CORTICAL INVOLVEMENT IN VISUAL SCAN IN THE MONKEY

Monkeys performed a visual search task for food reward. Green square targets were embedded in 3 x 3 arrays of colored forms. In distinct-feature arrays, all nontarget stimuli were red diamonds, whereas in shared-feature arrays, some nontarget stimuli shared either form (red square) or color (green diamond) with the target. Reaction time was slower for shared-feature arrays and linearly related to the number of shared-feature distractors. Errors were more common in shared-feature arrays, and shared-feature distractors were mistaken for targets more frequently than distinct-feature distractors. Event-related local field potentials were recorded from implanted transcortical electrodes. Significant task related differences were obtained from association cortex, but not from projection cortex. Results are discussed in terms of the relative contribution of inferotemporal, dorsolateral frontal, and parietal cortex to feature-driven visual scan.