Cortical involvement in visual scan in the monkey

Monkeys performed a visual search task for food reward. Green square targets were embedded in 3 × 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 inferotem-poral,