The role of verbal short-term memory in complex sentence comprehension: An observational study on aphasia

Background: The comprehension profile of people with agrammatism is a debated topic. Syntactic complexity and cognitive resources, in particular phonological short-term memory (pSTM), are considered as crucial components by different interpretative accounts. Aim: To investigate the interaction of syntactic complexity and of pSTM in sentence comprehension in a group of persons with aphasia with and without agrammatism. Methods & procedures: A cohort of 30 participants presenting with aphasia was assessed for syntactic comprehension and for pSTM. A total of 15 presented with agrammatism and 15 had fluent aphasia. Outcomes & results: Linear nested mixed-model analyses revealed a significant interaction between sentence type and pSTM. In particular, participants with lower pSTM scores showed a reduced comprehension of centre-embedded object relatives and long coordinated sentences. Moreover, a significant interaction was found between sentence type and agrammatism, with a lower performance for passives within the agrammatic group. Conclusions & implications: These results confirm that pSTM is involved in the comprehension of complex structures with an important computational load, in particular coordinated sentences, and long-distance filler gap dependencies. On the contrary, the specific deficit of the agrammatic group with passives is a pure syntactic deficit, with no involvement of pSTM.