16 - Short-term memory impairment and sentence processing: a case study

Summary

Introduction

As a task that requires the integration of temporally distributed input, sentence comprehension clearly involves short-term memory (STM) capacity. Little has been done to define the storage requirements for sentence-processing tasks, although the STM capacities underlying the retention of word list materials have been extensively studied. It is likely, however, since both tasks deal with strings of lexical items, that they have some mnestic requirements in common. This is implicit in the assumption that the phonological store, thought to be the primary vehicle for information storage in spantype tasks (see Baddeley, this volume, chapter 2), contributes to sentence processing as well (e.g., Clark & Clark, 1977). Studies that have demonstrated trade-offs between concurrent comprehension and list memory tasks (Savin & Perchonock, 1965; Wanner & Maratsos, 1978) provide prima facie support for this notion, as do indications that sentential input is held in phonological form prior to the identification of clausal units (Jarvella, 1971; but see Von Eckhardt & Potter, 1985).

Additional evidence for storage capacities common to sentence processing and list retention has come from neuropsychological investigations. Brain-damaged patients with selective STM deficits, as defined by Shallice and Vallar in chapter 1 of this volume, have invariably demonstrated some degree of impairment on tests of sentence comprehension. The difficulties of these patients appear to lie, moreover in structural aspects of sentence processing, which is where access to an information store that represents a linear array of lexical items is likely to be most useful.