Attention and the measurement of perceptual learning.

Novel and familiar letters were presented to Ss under conditions which controlled momentary attention states. The latencies of letter matching for the novel and familiar letters did not differ when Ss were expecting the particular letters which were presented. However, latencies to the two types of letters differed significantly when Ss were not expecting the particular letters which were presented. Additional exposures significantly reduced this difference, thereby generating a perceptual learning curve in terms of response latency. The main findings were interpreted in terms of a model of perceptual processing which involves mechanisms for hierarchical coding, selective attention, and automatic processing.