L-Dopa is the most common and most effective treatment for the symptoms of Parkinson's Disease (PD). After prolonged treatment with L-Dopa, patients experience fluctuations in motor performance. Changes in speech production have been documented perceptually during periods of fluctuation, however few quantitative speech changes have been found. The purpose of this study was to examine the acoustic speech characteristics and speech intelligibility of PD subjects before and after taking medication, to determine whether L-Dopa related fluctuations affected speech production. Based on the group statistical and individual descriptive analyses performed in the present study, it can be concluded that, because of heterogeneity of the PD population, descriptive analysis is the preferable method for examining the speech of individuals with PD. Descriptive analyses from the present study revealed that PD subjects were impaired compared to control subjects in speech measures related to phonation, articulation, and prosody. Following administration of L-Dopa, quantitative speech improvements were seen in PD subjects. In some individual subjects, results were indicative of reduced laryngeal rigidity, increased laryngeal stability, and decreased labial rigidity/bradykinesia. The greatest L-Dopa related speech improvements were found for percent pause time during reading. There were group differences in percent pause time across the medication cycle, indicating that subjects exhibited decreased akinesia or improved respiratory function following the administration of L-Dopa. Overall, it can be concluded that some quantitative speech fluctuations do occur across the medication cycle for PD subjects. While these fluctuations are not as pervasive as motor fluctuations, their presence is confirmed by the present investigation
