Long-term phonatory instability in ataxic dysarthria

Long-term phonatory instability can be quantified using cyclical and noncyclical measures. The objective of this study is to evaluate phonation in ataxic dysarthria and a control group of normal speakers to answer two main questions: (1) How common is elevated cyclical and noncyclical instability in ataxic dysarthria compared to that in a normal control group? (2) Is cyclical instability predictive of noncyclical instability?

Vowel prolongations of ataxic-dysarthric and normal speakers were compared using the Motor Speech Profile module of the Computerized Speech Lab. Cyclical measures included tremor rate, amplitude and periodicity. Noncyclical measures included the coefficient of variation for loudness and frequency.

Noncyclical measures are elevated in a subset of speakers with ataxic dysarthria regardless of whether cyclical instability (vocal tremor) is present. Cyclical instability was detected in nearly half the patients. Interestingly, elevations in both types of measures also described phonation of a number of the participants in the control group.

Combined use of cyclical and noncyclical measures can document aspects of phonation in ataxic dysarthria that have clinical implications.