Analysis of the Perceptual Learning Effect in Flavour Aversion Learning: Evidence for Stimulus Differentiation

Abstract

Rats received exposure to two compound flavours, AX and BX, where A and B were sucrose and saline and X was acid. For group intermixed (1), exposure consisted of alternating trials with AX and BX; group blocked (B) received a block of AX trials and a separate block of BX trials. Experiment 1 showed that generalization to BX after conditioning with AX was less profound in group 1 than in group B. Separate examination of the elements of the compound showed that the source of this difference lay in the strength acquired by the X element. X acquired less strength in group 1 than in group B (Experiments 1 and 2), whereas for the A element (Experiments 3 and 4) the reverse pattern was obtained. These results support the proposal that the perceptual learning effect (restricted generalization from AX to BX in group 1) depends on a process that enhances the effectiveness of unique stimulus elements (A and B) and reduces that of common elements (such as X).

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

“…Statistical analysis revealed no significant effects of the order variable: F(1, 11) ϭ 1.29 for the main effect of order, and F Ͻ 1 for the Group ϫ Order interaction. This pattern of results exactly matches those previously reported by Mondragón and Hall's (2002) Experiment 4 (although Bennett, Scahill, Griffiths, & Mackintosh, 1999, reported, in their Experiment 3, a formally equivalent study producing the opposite outcome). The pattern obtained here is consistent with the proposal that conditioning proceeded more readily in the intermixed than in the blocked condition, the difference in associative strength being obscured by a floor effect at the end of conditioning, but becoming evident as extinction occurred during the test trials.…”

“…This perceptual learning effect has frequently been demonstrated with rats in flavor aversion conditioning (e.g., Blair & Hall, 2003b;Mondragón & Hall, 2002). For example, in the procedure used by Blair and Hall (2003b) rats received preexposure consisting of alternating trials with the flavor compounds AX and BX and a separate block of trials with the compound CX.…”

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

“…Mondragón and Hall (2002) have argued, however, that even with long intertrial intervals, comparison of a sort could occur between the stimulus that is currently presented and the memory of what was presented on a previous trial. They noted that associative principles could supply a mechanism by which this might occur.…”

“…This effect has been taken to indicate that the opportunity to compare similar stimuli (as was available to Group I) increases the ease with which they can subsequently be discriminated. Mondragón and Hall (2002) postulated the existence of a special perceptual learning process that operated during the preexposure phase for Group I, acting to enhance the perceptual effectiveness or salience of the unique elements, A and B, and to reduce that of the common element, X. Because the salience of a CS may be assumed to determine the rate at which conditioning occurs to it, these changes in salience mean that associative strength should accrue principally to A rather than to X during conditioning with AX.…”

“…The effect obtained in this experiment, it will be argued, cannot be explained in terms of an account based on the degree to which common stimulus elements suffer latent inhibition. Subsequent experiments exploited the procedure in an attempt to determine the source of the effects obtained, specifically, to contrast the predictions made by the associative account of McLaren and Mackintosh (2000), with those of the alternative interpretation offered by Mondragón and Hall (2002). Experiments 1a,1b,and 1c In the first of these experiments (for a summary of the designs, see Table 1), all subjects (rats) received exposure trials with three compound flavor stimuli, AX, BX, and CX, followed by aversion conditioning with AX as the CS.…”