Rhetorical structure and Alzheimer's disease

Background: Language is one of the first faculties afflicted by Alzheimer's disease (AD). A growing body of work has focussed on leveraging automated analysis of speech to accurately predict the onset of AD. Previous work, however, did not address the effects of AD on the structure of discourse in spontaneous speech and literature. Aims: Our goal is to identify the effects of AD on the structure of discourse, both in spontaneous speech and in literature. Methods & Procedures: We use two existing data sets, DementiaBank and the Carolina Conversations Collection, to explore how AD manifests itself in spontaneous speech. This is done by automatically extracting discourse relations according to Rhetorical Structure Theory. We also study written novels, comparing authors with and without dementia using the same tools. Outcomes & Results: Several discourse relations, especially those involving elaboration and attribution, are significant indicators of AD in speech. Indicators of the disease in written text, by contrast, involve relations of logical contingency. Conclusions: Our work highlights how AD can alter discourse structures in both spontaneous speech and written text. Future work should combine discourse analysis with previously studied lexico-syntactic features.