The N2pc component and stimulus duration.

The N2pc component of the event-related potential is a moment-by-moment index of the deployment of visual-spatial attention. It is not clear whether the N2pc reflects pure top-down attentional activity or a positive interaction of top-down activity with bottom-up sensory activity. Here, we presented a bilateral visual display containing a target and a distractor for a duration of 50, 200, or 350 ms. The N2pc was smaller for the 350 ms duration than for the two shorter durations. These results go against the hypothesis that the N2pc reflects a long-lasting positive interaction of top-down and bottom-up activity, which would have predicted a larger N2pc as stimulus duration increased. Theoretical and practical implications of the results are discussed.