Is Expanded Retrieval Practice a
Superior Form of Spaced Retrieval?
A Critical Review of the
DAVID A. BALOTA, JANET M DUCHEK,
and JESSICA M. LOGAN
Consider the following scenario: You are in the age range of most of the
contributors to this volume and are at a neighborhood party. You are
introduced to a person named Mark Finglestein. What would be the best
procedure to learn this person’s name so you are not embarrassed in future chance
encounters in the neighborhood? One procedure would be to simply rehearse the
name over and over again via massed practice. Of course, as students of learning
and memory, we all know that this procedure is doomed to failure. Another
procedure would be to space one’s retrieval such that after every minute or so
one attempts to retrieve the name Mark Finglestein. Because of the well-known
beneﬁts of spaced practice, this procedure is much more likely to succeed. A third
procedure would be to gradually expand the intervals between the retrieval
attempts. For example, you may ﬁrst retrieve the name after 15 seconds, then
45 seconds, and then 2 minutes. This procedure takes advantage of the beneﬁts
of spacing but also maintains relatively high levels of retrieval success. There is
evidence suggesting that this procedure may indeed be better than the simple
spaced retrieval. In fact, the beneﬁts of expanded retrieval have been at the center
of considerable work in both educational and clinical settings.
The present chapter reviews the evidence concerning the beneﬁts of expanded
retrieval over equal interval conditions. We will ﬁrst provide some historical
background on the spacing effect, since expanded retrieval may be considered a
special case of spacing. We will then critically evaluate the evidence concerning
expanded and equal interval retrieval practice. We will conclude with a discussion
of some potential limits of expanded retrieval, theoretical implications, and
possible avenues for future research.
THE SPACING EFFECT
The spacing effect is one of the most ubiquitous ﬁndings in learning and memory.
Performance on a variety of tasks is better when the repetition of the to-be-learned
information is distributed as opposed to massed in presentation. This observation
was ﬁrst formalized in Jost’s law, which states that “if two associations are of equal
strength but of different age, a new repetition has a greater value for the older one”
(McGeogh, 1943). Spacing effects occur across domains (e.g., learning perceptual
motor tasks vs. learning lists of words), across species (e.g., rats, pigeons, and
humans), across age groups and individuals with different memory impairments,
and across retention intervals of seconds to months (see Cepeda, Pashler, Vul,
Wixted, & Rohrer, 2006; Crowder, 1976; Dempster, 1996, for reviews). In this
light, it is interesting that spacing effects have not received much attention in
Cognitive Psychology textbooks. In fact, in our sampling of seven such textbooks,
only one had a section dedicated to this topic, while virtually all cognitive text-
books discussed mnemonic techniques such as the pegword or method of loci.
Given the power and simplicity of implementing spaced practice, we clearly hope
this changes in the future.
As a sidebar, we felt it was particularly ﬁtting to discuss the spacing effect as
part of a book honoring the contributions of Roddy Roediger. Roddy’s mentor,
Robert Crowder (1976) devoted considerable discussion (over 40 pages) of his
classic book, The Principles of Learning and Memory, to the effects of spacing
on learning and memory. Moreover, Arthur Melton, Roddy’s academic grand-
father, wrote a deﬁnitive piece on this topic in 1970. As noted in Melton’s paper,
spacing effects, like many things, can be traced back to observations by William
James (Roddy’s great-great-great grandfather) concerning the beneﬁts of alter-
nating swimming in the summer and skating in the winter. In addition to his
academic lineage, spacing effects are also quite consistent with Roddy’s functional-
ist approach in his work and the importance of making a connection between
practical implications and basic experimental research. Recently, Roddy has been
exploring the application of cognitive principles to educational practice, and has
already made important contributions in this domain (see, for example, Roediger
& Karpicke, 2006). Expanded retrieval and the spacing effect have been at the
center of considerable work in educational settings, and Roddy has been exploring
this issue in a number of recent projects (e.g., Karpicke & Roediger, 2005).
