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Abstract:
Agrammatic aphasics have difficulty in comprehending
semanticallyreversible and implausible sentences. Numerous studies
have attempted toaccount for this comprehension deficit from a
syntactic point of view. Thecurrent study explores this issue from
a different vantage point. Namely,it investigates whether aphasic
patients have impairments in sentenceprocessing reflecting an
inability to process thematic relations derivedfrom lexical and
verbal semantics and also world knowledge. To this end, aset of
sentences was constructed which had the same syntactic
structure(simple active declarative) but which varied in terms of
the semanticplausibility and the valence of thematic relations of
the sentences. In thefirst two conditions, the sentences were
plausible and reversible butvaried in their degree of plausibility
and valence of thematic relations,e.g., "The kidnapper is hiding
the girl" vs. "The boy is hiding the girl".In the next two
conditions, both sentences were implausible but, similar tothe
plausible condition, they varied in their degree of implausibility
andvalence of thematic relations, e.g., "The squirrel is hiding the
girl" vs."The bracelet is hiding the girl". Normal control subjects
showed effectsof both plausibility and degree of thematic valence.
In contrast, although Broca's aphasics showed sensitivity to the
coarse-grained thematicrelations as shown by good performance on
plausibility judgments, theyfailed to show sensitivity to
fine-grained thematic relations within eachof the plausible and
implausible sentences. Wernicke's aphasic showed asimilar pattern
to Broca's aphasics, although, similar to normal subjects,they did
show sensitivity to the fine-grained thematic relations in
theimplausible sentences. Taken together, the results suggest that
aphasicpatients may have difficulty in processing thematic
relations, e.g.,accessing thematic features. Such an impairment
could influence the processof thematic role assignment and the
integration of the meaning of asentence, thereby contributing to
the deficits they display in the comprehension of semantically
reversible and implausible sentences.
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