Project Summary: Over 90% of individuals with Parkinson's disease (PD) suffer from speech problems characterized by impairments of voice and articulation, collectively termed “hypokinetic dysarthria”. These symptoms degrade speakers' functional communication through decreases in both naturalness and intelligibility. However, little is known about the relationship between these functional communication outcomes and their underlying neural sensorimotor bases. While previous work has evaluated disparate aspects of speech motor control in modest cohorts, the result thus far is a patchwork of seemingly conflicting information. To address this gap, this project will comprehensively examine the sensorimotor control of speech in PD in a single cohort, utilizing the DIVA model [34] as a theoretical framework to guide hypothesis development and allow for mechanistic interpretations of experimental findings. Feedback and feedforward mechanisms of speech motor control affecting both voice (larynx) and articulation (vocal tract) will be evaluated in 40 individuals with PD and 40 matched control speakers using behavioral and neural responses to perturbations in somatosensory and auditory feedback. Our primary hypotheses are that PD involves weaker-than-normal feedforward commands, leading to increased reliance on feedback control, as well as an impaired ability to update feedforward commands based on discrepancies between desired and actual movement outcomes. Comprehensive sensorimotor control parameters from each participant will be compared with their intelligibility and naturalness, determined through rigorous auditory- perceptual experiments. Identification of the specific sensorimotor bases of speech symptoms in PD are essential to guide the development of new therapeutic targets to improve communication. For instance, although speech therapy is the only current treatment, only 13% of patients with PD choose to pursue it, likely due to its low long-term effectiveness. Given the relatively slow progression of PD and the increased incidence of speech symptoms with disease progression, developing effective speech treatments is imperative for maintaining quality of life. This project will result in specific physiological markers that are linked to functional communication outcomes in PD and can act as critical targets for behavioral and surgical interventions. This will lead to new treatments that are specific, effective, and tied to functional communication outcomes.