SPACING EFFECTS, POSSIBLE LIMITATIONS, AND THE
APPEAL OF EXPANDED RETRIEVAL
Although spaced presentation is clearly beneﬁcial in most situations, as with every-
thing, there are some limitations. For example, there is evidence of a spacing
by retention interval interaction. Speciﬁcally, massed items are actually better
retained after a short retention interval, whereas spaced items are better retained
after a long retention interval. This observation was ﬁrst obtained by Peterson,
THE FOUNDATIONS OF REMEMBERING84
Wampler, Kirkpatrick, and Saltzman (1963), and was replicated by Glenberg (1977)
and Balota, Duchek, and Paullin (1989).
There are numerous theoretical accounts of the spacing effect (see Cepeda
et al., 2006, for a review); however, the spacing by retention interval interaction
would appear to be most consistent with an encoding variability account. Because
of the relevance of this theoretical framework to our discussion of the beneﬁts
of expanded retrieval in a later section, we will brieﬂy describe the encoding
variability account of the spacing by retention interval interaction. According to
encoding variability theory, performance on a memory test is dependent upon the
overlap between the contextual information available at the time of test and the
contextual information available during encoding. During massed study, there is
relatively little time for contextual elements to ﬂuctuate between presentations
and so this condition produces the highest performance in an immediate memory
test, when the test context strongly overlaps with the same contextual information
encoded during both of the massed presentations. In contrast, when there is
spacing between the items, there is time for ﬂuctuation to take place between the
presentations during study, and hence there is an increased likelihood of having
multiple unique contexts encoded. Because a delayed test will also allow ﬂuctu-
ation of context, it is better to have multiple unique contexts encoded, as in the
spaced presentation format, as opposed to a single encoded context, as in the
massed presentation format.
Because of evidence regarding a contextual encoding deﬁcit in older adults
(see Burke & Light, 1981; Duchek, 1984), Balota et al. (1989) investigated the
spacing by retention interval interaction in young and older adults, and found that
both groups produced clear evidence of the interaction, with older adults being
overall lower. More importantly, as suggested in Crowder (1976), Balota et al. ﬁt
their data to Estes’ (1955) stimulus sampling model (a precursor of encoding
variability theory), which was developed to account for aspects of extinction and
spontaneous recovery, among other ﬁndings, in the animal learning domain.
Interestingly, when animals are placed in an environment at varying times after
extinction of a response, the response appears to spontaneously recover, even
though it had been extinguished earlier. The results of this simple modeling
endeavor indicated that older adults were different from younger adults in two
parameter values. Speciﬁcally, older adults were less likely to store contextual
elements in memory and elements also ﬂuctuated between available and unavail-
able states across time at a slower rate in older adults than younger adults. As
shown in Figure 6.1, changes in these two parameters of the Estes’ model nicely ﬁt
the Balota et al. data (also see Spieler & Balota, 1996, for an extension to an
implicit memory task). Thus, the spacing by retention interval interaction nicely
extends to individuals with different levels of memory competence, and converges
on a particular theoretical account of the spacing effect that emphasizes contextual
drift (encoding variability) across time.
The spacing by retention interval interaction indicates that there are limita-
tions to the spacing effect. This tradeoff between lag (the amount of spacing
between two events) and retention interval has led some researchers (e.g., Greene,
1992) to speculate that the ratio between spacing and retention interval is the
A SUPERIOR FORM OF SPACED RETRIEVAL? 85
critical variable. Although there is some tradeoff between retention interval and
spacing, there are probably some limits even here. For example, if one considers
a spaced interval of 1 year between two repetitions, one may not expect much
beneﬁt even at a very long retention interval, since the initial trace may have either
decayed or been completely overwhelmed by interfering material. Of course, this
FIGURE 6.1 Percent correct recall as a function of group and retention interval from
Balota et al. (1989), along with the predictions from Estes’ (1955) stimulus ﬂuctuation
THE FOUNDATIONS OF REMEMBERING86
leads us to an important question. Are there ways to maintain the strength of the
initial encoding so as to minimize the disruptive effects at long lags? Enter
expanded retrieval practice. The goal in this procedure is to gradually increase the
lag between retrieval events, thereby maintaining relatively high levels of retrieval
success at long lags.
