Evoked potential correlates of visual selective attention

Two experiments are reported in which the relationship is explored between the N1 and P2 components of the visual evoked potential and visual selective attention. In both experiments, channels were defined in terms of stimulus attributes (experiment 1 — intensity; experiment 2 — shape) with all stimuli being presented at a common spatial locus in order to preclude fixation shifts. Under these circumstances, P2 was found in both experiments to correlate with visual selective attention whereas N1 did not. It is concluded from the null result for N1 that a precortical gating mechanism for visual inputs within a single spatial channel is not a component of the visual system. The P2 correlate of visual selective attention, because of its long latency, is attributed to the differential post-perceptual processing inevitably received by task-relevant and task-irrelevant inputs.