Discriminating dysarthria type and predicting intelligibility from amplitude modulation spectra.

Subtypes of dysarthria are often described in terms of particular disruptions in speech rhythms. In an attempt to quantify these differences, the envelope modulation spectrum (EMS) was computed on sentences read by speakers with hypokinetic, hyperkinetic, ataxic, and mixed flaccid‐spastic dysarthria, and a group of normal speakers (43 speakers total). The EMS consists of the spectra of the slow‐rate (up to 10 Hz) amplitude modulations of the full signal and within seven octave bands ranging in center frequency from 125–8000 Hz. From these spectra, six variables were calculated for each band relating to the peak frequency and amplitude and the relative energy above, below, and in the region of 4 Hz. According to stepwise discriminant analysis, six of these EMS variables could correctly discriminate speaker group membership with an accuracy of 84% (better performance was obtained for distinguishing individual groups). Further, 85% of the variance in the intelligibility of the dysarthric speakers (derived from a separate set of sentences) was predictable from a subset of six of these variables. These results suggest that there are reliable perturbations of speech temporal patterns associated with dysarthria subtypes and that these perturbations play an important role in intelligibility. [Work supported by NIH‐NIDCD.]