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Abstract:
Some investigators have argued that sentence comprehension
difficulty in Parkinson's disease (PD) is due to compromised
grammatical processing, but others have attributed impaired
sentence comprehension to an executive limitation. We assessed
these competing claims in 18 non-demented, right-handed,
mildly-impaired PD patients and 15 healthy controls with an on-line
word detection procedure. Subjects heard a word presented by
computer and were asked to press a computer key as soon as the word
was heard in the sentence that followed. Unbeknownst to subjects,
half of the target words followed a grammatical agreement violation
(e.g. violation of numerosity or quantification agreement). Half of
these agreement violations immediately preceded the target word,
and half preceded the target word by 8 words. We also administered
a traditional, off-line comprehension procedure, where subjects
answered questions about sentences with center-embedded or terminal
subordinate phrases that were subject-relative or object-relative.
We also administered executive measures assessing planning,
short-term memory, inhibition, and mental search. We found that PD
patients are as sensitive as control subjects to grammatical
agreement violations in an on-line procedure, but PD patients
differ significantly from controls in their ability to answer
questions about grammatically complex sentences presented off-line.
PD patients' impaired off-line sentence comprehension correlated
with executive measures. We conclude that PD patients'
comprehension difficulty is due in part to a cognitive resource
limitation for sentence processing.
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