Discourse in fluent aphasia and Alzheimer's disease: Linguistic and pragmatic considerations

This paper compares discourse performance across three groups, i.e., patients with mild to high-moderate aphasia (APH), mild to early-moderate stage Alzheimer's disease (AD), and normal control subjects (NC) across tasks that elicited discourse texts of varying linguistic and pragmatic difficulty using fables, single-frame pictures, and proverbs. We investigated discourse performance in terms of linguistic formulation and three pragmatic aspects including inferencing, interpreting communicative intentions, and ratio of language to information. The results revealed that the APH group received significantly lower scores than both the AD and NC groups on linguistic formulation. The patients with AD exhibited significant difficulties on the pragmatic domain of drawing inferences as compared to the APH and NC groups. For the majority of tasks, there were no significant group differences on the communicative intentions measure. However, there were significant differences on the domain of language-information balance for APH and AD groups on most tasks as compared to the NC group. The disparity in linguistic formulation and ability to draw inferences between AD and APH groups suggests that discourse differences at mild levels of impairment for these two neurological diseases are qualitatively different. Explanations for these difficulties as well as theoretical and clinical implications are delineated.