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Abstract:
We investigated unilateral extinction of left touch by right
visual stimuli in a patient with right hemisphere brain damage.
Recent research, using informal clinical confrontation, has
reported such crossmodal extinction. We confirmed this using
precisely controlled events, thus ruling out potential criticisms
of poorly controlled stimuli. Since extinction may reflect a
spatially biased competition for awareness, we further examined the
spatial coordinates of the bias from which tactile-visual
extinction might result. While keeping the stimulated visual and
tactile receptors constant, we deviated the patient's gaze so that
right visual events then fell at the same external location as the
left tactile events that they had previously extinguished. This
novel manipulation dramatically reduced crossmodal extinction,
while having no influence on unimodal tactile extinction. This
suggests that the severity of extinction depended upon the relative
positions of the competing stimuli in external space and not the
posture change itself. We conclude that crossmodal extinction
occurs at a relatively high level of spatial representation, with
remapping between the modalities occurring across changes in
posture.
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