In an often-cited chapter, Landauer and Bjork (1978) were the ﬁrst to carefully
explore expanded retrieval in two well-controlled experiments. In their ﬁrst
experiment, subjects were presented a deck of cards that included ﬁctitious ﬁrst
and second names of individuals during the acquisition phase. For present pur-
poses, we will focus on the trials in which subjects were ﬁrst presented both
the ﬁrst and second names intact followed at varying schedules of receiving cards
with only the ﬁrst name of the study pair as a retrieval cue for the second name.
For example, in an expanded retrieval schedule, subjects may receive the ﬁrst
name as a retrieval cue at 1, 4, and 10 intervening cards versus an equal interval
condition of 5, 5, and 5 intervening cards. A massed condition (study of the
name followed by three immediate tests) was used to obtain a baseline estimate
of the inﬂuence of simple repetition without spacing. The results of a later
cued recall test yielded a large beneﬁt for both the expanded and equal interval
condition over the massed condition. More importantly, there was a small, but
signiﬁcant effect (approximately a 5% beneﬁt, based on interpolation from their
Figure 2) of the expanded condition over the equal interval condition in the ﬁnal
cued recall test.
The Landauer and Bjork (1978) results have been quite inﬂuential and would
appear to naturally maximize the beneﬁts of spacing. They originally suggested
that the beneﬁt of expanded retrieval involves insuring successful retrieval at longer
and longer intervals, thereby increasing the difﬁculty of retrieval, while still yield-
ing success. One could also view these beneﬁts within an encoding variability
framework described above. Speciﬁcally, with the passage of time and intervening
information, there is an increased likelihood of greater ﬂuctuation of context,
and hence a greater likelihood of distinct encodings. The notion here is that
in a long-term retention test, stimuli that have more distinct encodings, afforded
by the longest interval in the expanded condition, would produce a greater
beneﬁt compared to stimuli with less distinct encodings due to shorter retention
Both of the above accounts emphasize the additional beneﬁt beyond success-
ful retrieval in the expanded condition compared to the equal interval condition.
In particular, the reason there is an advantage in the expanded condition is that the
participants are indeed retrieving items in the face of a longer retention interval
during the ﬁnal retrieval attempt in the expanded compared to the equal interval
condition. Importantly, Landauer and Bjork (1978) provided retrieval success data
during initial list presentation to directly examine this. Based on interpolation
from their Figure 1, Table 6.1 displays performance of an expanded condition
compared to an equal interval condition estimated from Landauer and Bjork’s
ﬁrst experiment. As shown, there is an initial beneﬁt of expanded retrieval that
actually decreases across subsequent retrieval attempts. Hence, the beneﬁt of
expanded over equal interval is larger during the acquisition phase than in ﬁnal
A SUPERIOR FORM OF SPACED RETRIEVAL? 87
recall. This is somewhat counterintuitive because one might expect an advantage
of expanding over equal interval schedules above and beyond the retrieval success
advantage produced during the acquisition phase. Speciﬁcally, at the last retrieval
event, the retrieved items have persisted in the face of a longer retention interval
and more intervening information in the expanded than in the equal interval
condition. On the other hand, the “expanded retrieval effect” may be due to the
fact that the ﬁrst retrieval success occurs soon after study, permitting greater
retrieval success in the expanding relative to the equal interval condition, as
opposed to greater retrieval efﬁciency at the longest delays. Of course, this could
ultimately overestimate the beneﬁts of expansion. We will return to this possibility
The Landauer and Bjork (1978) results are clearly provocative, and the bene-
ﬁts of expanded retrieval have been explored in both educational and clinical
settings. Below we will provide a review of the inﬂuence of expanded retrieval
in these areas. It will become clear that although expanded retrieval is clearly
a useful memory aid, there has been relatively little controlled work, akin to
Landauer and Bjork’s, that attempts to isolate the inﬂuence of expansion over
comparable equal spaced conditions. Given the potential importance of this
procedure, this is surprising.
