| Popis: |
Disfluencies are a commonly reported speech symptom associated with Parkinson disease (PD), though the cause remains unknown. Studies have consistently reported that people with PD experience more disfluencies, particularly atypical disfluencies compared to healthy controls. One proposed theory, known as the dualistic model of dopamine levels and stuttering, posits that abnormally high or low levels of dopamine may cause an increase in disfluencies. The aim of the current study is to examine how levodopa medication and deep-brain stimulation affect fluency in people with PD. Twenty-seven participants with PD underwent testing before (on and off medicine) and six months after deep-brain stimulator implant surgery (optimally medicated, on and off stimulation). Participants read a passage aloud and provided a 2-minute monologue. Speech samples were transcribed. The number of typical and atypical disfluencies were identified auditorily and using a wide-band spectrogram. After surgery, most participants reduced their levodopa equivalency dose from pre-implant levels. Results demonstrated no significant differences in frequency of disfluencies across time (pre-surgery, post-surgery) or condition (on/off medication/stimulation). Overall, participants produced more typical than atypical disfluencies and more disfluencies in the monologue task than the reading task. Results do not support the dualistic model of dopamine, but instead support a more nuanced and individualized role for dopamine in speech fluency. For example, patterns within individual subjects suggest changes in dopamine may play a role in speech fluency for individual patients with PD. Data support the effect of cognition and language formulation in the production of disfluencies, particularly typical disfluencies. |
