Reduced visual performance under transcranial magnetic stimulation (TMS)
of human visual cortex demonstrates suppression whose spatial extent is not
directly visible. We created an artificial scotoma (region missing from a
visual pattern) to directly visualize the location, size and shape of the
TMS-induced suppression by following a large-field, patterned, visual stimulus
with a magnetic pulse. The scotoma shifted with coil position according to
known topography of visual cortex. Visual suppression resulted in pattern-dependent
distortion, and the scotoma was filled in with temporally adjacent stimuli,
suggesting spatial and temporal completion mechanisms. Thus, perceptual measurements
of TMS-induced suppression may provide information about cortical processing
via neuronal connections and temporal interactions of neural signals.
