Beyond Lateralization: Sensory-Motor Control of Speech Production.
- Author(s): Kort, Naomi Sophia
- Advisor(s): Nagarajan, Srikantan S
- et al.
The task of speaking is the translation of thoughts into an acoustic wave through the coordination of hundreds of muscles. Sensory-motor transformations are continuously occurring during ongoing speech as feedback is monitored and errors in production are rapidly recognized and corrected. While it is known that auditory feedback is used to monitor and maintain proper pitch production, the neural control of this important aspect of speech production remains poorly understood. Modulation of the timing and frequency of vocal pitch conveys important semantic and affective information during speaking. The goal of this thesis was to study sensory-motor control of speech production by examining the neural circuits involved in the auditory feedback control of pitch. In order to achieve this aim we used a combination of magnetoencephalography (MEG) and real-time pitch altered auditory feedback. To this end, we conducted a series of experiments to understand the real-time cortical monitoring of one's own speech production, the recognition of errors in auditory feedback, the cortical processing of these errors, and the motor (and subsequently acoustic) compensatory change. In this series of studies we have described the cortical networks and their mechanisms in monitoring auditory feedback during speech production. We have demonstrated that the cortical monitoring of the onset of a vocalization occurs with the suppression of auditory, cerebellar and frontal regions in both the left and right hemisphere. We showed this suppression is released when the perceived auditory feedback does not match the expected auditory feedback. We investigated the cortical networks involved in monitoring ongoing productions for errors in feedback, and the behavioral and cortical response when an error is perceived. We have shown that while the cortical networks monitoring the onset of speech and mid-utterance are overlapping, that these networks have distinct timing, patterns of response, and anatomical locations. Importantly, both feedback monitoring and motor control of speech at onset and mid-utterance show changes in cortical dynamics in both hemispheres. Feedback control of pitch during a mid-utterance error has corresponding increased inter-hemispheric communication. The work in this thesis provides evidence that inter-hemispheric communication is important for the feedback control of vocal pitch production.