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Abstract:
Abstract: The aim of the present study is to clarify
electrophysiological characteristics of the early extrastriate
activity elicited in response to visual presentations in the blind
hemifield (right, RVF) of subject GY. Two issues were raised : (1)
Is this activity due to light scattering, a factor that may be
responsible of the delayed and reduced P1 component elicited in GY
when stimulated in the RVF ? (2) Is there a direct contribution
from the damaged hemisphere on the electrophysiological properties
of the P1 component generated in the good hemisphere? Visual
event-related brain potentials were recorded and processed
(Neuroscan - 64 channels) (1) while GY was discriminating facial
expressions randomly presented in his good or blind visual
hemifield and (2) while GY was judging the orientation of faces
presented either unilaterally or bilaterally. Experiment 1 allow us
to reject a possible interpretation of our results only in terms of
light scattering since facial expressions presented in his blind
visual hemifield yield a similar P1 component around 160 ms
post-stimulus whatever the mean luminance of the stimulus and the
background. Results of the second experiment suggest a possible
early interhemispheric competition since the presentation of a face
in the RVF significantly decreased the amplitude of the P1
component generated in response to simultaneous presentation in the
good visual hemifield.
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