Articulatory motor performance as a function of phonetic complexity in Parkinson's disease
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Purpose: This study sought to determine the feasibility of phonetic complexity manipulations to improve the detection of articulatory deficits in talkers with progressive dysarthria due to Parkinson's disease (PD). Methods: Articulatory kinematics were recorded using 3D electromagnetic articulography from 15 talkers with PD (58-84 years) and 15 healthy controls (55-80 years) while they produced target words embedded in a carrier phrase. Majority of the talkers with PD exhibited a mild dysarthria. For stimuli selection, phonetic complexity was calculated for a variety of words using the framework proposed by Kent (1992) and representative stimuli for low, medium, and high phonetic complexity levels were selected. Jaw, tongue back, and tongue tip kinematic measures that were used to test for phonetic complexity effects included movement speed, cumulative path distance, range of motion, movement duration, and spatiotemporal variability. Results: Significantly smaller movements and slower movement speeds were evident in talkers with PD, predominantly for words with high phonetic complexity. Additionally, the effect sizes of between-group differences were larger for several jaw kinematic measures compared to those of the tongue. Discussion and Conclusion: Findings suggest that systematic manipulations of phonetic complexity can support the detection of articulatory deficits during the early stages of dysarthria in talkers with PD. Phonetic complexity should therefore be leveraged for the assessment of articulatory performance in talkers with progressive dysarthria. Future work will be directed towards linking speech kinematic and perceptual findings to determine the clinical significance of the current kinematic results.