Handbook of Psychology, Volume 4: Experimental Psychology

432 Sensory and Working Memory

subjects: Rosen and Engle (1998), for instance, found that
low-span subjects were more likely to intrude previously
learned items into a current paired-associate recall task. It
is also possible to get high-span subjects, who presumably
possess more capacity for controlled attention, to mimic low-
span subjects’ susceptibility to interference by having them
perform an additional concurrent task (Kane & Engle, 2000).
The greater the amount of controllable attention, the easier it
is to inhibit or reject interfering material as well as to keep
target items active in memory through rehearsal.
It is also worth noting that some measures of capacity cor-
relate reasonably well with other cognitive measures, such as
reading comprehension, vocabulary learning, and even intel-
ligence. For example, Engle and colleagues developed the
operation span task, in which the presentation of to-be-
remembered items is interspersed with a requirement to solve
simple addition problems (e.g., Turner & Engle, 1989). The
number of words recalled is still of main interest, but the dual
task conditions (arithmetic plus immediate retention) seem to
tap attentional capacity to a greater extent than simple span
measures. The operation span task, as well as related mea-
sures (e.g., Daneman & Carpenter, 1980), turns out to predict
higher order cognitive abilities such as general fluid intelli-
gence or the verbal scholastic aptitude score (see Engle,
Kane, & Tuholski, 1999, for a review).
What emerges is a view proposing that the storage capac-
ity of short-term memory, as defined generally by a measure
such as memory span, is determined by a variety of factors,
not a single factor such as a magic number of seven plus or
minus two. The capacity to focus and sustain attention, en-
gage in strategic rehearsal, and even recall quickly (Dosher &
Ma, 1998) modulates the number of items that can be re-
membered over the short term. The characteristics of the
items also matter: Word frequency, imageability, and lexical
status all influence memory span, as does the similarity
among the items presented together in a list. Another impor-
tant factor is the rhythm and timing of stimulus presentation:
If temporal gaps occur predictably within list presentation,
immediate memory can improve substantially (e.g., Hitch,
Burgess, Towse, & Culpin, 1996; Ryan, 1969). All of these
factors need to be explained by a complete model of immedi-
ate retention.
It is also the case that any act of remembering will be influ-
enced by the nature of the retrieval environment, regardless of
whether the remembering occurs over the short or long term.
As I discuss in the next section, retrieval from short-term
memory, like long-term memory, is essentially cue-driven.
Moreover, the effectiveness of cues depends on how target
information has been encoded, as well as the extent to which
the cue uniquely specifies the to-be-remembered item. This
means that even with unlimited amounts of time, or an

unlimited amount of attentional capacity, there can still be for-

getting and, therefore, apparent limitations in storage capacity.

Although there may be a relatively fixed amount of resource or

attentional capacity available at any moment in time (see the

chapter by Egeth & Lamy in this volume), understanding this

limit will not explain, or effectively predict, all instances of

short-term retention.

Retrieval of Short-Term Memories

As defined earlier, short-term memories are the active, but

analyzed, contents of mind. By virtue of their activation,

some researchers have assumed that they are immediately

available for recall—that is, short-term memories exist in a

state that allows for direct and effortless retrieval (e.g.,

McElree, 1998; Wickens, Moody, & Dow, 1981). On reflec-

tion, however, it is difficult to see how such a mechanism for

remembering might actually work. For one thing, multiple

short-term memories exist concurrently (short-term memory,

as a whole, is often described as the set of activated knowl-

edge), so a mechanism is needed to select a particular

activated item for recall. More importantly, as just noted, the

success of immediate retention seems to depend critically on

the nature and extent of retrieval cues that are available.

Most recent models of short-term retention assume that

the short-term activity trace forms the basis of immediate

memory, but the trace needs to be interpreted, or deblurred,

prior to actual recall. Interference, or possibly decay, de-

grades the activity trace over time, rendering its identity

equivocal. The term redintegrationis widely used to describe

the interpretation process, which is assumed to rely on infor-

mation stored in long-term memory. It is here, during the

redintegration stage, that item characteristics such as word

frequency or concreteness probably exert their effects. For

example, one can assume that time-dependent rehearsal af-

fects the intactness of the activity trace at the point of recall,

but item-based characteristics (e.g., concreteness) affect the

ease of redintegration (see Schweickert, 1993). Separating

the status of the activity trace itself from its interpretation

prior to recall allows one to explain, for instance, how imme-

diate recall differences can occur despite the equating of pro-

nunciation time.

Retrieval Dynamics

Assuming that a set of activated information exists at any

moment in time, how does one select an appropriate candi-

date to recall? In the 1960s, Saul Sternberg developed a task

to investigate the retrieval process. In Sternberg’s task,

subjects are presented with short, below-span lists of items

(e.g., words, letters, digits) followed immediately by the