Location and salience of unique features in human perceptual learning

Preexposure to intermixed presentations of a pair of similar stimuli (AX and BX, where A and B represent distinctive features, and X the features the stimuli hold in common) facilitates subsequent discrimination between them. This perceptual learning effect has been interpreted as indicating that the loss of effective salience resulting from repeated presentation of a stimulus is attenuated or reversed by a salience-modulation process that operates on the unique stimulus features A and B during intermixed preexposure. In 3 experiments, we examined discrimination after intermixed preexposure to AX and BX, making comparison with a condition in which novel unique features were added to the preexposed background (CX and DX). In all experiments, we also monitored eye gaze during both preexposure and the test. Experiments 1 and 2 found discrimination of the preexposed stimuli to be superior. This result cannot be explained by salience-modulation theories that suppose that intermixed preexposure merely attenuates loss of salience to the unique features A and B; it suggests, rather, that intermixed preexposure to AX and BX enhances the salience of, or attention paid to, the distinctive features. Experiment 3 demonstrated that exposure increases sensitivity to the spatial location of the features, a conclusion confirmed by analysis of eye gaze.