DYNAMIC ASPECTS OF LOWER LIP MOVEMENT IN PARKINSONIAN AND NEUROLOGICALLY NORMAL GERIATRIC SPEAKERS PRODUCTION OF STRESS

Lower lip+jaw movement was evaluated for parkinsonian dysarthric and a ge-matched, neurologically normal speakers during the production of al ternating stress contrasts. Discrete measures of movement, including d isplacement amplitude, peak velocity, the relation of amplitude to pea k velocity, and movement durations were compared across groups for str essed and unstressed syllables. Additionally, quantitative (parameter c and the ratio of acceleration to deceleration) and qualitative indic es of dynamic characteristics of velocity profiles for lower lip+jaw o pening and closing gestures were compared across the subject groups. W ithin the dysarthric group, the relation between each discrete and dyn amic kinematic parameter and the perceived severity of the dysarthria was investigated. The discrete measures confirmed previous findings of reduced displacement and peak velocity for the parkinsonian speakers during opening and closing gestures for both the stressed and unstress ed syllables. However, the relation between amplitude and velocity did not differ for the two subject groups for any gesture. Movement durat ions were equivalent for the two groups during the production of openi ng gestures, but were significantly shorter for the parkinsonian speak ers during closing gestures. Quantitative indices of the velocity prof iles also failed to differentiate between the subject groups or betwee n dysarthric speakers as a function of severity. By contrast, the qual itative descriptions of the velocity profiles showed between-speaker d ifferences that were more pronounced for subjects with more severe dys arthria. These qualitative differences were evident in opening gesture s toward an unstressed vowel, only.