The purpose of this research is to investigate the role of articulatory recoding processes in speech perception using functional magnetic resonance imaging (fMRI). Four experiments are proposed to test the predictions of two contrasting models of speech perception, which postulate different types of phonetic representations (acoustically based versus articulatorily based representations). In each experiment, patterns of relative regional brain activity associated with phonetic processing will be assessed using fMRI methods. In addition, behavioral measures of reaction times and error rates will be collected to indicate differences in performance on speech discrimination tasks. The behavioral measures will assess differences in cognitive processes among conditions that may lead to different patterns of brain activity in the fMRI experiments. The first experiment will contrast speech discrimination tasks which do or do not require overt segmentation of the speech signal. Models of speech perception that map the acoustic signal onto articulatory representations predict inferior frontal as well as temporal lobe activation. In contrast, models that rely on acoustic information predict activation of temporal lobe regions, but not inferior frontal activation. The second experiment will address whether increased task demands due to segmentation processes can account for inferior frontal activation seen in previous segmentation studies. The third experiment will determine whether the lexical status of the speech stimuli contribute to different patterns of the extent and location of activity. The fourth experiment will determine whether skilled readers use orthographic strategies to perform speech discrimination tasks, which may affect the pattern of activation seen in phonetic processing tasks. Thus, neurobiological evidence about whether an area associated with articulatory processes participates in speech discrimination tasks will help to clarify the role of articulatory representations in models of speech perception. The results of these experiments will provide systematic evidence of the nature of speech processing for future studies of normal and impaired language processing using functional neuroimaging.
