Contributions of Speech Timing and Articulatory Precision to Listener Perceptions of Intelligibility and Naturalness in Parkinson's Disease

Purpose: Parkinson's disease (PD) results in hypokinetic dysarthria in as many as 90% of cases. Among the most distinctive features of hypokinetic dysarthria are atypical timing and articulatory imprecision in speech production. Here, we examined the contributions of perceived speech timing typicality and articulatory precision, both on their own and while controlling for the other, on intelligibility and naturalness in speakers with PD. Method: Twenty speakers with PD and four healthy older adults read aloud the first paragraph of the Rainbow Passage. Twenty inexperienced listeners with typical hearing listened to these recordings and rated intelligibility, naturalness, timing typicality, and articulatory precision using separate visual analog scales. Ratings were averaged across listeners and entered into linear regression models with intelligibility and naturalness as dependent variables and timing typicality and articulatory precision as independent variables in each. Results: Articulatory precision, but not timing typicality, was positively correlated with intelligibility on its own, but neither was associated with intelligibility after accounting for the other. Both timing typicality and articulatory precision were positively correlated with naturalness on their own as well as after controlling for the other variable. Conclusion: These results contribute to the overall understanding of speech factors associated with intelligibility and naturalness in speakers with PD and indicate that considering the unique contributions of related perceptual constructs may provide more information than bivariate relationships alone.