TRANSCRANIAL MAGNETIC STIMULATION OF EXTRASTRIATE CORTEX DEGRADES HUMAN MOTION DIRECTION DISCRIMINATION

The human temporo-parieto-occipital junction is an extrastriate visual area that may mediate motion vision processing. We determined if tran scranial magnetic stimulation (TMS) delivered over this extrastriate a rea would degrade motion discrimination, similar to the transient decr ease in spatial acuity observed when TMS is delivered over striate cor tex. TMS was delivered 50-250 msec after the onset of a brief, random dot, motion direction discrimination task or a spatial acuity task; TM S significantly reduced correct motion discrimination when delivered 1 00-150 msec after the random dot stimulus. During the same time window TMS did not significantly effect spatial acuity. TMS over the left ex trastriate cortex reduced motion discrimination in both hemifields and its effect had a crude topographical organization. TMS safely perturb s extrastriate visual areas and may reveal the temporal sequence of hi gher perceptual processing.