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Abstract:
Visual attention can select a cued spatial area or fill an
object's boundaries. We used single-trial event-related echoplanar
fMRI to ask whether space-based and object-based selection involve
different neural structures. In a speeded letter identification
task, attention was cued by a central arrow pointing toward an area
of space or by a geometric shape within whose boundaries the letter
was likely to occur. Both types of cues influenced
letter-identification reaction times. Activity in eighteen brain
regions discriminated between cueing conditions. In every case
activation was greater with object-based cueing, suggesting that
object-based selection imposes additional constraints on top of
those that implement attention to an area of space. Brain
structures supporting object-based selection were found in primary
visual cortex, parietal and superior temporal cortex associated in
other work with deployment of attention, medial temporal cortex
associated with representing the organization of visual scenes,
inferior temporal cortex associated with object recognition, and
lateral and medial prefrontal cortex associated with working memory
and executive control. Thus object-based selection is implemented
by an extensive network of brain regions related to object
processing, spatial organization, and attention, rather than by a
single localized structure. Except for the most posterior visual
components and the most anterior midline-prefrontal components,
where activity is bilateral, this network is strongly left
lateralized.
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