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Abstract:
This study was conducted to determine the nature and extent
of attentionally modulated visual processing due to sustained
attention to one location in the visual field. Within the central
15.6 degrees of the visual field, 60 task irrelevant probes were
simultaneously and independently modulated, according to a binary
m-sequence, such that the flash response across a dense electrode
array could be determined for each probe. During central fixation,
participants counted the number of times a small circle centered on
an eccentric stimulus probe, in either the right or left hemifield,
reversed in color. As expected, the peak-to-peak amplitude of the
evoked response (and magnitude of the best fitting dipole current
source) corresponding to the probe at the attended position were
increased relative to the response to that probe when attention was
directed to the opposite hemifield. This facilitory effect of
attention was shown to extend toward the fixation point and was
roughly elliptical in shape. Additionally, a broad region of
inhibition, also roughly elliptical in shape, was shown to surround
the region of facilitation. These results indicate that the
allocation of attention to one locus in space can have broad
modulatory effects, both facilitory and inhibitory, across space at
unattended locations.
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