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Abstract:
Research has shown that the identification of letters in
compound displays (large letters made up of smaller letters)
depends on the visual field location of the display. The large
letter is generally identified more efficiently in the left and
lower visual fields whereas the small letter is identified more
efficiently in the right and upper visual fields. Our experiments
indicate that these differences are dependent on the observer's
allocation of attention. For instance, if the displays are
presented to a single visual quadrant, allowing observers to attend
to a single location, the differences are weak or nonexistent.
However, if more than one quadrant contains a compound letter, or
the observer is asked to also process a simultaneously presented
single letter, then the field differences are very large. Finally,
if the single letter is presented to the visual field opposite the
compound letter, visual field differences in global-local effects
are again eliminated, suggesting some possibility for parallel
processing. These results are consistent with visual field
differences emerging not from differences in cortical
representations, but from dynamic interactions within a distributed
network of brain regions.
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