Before turning to the review of the literature, we believe that it is noteworthy
to identify the conditions that are important to make strong inferences regarding
the speciﬁc role of expanding retrieval, many of which were available in Landuaer
and Bjork’s seminal study. For example, it is important to include at least three
levels of spacing: an expanded condition (e.g., 1, 4, 10), an equal interval condition
that matches the average spacing of the expanded condition (e.g., 5, 5, 5), and a
massed condition (e.g., 0, 0, 0). With these three levels, one can both measure the
inﬂuence of expansion with spacing equated (e.g., 1, 4, 10 vs. 5, 5, 5), and also the
beneﬁts of spaced (1, 4, 10 and 5, 5, 5) over massed practice (e.g., 0, 0, 0) to insure
one obtains a clear spacing effect. In addition, it is useful to measure retrieval
success during the initial acquisition phase to obtain an estimate of the original
level of learning. As we shall discuss below, it is preferable to include two different
delays for the ﬁnal memory test, because it appears that one can obtain different
effects depending upon the delay. Of course, this has some resemblance to the
spacing by retention interval interaction. Finally, it would also be useful to include
a study alone condition with the same spacing and testing conditions to measure
the speciﬁc inﬂuence of retrieval during study. Unfortunately, as noted, these
conditions have rarely been available in the same study to isolate the speciﬁc
beneﬁts of expanded retrieval.
TABLE 6.1 Interpolated Results from Landauer and Bjork (1978)
Retrieval attempt Final recall
Expanded .61 .55 .50 .45
Equal interval .42 .42 .43 .40
THE FOUNDATIONS OF REMEMBERING88
EXPANDED RETRIEVAL PRACTICE IN
The additional beneﬁt of expanded retrieval over equal interval spacing obviously
has important implications for educational settings. Although Landauer and Bjork’s
(1978) work sparked considerable interest in applying expanded retrieval to edu-
cational settings, Roddy informed us of relevant work nearly 40 years before
Landauer and Bjork’s study. Speciﬁcally, Spitzer (1939) incorporated a form of
expanded retrieval in a study designed to assess the ability of sixth graders to learn
science facts. Impressively, Spitzer tested over 3600 students in Iowa—the entire
sixth-grade population of 91 elementary schools at the time. The students read two
articles, one on peanuts and the other on bamboo, and were given a 25-item
multiple choice test to assess their knowledge (such as “To which family of plants
does bamboo belong?”). Spitzer tested a total of nine groups, manipulating both
the timing of the test (administered immediately or after various delays) and the
number of identical tests students received (one to three). Spitzer did not
incorporate massed or equal interval retrieval conditions, but he had at least two
groups that were tested on an expanding schedule of retrieval, in which the inter-
vals between tests were separated by the passage of time (in days) rather than by
intervening to-be-learned information. For example, in one of the groups, the ﬁrst
test was given immediately, the second test was given seven days after the ﬁrst test,
and the third test was given 63 days after the second test. Thus, in essence, this
group was tested on a 0-7-63 day expanding retrieval schedule. Spitzer compared
performance of the expanded retrieval group to a group given a single test 63 days
after reading the original article. On the ﬁrst (immediate) test, the expanded
retrieval group correctly answered 53% of the questions. After 63 days and two
previous tests, their score was still an impressive 43%. The single test group cor-
rectly answered only 25% of the original items after 63 days, giving the expanded
retrieval group an 18% retention advantage. This is quite impressive, given that
this large beneﬁt remained after a 63-day retention interval. Similar beneﬁcial
effects were found in a group tested on a 0-1-21 day expanded retrieval schedule
compared to a group given a single test after 21 days. Of course, this study does not
decouple the effects of testing from spacing or expansion, but the results do clearly
indicate considerable learning and retention using the expanded repeated testing
procedure. Spitzer concluded that “. . . examinations are learning devices and
should not be considered only as tools for measuring achievement of pupils”
(p. 656, italics added), and we are sure Roddy would agree (see Roediger &
Since Spitzer (1939), there was very little work was published on expanded
retrieval using educationally-relevant materials for 45 years until Rea and
Modigliani (1985) tested the effectiveness of expanded retrieval in a third-grade
classroom setting. In separate conditions, students were given new multiplication
problems or spelling words to learn. The problem or word was presented audio-
visually once and then tested on either a massed retrieval schedule of 0-0-0-0 or an
expanding schedule of 0-1-2-4, in which the intervals involved being tested on old
items or learning new items. After each test trial for a given item, the item was
A SUPERIOR FORM OF SPACED RETRIEVAL? 89
re-presented in its entirety so students received feedback on what they were
learning. Performance during the learning phase was at 100% for both spelling
words and multiplication facts. On an immediate ﬁnal retention test, Rea and
Modigliani found a performance advantage for all items—math and spelling—
practiced on an expanding schedule compared to the massed retrieval schedule.
