Productive vocabulary across discourse types

Aims: The goals of the study were (a) to examine the effect of discourse type on lexical diversity by testing whether there are significant differences among language samples elicited using four discourse tasks (procedures, eventcasts, story telling, and recounts); and (b) to assess the extent to which age influences lexical diversity when different types of discourse are elicited. Methods & Procedures: A total of 86 cognitively healthy adults participated in the study and comprised two groups - young adults (20-29 years old) and older adults (70-89 years old). Participants completed the discourse tasks and their language samples were analysed using dedicated software (voc-D) to obtain estimates of their lexical diversity. Outcomes & Results: Amixed 2 x 4 ANOVA was conducted and followed by an investigation of simple main effects. A lexical diversity hierarchy was established that was similar for both age groups. The study also uncovered age-related differences that were evident when the stimuli were verbally presented but were eliminated when the language samples were elicited using pictorial stimuli. Conclusions: Results indicated that lexical diversity is one of the microlinguistic indices that are influenced by discourse type and age, a finding that carries important methodological implications. Future investigations are warranted to explore the patterns of lexical diversity in individuals with neurogenic language disorders and assess the clinical utility of measures of lexical diversity.