Amplitude Distribution Characteristics of the Tongue, Lower Lip, and Jaw in Talkers With Dysarthria Due to Parkinson’s Disease

Purpose: This study sought to provide comprehensive insights into the size of articulatory movements (stroke amplitudes) in talkers with Parkinson’s disease (PD) and determine the extent to which hypokinesia is related to perceived artic-ulatory subsystem impairment severity. Method: Forty talkers with PD and 40 controls participated. Perceptual ratings of the articulatory and phonatory subsystem impairment severity were obtained for all talkers with PD. On the basis of these ratings, the PD group was divided into talkers with and without an articulatory impairment (18 PDdys+artic, 22 PDdys−artic). Jaw, lower lip, anterior tongue, and posterior tongue movements were recorded during a paragraph reading task using three-dimensional electro-magnetic articulography. Stroke amplitudes of all opening and closing movements were measured for each articulator, and frequency distributions across seven or 12 amplitude levels were established for the jaw and lower lip/tongue, respectively. To determine hypokinesia, stroke counts were compared among the two PD sub-groups and controls at each amplitude level for each articulator. Articulatory impairment severity ratings of the PDdys+artic subgroup were correlated with the stroke counts at higher amplitude levels. Results: Group × Amplitude Level interactions were significant for all articula-tors. Post hoc pairwise comparisons revealed that the PDdys+artic subgroup produced significantly more tongue and lower lip strokes with small amplitudes and significantly less tongue and lower lip strokes with large amplitudes than controls, at times also the PDdys−artic subgroup. At a higher amplitude level, the PDdys−artic subgroup produced significantly less posterior tongue strokes than controls. However, post hoc group comparisons for jaw strokes were non-significant at all amplitude levels. Significant inverse correlations were found between tongue stroke counts and articulatory impairment severity ratings. Conclusions: Findings suggest that hypokinesia manifests in the tongue and lip more so than in the jaw. Only hypokinesia of the tongue may be reflected in severity ratings of articulatory subsystem impairment.