Following recent attempts to quantify articulatory impairment in speech, we evaluate the usefulness of a novel measure of motor stability to characterise dysarthria. We investigated 8 speakers with ataxic dysarthria (AD), 16 speakers with hypokinetic dysarthria (HD) as a result of Parkinson's Disease and 24 unimpaired control participants. Each participant performed a series of sentence repetitions under habitual, fast and slow speaking rate conditions. We used an algorithm to measure utterance-to-utterance spectro-temporal variation (UUV; Cummins, 2009). Speech rate and intelligibility were also measured. UUV scores were significantly correlated with perceptually based intelligibility scores. There were significant differences in UUV between control speakers and the ataxic, but not the HD groups, presumably due to differences in intelligibility in the samples employed, and not to differences in pathology. Habitual speaking rate did not correlate with UUV scores. All speaker groups had greater UUV levels in the slow conditions compared to habitual and fast speaking rates. UUV results are consistent with those of other variability indices and thus appear to capture motor control issues in a similar way. The results suggest that the UUV could be developed into an easy to use clinical tool that could function as a valid and reliable assessment and outcome measure.
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