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Abstract:
Neuropsychological evidence suggests that different sorts of
memory storage are responsible for category learning and
recognition. To directly compare neural correlates of these two
types of memory, we recorded event-related potentials (ERPs) to dot
patterns. Participants learned each dot pattern category by
studying 40 stimuli derived from a single prototype. In the
categorization test, they viewed a set of new dot patterns and
attempted to distinguish between those that belonged to the studied
category and those that didn't. In the recognition test, they
attempted to recognize five studied dot patterns among new dot
patterns. Prior fMRI results using the same design showed that
categorization was associated with decreased activation in early
visual areas for categorical relative to noncategorical stimuli,
whereas recognition was associated with widespread increases in
activity (Reber, Stark, & Squire, 1998). We found that
processing of category members was associated with a reduction in
the amplitude of a positive peak at 100 ms. The posterior
topography and short latency of this ERP effect suggest that early
visual processing was altered by category learning, consistent with
the FMRI results. In addition, our ERP results suggest that the
early visual processing difference is not present during
recognition. Recognition ERPs showed a broad positivity from
300-700 ms for old relative to new patterns, but no early
difference. The different timing and scalp distribution of the ERP
differences during categorization and recognition support the idea
that distinct neural mechanisms underlie these two memory
phenomena.
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