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Abstract:
Kosslyn (1994) hypothesized that visual mental imagery and
visual perception share the same processing systems in the brain.
This hypothesis has been surrounded with controversy, after
conflicting results were reported from positron emmission
tomography (PET) studies on primary visual cortex involvement in
visual imagery. In this study we investigated whether transcranial
magnetic stimulation (TMS) over the occipital pole would interfere
with visual imagery. Previous studies have shown TMS at the
occipital cortex to be able to supress visual perception. Subjects
had to image capital letters into a 4x5 grid containing an X-mark
that was presented for 16 ms and had to decide whether the X-mark
would fall on the letter or not. TMS was applied with a delay of 80
or 100-1000 ms (intervals of 100 ms) after stimulus presentation
with a 9 cm round coil placed on the midline, 2 cm above the inion
(90% of the maximal output). For all four subjects, there was an
increase in reaction times at one of the delays between 200 and 500
ms. No effects of stimulation at 80 and 100 ms were found on
reaction times, implying that TMS effects were not due to
disruption of perceptual processing. These findings provide
preliminary TMS evidence for primary visual cortex involvement in
visual imagery.
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