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Abstract:
Abstract: H.M., an amnesic patient with a bilateral medial
temporal lobe resection, was tested for his ability to form
associations between visual stimuli and motor responses. His
performance was compared with that of 6 age- and education-matched
control subjects. In the first task, subjects were required to
learn which direction of movement was associated with each of 2
complex visual stimuli. Then the contingencies were reversed and
subjects had to learn the new associations. H.M. was able to
acquire the initial stimulus-response associations and learn the
reversals as well as control subjects. In the second task, subjects
had to learn which one of 4 possible directions was associated with
either 2 or 3 visual stimuli, with fixed stimulus-response
pairings. Consistent with the results from the first task, H.M. was
not impaired with 2 stimuli. When the number of stimulus-response
associations was increased to 3, however, H.M. was impaired
relative to control subjects. These results suggest that the
ability to learn multiple arbitrary associations between visual
stimuli and motor responses may be mediated by the hippocampus and
surrounding structures. H.M.'s ability to perform the tasks with
just 2 associations may be due to his ability to maintain the
stimuli and/or responses in short-term memory.
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