Understanding how auditory feedback is processed during speaking provides insights into fundamental mechanisms underlying speech production and perception. This knowledge might also ultimately contribute to the early detection and lead to treatment strategies for a number of prevalent clinical conditions where impairments in abnormal processing of auditory feedback have been reported (e.g. stuttering, Parkinson's disease, schizophrenia). While many behavioral studies have examined how auditory perception affects speech production, only recently have functional neuroimaging studies begun examining how producing speech affects the neural processes serving auditory perception. Recent studies have shown that in auditory cortex and other areas in the superior temporal plane, speaking causes """"""""speaking-induced suppression"""""""" (SIS): response to self-produced speech is suppressed when compared to identical speech from an external source. In our recent work, we have shown that SIS in auditory cortex does not result from overall inhibition of this area during speaking. Rather, SIS appears to be a neural correlate of a feedback prediction error (FPE) - a comparison between actual auditory input and an internal """"""""speaking-induced prediction"""""""" (SIP) of that auditory input. SIS expression in auditory cortex has led to the hypothesis that SIS reflects auditory discrimination of self-produced from externally produced stimuli (Self-non-Self Hypothesis). However, refinements in our understanding of auditory feedback in speech motor control, that are supported by behavioral studies and our preliminary data, suggest that SIS may also reflect feedback processing for speech motor control (Speech Motor Control Hypothesis). We have developed a unifying conceptual model that embodies both hypotheses, and our proposed experiments use SIS to test the neural correlates and the validity of this model.
The specific aims are to determine how SIS is modulated by 1) altered feedback, 2) speech target dynamics and 3) speech motor adaptation. These manipulations not only help us to unravel the functional significance of SIS but also help us determine if there is a differentiation of the function of SIS across the superior temporal plane. Furthermore, how activity in other parts of the brain is affected by our experimental manipulations will allow us to determine the neural correlates of the mechanisms that generate SIS. Our approach capitalizes on unique real-time speech feedback alteration methods used with functional magnetic resonance imaging (fMRI) and magnetic source imaging (MSI). The excellent spatial resolution of fMRI will enable reconstruction of spatial locations of activity related to SIS and SIP while the excellent temporal resolution of MSI will enable us to reconstruct the sequence of activation in these areas.
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