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Abstract:
Abstract: Visual extinction is a disorder of attention
associated with hemispatial neglect, in which patients can perceive
stimuli in the contralesional field when presented alone but not
when presented with competing stimuli in the ipsilesional field.
Neuropsychological evidence suggests that extinguished stimuli may
still be processed up to a level where shape, color, or semantic
features are extracted, yet without awareness. We studied a patient
with right parietal damage and left visual extinction in a task
where faces or shapes were briefly shown in the right, left, or
both fields, using ERPs to examine the neural activity evoked by a
left-side face presented with a right-side shape when patients
perceived or extinguished the face. Compared to perceived faces,
extinguished faces evoked similar early visual responses at
contralateral occipital sites with only moderately decreased P1-N1
components, and a similar face-specific N170 at posterior temporal
sites. Compared to extinguished faces, perceived faces evoked later
positive components (P190) in central, anterior temporal, and
midline regions, as well as negative components in frontotemporal
regions. This provides the first neurophysiological demonstration
of category-specific processing without awareness in neglect, and
suggests that contralesional stimuli can still activate striate and
extrastriate ventral pathways without conscious perception. These
results are consistent with results we obtained using event-related
fMRI in the same task.
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