In the present task, series of visual stimuli are
rapidly presented left and right, containing two target
stimuli, T1 and T2. In previous studies, T2 was better
identified in the left than in the right visual field. This
advantage of the left visual field might reflect dominance
exerted by the right over the left hemisphere. If so, then
repetitive transcranial magnetic stimulation (rTMS) to the
right parietal cortex might release the left hemisphere from
right-hemispheric control, thereby improving T2 identification
in the right visual field. Alternatively or additionally,
the asymmetry in T2 identification might reflect capacity
limitations of the left hemisphere, which might be aggravated
by rTMS to the left parietal cortex. Therefore, rTMS
pulses were applied during each trial, beginning simultaneously
with T1 presentation. rTMS was directed either to
P4 or to P3 (right or left parietal cortex) either as effective
or as sham stimulation. In two experiments, either one of
these two factors, hemisphere and effectiveness of rTMS,
was varied within or between participants. Again, T2 was
much better identified in the left than in the right visual
field. This advantage of the left visual field was indeed
modified by rTMS, being further increased by rTMS to the
left hemisphere rather than being reduced by rTMS to the
right. It may be concluded that superiority of the right
hemisphere in this task implies that this hemisphere is less
irritable by external interference than the left hemisphere.