Differential effects of increased loudness on tongue kinematics in individuals with PD? Analyses of two cases

Previous studies have suggested significant variation in the perceptual speech deficit displayed by individuals with Parkinson's disease (PD). This heterogeneity is partly attributed to differential changes in the underlying articulatory kinematics across speakers. Loudness-based treatment has been frequently used in individuals with PD. An improved understanding of individual differences and the effects of loudness on tongue movement in individuals with PD may help optimize speech intervention. The present study aimed to (1) examine individual differences in tongue kinematics during habitual and loud sentence production in two dysarthric speakers with PD, and (2) examine the effect of loudness manipulations on tongue kinematics during sentence production within each dysarthric speaker with PD. Electromagnetic articulography was used to record tongue tip movement during habitual and loud sentence productions in two participants with PD. Their performance was first matched with the performance of an age and gender-matched healthy individual. Subsequently, a within-participant comparison between habitual and loud sentence production was carried out to examine the effect of increased loudness. When compared with an age and gender-matched healthy control, both PD individuals showed greater tongue kinematic parameters during habitual and loud sentence productions. Subsequently, a within-participant comparison showed that, from habitual to loud speech, one PD speaker increased distance and maximum velocity of tongue movement while the other reduced maximum acceleration of tongue movement. The observed individual differences in tongue kinematics may be predictive of the efficacy of loudness-based treatments for articulatory and consequent perceptual improvements for individual participants