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

Abstract

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...

The role of comparison in perceptual learning: Effects of concurrent exposure to similar stimuli on the perceptual effectiveness of their unique features

“…Evidence supporting the notion that alternating preexposure enhances the effective salience of the unique stimulus features comes from studies comparing the effects of alternating and blocked preexposure schedules (e.g., Blair & Hall, 2003;Blair et al, 2004;Mondragón & Hall, 2002). If-as our interpretation of results of Experiment 2 suggests-concurrent and alternating preexposure are equally effective in enhancing effective salience, then the effect should be evident in both when comparison is made with subjects exposed to an equivalent blocked preexposure regime.…”

“…It has been shown that a unique feature presented according to the alternating schedule is more effective than one presented according to the blocked schedule in eliciting its unconditioned response (UR; Blair, Wilkinson, & Hall, 2004, Experiment 1), as an unconditioned stimulus (US) in classical conditioning (Blair et al, 2004, Experiment 2), and as a conditioned stimulus (CS) in classical conditioning (Blair et al, 2004, Experiment 3;Mondragón & Hall, 2002, Experiment 4; see also Lombas, . Such a feature is also particularly effective in interfering with the conditioned response (CR) controlled by some other stimulus (Blair & Hall, 2003, Experiment 5) when the feature and this other stimulus are presented in compound.…”

Varieties of perceptual learning

“…The results of a number of experiments have provided evidence for this account (Blair & Hall, 2003;Blair, Wilkinson, & Hall, 2004). They have shown that if rats are exposed to AX and X in alternation and, in a separate block of trials, to CX, subsequent conditioning proceeds more rapidly to A than to C. Intermixed exposure to AX and X preserves the salience of A, whose representation is retrieved on the intervening X-alone trials, whereas no such effect is observed to C after a block of CX exposure trials.…”

Perceptual learning with complex visual stimuli is based on location, rather than content, of discriminating features.

“…salt or lemon -A/B) (e.g., Mackintosh, Kaye, & Bennett, 1991). This allows testing of the elements alone as a means of assessing the effects of perceptual learning on those elements themselves, and has provided evidence for both changes in stimulus salience (e.g., Blair & Hall, 2003;Blair, Wilkinson, & Hall, 2004), and for the development of mutual inhibition (e.g., Dwyer, Bennett, Mackintosh, 2001;Dwyer & Mackintosh, 2002).…”