They suggested, as have others, that spacing combined with the high success rate
inherent in the expanded retrieval schedule produced better retention than
massed retrieval practice. However, as in Spitzer’s study, Rea and Modigliani did
not test an appropriate equal interval spacing condition. Hence, their ﬁnding that
expanded retrieval is superior to massed retrieval in third graders could simply
reﬂect the superiority of spaced versus massed rehearsal—in other words, the
More recently, Cull (2000) compared expanded retrieval to equal interval
spaced retrieval in a series of four experiments designed to mimic typical teaching
or study strategies encountered by students. He examined the role of testing
versus simply restudying the material, feedback, and various retention intervals on
ﬁnal test performance. Paired associates (an uncommon word paired with a com-
mon word, such as bairn–print) were presented in a manner similar to the ﬂash-
card techniques students often use to learn vocabulary words. The intervals
between retrieval attempts of to-be-learned information ranged from minutes in
some experiments to days in others. Interestingly, across four experiments, Cull
did not ﬁnd any evidence of an advantage of an expanded condition over a uniform
spaced condition (i.e., no signiﬁcant expanded retrieval effect), although both
conditions consistently produced large advantages over massed presentations. He
concluded that distributed testing of any kind, expanded or equal interval, can be
an effective learning aid for teachers to provide for their students.
Karpicke (2004) investigated the effectiveness of using expanded retrieval to
learn material commonly encountered by students—prose passages. Participants
were given 7 minutes to read an encyclopedia article and practice free recalling
the article on an expanding or equal interval schedule. An important feature of
Karpicke’s study was that he matched the timing of the ﬁrst recall attempt in the
acquisition phase in the expanded and equal interval conditions. As noted, in
most expanded retrieval studies, the ﬁrst practice for the expanded items comes
sooner than practice for the equal interval items. Hence, in Karpicke’s study, the
ﬁrst recall attempt for both equal and expanded conditions was either immediate
(given just after reading the article) or delayed (given after 7 minutes of a
distractor task). He tested a total of four recall schedules in the acquisition
phase: 0-2-4, 0-2-2, 2-2-4, 2-2-2. The ﬁnal free recall test was given 1 week later.
In both the immediate and delayed practice conditions, Karpicke found no
difference in memory performance when expanded and equal interval schedules
were matched on the timing of the ﬁrst retrieval attempt. This was true in the
acquisition phase as well as the ﬁnal free recall test. However, one might com-
pare the 0-2-4 condition to the 2-2-2 conditions to investigate the expanded
Interestingly, Karpicke (2004) did ﬁnd an advantage for the expanded condi-
tion in both the acquisition phase as well as the ﬁnal free recall test, similar to
THE FOUNDATIONS OF REMEMBERING90
Landauer and Bjork (1978). Because there was no delay in the ﬁrst retrieval event
in the immediate retrieval conditions in this study, and the 0-2-4 and 0-2-2 pro-
duced equivalent and better performance than the 2-2-2 and the 2-2-4, Karpicke
points out that it is difﬁcult to isolate the inﬂuence of expansion from the immedi-
acy of the ﬁrst recall event. In this light, it would have been useful to have 0-1-2-3
and 0-2-2-2 conditions for comparison. In any case, Karpicke’s ﬁndings support
the notion that any expanded retrieval effect at a ﬁnal test is strongly linked to
greater retrieval success for the expanded condition compared to the equal inter-
val condition during the ﬁrst acquisition phase. When these two conditions were
matched in performance during the acquisition phase, the expanded retrieval
effect did not emerge.
