Argument structure deficit in aphasia: it’s not all about verbs

Abstract

Background: Verb difficulties in aphasia often co-occur with difficulties specifying argument structure of the sentence. Recent exploration of verb and argument structure deficits has shown dissociations between lexical semantic information, argument structure information, and production of the argument structure. There is currently limited evidence regarding the implications of these dissociations for treatment. Aims: This paper explores the patterns of generalisation following intervention to increase access to verb argument structure for a 62-year-old woman (YR) with chronic agrammatic aphasia. YR had good access to nouns and verbs in picture naming alongside severe sentence production difficulties characterised by difficulty specifying argument structure. Methods & Procedures: Detailed pre-therapy language assessment investigated single word and sentence comprehension and production, with a specific focus on whether YR could produce argument structure. Intervention targeted verb retrieval, awareness of argument structure information, cueing of arguments, and production of argument and syntactic structure involving transitive verbs. A single-subject multiple baseline design was used to monitor the effectiveness of treatment. The primary outcome measure was accuracy of two-argument structures in sentence production to picture and sentence generation to written word tasks, with effects on treated and untreated verbs considered. Other measures of sentence comprehension and production were also obtained to determine any further generalisation. Outcomes & Results: Following the first phase of therapy, YR showed a significant improvement in the production of two-argument structures across both treated and untreated verbs in sentence production to pictures, with a corresponding significant reduction in incomplete argument structures. No change was seen in two-argument structures in sentence generation to written words. After the second phase of therapy, significant gains were seen in two-argument structures with both treated and untreated verbs in the sentence generation task while sentence production to picture performance maintained. Gains in sentence generation were more vulnerable following the cessation of therapy. Other tasks of sentence production also improved with no change seen on a control task. Conclusions: Argument structure can be selectively impaired in aphasia, in the presence of good verb and noun access at the single word level, and targeted in therapy to improve sentence production. The study highlights the complexity of the relationship between verbs and argument structure and that argument structure difficulties are not always a consequence of a semantic verb deficit. Generalised improvement in argument structure production provides evidence that therapy targeted general processes rather than lexically specified argument structure information.