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Abstract:
Abstract: Recent studies have documented crossmodal
visual-tactile extinction in right-hemisphere patients (e.g. a
light near the right hand may prevent awareness of a touch on the
left hand).Visual-tactile spatial interactions shown at the
single-cell level in monkeys, suggest a possible neural basis for
crossmodal extinction. Interestingly, the visual receptive field of
visual-tactile bimodal cells in the Intraparietal Sulcus can be
extended when monkeys wield a tool that extends their reaching
distance. Similarly, using a tool showed to modulate the amount of
far-space extrapersonal neglect (Berti & Frassinetti, in
press). Here we tested whether using a tool might influence the
spatial nature of crossmodal extinction. Following a
right-hemisphere stroke, patient BV showed extinction of left hand
tactile stimuli by visual stimuli close to the right hand.
Crossmodal extinction was reduced if the right light was placed
distant from the patients right hand (keeping retinal eccentricity
constant). However, if the patient held sticks in both hands, so
that the light was now at the far end of the stick in his right
hand, the crossmodal extinction increased. Further conditions
showed that this effect depended on the patient holding a
continuous stick which extended to the far light. Holding the stick
may induce a re-mapping of space, possibly by elongating the
patient's 'body schema', thus influencing the spatial nature of
crossmodal extinction, as suggested by previous animal and
neuropsychological data.
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