Ataxic Dysarthria (AD) is a speech disorder caused by damage to the cerebellum from stroke, tumor, trauma, or, most commonly degenerative disorders of the cerebellum. People with AD produce speech with a number of temporal abnormalities. Their speech is excessively slow, with equal stress and little variation in duration between syllables. Surprisingly, the cause of these speech problems is unknown. We hypothesize that these deficits result from the patients' difficult to use feed forward, or predictive processes to control speech movements, similar to what has been described for arm movements and locomotion. The impaired capability to use feed forward processes due to cerebellar pathology interferes with the ability to correctly plan and coordinate the articulatory gestures for speech. A consequence of this deficit is that AD patients are highly reliant on sensory feedback to guide their speech. By using feedback AD patients can produce speech accurately but, because of inherent delays in feedback-based control, the patients reduce their speech rate and have difficulty in modulating syllable duration in an anticipatory manner to reflect contextual factors such as stress or word length. We test these hypotheses by manipulating the feedback that AD patients and matched control participants will hear when producing speech, and look at their ability to adjust or compensate for these perturbations. This strategy has been highly effective in understanding the role of the cerebellum in sensorimotor control and learning in studies of locomotion and reaching, but has not been applied in studies of speech disorders or AD. We expect the AD patients will be sensitive to the perturbations, adjusting the on-line output of their speech, but fail to show learning effects across trials. The results of this project will help us to understand the underlying mechanism associated with AD. It will also provide a more general framework for examining speech disorders and to identify similarities and differences between speech and other types of movements. As such, the work will advance our understanding of how speech is planned and executed in healthy individuals.
The research project proposed here aims to characterize the role of the cerebellum in speech motor control by studying patients with ataxic dysarthria, a relatively common motor speech disorder associated with damage to the cerebellum. The focus of the work will be on assessing the operation of predictive and feedback mechanisms required for coordinating the articulatory gestures of speech.
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