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Abstract:
The present experiment offers event-related brain potential
evidence that attentional capture depends on top-down modulation of
neural activity in visual cortex. Participants performed a covert
visual search task where they identified the unique stimulus in a
brief, four-location display. Targets defined by unique color or
onset were run in separate blocks, encouraging observers to adopt
different attentional sets in each. In both cases, a brief, white,
abrupt-onset cue highlighted one of the locations 100 or 200 ms
prior to the target display. Participants were informed that there
was no predictive relation between the location of the cue and that
of the target. Reaction times were faster for targets occurring at
the cued location in the onset block, but not in the color block,
indicating that attention was only captured when the cue contained
a target-relevant feature. Evoked potentials over right central
parietal regions were enhanced during the onset block just prior to
the cue's appearance. Additionally, the N1 wave elicited by the cue
was enhanced over occipital regions during the onset block relative
to the color block. These findings support the contingent-orienting
hypothesis of attentional capture as well as contemporary
attentional theories positing top-down biasing effects on sensory
brain areas.
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