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Abstract:
welve amnesic patients of mixed etiology were compared to 12
matched controls. Subjects read single nouns which were congruent
or incongruent with a preceding category label ("A type of
furniture: couch" vs "bacon"). Half of the stimuli were repetitions
(lag of 0 to 13 trials), half were new. On initial presentation,
incongruent words elicited larger N400 components of the
event-related potential (ERP) than congruent, in both patients and
controls. With repetition, the N400 to incongruent items was
reduced in both patients and controls. Repetition of congruent
items instead influenced a late positive component of the ERP in
the controls. Considered as a group, the patients failed to show
this late positive repetition effect which has been previously
linked to episodic memory. However, the patients were variable both
in the extent of their memory impairment and the amplitude of the
late positivity. Neuropsychological measures of memory ability were
significantly correlated with the late positive, but not the N400
repetition effect. The results thus suggest that the late positive
ERP repetition effect reflects retrieval from episodic memory, but
that the N400 repetition effect indexes an aspect of memory which
is not impaired in organic amnesia-perhaps a relatively short term
record of recent input which is necessary for language
comprehension.
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