Relations between formant slopes and speech intelligibility in neurologically impaired talkers

Abstract

The relation between F1 and F2 slopes measured from monosyllabic words and speech intelligibility scores for these words was studied for 25 men with amyotrophic lateral sclerosis. The formant slopes were estimated from digitized formant tracks for each test word. The intelligibility scores were computed as the percentage of words correctly identified for each talker by a listener panel of ten young women. The intelligibility scores for the group of 25 talkers ranged from 41%–99%. The correlation coefficient computed between the F2 slopes and the intelligibility scores was 0.76. The F1 slope was not as predictive of intelligibility, perhaps because the dysarthric talkers compensated for impaired tongue control with large jaw movcmcnta (and, hence, large F1 shifts). It is concluded that F2 slope, a dynamic measure of acoustic structure, bears a moderately high correlation with intelligibility in these subjects. Examples of formant patterns are shown for different degrees of speech impairment. [Work supported, in part, by NINCDS.]