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Abstract:
Purpose:
The purpose of this study was to determine whether increases in
regional cerebral blood flow (rCBF) that had previously been
reported in association with processing syntactically more complex
sentences (compared to syntactically less complex sentences) could
be attributed to greater rehearsal associated with processing the
more complex sentences.
Method:
rCBF was measured with positron emission tomography (PET) when
eleven subjects made speeded plausibility judgments about written
sentences that varied in their syntactic complexity. More complex
sentences consisted of "subject object" relatives, such as
The juice that the child enjoyed stained the rug,
and less complex sentences consisted of object-subject sentence
with the same words and propositional content such as
The child enjoyed the juice that stained the rug.
While making their judgments, subjects uttered the word "double"
aloud at a rate of one utterance per second to inhibit their
ability to rehearse the sentences.
Results:
Reaction times and error rates were higher for the more complex
sentences. Blood flow increased in Broca's area when subjects made
judgments about the more complex sentences.
Discussion:
This result replicates and extends previous findings that blood
flow increases in this region when subjects process complex syntax
under no interference conditions (Stromswold et al., 1996; Caplan
et al., 1998). The results of this experiment provide strong
evidence that the increase in blood flow seen in Broca's area in
association with processing syntactically complex structures is not
due to subvocal rehearsal of those structures but rather results
from processing syntactic forms themselves. The range of syntactic
forms that is processed in this area remains to be established.
References
Caplan, D. Alpert, N., & Waters, G. S. (1998). Effects of
syntactic structure and propositional number on patterns of
regional cerebral blood flow.
Journal of Cognitive Neuroscience,
10, 541-552.
Stromswold, K., Caplan, D., Alpert, N., & Rauch, S. (1996).
Localization of syntactic comprehension by positron emission
tomography.
Brain and Language,
52, 452-473.
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