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Abstract:
The present study investigated motion and
brightness-increment processing in human visual areas V1 and V5 and
tested the hypothesis that V5 activity for motion might be heavily
masked in electrophysiological scalp recordings by strong and
temporally overlapping activity in V1 and other early sensory
areas. A stimulus expected to elicit strong activity in V1 and
other early sensory areas (a bright flash) was presented prior to a
motion stimulus or to a brightness-increment stimulus. Combined EEG
and MEG recording was used to measure brain responses to these
stimuli. Source analysis indicated that the flash stimulus as well
as the brightness increment stimulus were both processed in V1
while the motion stimulus was processed in both V1 and V5. The
prior presentation of a flash strongly affected the processing of
the brightness increment stimulus. The processing of the motion
stimulus was not affected in the same manner. The subtraction of
the activity elicited by a flash stimulus followed by a motion
stimulus minus the activity elicited by a flash stimulus alone
unmasked activity generated in the V5 region. These results provide
evidence that the processing of motion in V5 is mostly independent
of activity saturation in V1 and provide evidence for an
alternative pathway to V5 that bypasses V1.
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