Researchers from universities and medical facilities in Italy (Milan, Trento) and France (Paris) have collaborated to compare comprehension performance in persons with agrammatic and fluent aphasias when presented with sentences of varying syntactic structures and challenge levels. The researchers focused on how phonological short-term memory (pSTM) interacts with syntactic complexity to affect sentence comprehension in persons with aphasia of the differing types.
Subjects were 30 Italian adults, 15 of whom presented with agrammatic aphasia and 15 – with fluent aphasia. Participants were at least 3 months postonset, following a first stroke that produced left-hemisphere damage. Subjects were balanced by gender, of mean age of 67.0 y/o (SD = 11.2), with 12.6 mean years of schooling. All were administered the Token Test and BADA, an Italian aphasia assessment battery. Auditory pSTM was evaulated using the Forward Digit Span task, standardized on an Italian adult population. Language comprehension was assessed using a standardized, Italian-language battery in which subject match pictures to descriptive sentences of 10 linguistic types, such as ‘active sentences’, ‘passive sentences’, ‘coordinated verb phrases’, ‘center-embedded object relatives’, and the like.
In data analysis, means and standard deviations of performance with each type of sentence, and with the digit span task, were calculated for each of the ten sentence types, first for the overall sample and then for each of the two subgroups (fluent, non-fluent). Sequential nested linear mixed model analyses of increasing complexity were performed to predict the combined effects of the pSTM, syntactic structure, and other independent variables on subjects’ sentence comprehension. Results show that subjects with lower phonological short term memory scores showed reduced comprehension of center-embedded object relatives – such as ‘The cat that the dog bit died’ – and long coordinated sentences. The difficulty that agrammatic subjects have understanding passive sentences, in contrast, appears to be a purely syntactic issue, and does not vary between agrammatic subjects with higher or lower phonological short term memory scores. These results support the views that difficulty comprehending passive sentences is an indication of agrammatism, while comprehension difficulties with longer coordinated sentences is indicative of pSTM involvement, and challenges with objects relatives and center derive from combined syntactic considerations and resource-based factors.
For further reading: G. Gilardone, M. Viganò, G. Costantini et al. 2023. The role of verbal short-term memory in complex sentence comprehension: an observational study on aphasia. International Journal of Language & Communication Disorders, 1–9. https://doi.org/10.1111/1460-6984.12851