While significant progress has been made in recent years in describing the neural systems that are responsible for mapping the speech signal to meaning, the role of inferior frontal brain structures in this process remains poorly understood. The current project is designed to investigate the hypothesis that the left inferior frontal gyrus plays an active role processing the sounds of speech in order to map them to meaning. First, we suggest that the left inferior frontal gyrus is implicated under conditions of phonetic competition as speech sounds are mapped to meaning. Second, we investigate the role of inferior frontal regions in the acquisition of new speech categories in both implicit and explicit training paradigms. These questions will be addressed via functional neuroimaging (fMRI) studies of unimpaired individuals together with yoked behavioral studies of aphasic individuals with lesions in either frontal or temporal brain structures. Behavioral measures include the use of eye-tracking measures which allow for the collection of online, implicit measures of sensitivity to phonetic category variability. Results of these studies will refine existing models of the neural underpinnings of speech perception. The knowledge gained as a result of this project will better characterize impairments at the level of speech processing in aphasic individuals with frontal and temporal damage. This knowledge, together, with an enhanced understanding of the capacity of aphasics to learn new speech sound sensitivities, may be used to inform rehabilitative strategies for aphasics with frontal and temporal damage.
The proposed research will shed light on the role of inferior frontal and temporal brain structures in the perception and acquisition of the sounds of speech, and this information may ultimately be used to inform treatment strategies for aphasic individuals with damage to these brain structures. A more complete understanding of the function of these brain areas will also add to our understanding of other language disorders such as SLI and dyslexia which may involve impairments in processing the sounds of speech.