Objective: Individuals with Parkinson’s disease (PD) often experience speech deficits as result of changes to the respiratory, phonatory, and articulatory subsystems. Clear speech cueing is a behavioral strategy used in speech therapy to elicit increased intelligibility. Clear speech directly targets the articulatory subsystem and has been shown to result in changes to articulatory outcomes. However, little is known about how clear speech might influence voice outcomes as a result of changes to the phonatory and respiratory subsystems. This study aimed to investigate voice outcomes of clear speech in individuals with PD.

Methods: Speakers with PD produced conversational speech and a standard reading passage in two speaking conditions: typical speech and clear speech. Four acoustic parameters were extracted: vocal intensity (dB SPL), fundamental frequency variation (fo SD; ST), cepstral peak prominence (CPP; dB), and low-to high (L/H) ratio (dB). Additionally, we are in the process of having N = 10 expert listeners complete auditory-perceptual ratings of overall severity of dysphonia. We hypothesized that voice outcomes during clear speech would be significantly different from typical speech, with increased vocal intensity, increased fo SD, increased CPP, decreased L/H ratio, and lower ratings of overall severity of dysphonia, consistently with a less hypophonic voice. We also investigated the portion of the variance in voice measures between conditions that was due to vocal intensity changes.

Results: Intensity, fo SD, and CPP were significantly increased in the clear speech condition, as compared to the typical speech condition. L/H ratio values did not differ between the clear vs. typical speech conditions. There were no interaction effects between condition and task (reading passage vs. conversational speech). Differences in intensity between conditions accounted for <1% of the variance in differences in fo SD, 47% of the variance in CPP, and 17% of the variance in L/H ratio.

Conclusion: Clear speech cueing for individuals with PD does indeed influence voice outcomes, with increases in intensity, fo variation, and CPP, compared to typical speech. Differences observed in CPP are partially, but not fully due to intensity differences. Auditory-perceptual results will be completed by the time of the conference.