Back and Looking Forward

NATURE REVIEWS | NEUROSCIENCE VOLUME 4 | OCTOBER 2003 | 8 2 9 The theoretical concept of working memory assumes that a limited capacity system, which temporarily maintains and stores information, supports human thought processes by providing an interface between perception, long-term memory and action1–3. There are many approaches to the study of working memory, using a range of empirical and theoretical techniques. However, most theories agree on the need for a system of limited attentional capacity, supplemented by more peripherally-based storage systems4. The account that follows emphasizes this fractionation, stressing the importance of executive control, but concentrating initially on the more tractable peripheral storage systems. Within experimental cognitive psychology there are several different but complementary approaches to working memory: some emphasize the role of attentional control in memory5, whereas others attempt to explain working memory data in terms of models that were originally developed for long-term memory (LTM)6,7. An example of this approach is provided by Nairne8, whose account seems to criticize the multi-component model of working memory. However, most of Nairne’s criticisms apply only if one attempts to explain all the phenomena of working memory in terms of the phonological loop — one component of a complex system. As this review shows, the phonological loop has received more attention than other components, but this reflects its relative tractability, compared with the visuospatial and executive subsystems. A third, influential approach relies on correlational techniques that capitalize on individual differences across the various components of working memory (BOX 1). Rather than attempting to give an account of each of these approaches, I describe a single multi-component model of working memory. In general,deviations from the other models represent difference of emphasis and scope, rather than direct conflict. Points of clear disagreement will,however,be identified and discussed. The term ‘working memory’ seems to have been invented by Miller, Galanter and Pribram9, and was adopted by Baddeley and Hitch10 to emphasize the differences between their three-component model and earlier unitary models of short-term memory (STM). These differences include its multi-component character, its emphasis on combined processing and storage, and the stress on its functional importance as a system that facilitates a range of cognitive activities, such as reasoning, learning and comprehension. This approach resulted in the development of a set of experimental tasks that could be used to analyse different activities and subject populations1. Because the available empirical evidence provided few constraints, the model was initially loosely specified: for example, it had no mechanism for storing serial order. However, it was simple and robust, and had the potential to develop and become much richer and more clearly specified. The Baddeley and Hitch model continues to flourish, and will be used as a basis for this review. The article will, however, extend beyond WORKING MEMORY: LOOKING BACK AND LOOKING FORWARD