Researchers have also attempted to extend the utility of expanded retrieval to
other “real world” settings such as in our original example of learning the name
Mark Finglestein (remember Mark?) at a neighborhood party. Morris and Fritz
(2000; see also Morris & Fritz, 2002; Morris, Fritz, & Buck, 2004) modiﬁed the
expanded retrieval technique to create a “name game” to help individuals learn the
names of members in their group. In the name game, an individual introduces
herself, while a group leader writes their name on a board and then erases it once
the other group members had read it. A second individual then repeats the ﬁrst
person’s name aloud and introduces himself to the group. The third individual
then repeats the names of the ﬁrst and second individuals (in that order) and adds
her name, etc. This technique of repeating previous names (starting with the ﬁrst
person’s name) then adding a new name to the group is followed until all group
members are introduced. Thus, the interval between hearing a given name pro-
gressively expands as each new person is introduced. In the Morris and Fritz (2000)
study, participants were given a ﬁnal recall test on the names after 30 minutes and
again after 2 weeks and 11 months. Performance in the name game condition was
compared to a condition in which individuals were simply paired with another
group member and then asked to introduce their partners aloud to the group. In
two experiments, participants recalled signiﬁcantly more full names from the name
game condition than the partner condition, even after 11 months. This condition
also produced superior performance compared to when the group leader simply
read the previous names back after each new introduction without ever asking
individuals to retrieve the names. In a follow-up study, Morris and Fritz (2002)
found that a reversed version of the name game, in which names were recalled
in reverse chronological order, produced better performance than the original
version used in the previous study. They noted that the reversed name game
more closely mimics the technique originally employed by Landauer and Bjork
(1978), and it was more effective than the original name game because there was
less chance of forgetting a new name when the delay between learning and
retrieval was reduced. Although the name game clearly does work, there is again
no comparable equal interval condition to examine if the schedule is the critical
dimension or the spacing.
The studies reviewed above speciﬁcally cited a desire to apply the expanded
retrieval technique to nonlaboratory settings and explored its applications to a
variety of learning situations (science and multiplication facts, spelling words, and
A SUPERIOR FORM OF SPACED RETRIEVAL? 91
ﬁrst and last names). The studies found an advantage for expanded retrieval com-
pared to information that is simply repeated or reread (Cull, 2000; Morris & Fritz,
2000, 2002), tested only once (Spitzer, 1939), or tested on a massed retrieval
schedule (Cull, 2000; Rea & Modigliani, 1985). In addition, Karpicke (2004) pro-
vides intriguing evidence that provides support for the utility of expansion for text
materials, but overall his results primarily show the importance of the immediacy
of a ﬁrst testing session. Only Cull (2000) directly compared the utility of expanded
retrieval to other schedules of spaced retrieval and this study did not obtain any
beneﬁts of expanded retrieval over an equal interval schedule. In a later section,
we will further discuss the Cull study and other studies that have attempted to
decouple the inﬂuence of spacing from expansion in more traditional laboratory
EXPANDED RETRIEVAL PRACTICE IN COGNITIVELY
Another area where expanded retrieval has been viewed as having considerable
potential is as a cognitive rehabilitation technique for various memory-impaired
populations. This area has been very active. The speciﬁc appeal of expanded
retrieval is that the beneﬁts of expanded retrieval are relatively automatic and
nonstrategic, as opposed to teaching memory impaired individuals mnemonic
techniques such as the pegword method or method of loci, which demand
considerable strategic/attentional control processes.
Schacter, Rich, and Stampp (1985) utilized the expanded retrieval procedure
to improve memory performance in four patients with cognitive impairment due
to a variety of etiologies. In this study, subjects ﬁrst studied faces and associated
characteristics (i.e., names, hometowns, occupations, hobbies) and then utilizing
the face cue, engaged in retrieval practice for the associated characteristics at
expanded time intervals. Initially subjects were given a verbal prompt to engage
in retrieval practice and over time the verbal prompt was removed to see if sub-
jects would engage in expanded retrieval practice on their own. The results indi-
cated that memory performance for the associated characteristics improved after
expanded retrieval practice relative to baseline performance as measured prior
to the introduction of the expanded retrieval strategy. Importantly, two out
of the four subjects were relatively successful in spontaneously using expanded
retrieval practice without prompts. Thus, Schacter et al. concluded that expan-
ded retrieval practice might be a particularly effective strategy for memory
enhancement in cognitively impaired populations.
