KINEMATIC ANALYSIS OF LOWER LIP MOVEMENTS IN ATAXIC DYSARTHRIA

The present study investigates the influence of cerebellar:disorders o n articulatory performance. A linear trend between peak velocity and m ovement amplitude seems to represent a basic organizational principle both of upper limb and speech motor control. This relationship is pres erved in arm movements of patients with cerebellar dysfunction. Howeve r, these subjects show a decreased slope of the respective regression lines under the instruction to perform movements as fast as possible. In order to find out whether these findings also hold for speech motor control, peak velocity, range, and duration both of the opening and c losing gestures during production of /pap/- as well as /pa:p/-sequence s-embedded into a carrier phrase each-were measured using an optoelect ric system. In addition, vowel length (/a/, /a:/) was determined at th e acoustic speech signal: (a) The cerebellar patients showed a prolong ation of both vowel targets. Most of them, nevertheless, presented wit h discernible durational contrasts; (b) The articulatory gestures were characterized by a highly linear relationship between peak velocity a nd movement range in the cerebellar as well as in the control group; ( c) As a rule, the cerebellar subjects had decreased velocity-displacem ent ratios as compared to the normals; (d) The discrepancy in slope of the computed regression lines between the controls and the patients v aried according to the type of movement (opening vs. closing gesture) and-to a lesser degree-linguistic demands (short vs, long vowel). Thes e data indicate an impaired ability of cerebellar patients to increase muscular forces iri order to produce adequately scaled articulatory g estures of short duration.