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Abstract:
Abstract: Recognition of a specific visual target among
equally familiar distracters requires neural mechanisms for
tracking items in working memory. Event-related functional magnetic
resonance imaging (fMRI) revealed evidence for two such mechanisms:
(1) Enhanced neural responses, primarily in frontal cortex, were
associated with the target and were maintained across repetitions
of the target. The response enhancement may signal the target
status of a stimulus. (2) Reduced responses, primarily in
extrastriate visual cortex, were associated with stimulus
repetition, regardless of whether the stimulus was a target or a
distracter. This repetition reduction may reflect a process that
enables more efficient processing of stimuli when they are
encountered repeatedly during an active working memory search. In
addition, the neural response to a particular item "reset" to its
initial level for each new trial. This restoration of response
between trials strongly suggests that the response reductions we
observed were specific to the context of an active working memory
search and not associated with long-term memory processes. These
complementary neural mechanisms track the status of familiar items
in working memory, allowing for the efficient recognition of a
currently relevant object and rejection of irrelevant
distracters.
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