Perceptual learning after test-stimulus exposure in humans

Exposure to a to-be-tested stimulus produces a reduction in generalization to that stimulus from another similar conditioned stimulus (e.g. Bennett et al., 1994; Symonds and Hall, 1997). Generally, this effect has been interpreted as the result of a loss of effectiveness of the common elements of the stimulus to be conditioned (e.g., latent inhibition). However, Sanjuan et al. (2006) questioned this interpretation after finding that exposing rats to either the test stimulus or to its elements had different effects when the amount of exposure to the common elements was equated. Only exposure to the test stimulus reduced generalization. In the study presented here, this effect was assessed in human participants using a videogame method and colors as stimuli. Generalization after exposure to the test stimulus, or to its elements was assessed. Results show that with people, as in rats, pre-exposure to the test stimulus leads to a greater reduction in generalization than to the elements. Therefore, latent inhibition cannot be the only mechanism responsible for this perceptual learning effect. Results are discussed in terms of current associative theories addressing perceptual-learning phenomenon.