Language comprehension is a complex process in which multiple, including semantic and syntactic, representations of the material are constructed as the input unfolds. Sometimes more than one way to interpret a sentence or sequence of sentences is possible and reliable sources of information may mislead us into developing an ultimately incorrect interpretation. Several questions could be asked about language comprehension in these cases. First, how good are we at recovering from misinterpretations? Second, do we vary in ability to recover from misinterpretations? Third, if there are individual differences in recovery ability, what cognitive factors underlie the differences? And fourth, are those cognitive factors subserved by specific areas in the brain?
Answers to the first question may depend on the type of sentences involved (Gorrell, 1995; Pritchett, 1992; Sturt, 1995; Sturt, Pickering, & Crocker, 1999). Some sentences appear to be hard (e.g., The horse raced past the barn fell, cf. the horse that was raced past the barn fell) (Bever, 1970) while others are relatively easy to reinterpret (e.g., John saw the girl was cheating, Ferreira & Henderson, 1990). Several theories (e.g., Gorrell, 1995; Pritchett, 1992; Sturt, 1995) categorize sentences into those that could be recovered "unconsciously" — the ones we typically do well at reinterpreting and those that are "consciously" difficult, which we may or may not succeed in reinterpreting.
Using sentences shown to induce noticeable degree of reinterpretation difficulty (the "garden path" sentences), this thesis examined the role of executive control, particularly ability to attend to relevant information and ignore salient but irrelevant information, in reinterpretation. To the extent that executive control ability varies from individual to individual, ability to recover from misinterpretations should vary accordingly. Further, the brain areas that are important for executive control, particularly the left inferior frontal gyrus (LIFG), should be important for recovering from misinterpretations. Experiment 1-3 examined the issue by focusing on individual differences in executive control among healthy younger comprehenders. Experiment 4-6 examined the same issue by focusing on LIFG-based executive control patients. The thesis shows that LIFG-based executive control is critical for both semantic and syntactic reinterpretation of garden path sentences.