Project Summary Approximately 90% of individuals with Parkinson's disease (PD) experience speech symptoms that can drastically reduce quality of life, as well as the ability to maintain effective communication abilities. Therefore, these speech changes in PD are vital to understand and address. Yet the associations between the progression of PD (years since diagnosis), specific motor impairments, and the development of specific speech difficulties are not well understood. The progression of PD does not appear to correlate with speech symptom severity: overall motor severity via clinical assessments and the years since PD diagnosis are not always associated with a decline in functional speech outcomes (i.e., speech intelligibility and naturalness) or acoustic measures of speech. In particular, the association appears to differ by speech subsystem: articulatory features of speech relate to the progression of PD, whereas measures of voice do not. However, it is not clear if these findings are due to different underlying causes or because of high individual variability in PD motor symptoms. In fact, recent work suggests that there are two distinct motor phenotypes of PD: postural insufficiency and gait dominant (PIGD) and tremor dominant (TD). A higher incidence of communication difficulties and worse speech scores are found in speakers with PIGD compared to TD, which may be a result of increased laryngeal muscle rigidity. Thus, it is critical to understand how speech symptoms progress within an individual by speech subsystem, and moreover, how speech changes relate to specific motor symptoms in PD. Functional speech outcomes may also show differences across PD phenotype since speech intelligibility and naturalness are affected by articulatory precision and voice quality. No studies have yet completed a robust acoustic characterization of speech changes and measures of functional speech outcomes within the same speakers with PD over time. Therefore, this proposal will comprehensively examine how longitudinal changes in acoustic features of speech production relate to motor phenotype and functional speech outcomes of speech intelligibility and naturalness in the same speakers with PD. Speech data will be collected in 44 speakers with PD (with an even PIGD-to-TD motor- phenotype ratio) at two time points, leveraging a previous database as the first time point. Aim 1 will evaluate longitudinal changes in acoustic measures of articulation and voice to provide insight into how different speech impairments progress in within speakers with PD over time by motor phenotype. Aim 2 will determine how longitudinal changes in acoustic measures of speech are related to functional speech outcomes in PD. The results of Aim 2 will elucidate which specific acoustic measures are tied to functional speech outcomes in PD and enhance the ability to objectively track the most critical features of communication in PD. This work will clarify the relationship between PD motor...