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Abstract:
Prior studies have demonstrated that when processing demands
are relatively high, performance is better when a task is divided
across both hemispheres of the brain as compared to just one (e.g.,
Banich and Belger, 1990). In the present experiment, we
investigated which processing mode (i.e., within- or
across-hemisphere) underlies performance when within- and
across-hemisphere processing are equally possible. On each trial,
participants decided whether a lateralized target item beneath
fixation came from the same category (i.e., letters, numbers, or
symbols) as any of four lateralized probe items above fixation. On
match trials, two probes came from the same category as the target.
The matching probes were positioned either in the same visual field
as the target (within-hemisphere trials), the opposite visual field
as the target (across-hemisphere trials), or divided such that one
probe was in the same visual field as the target while the other
was in the opposite visual field (divided trials). Processing
demands were manipulated by varying whether the target and probe
items appeared simultaneously (more demanding) or sequentially
(less demanding). As predicted, performance on divided trials
resembled that on across-hemisphere trials and differed from that
on within-hemisphere trials when processing demands were relatively
high. This finding suggests that interaction between the cerebral
hemispheres is a neural mechanism that is recruited for performance
under demanding conditions.
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