Productive vocabulary across discourse types

Abstract

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: A mixed 2 × 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.

Keywords:

• Lexical diversity
• Ageing
• Linguistics
• Diversity

Acknowledgments

This research was supported by the National Institute on Aging Grant R01AG029476. We are especially grateful to the study participants. We also thank Marissa Stoltzfus, Sarah Germaine, and the volunteers in the Aging and Adult Language Lab at ASU for assistance with transcription and language analyses. Finally, we thank the anonymous reviewers for their thoughtful comments on previous versions of the manuscript.

Notes

¹For the purposes of this study, discourse type is defined as the discourse that is predominantly produced as a response to a specific elicitation task.

²For a brief collection of the terms and definitions that have been used for lexical diversity, the interested reader is referred to Yu (2010).

³For, example, Split TTR (Engber, 1995), Root TTR (Guiraud, 1960), Corrected TTR (Carroll, 1964), Log TTR (Herdan, 1960).

⁴It is important to note, however, that both studies referenced here used TTR to estimate LD; therefore their findings could have been confounded with sample length as well.