Articulatory Correlates of Stress Pattern Disturbances in Talkers with Dysarthria

Purpose: Reduced stress commonly occurs in talkers with Parkinson's disease (PD), whereas excessive and equal stress is frequently associated with dysarthria of talkers with amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS). This study sought to identify articulatory impairment patterns that underlie these two impaired stress patterns. We further aimed to determine if talkers with the same stress pattern disturbance but different diseases (ALS and MS) exhibit disease-specific articulatory deficits. Method: Fifty-seven talkers participated in the study--33 talkers with dysarthria and 24 controls. Talkers with dysarthria were grouped based on their medical diagnosis: PD (n = 15), ALS (n = 10), MS (n = 8). Participants repeated target words embedded in a carrier phrase. Kinematic data were recorded using electromagnetic articulography. Duration, displacement, peak speed, stiffness, time-to-peak speed, and parameter c were extracted for the initial lower lip opening stroke of each target word, which was either stressed or unstressed. Results: Stress effects were significant for all kinematic measures across groups except for stiffness and time-to-peak speed, which were nonsignificant in ALS. For comparisons with controls, more kinematic measures significantly differed in the ALS group than in the PD and MS groups. Additionally, ALS and MS showed mostly similar articulatory impairment patterns. Conclusions: In general, significant stress effects were observed in talkers with dysarthria. However, stress-specific between-group differences in articulatory performance, particularly displacement, may explain the perceptual impression of disturbed stress patterns. Furthermore, similar findings for ALS and MS suggest that articulatory deficits underlying similar stress pattern disturbances are not disease-specific.