Long-Term Average Spectral (LTAS) Measures of Dysarthria and Their Relationship to Perceived Severity.

This study investigated the relationship between measures of Long-Term Average Spectrum (LTAS) for speakers with Parkinson's disease (PD) and Multiple Sclerosis (MS) and scaled estimates of perceived speech severity. Perceived severity was operationally defined as listeners' overall impression of voice, resonance, articulatory precision, and prosody without regard to intelligibility. Healthy control talkers were also studied. Speakers were audio recorded while reading Harvard Sentences and the Grandfather Passage. Using TF32 (Milenkovic, 2005), the LTAS was computed for sentences. Coefficients of the first four moments were used to characterize energy across the speech spectrum. Supplemental acoustic measures of articulatory rate, vocal intensity, and fundamental frequency also were obtained. Three speech-language pathologists scaled speech severity for the reading passages. Results indicated no group differences in acoustic measures. The absolute magnitude of correlations between LTAS moment coefficients and perceptual estimates of scaled severity within and across speaker groups ranged from .16 to .53, with the strongest correlations for the PD group. These results suggest that the LTAS may prove useful in conjunction with perceptual judgments to document speech spectral changes related to treatment or disease progression. Findings further suggest that different acoustic models of severity are likely needed for dysarthria secondary to PD and dysarthria secondary to MS.