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Abstract:
Recent neurophysiological research has revealed bimodal
neurons that respond to visual and tactile stimuli, coding them in
spatial register. Cells with tactile receptive fields (RFs) on the
hand have visual RFs that follow the hands as they move, suggesting
the existence of a bimodal map of space (Graziano & Gross,
1998). Does this map require cross-cortical connections? We
addressed this question by testing a split-brain patient (J.W.) and
age-matched controls on a crossmodal interference task adapted from
Pavani et al. (submitted). Subjects made speeded finger/thumb
discriminations (using right foot toe/heel responses) to random
vibrotactile stimuli presented to the right hand while trying to
ignore simultaneously presented visual stimuli presented to left or
right hemispace. In the control group, visual distractors located
in the same hemispace as the hand interfered more with tactile
discriminations than lights in contralateral hemispace (i.e., right
lights interfered when the stimulated hand was in right hemispace,
left lights interfered when the stimulated hand was in left
hemispace). By contrast, right lights interfered with J.W.'s
tactile discriminations more that left lights whether his hand was
placed in right or left hemispace. These results, when taken
together with the crossmodal interference effects reported in a
range of different postures, suggest that cross-cortical
connections are required to maintain an up-to-date bimodal
representation of visuotactile space.
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