Double dissociation of V1 and V5/MT activity in visual awareness.

The critical time windows of the contribution of V1 and V5/MT to visual awareness of moving visual stimuli were compared by administering transcranial magnetic stimulation (TMS) to V1 or V5/MT in various time intervals from stimulus offset during performance of a simple motion detection task. Our results show a double dissociation in which the critical period of V1 both predates and postdates that of V5/MT, and where stimulation of either V1 at V5/MT's critical period or V5/MT at V1's critical period does not impair performance. These findings demonstrate the importance of back-projections from V5/MT to V1 in awareness of real motion stimuli.