Interference with vision by TMS over the occipital pole: a fourth period.
We investigated the effect of single-pulse transcranial magnetic stimulation (TMS) over the occipital pole on a forced-choice visual letter-identification task. Magnetic stimuli were applied on the midline but with the initial current directed pseudorandomly toward either left or right hemisphere; visual stimuli were presented randomly in either left or right hemifield; magnetic-visual stimulus onset asynchrony varied randomly between 12 values: -500 ms and from -50 ms to +50 ms in 10 ms steps. The data revealed the existence of a hitherto unknown fourth task-interfering TMS effect that was maximal at -10 ms and specific for magnetic stimulus polarity and visual stimulus location. This -10 ms effect cannot be explained by reflex blinking (as the -50 ms effect can) and direct disruption of letter-induced activity (as the +20 ms and +100 ms effects can), but it could be explained by direct disruption of pre-letter activity or indirect disruption of letter-induced activity.
Corthout
Erik
E
Department of Experimental Psychology, University of Oxford, Oxford, UK. erik.corthout@lincoln.ox.ac.uk
Hallett
Mark
M
Cowey
Alan
A
D000328:Adult; D001931:Brain Mapping; D002755:Choice Behavior / Q000502:physiology; D004192:Discrimination, Psychological; D004558:Electric Stimulation / Q000379:methods; D005260:Female; D007839:Functional Laterality; D006801:Humans; D008280:Magnetics; D008297:Male; D009778:Occipital Lobe / Q000502:physiology*; D010775:Photic Stimulation; D011930:Reaction Time; D014796:Visual Perception / Q000502:physiology*