Changes to articulatory kinematics in response to loudness cues in individuals with Parkinson's disease.

PURPOSE: Individuals with Parkinson's disease (PD) exhibit differences in displacement and velocity of the articulators as compared with older adults. The purpose of the current study was to examine effects of 3 loudness cues on articulatory movement patterns in individuals with PD. METHOD: Nine individuals diagnosed with idiopathic PD and 9 age- and sex-matched healthy controls produced sentences in 4 conditions: (a) comfortable loudness, (b) targeting 10 dB above comfortable, (c) twice as loud as comfortable, and (d) in background noise. Lip and jaw kinematics and acoustic measurements were obtained. RESULTS: Both groups significantly increased sound pressure level (SPL) in the loud conditions as compared with the comfortable condition. For the loud conditions, both groups had the highest SPL in the background noise and the 10 dB conditions, and the lowest SPL in the twice as loud condition. Control participants produced the largest opening displacement in the background noise condition and the smallest opening displacement in the twice as loud condition. Conversely, individuals with PD produced the largest opening displacement in the twice as loud condition and the smallest opening displacement in the background noise condition. CONCLUSIONS: Control participants and individuals with PD responded to cues to increase loudness in different ways. Changes in SPL may explain differences in kinematics for the control participants, but they do not explain such differences for individuals with PD.