Objective: To evaluate the effects of self-speech as an internal cue on reaching performance in people with Parkinson's disease.
Subjects: Eight people with Parkinson's disease were voluntarily recruited from the upstate New York community.
Design and setting: This study was a repeated measure analysis of reaching performance under four randomized counterbalanced vocalization (speech) conditions that include a no vocalization control condition. The study was conducted in a university-based motion analysis laboratory. Participants performed a simple sequential daily reaching performance of reaching for a bottle, grasping and placing it on a simulated cabinet. Under counterbalanced randomized conditions, before each performance, participants either self-vocalized the word 'yaah' (self-cue), listened to the word 'yaah' vocalized by the experimenter (external cue), imagined vocalizing the word 'yaah', or just simply performed the task without any vocalization (control - no vocalization).
Main measures: The following dependent kinematic measures were extracted from the movement: total movement time, total movement unit, peak velocities and durations of reaching and placing segments.
Results: People with Parkinson's disease took significantly shorter time under self-vocalization conditions (2390.00 (326.63) ms) compared with the other three conditions including control - no vocalization conditions (no_voc, 3015.66 (340.83) ms; ext_voc, 2853.12 (376.44) ms; imaginary-voc, 3000.37 (320.54) ms). Under self-vocalization conditions the movements were also significantly smoother as evidenced by significantly lower numbers of movement units (3.43 (0.41)) compared with the other three conditions (no_voc, 4.47 (0.57); ext_voc, 4.16 (0.51); imaginary-voc, 4.16 (0.55)).
Conclusions: Self-vocalization of a positive reinforcing word enabled people with Parkinson's disease to perform a daily upper extremity task faster and more smoothly.