Lexical diversity for adults with and without aphasia across discourse elicitation tasks

Background: Differences in lexical diversity (LD) across different discourse elicitation tasks have been found in neurologically intact adults (NIA) (Fergadiotis, Wright, & Capilouto, 2010) but have not been investigated systematically in people with aphasia (PWA). Measuring lexical diversity in PWA may serve as a useful clinical tool for evaluating the impact of word retrieval difficulties at the discourse level. Aims: The study aims were (a) to explore the differences between the oral language samples of PWA and NIA in terms of LD as measured by dedicated computer software (voc-D), (b) to determine whether PWA are sensitive to discourse elicitation task in terms of LD, and (c) to identify whether differences between PWA and NIA vary in magnitude as a function of discourse task. Method & Procedures: Oral language samples from 25 PWA and 27 NIA were analysed. Participants completed three commonly used discourse elicitation tasks (single pictures, sequential pictures, story telling) and voc-D was used to obtain estimates of their LD. Outcomes & Results: A mixed 2 x 3 ANOVA revealed a significant group x task interaction that was followed by an investigation of simple main effects and tetrad comparisons. Different patterns of LD were uncovered for each group. For the NIA group results were consistent with previous findings in the literature according to which LD varies as a function of elicitation technique. However, for PWA sequential pictures and story telling elicited comparable estimates of LD. Conclusions: Results indicated that LD is one of the microlinguistic indices that are influenced by elicitation task and the presence of aphasia. These findings have important implications for modelling lexical diversity and selecting and interpreting results from different discourse elicitation tasks.