Measuring the coherence of normal and aphasic discourse production in Chinese using rhetorical structure theory (RST)

Abstract

The study investigated the difference in discourse coherence between healthy speakers and speakers with anomic aphasia using Rhetorical Structure Theory (RST). The effect of genre types on coherence and potential factors contributing to the differences were also examined. Fifteen native Cantonese participants of anomic aphasia and their control matched in age, education and gender participated. Sixty language samples were obtained using the story-telling and sequential description tasks of the Cantonese AphasiaBank protocol. Twenty naïve listeners provided subjective ratings on the coherence, completeness, correctness of order, and clarity of each speech sample. Results demonstrated that the control group showed significantly higher production fluency, total number of discourse units, and fewer errors than the aphasia group. Controls used a richer set of relations than the aphasic group, particularly those to describe settings, to express causality, and to elaborate. The aphasic group tended to omit more essential information content and was rated with significantly lower coherence and clarity than controls. The findings suggested that speakers with anomic aphasia had reduced proportion of essential information content, lower degree of elaboration, and more structural disruptions than the controls, which may have contributed to the reduced overall discourse coherence.