Salience modulation in serial preexposure: implications for perceptual learning.

In three experiments rats were given serial preexposure to two flavor stimuli. In Experiment 1, some animals were given exposure to AX followed by the presentation of BX, a forward schedule; the others were given backward preexposure (BX→AX). Conditioning and test trials with the A element showed that salience or effectiveness of A was better protected in the forward than in the backward condition. Experiments 2 and 3 assessed the relevance of this salience modulation mechanism for perceptual learning. In these experiments, generalization of a conditioned aversion from AX to BX was reduced in the forward (but not in the backward) condition only after prolonged exposure, indicating that the establishment of an inhibitory link from B to A is required for successful discrimination. However, generalization to a novel compound stimulus, NX, was reduced in the forward group both after short and long preexposure, suggesting the existence of salience modulation processes that work in parallel with associative inhibition. These results seem to support the existence of a salience modulation mechanism that seems to be beyond the scope of current theories of perceptual learning.

Salience modulation and associative inhibition interaction: short but not long exposure to similar stimuli protects the salience of the unique elements.

In three experiments, rats were given preexposure to two similar flavour compounds, AX and BX. Following preexposure, conditioning trials took place in which AX was paired with an illness-induced unconditioned stimulus. Animals that were given short alternated preexposure to AX and BX, showed higher generalization of conditioned aversion to AX to a new compound, AN, than animals that were given blocked preexposure (short and long) and long alternated preexposure (Experiments 1 and 2); and showed less preference for A when they were given a choice between A and X (Experiment 3). These results have been taken to indicate that the salience of the A element is well preserved after short alternated preexposure, but declines when preexposure goes on for some more trials. The results reported support the notion that perceptual learning is a multi-determined phenomenon that depends on salience modulation processes after relatively short preexposure, and on an associative inhibition mechanism after prolonged preexposure.