Attention modulates responses to motion reversals in human visual cortex.

Selective attention modulates brain responses in visual cortex. A common finding, using functional magnetic resonance imaging or event-related potentials, is that responses to attended relative to unattended stimuli are potentiated. We report an exceptional circumstance in a motion-processing paradigm. Participants viewed superimposed stationary and moving dots and were instructed to attend to one or the other subset. Changes in the direction of dot motion triggered an event-related potential over posterior scalp sites, with a prominent negative peak at 200 ms that was larger when attention was directed at the stationary dots. This effect was localized to extrastriate visual cortex and may be due to reflexive effects of attention orienting triggered by unattended peripheral motion.