The role of the cerebellum in three components of predictive motor control in speech

Project Summary/Abstract Accurate speech production requires the precise control of multiple articulators in space and time. Ataxic dysarthria is a speech motor disease caused by damage to or degeneration of the cerebellum. Symptoms are varied, including both temporal and articulatory symptoms, and result in decreased speech naturalness and intelligibility, significantly impacting quality of life. In addition, there is wide variation across speakers with ataxic dysarthria, leading some to propose multiple subtypes of ataxic dysarthria. While the range of symptoms of ataxic dysarthria are well established, their underlying causes are poorly understood. As such, there are currently no evidence-based treatments that target the specific symptoms in this population. The experiments in this proposal test the hypothesis that predictive control is impaired in people with cerebellar disease. The studies test three components of predictive control in three aims. The first aim tests the hypothesis that speakers with ataxic dysarthria have impaired predictive state estimation. To generate the correct motor commands to reach a goal, it is necessary to know where the articulators start from; inaccurate estimates of the starting point could lead to inaccurate production. Variability will be measured in the final syllable of words when speakers are speaking quickly, necessitating predictive state estimation, and when speakers are speaking slowly, which allows the use of sensory feedback for state estimation. The second aim tests the hypothesis that speakers with ataxic dysarthria have impaired temporal predictions. As speech production relies on the coordination of multiple articulators, speakers must be able to accurately estimate how long each articulator will take to reach its next goal. This study examines the relationship between movement timing and articulatory distance in disyllabic words, building on work that indicates that typical speakers adjust the timing of vowel movement initiation depending on the distance to the next target. The third aim tests the hypothesis that speakers with ataxic dysarthria have a shortened planning horizon. To generate optimal motor trajectories, it is necessary to plan in advance. Non-speech work indicates that planning is impaired in individuals with cerebellar disease. This study measures anticipatory vowel-to-vowel coarticulation in multisyllabic utterances, which has been previously shown to reflect planning. The proposed studies will establish the status of three components of predictive control in speakers with ataxic dysarthria. Although it is predicted that speakers with ataxic dysarthria as a group will show deficits in all components of predictive control, it may be the case that individual speakers have different levels of impairment in each component. This work lays the groundwork for investigating the wide inter-speaker variability in symptoms in ataxic dysarthria, and is a critical first step towards the development of therapies that target the specific impairments that result in reduced naturalness and intelligibility in this population.