Temporal Aspects of Global Coherence during Discourse Production in Early Stage Parkinson’s Disease

Introduction: Parkinson’s Disease (PD) is a devastating neurodegenerative disease that significantly influences motor performance. Recent studies suggest expressive language deficits may also exist among individuals with PD even though the condition is primarily known for changes in motor skills. The purpose of this pilot study was to examine the influence of early stage PD on global coherence or the ability to maintain consistency of a theme or topic. Methods: Discourse samples were collected from eleven individuals with PD and compared to eleven matched controls to examine measures of global coherence. Two-minute speech samples describing a “typical day” were transcribed and rated on mean global coherence and percentage high global coherence. Results: Greater declines in global coherence were observed among individuals with PD, however, comparisons of both mean global coherence ratings and percentage high global coherence were not statistically significant between the two groups. A significant downward linear trend was observed for both mean global coherence ratings and percentage high coherence among all participants indicating decreases in global coherence over time. Conclusion: Approaches to the study of global coherence as a measure of expressive language performance should consider the temporal changes especially among neurological conditions known to reduce expressive language ability.