Statistical models of F2 slope in relation to severity of dysarthria

This study investigated the distribution of second-formant (F2) slopes in a relatively large number of speakers with dysarthria associated with two different underlying diseases.

Forty speakers with dysarthria (20 with Parkinson's disease, PD; 20 with stroke) and 5 control speakers without a history of neurological disease were asked to repeat six words (coat, hail, sigh, shoot, row and wax) 10 times. Acoustic analysis was performed to derive F2 slope, and speech intelligibility data were collected using a direct magnitude estimate technique to examine its relationship to F2 slope.

Statistical analysis revealed that both clinical groups showed significantly reduced F2 slopes compared to healthy speakers for all words but row. No group difference was found between speakers with PD and stroke; however, different words showed varying sensitivity to the speech motor control problems. The F2 slopes of only two words, shoot and wax, were significantly correlated with scaled speech intelligibility.

The findings support the idea that distributional characteristics of acoustic variables, such as F2 slope, could be used to develop a quantitative metric of severity of speech motor control deficits in dysarthria, when the materials are appropriately selected and additional distributional characteristics are studied.