Articulatory movements during vowels in speakers with dysarthria and healthy controls

Purpose: This study compared movement characteristics of markers attached to the jaw, lower lip, tongue blade, and dorsum during production of selected English vowels by normal speakers and speakers with dysarthria due to amyotrophic lateral sclerosis (ALS) or Parkinson disease (PD). The study asked the following questions: (a) Are movement measures different for healthy controls and speakers with ALS or PD, and (b) Are articulatory profiles comparable for speakers with ALS and speakers with PD? Method: Nineteen healthy controls and 15 speakers with dysarthria participated in this study. The severity of dysarthria varied across individuals and between the 2 disorder groups. The stimuli were 10 words (i.e., seed, feed, big, dish, too, shoo, bad, cat, box, and dog) embedded into sentences read at a comfortable reading rate. Movement data were collected using the X-ray microbeam. Movement measures included distances, durations, and average speeds of vowel-related movement strokes. Results: Differences were found (a) between speakers with ALS and healthy controls and (b) between speakers with ALS and PD, particularly in movement speed. Tongue movements in PD and ALS were more consistently different from healthy controls than jaw and lower lip movements. This study showed that the effects of neurologic disease on vowel production are often articulator-, vowel-, and context-specific. Conclusions: Differences in severity between the speakers with PD and ALS may have accounted for some of the differences in movement characteristics between the groups. These factors need to be carefully considered when describing the nature of speech disorder and developing empirically based evaluation and treatment strategies for dysarthria.