Coordination and timing of speech gestures in Parkinson’s disease
Many individuals with Parkinson's disease (PD) experience articulatory difficulties, which often have a considerable impact on their quality of life. It is currently poorly understood which mechanisms underlie these articulatory difficulties. In order to learn more about these mechanisms, this dissertation examined the coordination and timing of speech gestures in PD speech. Both these aspects are intrinsic to articulation, but at current it is unknown how they relate to the articulatory difficulties observed in PD speech. The studies in this dissertation address this issue using state-of-the-art methods. In the first study of this thesis, the effect of levodopa on vowel articulation in PD was examined. The results from this study suggest that articulation of vowels is not influenced by levodopa. In the following two studies, spatial and temporal aspects of speech gestures have been examined. The results from these studies suggest that the timing of speech gestures, and also the coupling between speech gestures is impaired in PD. In the final study of this dissertation, the prevalence and nature of tongue tremor in individuals with PD were investigated. Using a computer algorithm, we found different types of tongue tremor in our data, which we believe may affect the timing of speech gestures. Together, the studies in this dissertation show that coordination and timing are indeed impaired in the speech of (at least some) individuals with PD. We believe that this impairment may be caused by the presence of malfunctioning regulatory mechanisms in PD speech.