A typical visual scene contains many different objects, which compete for visual processing. Neurophysiological, neurobehavioral, and brain imaging studies suggest that top-down attentional mechanisms bias this competition in favor of behaviorally relevant stimuli. In the absence of this top-down bias, visual processing in extrastriate cortex may be captured by salient distracters. Consistent with this idea, it has been previously shown that monkeys (De Weerd et al., Nature Neurosci, 1999) and humans (Mazer et al., SFN Abs, 1999) with V4 and/or TEO lesions were impaired at orientation discrimination in the presence of distracters in a visual field quadrant affected by the lesion, but not in a normal quadrant. As predicted, the impairment increased with increasing distracter contrast. V4 and TEO thus appear to be sites where top-down bias can counteract the competitive advantage of strong distracters. What is the source of this top-down bias? We have previously reported that monkeys with prefrontal lesions ...