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Abstract:
We tested normal young, older, and Alzheimers subjects on
their ability to learn a novel category, in order to demonstrate
that this skill does not require intact declarative processes.
Subjects viewed category members and later, were tested on their
ability to discriminate new category members from non-members.
Older and younger subjects performances were indistinguishable from
each other and both were better than chance. This confirms earlier
findings (Davis et al., 1998) and stands in contrast to the
age-related decline of recognition memory and of some forms of
implicit learning. Alzheimers patients performed above chance on
the categorization task, though they tended to be worse than
age-matched controls. These findings contradict an earlier report
of Alzheimers patients failure to learn a category (Keri etal.,
1999). In answer to recent criticism of similar work, we also
compared subjects performances to those of subjects who had not
first viewed category examples: our findings were confirmed. The
relative preservation of the ability to learn a new category in the
face of explicit memory impairment lends renewed support to the
hypothesis that the two are functionally dissociated and that
category learning does not require an intact medial temporal lobe.
This is in keeping with the theory that categorization can utilize
(implicit) prototypic representations rather than (explicit)
exemplar matching.
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