SPATIAL-FILTERING DURING VISUAL-SEARCH - EVIDENCE FROM HUMAN ELECTROPHYSIOLOGY

The identification of targets in visual search arrays may be improved by suppressing competing information from the surrounding distractor i tems. The present study provided evidence that this hypothetical filte ring process has a neural correlate, the ''N2pc'' component of the eve nt-related potential waveform. The N2pc was observed when a target ite m was surrounded by competing distractor items but was absent when the array could be rejected as a nontarget on the basis of simple feature information. In addition, the N2pc was eliminated when filtering was discouraged by removing the distractor items, making the distractors r elevant, or making all items within an array identical. Combined with previous topographic analyses, these results suggest that attentional filtering occurs in occipital cortex under the control of feedback fro m higher cortical regions after a preliminary feature-based analysis o f the stimulus array.