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Abstract:
Behavioral studies have shown that subjects can switch from
controlled to automatic processing in visual search tasks with
consistent practice. Subjects were trained to search for letters
using consistent and varied mapping over four one-hour sessions.
Consistent mapping (CM) produced fast search, reducing processing
time from 400ms to 150ms for two character searches. Behavioral
testing showed obligatory processing of CM characters placed as
foils within a varied mapping search. A previous set of fMRI
experiments using a surface coil showed that CM foils produced
activation in extrastriate cortex both in CM search, and in
fixation monitoring when the CM characters were to be ignored. In
this set of experiments we used a head coil to examine differences
in processing between controlled and automatic search. Regions in
parietal, occipital, frontal, and premotor cortex were activated
during both controlled and automatic search. We compared controlled
and automatic search directly by having subjects switch between
varied and consistent mapping. Subjects performed both search
conditions at the same frame time so that accuracy was above 90%
with CM search and near 70% with VM search. Despite this difference
in effort, little difference was seen in brain activation between
the two conditions. Future studies will use dual task conditions
and event related neuroimaging to attempt to examine the role of
effort in controlled and automatic visual search.
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