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Abstract:
Abstract: In this study we combined electrophysiological
(ERP) and functional neuroimaging (fMRI) methods in order to
investigate the time course and anatomical loci of visual
processing during spatial-selective attention. Subjects received
identical stimuli and performed identical tasks in separate ERP and
fMRI sessions. In an initial passive condition, checkerboard
stimuli were rapidly delivered to each of the four visual quadrants
while subjects maintained central fixation. These stimuli produced
discretely localized fMR signal changes within several
retinotopically organized visual areas of striate and extrastriate
cortex. These changes were related to the estimated dipolar sources
of the short-latency components of the visual evoked potential. In
a second condition, the same group of subjects attended to a single
quadrant at a time and detected infrequent targets embedded within
the stream of checkerboard stimuli. Attention-related activations
were observed in several extrastriate areas with fMRI and were
related to the temporal sequence of ERP components modulated by
spatially-focused attention.
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