The role of inhibitory associations in perceptual learning

Abstract

Preexposure to two compound flavors (AX and BX) typically enhances their discriminability: An aversion conditioned to AXwill generalize less to BX,especially if the preexposure regime has involved altemated presentations ofAX and BX rather than presenting all AX trials before BX trials (or vice versa). One possible explanation ofthis finding is that altemating preexposure establishes inhibitory associations between the two unique features A and B, thus counteracting the generalization produced by excitatory associations between X and A and between X and B, which might result in either the retrieval of B on a conditioning trial to AX, or the retrieval of A on a test trial to BX.Three experiments on flavor aversion conditioning in rats tested these predictions. Experiment 1 suggested that the more important of these excitatory associations was that which allowed X to retrieve A on the test trial to BX. Experiment 2 suggested that the more important inhibitory association was that which allowed B to inhibit the representation of A on this test trial. Experiment 3 provided direct evidence of the role of this inhibitory B-IA association.Discrimination between two or more complex stimuli is often enhanced by prior exposure to one or more ofthem (see Hall, 1991, for a review). Such perceptualleaming effects have been weil established in flavor aversion conditioning, where discrimination between compound flavors such as mixtures of sucrose-Iemon and saline-lemon is enhanced by exposure to one or both ofthese flavors prior to conditioning an aversion to one and testing generalization to the other (see, e.g., Bennett, Wills, Wells, & Mackintosh, 1994;Mackintosh, Kaye, & Bennett, 1991;Symonds & Hall, 1995). Mackintosh et al. (1991) showed that this perceptua1 learning effect was dependent on the use of compound flavors sharing an element or feature in common. If an aversion was conditioned to saline alone, it did not generalize strongly to sucrose, and prior exposure to saline and sucrose did nothing to reduce the generalization that did occur. This is hardly surprising. According to one popular account, generalization between two stimuli occurs to the extent that they share elements in common (Estes, 1950). Ifwe represent two compound stimuli sharing elements in common as AX and BX, where A and Bare the elements unique to each stimulus, and X are those common to both, then conditioning to AX will generalize to BX because some of that conditioning accrues to the X elements shared by BX. There is, moreover, a very simple reason why preexposure to two compound stimuli, AX and BX, should reduce generalization between them (McLaren, Kaye, & Mackintosh, 1989). One of the best established consequences of preexposure to a stimulus that sub sequently serves as the conditional stimulus (CS) in a conditioning experiment is a retardation of subsequent conditioning to that stimulus-the phenomenon of latent inhibition (Lubow, 1989). But preexposure to both AX and BX will ensure twice as much preexposure to X as to A and B. It seems pr...

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.…”

The Relative Activation of Associations Modulates Interference between Elementally Trained Cues

“…Thus, although it seems clear that A interferes with X for activation of the outcome representation, it still needs to be explained why the strong activation of the A-O association during the test phase does not produce a response. One possibility could be to assume that an inhibitory association between X and A is acquired during training (because when A is present, X is absent, see Espinet, Iraola, Bennett, & Mackintosh, 1995), and this inhibitory association then prevents responding to the representation of the absent cue, A, which is activated at testing when X is presented (Bennett, Scahill, Griffiths, & Mackintosh, 1999;Mackintosh & Bennett, 1997). Although this explanation was suggested to account for a rather different phenomenon, Matute and Pineño (1998b) suggested that it could plausibly be extended to explain why the strong activation of A did not produce responding at test in the experiments of interference between elementally trained cues.…”

Dissociation between the Espinet and perceptual learning effects in flavour aversion conditioning

“…The rats then received conditioning trials with AX as the conditioned stimulus (CS) and an injection of lithium chloride (LiCl) as the unconditioned stimulus (US). A subsequent generalisation test showed that the rats given the intermixed pre-exposure schedule consumed BX more readily than the rats given the blocked schedule of pre-exposure (see also Bennett et al, 1999;Mondragón and Hall, 2002). This result has been taken to be an instance of perceptual learning-as evidence that alternating pre-exposure to AX and BX engages learning processes that enhance the discriminability of the stimuli.…”