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Abstract:
Neuroimaging studies have repeatedly documented the
involvement of Broca's area in syntactic analysis. Here we
demonstrate that this region implements one specific component of
syntax - grammatical transformations. An fMRI experiment was
conducted, contrasting minimally different Hebrew sentences with
and without transformations, presented to 12 healthy subjects.
Other measures of complexity (degree of embedding, length,
propositional content) were kept constant. A grammaticality
judgment task was used, forcing subjects to engage in syntactic
processing. To prevent response prediction, we used a "hidden
block" design: experimental blocks were embedded within alternating
filler sentences. Consequently, activation recorded during filler
judgment was used to define individual ROIs. Four bilateral ROIs
were thus defined: inferior frontal gyrus (IFG), posterior superior
temporal sulcus (PSTS), anterior insula (AI) and transverse
temporal gyri (TTG). We found (a) a significant effect of
transformations in left (but not in right) IFG, (b) a highly
significant interaction between transformations and hemisphere in
IFG, (c) no effect or interaction in AI or TTG, (d) a small effect
of transformations in PSTS, and no interaction with hemisphere.
Combined with behavioral results from aphasia, these results point
to the critical role of Broca's area in computation of grammatical
transformations, rather than syntactic complexity in general. The
results also suggest that parts of Wernicke's area participate in
this computation.
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