Kinematic Analysis of Lower Lip Movements in Ataxic Dysarthria

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Abstract
The present study investigates the influence of cerebellar disorders on articulatory performance. A linear trend between peak velocity and movement amplitude seems to represent a basic organizational principle both of upper limb and speech motor control. This relationship is preserved in arm movements of patients with cerebellar dysfunction. However, 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 closing gestures during production of /pap/- as well as /pa:p/-sequences—embedded into a carrier phrase each—were measured using an optoelectric system. In addition, vowel length (/a/, /a:/) was determined at the acoustic speech signal: (a) The cerebellar patients showed a prolongation of both vowel targets. Most of them, nevertheless, presented with discernible durational contrasts; (b) The articulatory gestures were characterized by a highly linear relationship between peak velocity and movement range in the cerebellar as well as in the control group; (c) As a rule, the cerebellar subjects had decreased velocity-displacement ratios as compared to the normals; (d) The discrepancy in slope of the computed regression lines between the controls and the patients varied according to the type of movement (opening vs. closing gesture) and—to a lesser degree—linguistic demands (short vs. long vowel). These data indicate an impaired ability of cerebellar patients to increase muscular forces in order to produce adequately scaled articulatory gestures of short duration.

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