Acoustic analysis of lexical tone contrasts in dysarthria

Abstract

The aim of this study was to investigate lexical tone production in adults with dysarthria and control speakers without neurologic impairment, using acoustic analysis. The speakers with dysarthria included 19 Cantonese-speaking adults with cerebral palsy. The speech material consisted of 12 single words that provided contrasts between high level, mid level, and low level tones. Fundamental frequency (f0) was measured at the beginning, middle, and end of each vowel. The speakers with dysarthria had significantly higher mean f0s than the control speakers for high, mid, and low level tones, except for females during high tone productions, where the difference was not significant. The speakers with dysarthria had significantly larger variability than the control speakers. Only four of the 19 speakers with dysarthria had contrastive systems for the three level tones. Abnormal f0 patterns in the speakers with dysarthria included: 1) excessive variability, 2) excessively falling frequencies, 3) lowering of the high level tone, 4) rising tones, and 5) abnormal contour patterns. The results of the acoustic analysis supported previous perceptual findings of difficulty in tone level contrasts for Cantonese speakers with dysarthria.