The vast majority of the work employing the use of expanded retrieval in
clinical populations has been conduced by Camp and his colleagues, with indi-
viduals in various stages of Alzheimer’s disease (AD; for a review, see Camp, Bird,
& Cherry, 2000). Given that memory loss is the hallmark symptom of Alzheimer’s
disease, targeting this population with such a behavioral intervention could prove
quite beneﬁcial to both patients and caregivers. In an effort to apply Landauer
and Bjork’s (1978) expanded retrieval practice to the AD population, Camp and
THE FOUNDATIONS OF REMEMBERING92
colleagues adopted a clinical protocol for teaching AD patients new information
using spaced retrieval practice (Camp, 1989; Camp & McKitrick, 1992). In this
procedure, subjects are ﬁrst given one piece of information to remember (e.g., the
name of a staff person) and are then tested for immediate recall. If this immediate
recall attempt is successful, then the next retrieval attempt is queried after 5 s, and
then expanded to 10 s, 20 s, 40 s, 60 s. After successful retention of the item for
60 s, intervals are increased by 30 s (90 s, 120 s, etc.). If a person does not
successfully retrieve the information, he/she is given the correct response, asked to
immediately repeat the correct response, and then is tested at the last successful
interval. Expanded retrieval attempts are again initiated from that point forward
on successful retrieval events.
As Camp, Foss, Stevens, and O’Hanlon (1996) describe, there are some key
features of this spaced retrieval strategy that promote success in memory-impaired
patients. First, the expansion of retrieval attempts occurs over time, not over
intervening to-be-remembered items. Thus, the time intervals are typically ﬁlled
with social conversation or other non-related activities. Hence, as Camp and
Mattern (1999) argue, the expanded retrieval training can be efﬁciently used
within a therapy session wherein the intervening time intervals can be used for
other therapeutic activities. Second, this technique is analogous to a shaping pro-
cedure wherein an association is formed between a stimulus (i.e., the retrieval
query) and a single response (i.e., the name). Because the learning occurs very
gradually over time, the initial retrieval attempts are likely to be successful, even
for individuals in the moderate stages of AD. Third, the expanded retrieval strat-
egy incorporates the neurorehabilitation technique of errorless learning (Wilson,
Baddeley, Evans, & Shiel, 1994). Wilson and colleagues have argued that memory-
impaired populations show better long-term retention for information when they
are not allowed to make errors during training (Baddeley & Wilson, 1994; Wilson
& Evans, 1996). The notion is that explicit memory is necessary for error recogni-
tion and elimination during learning. When the explicit system is deﬁcient, then
errors may be implicitly incorporated into the learning and thus each repetition of
an erroneous response may serve to further strengthen that incorrect response,
thereby hindering the retention of the correct information. Thus, the expanded
retrieval procedure used by Camp and colleagues requires that when there is
a failure of retrieval, the correct response be given immediately and repeated by
the subject. Finally, the implementation of the expanded retrieval strategy
requires little cognitive effort and/or resources on the part of the learner. Camp
and colleagues have argued that expanded retrieval training makes use of implicit
memory, which is relatively spared even in the later stages of AD (e.g., Balota &
Ferraro, 1996; Camp et al., 2000; Faust, Balota, & Spieler, 2001). Thus, it is ideally
suited for memory-impaired patients.
Indeed there have been numerous reports in the literature of the successful
use of expanded retrieval practice in teaching new information to individuals in
the relatively advanced stages of AD. Speciﬁcally, Camp and colleagues have used
this technique to teach AD individuals various types of information, such as names
of common objects (e.g., McKitrick & Camp, 1993), face-name associations (e.g.,
Camp & Schaller, 1989), object-location associations (e.g., Camp & Stevens, 1990),
A SUPERIOR FORM OF SPACED RETRIEVAL? 93
and even prospectively remembering to perform a task (e.g., McKitrick, Camp, &
Black, 1992). Moreover, long-term retention of information has been demonstrated
over several days in some cases (e.g., Camp et al., 1996). For example, in the latter
study, Camp et al. employed an expanding retrieval strategy to train 23 individuals
with mild to moderate AD to refer to a daily calendar as a cue to remember to
perform various personal activities (e.g., take medication). Following a baseline
phase to determine whether subjects would spontaneously use the calendar,
spaced retrieval training was implemented by repeatedly asking the subject the
question, “How are you going to remember what to do each day?” at expanding
time intervals. The results indicated that 20/23 subjects did learn the strategy
(i.e., to look at the calendar) and retained it over a 1-week period.
