Intelligibility as a linear combination of dimensions in dysarthric speech

Speech samples of 79 dysarthric patients (native speakers of English) were judged by two experienced judges by means of a perceptual rating scale covering the four main dimensions of speech production: voice quality, articulation, nasality and prosody as well as overall intelligibility. In order to determine the relative influence of the four basic dimensions on intelligibility in this study group, a multiple regression model was applied. This model shows that intelligibility can be expressed as a linear combination of weighted perceptual dimensions (R2 = 0.89). This expression reveals the relative importance of the individual dimensions on overall intelligibility. Articulation is shown to be the strongest contributor to intelligibility. A group of 16 dysarthric patients (native speakers of Dutch) was used as a control group in order to evaluate the validity of the expression. Judged and calculated ratings (within the 95% prediction intervals) were in agreement for 75% of the patients. These findings may contribute in the construction of a better balanced measure of functional intelligibility.

2. The impact of articulation on intelligibility is dominant but inclusion of the dimensions "nasality", "voice" and "prosody" results in a more balanced estimation of intelligibility.