Lexical diversity and lexical errors in the spoken discourse of people with aphasia and typical speakers in Croatian: A comparison of different discourse types

Adequate vocabulary is essential for functional communication. Lexical diversity (LD), the number of different words produced, reflects vocabulary knowledge. However, valid and reliable LD measurement remains challenging, especially in clinical groups. Linguistic features like LD can vary across discourse types. Research shows inconsistent evidence on LD differences within and between group of people with aphasia (PwA) and typical speakers (TS) across discourse types. This study aimed to clarify how LD varies across different discourse types in TS and PwA and to explore the relationship between LD and lexical errors (LEs). Language samples from 34 speakers (17 PwA, 17 TS) were analysed. TS outperformed PwA in LD across all discourse types. Although both groups showed similar LD patterns across discourse types, statistically significant within-group differences were observed only in TS, with LD in narrative and expositional both higher than in procedural discourse. A negative correlation was observed in PwA's discourse between LD and LEs, the most frequent of which were phonemic, phonological, and apraxia-related. These findings highlight how task properties can affect language production.