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Abstract:
Prior neuroimaging studies have investigated the functional
neuroanatomy of global and local processing (e.g., Fink et al.,
1996; Heinze et al., 1998), but have not distinguished activity
related to attentional control from that related to global/local
target processing. We used event-related fMRI during a cued
attention task to dissociate the neural networks involved in
voluntary orienting from the networks that process hierarchical
target stimuli. Twelve volunteers performed a task in which a cue
directed attention to either the global or the local level of a
hierarchical letter stimulus. Both global and local cues activated
the middle frontal gyrus (MFG), supplementary motor area (SMA)
and/or anterior cingulate cortex (ACC), superior and inferior
parietal lobes (SPL and IPL), and visual cortex. These activations
reflect voluntary orienting rather than sensory processing of the
cue stimuli because they occurred relative to passively viewed
cues, and even when no target followed a cue. Similar regions of
parietal cortex were more activated during incongruent compared
with congruent targets, suggesting a role for voluntary orienting
during stimulus situations that engender response conflict.
Finally, local cues produced greater activation in parietal and
visual cortex than did global cues, while global cues produced
greater activation in SMA/ACC. However, little evidence of
hemispheric asymmetries for global/local processing was observed
for either cues or targets. These findings have important
implications for models of attentional control.
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