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Abstract:
We report results from two cross-modal naming experiments
designed to examine the processing of number agreement in sentences
and in discourse by patients with Alzheimer's disease and
age-matched normal controls. Experiment 1 tested the processing of
subject-verb number agreement within sentences and Experiment 2
investigated the processing of pronoun-antecedent number agreement
across sentences. Both experiments included a length manipulation
such that processing was tested with varying amounts of intervening
material between the agreeing constituents. Verbal working memory
was assessed for all participants.The results of these two
experiments revealed a 3-way dissociation between processing number
agreement in sentences and in discourse: 1. Intervening material
only hindered agreement processing in sentences (Experiment 1) but
not in discourse (Experiment 2). 2. The Alzheimer's patients were
only impaired in discourse processing (Experiment 2) but not in
sentence processing (Experiment 1). 3. Working memory performance
correlated with discourse processing performance (Experiment 2) but
not with sentence processing performance (Experiment 1). These
results are not only compatible with a modular view of separate
processors for sentences and for discourse but are also compatible
with an integrated view whereby difference in processing do not
implicate different processors but merely reflect the different
properties of the input. We present a Bayesian model which, based
on a single mechanism, explains our findings in terms of
differences in the frequency of the dependencies we tested, and the
predictability of the dependent constituent given the other
constituent.
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