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Abstract:
Recent single cell electrophysiological and functional
imaging studies of visual selective attention have suggested that
attention may modulate incoming information as early as primary
visual cortex. However, it has been unclear based on neuroimaging
findings whether the modulation of signals occur during the initial
entrance of visual information into striate cortex, or whether the
modulation represents a re-entrant feedback of enhanced visual
information from higher visual areas. In addition, event related
potential (ERP) studies have not found the C1 component from
striate cortex to be modulated with attention. We investigated this
using a method in which distractor stimuli were present or absent
from the surround of a target. In the present study, ERPs were
recorded to determine the role of multiple competing stimuli for
attentional modulation of input signals in striate cortex. ERPs
were recorded from twelve subjects while they performed a
discrimination task. The task required subjects to discriminate
between an upright and inverted T. For half the trials, the T's
were surrounded by + signs as distractors. The presence of the
distractors reduced target discrimination accuracy. In the ERPs, a
P1 and N1 attention effect was observed, which is consistent with
prior studies. There was no modulation of this effect by the
presence or absence of distractors. Neither attention nor
distractors modulated the C1.
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