Loss of attentional stimulus selection after extrastriate cortical lesionsin macaques

Many objects in natural visual scenes compete for attention. To identify th e neural mechanisms necessary for visual attention, we made restricted lesi ons, affecting different quadrants of the visual field but leaving one quad rant intact, in extrastriate cortical areas V4 and TEO of two monkeys. Monk eys were trained to discriminate the orientation of a target grating surrou nded by distracters. As distracter contrast increased, performance deterior ated in quadrants affected by V4 and TEO lesions, but not in the normal qua drant. Performance in affected quadrants was restored by increasing the con trast of the target relative to distracters. Thus, without V4 and TEO, visu al attention is 'captured' by strong stimuli, regardless of their behaviora l relevance.