of this effect, we have found that preexposure in which two similar stimuli are presented in alternation appears to enhance the effective salience of their unique features (e.g., Blair & Hall, 2003a, 2003bMondragón & Hall, 2002). That is, alternating presentations of stimuli that may be represented as AX and BX (where A and B stand for the unique features of these stimuli and X for those features that, being similar, they hold in common) results in an enhancement of the salience of A and B (relative to a control condition in which AX and BX are presented on separate blocks of trials).…”

“…The empirical basis for the suggestion that stimulus salience can be modified in this way comes largely from work on the perceptual learning effect (Blair & Hall, 2003a, 2003bMondragón & Hall, 2002)-from studies of the effects of preexposure to events used as conditioned stimuli (CSs) in discrimination learning procedures. But, as Hall (2003) has noted, there is no reason to suppose that the effects of interest will be restricted to stimuli of this type.…”

Assessments of Changes in the Effective Salience of Stimulus Elements as a Result of Stimulus Preexposure.

“…Blair and Hall argued that the aversion shown to these compounds on the generalization test will be largely a consequence of the associative strength acquired by the X element as a result of aversive conditioning with AX as the conditioned stimulus (CS). But the ability of X to evoke its conditioned response (CR) will be modulated by the other stimuli that are present on the test-the more salient B element will be more likely to interfere with the CR to X than will the less salient C element, so that generalized responding will be less vigorous to BX than to CX.The central feature of this interpretation is the suggestion that the preexposure procedure used by Blair and Hall (2003b) results in B having a greater effective salience than C. We have shown how the results of the generalization test with BX and CX can be interpreted in these terms. But if this characterization is correct, the difference between B and C should be evident on a range of other measures.…”

“…It follows from the hypothesis under consideration that, after preexposure of the sort used by Blair and Hall (2003b), the UR evoked by stimulus B should be greater than that evoked by C. This prediction was investigated in Experiment 1. A further property of the salience of an unconditioned stimulus (US) is evident when the stimulus is used as a reinforcer in classical conditioning-the acquisition of the CR to a given CS will proceed more rapidly the more salient the US.…”