Speech-muscle visuomotor tracking in dysarthric and nonimpaired speakers.

Assessment of speech-muscle function during nonspeech tasks may provide an important component in the clinical evaluation of speech-motor disorders. Various methodological problems have limited the value of such data in the past. The goal of the present study was to evaluate a set of instrumental, objective procedures for assessment of the nonspeech performance capabilities of different speech-muscle systems. Subjects included 10 nonimpaired adults and a diverse group of 6 adult dysarthric individuals. Each subject performed visuomotor tracking of a 0.6-Hz sinusoidal target with the lower lip, jaw, larynx, and respiratory systems. Cross correlation and phase data were used to describe tracking performance. The nonimpaired subjects showed consistently high cross correlations with little phase shift. The dysarthric subjects showed a wide range of tracking performance which was generally consistent with their overall levels of speech performance and levels of neurological impairment. Differential levels of performance were noted across speech subsystems in some dysarthric subjects. In general, the results suggest that visuomotor-tracking paradigms provide a viable approach to clinical evaluation of speech-muscle function in nonspeech tasks.