Cognitive control and the role of Broca's area in sentence processing
A century of investigation into the role of the human frontal lobes in complex cognition, including language processing, has revealed several interesting but apparently contradictory findings. In particular, the results of numerous studies suggest that left inferior frontal gyrus (LIFG), which includes Broca's area, plays a direct role in sentence-level syntactic processing. In contrast, other brain-imaging and neuropsychological data indicate that LIFG is crucial for cognitive control--specifically, for overriding highly regularized, automatic processes, even when a task involves syntactically undemanding material (e.g., single words, a list of letters). This thesis provides a unifying account of these findings, which is motivated by a review of the neurocognitive and sentence processing literatures, and emphasizes the importance of general cognitive control mechanisms for the syntac tic processing of sentences. In support of this account, I present the results of six new experiments that explore the cognitive control abilities of both healthy adults and patients with frontal damage within both parsing and non-parsing domains. Taken together, I will defend the following three claims: (1) LIFG is part of a network of frontal lobe subsystems generally responsible for the detection and resolution of incompatible stimulus representations; (2) The role of LIFG in sentence comprehension is to implement re-analysis in the face of misinterpretation; and (3) Individual differences in cognitive control abilities in non-syntactic tasks predict correlated variation in sentence processing abilities pertaining to recovery from misinterpretation.