Investigation of pretreatment sentence production impairments in individuals with aphasia: towards understanding the linguistic variables that impact generalisation in Verb Network Strengthening Treatment

Abstract

Background: Verb Network Strengthening Treatment (VNeST) is an aphasia treatment that aims to promote generalisation to sentence production in untrained contexts, including connected speech. VNeST’s fundamental premise is that verbs and their thematic roles are interrelated and as such can be strengthened by systematic retrieval of thematic roles related to trained verbs. In a recent group study, the hypothesised effects of VNeST were observed in a small group of people with aphasia who showed increased lexical retrieval within single words, sentence production, and discourse. However, variable patterns of improvement were observed across participants.Aims: The purpose of the current study was to conduct a theoretically based analysis of pretreatment language abilities for each participant from a previous group study in order to characterise patterns of impairment and improvement. Pretreatment profiles were compared against posttreatment outcomes to provide insight into potential mechanisms of improvement within participants and to determine whether there are common or different mechanisms of improvement across participants.Methods & Procedures: Pretreatment and posttreatment results of 11 people with aphasia who received 35 hr of VNeST across 10 weeks were analysed. As the basis of our analysis, we drew from evidence of dissociations in grammatical class abilities, theories of thematic role production, and empirical evidence of discrete thematic role subprocesses to evaluate each person’s pretreatment ability to (1) produce nouns and verbs in single words and sentences, (2) specify correct predicate argument structure for sentences, and (3) assign thematic roles within a syntactic frame.Outcomes & Results: Our results suggest that persons with different pretreatment linguistic impairment patterns can and do exhibit generalisation to untrained sentence and discourse contexts. The common mechanism of improvement to all participants was increased lexical retrieval. Participants with relatively strong pretreatment sentence construction abilities integrated increased lexical retrieval into already well-formed sentences, including complex sentences, while participants with weaker sentence construction abilities better integrated lexical retrieval into simpler sentences, which may have also benefited from strengthened predicate argument specification. Analyses of cases where optimal generalisation was not achieved revealed a number of root causes, including persistent pronoun production, light verb usage, sentence construction difficulties, and reduced self-monitoring.Conclusion: Overall, VNeST is a highly generalising treatment, and our findings are fairly generalisable to a range of aphasia types and severities with differing impairment patterns.