Abstract
Purpose Discourse analysis is commonly used to assess language ability and to evaluate language change following intervention in aphasia. The purpose of this study was to identify differences in language produced during different discourse tasks in a large aphasia group and an age- and education-matched control group. Method Four structured discourse tasks across 3 discourse types (expositional, narrative, and procedural) were evaluated in a group of adults with aphasia (n = 90) and an age-matched control group (n = 84) drawn from AphasiaBank. CLAN software was used to extract primary linguistic variables (mean length of utterance, propositional density, type-token ratio, words per minute, open-closed class word ratio, noun-verb ratio, and tokens), which served as proxies for various language abilities. Using a series of repeated-measures analyses of covariance, with significantly correlated demographic and descriptive variables as covariates, main effects of discourse type were evaluated. Results Despite an impoverished output from the aphasia group (i.e., the control group produced significantly more overall output), there was a main effect of discourse type on most primary linguistic variables in both groups, suggesting that, in adults with and without language impairments, each discourse type taxed components of the spoken language system to varying extents. Post hoc tests fleshed out these results, demonstrating that, for example, narrative discourse produced speech highest in propositional density. Conclusion Each discourse type taxes the language system in different ways, verifying the importance of using several discourse tasks and selecting the most sensitive discourse tasks when evaluating specific language abilities and outcomes.