In the context of speech-language therapy, Parkinson's disease (PD) is typically associated with its consequences on speech production. Interventions generally focus on learning or relearning skills to accomplish successful production. However, the disease itself, as well as patient responses to interventions, are variable. Individuals differ widely in how typical their speech output is before intervention and in how much they learn from treatment. One plausible explanation for this variation comes from a less-studied aspect of speech and language in PD: speech perception, especially speech perceptual learning. There is a key gap in the PD literature about whether people who produce atypical rate and intensity properties in their own speech also find it more difficult to learn rate and intensity properties from others' speech. There is, therefore, a critical need for a full understanding of the relationship between speech production and speech perceptual learning in PD. The long- term goal of this research program is to systematically interrogate the relationship between speech learning and production in people with PD and to leverage that knowledge to promote effective communication. The overall objective of this project is to use acoustic measures to determine how challenges with speech perception or learning can predict individual differences in speech production. The central hypothesis is that individual differences between people with PD in speech perception or learning can predict individual differences between people with PD in speech production. This project adopts an individual differences approach to investigate two major aims: (1) relating individual differences in the perceptual learning of speech rate to the production of speech rate, and (2) relating individual differences in the perceptual learning of intensity to the production of intensity. To investigate these aims, each participant will record a speech sample and conduct tasks that involve learning regularities in rate or intensity in the speech of others. Participants will also complete tasks that require the ability to distinguish between sentences based on their rate and intensity. Participants' speech samples will additionally be judged by naive listeners to assess the samples' intelligibility and the effort that it takes to understand the speakers. If individual differences in perceptual learning predict individual differences in production, then differences in speech perception may predict differences in speech-language therapy outcomes that could be targeted to patient needs. A precision medicine approach would allow for interventions that titrate the amount, level, and type of intervention on an individualized basis to make sure that treatments are focused on participants who will respond to them in dosages that they will benefit from. For instance, a therapist could provide speech perception training to accelerate outcomes of production-related treatments. Furthermore, by applying more naturalistic measures of speech perception to this population, especially ones that rely on participants to change over the course of a session, this project provides an innovative opportunity to examine the sensory and perceptual consequences of PD and to link those to better-documented motor outcomes
