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

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.

To investigate the interaction of syntactic complexity and of pSTM in sentence comprehension in a group of persons with aphasia with and without agrammatism.

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.

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.

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.