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Abstract:
Category learning was investigated in amnesiac, Huntington's
disease (HD) and Parkinson's disease (PD) patients. Subjects were
asked to categorize stimuli that were constructed from a horizontal
and vertical line into one of two categories. In the
nonlinearly-separable (NLS) condition, correct classification was
based on a non-linear relationship between the line lengths. In the
linearly-separable (LS) condition, correct classification was based
on a simple linear relationship between the line lengths. All other
procedural aspects were fixed across conditions (e.g., optimal
accuracy, nature of the feedback, response requirements, etc). Each
subject completed 6-100 trial blocks in each condition, and
single-subject analyses were performed. The results suggested that
(a) amnesiacs were not impaired in either the NLS or LS conditions,
(b) HD and PD patients were impaired in both the NLS and LS
conditions, and (c) HD and PD patients showed a larger impairment
in the LS, than in the NLS condition. These findings further
support the notion that the hippocampus in not involved in category
learning, whereas the basal ganglia may play an intricate role.
These data also provide a first step toward identifying potential
relationships between the locus of brain lesions and the learning
of different types of categorization decision rules.
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