Short-Term or Working Memory 435Baddeley (e.g., Baddeley, 2000; Baddeley & Logie, 1999).
The working memory model was developed initially to
counter the view that short-term memory is a unitary storage
system: a single place, or store, where complex forms of cog-
nitive processing (e.g., reasoning or language comprehen-
sion) occur concurrently with temporary storage. Baddeley
and Hitch (1974) argued instead for a multicomponent sys-
tem with separate subsystems designed to handle particular
kinds of processing, such as the temporary storage of visual
versus phonological information. The working memory
model maintains a strong distinction between short- and
long-term memory, but it fractionates short-term memory
into separate parts.
Baddeley and Hitch (1974) noted, for example, that re-
membering a span-length list of items produces little dis-
ruption of a concurrent reasoning or problem-solving task. If
both temporary storage and on-line cognitive processing
are controlled by the same processing machinery—the same
processing store—then significant interference should have
occurred between the two. The fact that little interference is
found suggests that temporary storage and attention-based
central processing may be controlled by separate mecha-
nisms. Data from the study of brain-damaged patients proved
troubling as well: It was discovered, for example, that patients
with severely impaired short-term memory can show rela-
tively intact long-term memory (e.g., Shallice & Warrington,
1970); a view proposing that both temporary storage and
long-term learning are controlled by the same system has
trouble accounting for this pattern.
The working memory model has undergone significant
changes since its inception, but its core architecture still con-
sists of three basic components: the central executive, the
phonological loop, and the visuo-spatial sketchpad. The cen-
tral executive,as the name suggests, controls and coordinates
the actions of the remaining subsystems. It is assumed to be a
limited-capacity attentional system that directs the focusing
and switching of attention, and it may play a role in activat-
ing structures in long-term memory as well (see Baddeley,
1996). The central executive plays no role in storage per se,
except as the controller of the loop and the sketchpad. The
central executive is the least well-specified working memory
component and, as Baddeley readily admits, it often serves as
a kind of theoretical “grab bag” for intractable problems (see
Baddeley, 2000).
The Phonological Loop
The bulk of the empirical effort on working memory has
been spent on the phonological loop, which is the system as-
sumed to control the temporary storage of acoustic and verbal
information. The loop is divided into two components: a
phonological store, which is the actual storage location for
to-be-used information, and a rehearsal/recoding device
called the articulatory control process. Information residing
in the phonological store decays in roughly 2 s, although it
can be refreshed, via rehearsal, through the articulatory con-
trol process. Capacity limitations in immediate retention—
for example, the magic number seven—are assumed to arise
from trade-offs between decay and loop-based rehearsal. In
essence, the phonological loop account is a prototypical in-
stantiation of the standard juggler model described earlier in
the chapter (see Nairne, 1996, 2002).
The success of the working memory account hinges on its
ability to explain a wide range of standard empirical phe-
nomena. For example, the loop provides a nice account of the
word length effect, discussed earlier, by assuming that there
are inherent limitations in the operation of the articulatory
control process. Memory span is limited to roughly what a
person can rehearse within the time window established by
decay—that is, about 2 s. When words are long, fewer can be
refreshed before decay renders the short-term memory traces
unreadable. The model also successfully predicts that the
word length effect should be eliminated under conditions of
articulatory suppression (Baddeley et al., 1975). Articulatory
suppression—repeating a redundant item (e.g., the) aloud—
acts to block rehearsal, thereby eliminating the mechanism
that produces the word length effect.
In addition to refreshing decaying activity traces, the artic-
ulatory rehearsal mechanism serves an additional recoding
function: It translates verbal material into phonological form.
Representing stored traces phonologically, in the phonological
store, enables the model to handle the phonological similarity
effect, the finding that lists containing similar-sounding items
(e.g.,g,c,b,t) are harder to recall than lists of dissimilar-
sounding items (Conrad, 1964). Moreover, by linking the
phonological translation process to rehearsal, the model gen-
erates the unique prediction that the phonological similarity
effect should be eliminated under articulatory suppression, at
least for visually presented material. Preventing rehearsal
blocks the recoding function, forcing one to rely on nonphono-
logical forms of storage. In fact, articulatory suppression does
seem to eliminate the phonological similarity effect when ma-
terials are presented visually (e.g., Murray, 1968). When list
items are presented aloud, the effect remains under suppres-
sion, presumably because auditory materials are automatically
registered in the phonological store (see Baddeley, 1986).
Along with its temporary storage functions, the phonolog-
ical loop is also assumed to play a very important role in
language processing, particularly the learning of new phono-
logical material. Variables known to affect the functioning of