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October 2003 Vol 4 No 10 REVIEW
Nature Reviews Neuroscience 4, 829 -839 (2003); doi:10.1038/nrn1201
WORKING MEMORY: LOOKING BACK AND
LOOKING FORWARD
Alan Baddeley about the author
Preface
The concept of working memory proposes that a dedicated system
maintains and stores information in the short term, and that this
system underlies human thought processes. Current views of
working memory involve a central executive and two storage
systems: the phonological loop and the visuospatial sketchpad.
Although this basic model was first proposed 30 years ago, it has
continued to develop and to stimulate research and debate. The
model and the most recent results are reviewed in this article.
Summary
 The concept of working memory assumes that a limited capacity
system temporarily stores information and thereby supports human
thought processes. One prevalent model of working memory
comprises three components: a central executive, a verbal storage
system called the phonological loop, and a visual storage system
called the visuospatial sketchpad.
 The phonological loop consists of a store that can hold memory traces
for a few seconds, and an articulatory rehearsal process. Retrieval and
re-articulation are used to refresh memory traces, and the span of
working memory is limited by the amount of material that can be
articulated before the first item fades from the store. Word length and
similarity between items strongly influence performance on tests of
verbal working memory.
 Various models have been proposed to account for how serial order is
remembered. In chaining models, each item is a cue for the next item,
but these models run into problems with sequences in which an item
recurs and with similarity effects. Contextual models assume that
successive items are associated with a contextual cue or that recall of
order is based on positional associations between items.
 It has been proposed that the phonological loop evolved to facilitate
the acquisition of language. In support of this, phonological loop
capacity is a good predictor of second language learning. Future
studies seem likely to link the phonological loop more closely to
theories of language perception and production.
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 The visuospatial sketchpad is less well understood than the
phonological loop. Spatial and visual working memory also have
limited capacity and the two can be dissociated. Visuospatial working
memory predicts success in fields such as architecture and
engineering.
 One model proposes that the sketchpad is divided into two
components, a visual cache and a retrieval and rehearsal process
called the 'inner scribe', analogous to the storage and articulatory
components of the phonological loop.
 The central executive is the least understood component of working
memory. In one model, control is divided between 'automatic' habits
or schemas, and an attentional system called the supervisory
activating system that intervenes to overrule habitual control.
 To move our concept of the supervisory activating system beyond a
simple 'homunculus', we need to specify the processes attributed to it,
and then to explain them. The processes needed are to focus, divide
and switch attention, and to connect working memory with long-term
memory. To account for the latter capacity, a fourth component of
working memory has been proposed: the episodic buffer, a limited
capacity store that binds information to form integrated episodes.
 Neuroimaging and neuropsychology have provided evidence for
localization of the components of working memory. The phonological
loop is associated with the left temporoparietal region, and
visuospatial working memory with analogous areas in the right
hemisphere. The central executive is probably associated with the
frontal lobes.
 Work on the phonological loop, the visuospatial sketchpad and the
central executive should be more closely linked to studies on
language, visual processing and motor control, and executive control,
respectively. In addition, more work is needed on what drives working
memory.
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