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.

No abstract

In 3 experiments, rats received preexposure to presentations of a compound flavor BX. The effective salience of B was then tested by assessing its ability to interfere with the aversion controlled by another flavor or the tendency to drink a saline solution after the induction of a salt need. It was found that the effective salience of B was maintained when during preexposure, presentations of BX alternated with presentations of X alone. This was true both when BX was presented as a simultaneous compound (Experiment 1) and as a serial compound (X-->B; Experiments 2 and 3); salience was not maintained when the serial compound took the form B-->X (Experiments 2 and 3a). It was argued that the salience of B declines during preexposure but is restored when presentations of X are able to activate the representation of B by way of the associative X-B link.

Rats received exposure to 3 flavor compounds, AX and BX, presented in alternation, and CX, presented on a separate block of trials. The hypothesis that this treatment would leave B effectively more salient than C was tested in 3 ways. Experiment 1 showed that the unconditioned response evoked by B was stronger than that evoked by C. Experiment 2 showed that B was more effective than C when used as a reinforcer in a sensory preconditioning procedure. Experiment 3 showed that B was learned about more readily than C as a conditioned stimulus in flavor aversion conditioning. Alternating preexposure to 2 similar stimuli may protect their distinctive features from the loss of salience normally produced by nonreinforced exposure to a stimulus.Certain schedules of preexposure to two similar stimuli (call them AX and BX, where A and B represent the unique features of the stimuli and X features that, being similar, they hold in common) can facilitate subsequent discrimination between them. 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. (A, B, and C were saline, sucrose, and lemon, and X included an explicitly added common element, quinine.) An aversion was then established to the AX compound and generalization to BX and CX was tested. It was found that the aversion generalized less readily to BX than to CX; that is, discrimination between AX and BX appeared to be enhanced. Blair and Hall (2003b; see also Blair & Hall, 2003a;Hall, 2003) explained their results in terms of the suggestion that the preexposure procedure engages a learning process that modifies the perceptual effectiveness (the effective salience) of the various stimulus elements. They suggested that repeated presentation of a stimulus will result in a decline in its effective salience and that such was the fate of the C and X elements in their experiment. But they also suggested that presenting the AX and BX in alternation attenuates or reverses this process for the unique features that distinguish these similar stimuli. It was proposed that this form of exposure enhances the salience of A and B (or at least, results in a less dramatic decline than that suffered by C). The test performance shown to BX and CX was explained in terms of these changes. 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...

Rats were given intermixed preexposure to the compound flavors AX and BX and to the compound CX in a separate block of trials (4 presentations of each compound). In Experiment 1, rats showed less generalization of conditioned aversion from AX to BX than from CX to BX, a perceptual learning effect. Experiment 2 showed that the formation of an excitatory association proceeded more readily between A and B than between C and B, suggesting that intermixed preexposure maintains the effective salience of A and B and does not establish inhibition between them, a process that would require prolonged preexposure. According to this analysis, salience modulation and associative inhibition may contribute to perceptual learning at different stages of preexposure.