Acoustic and perceptual correlates of faster-than-habitual speech produced by speakers with Parkinson's disease and multiple sclerosis

Acoustic-perceptual characteristics of a faster-than-habitual rate (Fast condition) were examined for speakers with Parkinson's disease (PD) and multiple sclerosis (MS). Judgments of intelligibility for sentences produced at a habitual rate (Habitual condition) and at a faster-than-habitual rate (Fast condition) by 46 speakers with PD or MS as well as a group of 32 healthy speakers revealed that the Fast condition was, on average, associated with decreased intelligibility. However, some speakers’ intelligibility did not decline. To further understand the acoustic characteristics of varied intelligibility in the Fast condition for speakers with dysarthria, a subgroup of speakers with PD or MS whose intelligibility did not decline in the Fast condition (no decline group, n=8) and a subgroup of speakers with significantly declined intelligibility (decline group, n=8) were compared. Acoustic measures of global speech timing, suprasegmental characteristics, and utterance-level segmental characteristics for vocalics were examined for the two subgroups. Results suggest acoustic contributions to intelligibility under rate modulation are complex. Potential clinical relevance and implications for the acoustic bases of intelligibility are discussed.Learning outcomes: Readers will be able to (1) discuss existing evidence for the use of rate change to facilitate intelligibility, (2) describe acoustic-perceptual characteristics of a faster-than-habitual rate among speakers with mild dysarthria, (3) discuss the relationships between rate, intelligibility, suprasegmental variables, and segmental variables, (4) identify the need to further investigate the acoustic basis for intelligibility and its potential theoretical and clinical implications.