Interarticulator coordination in dysarthria: an X-ray microbeam study

Articulatory discoordination is often said to be an important feature of the speech production disorder in dysarthria, but little experimental work has been done to identify and specify the coordination difficulties. The present study evaluated the coordination of labial and lingual gestures for /u/ production in persons with Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and in control participants. Both tongue backing/raising and reduction of the area enclosed by the lips can produce the characteristic low F2 of /u/. The timing of these articulatory gestures with respect to the acoustic target of a low F2 was inferred from X-ray microbeam data. Pellet motions of the tongue dorsum and lips revealed the timing of the lingual and labial gestures to be strongly linked together (synchronized), predictive of the temporal location of the lowest F2 within the vocalic nucleus, and scaled proportionately to the overall vowel duration in control participants. Somewhat surprisingly, essentially the same findings were obtained in the speakers with dysarthria. These relationships were noisier among the speakers with dysarthria, but the global synchronization patterns applied to all 3 groups. Further analyses revealed the synchronization to be less well defined and more variable across speakers with ALS, as compared to speakers with PD and the controls. Results are discussed relative to concepts of coordination in dysarthria.