Processing of syntactically complex sentences relies on verbal short-term memory: evidence from a short-term memory patient

The role of the phonological loop in auditory sentence comprehension was examined in a 35-year-old woman with a selective deficit of verbal short-term memory (STM). More specifically, the objective of the experiment was to test whether sentence comprehension is limited by number of propositions, as suggested by Rochon, Waters, and Caplan (2000), or whether it depends on syntactic complexity. In an offline task, severe impairment was present on cleft objects and centre-embedded structures; the deficit on object relatives in right peripheral position was less relevant, and the patient was able to handle sentential coordination easily. In an online task, her processing of centre-embedded structures and object relatives in right peripheral position was significantly slower than that in controls. She was also significantly slower in processing the verb of the object relative in centre-embedded structures. The results obtained do not support the claim that the difficulties encountered by patients with limited working-memory resources are due to the number of propositions in the sentence; they do, however, suggest a direct involvement of the phonological loop in processing syntactically complex sentences.