Although the role of the cerebellum for the smooth and coordinated execution of movement is generally understood, little is known about how the cerebellum facilitates speech movement for natural and accurate prosodic production.3 Individuals with ataxic dysarthria due to a cerebellar damage exhibit atypical prosodic patterns, including a monotone vocal quality, a variable rate of speech, and atypical phrasal stress patterns.6,7 Our objectives are to measure the differences in reflexive and predictive voice responses between speakers with and without ataxic dysarthria to provide indicators of the accuracy of the cerebellum for the integration of sensory feedback with motor plans for speech. The rational for this study is that atypical prosody disrupts speech naturalness and intelligibility which current speech therapy approaches are not effective in fully restoring due to a poor understanding of the underlying impairment. The long-term goal is to characterize the deficits in sensorimotor integration in ataxic dysarthria to better understand the underlying mechanism for prosodic impairment. The central hypothesis of this project is that prosody in ataxic dysarthria is impaired because of a diminished ability to integrate sensory feedback with (i) prior motor plans for speech, affecting reflexive corrective mechanisms for intonation, as well as (ii) future motor plans for speech, affecting predictive scaling mechanisms for adjusting downstream intonational targets. This hypothesis will be tested by perturbing voice pitch auditory feedback of speakers with and without ataxic dysarthria to compare reflexive and predictive vocal responses in sustained vocalization and in anticipatory f0 changes. The differences in responses between speakers with and without ataxic dysarthria will provide indicators of the accuracy of the cerebellum in incorporating sensory feedback with online speech production. More specifically, the following aims will be measured: 1) measure the reflexive vocal response mechanism to examine sensorimotor integration with prior motor plans, and 2) measure the predictive vocal scaling mechanism to examine sensorimotor integration with future motor plans of downstream intonation targets. These two aims were derived from evidence of impairments to reflexive and anticipatory control of posture, gait, and arm movement in response to movement displacements in individuals with cerebellar lesions.15?17 The same disrupted cerebellar functions for movement may underlie the atypical prosodic patterns in speech. The proposed research is significant because it is expected to provide a greater understanding of the underlying cerebellar mechanism of the prosodic impairment in ataxic dysarthria so that effective therapy treatments can be developed to improve speech intelligibility and naturalness. Additionally, these results will provide clarity of the cerebellum's involvement in the speech production process for feedback integration with motor plans for speech.
The proposed research is relevant to public health because it seeks to understand the underlying impairment for atypical prosody in ataxic dysarthria. The results can be applied to develop effective therapy tools to improve speech naturalness, relevant to the part of the NIH?s mission that concerns reducing illness and disability.