Long term average spectral moments in hypokinetic dysarthria

By C. Dromey

The present study arose out of the observation that while a group of individuals with PD sounded impaired compared to controls, the acoustic measures that were presumed to most clearly reflect the perceptual deficits failed to differentiate the groups. Participants were ten men with PD and ten controls. Speakers produced vowels at a comfortable effort level, read a passage and spoke a monologue. Acoustic measures were made of intensity, fundamental frequency variability and vowel perturbation. Additionally, statistical moments from the long term average spectrum (LTAS) were calculated. Reduced loudness and monotone speech patterns have been identified as hallmarks of hypokinetic dysarthria, yet their acoustic correlates (mean SPL and F₀ variability) did not differentiate between the groups in speech. However, the spectral moment variables discriminated clearly between them. For both reading and monologue tasks, the spectral moment measures from the LTAS analysis significantly differed between groups. Vowel phonation SPL was higher for the controls than for the patient group. The perturbation measures did not differ between groups. The LTAS spectral mean was lower and the skewness and kurtosis were higher for the dysarthric speakers. LTAS moments may provide a useful index of speech impairment in speakers with PD.