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Abstract:
Probabilistic category learning was investigated in a patient
with bilateral hippocampal lesions and patients with Huntington's
disease or Parkinson's disease. Subjects were asked to categorize
stimuli that were constructed from horizontal and vertical lines
into one of two categories. Correct classification was based on a
non-linear relationship between the lengths of the two stimulus
dimensions. Results indicated that the patient with amnesia
secondary to bilateral hippocampal lesions was normal in learning
the non-linear rule. In contrast, the patients with Parkinson's
disease or Huntington's disease were impaired in learning this
complex categorical rule. The results further support the notion
that the hippocampus is not involved in learning certain types of
categorical rules, especially those that are non-linear, whereas
the basal ganglia may play an intricate role in the learning of
this sort of categorical rule.
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