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Summary: Research Article
Independent Resources for
Attentional Tracking in the Left
and Right Visual Hemifields
George A. Alvarez and Patrick Cavanagh
Harvard University
ABSTRACT--The ability to divide attention enables people to
keep track of up to four independently moving objects. We
now show that this tracking capacity is independently
constrained in the left and right visual fields as if separate
tracking systems were engaged, one in each field. Specifi-
cally, twice as many targets can be successfully tracked
when they are divided between the left and right hemifields
as when they are all presented within the same hemifield.
This finding places broad constraints on the anatomy and
mechanisms of attentive tracking, ruling out a single at-
tentional focus, even one that moves quickly from target to
target.
The brain is divided into separate left and right hemispheres that
are connected by the corpus callosum, a large network of fibers
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