Perceptual processing of auditory feedback during speech production and its neural substrates
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One enduring question in the study of speech concerns the nature of the link between speech perception and production. Although accumulating evidence suggests that these two facets of spoken language are tightly coupled, the cognitive structure and neural organization underlying the interactions between the two processes are not well understood. In this thesis, I focus on questions that arise from observations related to when individuals are both talking and listening, and assess the sensitivity of talkers and listeners to the same change in the acoustics of speech. First, I aim to elucidate the neural substrates of auditory feedback control during vocalization by examining the brain response to acoustic perturbations towards auditory concomitants of speech using functional magnetic resonance imaging (fMRI) (Chapters 2 and 3). I demonstrate, for the first time, an extensive network of brain regions involved in the detection and correction of auditory feedback errors during speech production, for which three functionally differentiated neural systems can be delineated. Then I set out to address the online perception of own voice identity as individuals are talking. Chapters 4 and 5 measure the perceptual sensitivity of individuals to the auditory concomitants of their own speech by presenting temporally gated auditory feedback in stranger’s voices during talking. The results show that people perceive stranger’s voices as a modified version of their own voice and adjust their vocal production accordingly, when their utterances and heard feedback are phonetically congruent. Chapter 6 further examines this perceptual effect by using experimental paradigms in the domain of body ownership and shows that the misattribution of the stranger’s voice, is not predicted by individual differences in suggestibility; rather it is related to the integration of multimodal cues. In summary, by focusing on how the acoustics of speech are simultaneously processed for both the perception and production sides of spoken language, the series of studies add significantly to our understanding of the psychophysical, cognitive and anatomical relationships between speech perception and production, and are relevant to a wide range of clinical pathologies (e.g., stuttering, schizophrenia).