SEVERAL examples of experience-dependent perceptual improve-ment (perceptual learning) suggest that plasticity in specific neu-ronal loci could underlie the learning process For a basic visual discrimination task (using an optimal stimulus for 'automatic' pre-attentive texture segregation 7-10), discrete retinal input-dependent changes within a very early stage in the stream of visual processing were indicated as the locus of a large and consistent learning effect5. When do these changes occur? Here we report that except for a fast, rapidly saturating improvement early in the first practice session, performance was very stable within sessions. Indeed, observers showed little or no improvement until up to 8 hours after their last training session (latent phase). But large improvements occurred thereafter. Finally, there was almost no forgetting; what was gained was retained for at least 2-3 years. We conjecture that some types of perceptual experience trigger permanent neural changes in early processing stages of the adult visual system. These may take many hours to become functional.
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