Loss of attentional stimulus selection after extrastriate cortical lesions in macaques.

Many objects in natural visual scenes compete for attention. To identify the neural mechanisms necessary for visual attention, we made restricted lesions, affecting different quadrants of the visual field but leaving one quadrant intact, in extrastriate cortical areas V4 and TEO of two monkeys. Monkeys were trained to discriminate the orientation of a target grating surrounded by distracters. As distracter contrast increased, performance deteriorated in quadrants affected by V4 and TEO lesions, but not in the normal quadrant. Performance in affected quadrants was restored by increasing the contrast of the target relative to distracters. Thus, without V4 and TEO, visual attention is 'captured' by strong stimuli, regardless of their behavioral relevance.