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Abstract:
Orienting spatial attention to non-foveal locations in the
visual field facilitates the processing of events within the
attended location (e.g., Posner, 1980). However, it has also been
suggested that as the perceptual load of task-relevant stimuli
increases, the processing of task-irrelevant stimuli at other
locations decreases (e.g., Lavie & Tsal, 1994). In both
scenarios, spatial selection is assumed to occur at
perceptual-level processing stages, but is the selection in the two
cases occurring at a common neural locus? To address this question,
event-related potentials (ERPs) were recorded during distracter
interference tasks under conditions of low and high perceptual
load. The results from two experiments showed that changes in load
during the distracter task produced spatial-based modulations in
the same lateral-occipital ERP components that are typically
modulated in attentional orienting paradigms. Our findings indicate
that a common mechanism of selection underlies both the orienting
and load models of spatial attention. In particular, spatial
selection arises from a non-homogenous distribution of attentional
resources within the visual field, a situation that occurs both
with attentional orienting and high perceptual load. Further, these
effects are mediated in extrastriate visual cortex, during the
perceptual processing of stimulus inputs.
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