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Abstract:
It has recently been suggested that the "hippocampal system"
is important for language comprehension (McKay, Stewart and Burke
1998). This proposal was based on data that assessed patient H.M.'s
capacity for detecting and explaining ambiguous sentences. H.M. is
profoundly amnesic as a result of a bilateral medial temporal lobe
resection that includes the hippocampus, the amygdala and adjacent
cortex. We studied three amnesic patients with lesions limited to
the hippocampal formation, one amnesic patient with a left thalamic
lesion (case N.A.), and 13 healthy controls using the same
materials administered to H.M. by Lackner (1974) and also by McKay
et al. (1998). Participants first identified each of 90 sentences
as ambiguous or not and then explained the ambiguity. There were no
differences between patients and controls in their overall ability
to detect and explain ambiguities. Amnesic patients detected 71.6%
of the ambiguities and obtained 83.4% of the maximum score for
ambiguity explanation (controls 78.6% and 81.5%). The perfomance of
the control group suggested that there is considerable variability
in the normal population on this task. Performance was
significantly correlated with verbal IQ measures in the controls
and patients (WAIS-R Information and Vocabulary subtests) and with
immediate auditory memory (WMS 3) in the patient group. We conclude
that the hippocampal formation is not needed for language
comprehension. Furthermore, the results suggest that comprehension
of sentence ambiguity relies mainly on processes measured by verbal
IQ.
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