Visual feature selectivity in frontal eye fields induced by experience in mature macaques.

When examining a complex image, the eye movements of expert observers differ from those of novices; experts have learned to ignore features that are visually salient but are not relevant to the interpretation of the image. We have studied the neural basis of this form of perceptual-motor learning using monkeys that have learned to search for a visual target among distractors. Monkeys trained to search only for, say, a red stimulus among green distractors will ignore green stimuli even if they subsequently appear as targets in a complementary search array, that is, among red distractors. We recorded from neurons in the frontal eye field (FEF), a cortical area that responds to visual stimuli and controls purposive eye movements. Normally, FEF neurons do not exhibit feature selectivity, but their activity evolves to signal the target for an incipient eye movement. In monkeys trained exclusively on targets of one colour, however, FEF neurons show selectivity for stimuli of that colour. Because this selective response occurs so soon after presentation of the stimulus array, and is independent of location within the visual field, we propose that it reflects a form of experience-dependent plasticity that mediates the learning of arbitrary stimulus-response associations.