Digging beneath the surface behavioral and neural indices of lexical access during idiom comprehension in aphasia : a multi-modal approach

Includes bibliographical references (p. 194-212)This project examines spoken language comprehension in Broca's aphasia, a non-fluent language disorder acquired subsequent to stroke. Broca's aphasics demonstrate impaired comprehension for complex sentence constructions. To account for this deficit, one current processing theory claims that Broca's patients retain intrinsic linguistic knowledge, but that a delay in lexical access in these patients disrupts an intact syntactic system. The current work exploits the properties of long lexical items (idioms) that have multiple meanings (literal and figurative) represented in the lexicon to investigate this theory of lexical deficit in Broca's aphasia. This work postulates that idioms allow for a temporally-extended investigation of lexical access in aphasia, as prior research demonstrates that healthy listeners access the figurative meaning of an idiom slightly prior to the literal meanings associated with the idiom's constituent words. This temporal discontinuity will allow a close examination of the time course of lexical access in Broca's aphasia. This dissertation investigates both the real-time psycholinguistic indices of lexical processing during auditory idiom comprehension in aphasia, as well as the neural manifestations of this processing. Chapter 1 reviews hypotheses of lexical access deficits in Broca's aphasia and motivates the use of idioms as a tool to investigate lexical processing in this population. Chapter 2 examines real-time lexical access for an idiom's multiple meanings during sentence comprehension, in unimpaired and aphasic individuals. Chapters 3 and 4 examine the neural correlates of this lexical processing. Chapter 3 studies cerebral blood flow, an important variable in functional neuroimaging, among stroke survivors with aphasia, finding that special care must taken when analyzing functional neuroimaging data from this population in order to capture the full time course of the neural signal. Chapter 4 investigates lexical access during idiom comprehension via functional neuroimaging, localizing the neural indices of this processing. This dissertation provides the first investigation of lexical access in Broca's aphasia using idioms as a research tool. The results extend our understanding of lexical processing in this population, both behaviorally and neurally, during auditory sentence comprehensio