There have been numerous other studies utilizing this protocol of expanded
retrieval practice to induce memory-impaired patients to learn clinically relevant
behaviors. For example, this technique has been employed to teach a demented
client with dysphagia (i.e., a swallowing disorder) to use a compensatory strategy of
alternating bites of food with sips of liquid to prevent aspiration (Brush & Camp,
1998a). Expanded retrieval training has been applied to attaining goals during
speech therapy sessions (Brush & Camp, 1998b) with demonstrated retention over
a 4-week period in demented clients. Patients with dementia associated with
Parkinson’s disease have successfully learned new motor tasks (Hayden & Camp,
1995) and patients with dementia associated with HIV have been trained in the
use of external aids (Lee & Camp, 2001) with expanded retrieval practice.
Likewise, a client with AD was able to learn the names of 11 members of his social
group with a combined intervention of errorless learning and expanded retrieval
(Clare et al., 2000). There has even been a case report of an individual in the early
stages of AD who trained himself to spontaneously use expanded retrieval practice
to remember new information (Riley, 1992). Thus, the beneﬁts of expanded
retrieval have been widely documented in the literature across various targeted
behaviors and clinical populations.
What is somewhat surprising in reviewing all of these studies is that there has
been no attempt to systematically compare expanded retrieval practice with other
schedules of spaced retrieval practice, such as equal interval spacing or even
massed spacing of retrieval practice. In most of these studies, performance after
expanded retrieval practice is simply compared relative to baseline performance
(e.g., Camp et al., 1996; Cherry, Simmons, & Camp, 1999). More recently,
Bourgeois et al. (2003) compared expanded retrieval training with a modiﬁed
cued hierarchy training in teaching demented individuals to use various external
memory aids. The modiﬁed cued hierarchy training is initiated in a similar way
as the expanded retrieval training in that patients are ﬁrst given the target informa-
tion (e.g., when you want to know what activity to perform today—look at your
activity list) and then immediately queried for that information. If patients cannot
immediately give the correct response or give an incorrect response, they are given
a hierarchy of cues in the following order until the correct response is given:
semantic (“Something to look at”), phonemic (the ﬁrst syllable of “activity list”),
visual (point to list), tactile (touch list), imitation (“I look at my activity list”). No
cues are given in the expanded retrieval training. The results indicated that both
THE FOUNDATIONS OF REMEMBERING94
strategies improved usage of external aids, but the expanded retrieval strategy was
more effective. Of course, the latter study simply indicates that spaced retrieval
practice leads to better retention than providing a hierarchy of cues. It did not
address the question of which speciﬁc pattern of spacing leads to the greatest
beneﬁt in long-term retention.
This issue of isolating which component of expanded retrieval is critical with a
clinical sample was more systematically addressed in a recent study by Hochhalter,
Overmier, Gasper, Bakke, and Holub (2005). Individuals with AD were presented
pill names (Exp. 1; n = 10) under ﬁve different schedules of retrieval practice:
massed, uniform distributed (i.e., equal interval), spaced/expanded adjusted based
on performance (similar to the Camp protocol), expanded without adjustment,
and random. The results indicated that only 6/10 individuals showed long-term
retention for at least one pill name and there was no difference in the number of
“learners” across the different schedules of retrieval practice. Thus the spaced/
expanded retrieval condition did not show a beneﬁt relative to any of the other
schedules of practice. If anything, more subjects showed long-term retention in
the random condition (n = 5) than the spaced/expanded condition (n = 3) and also
had fewer errors during training.
The Hochhalter et al. (2005) study is clearly informative, but the relatively
small number of subjects and more variable applied therapeutic setting makes
it difﬁcult to draw any ﬁrm conclusions. However, as described below, Balota,
Duchek, Sergent-Marshall, and Roediger (2005) provide a study comparing equal
interval and expanded practice in a laboratory context with a large set of healthy
young, older adults, and individuals with early stage Alzheimer’s disease and come
to a very similar conclusion as the Hochhalter et al. study regarding comparisons
of equal interval and expanded retrieval.
It is interesting to note that in their initial study, Schacter et al. (1985) acknow-
ledged that it was unclear whether it was the actual expanding pattern of retrieval
that led to the performance beneﬁt in their study or whether it was merely due to
the simple repetition of retrieval attempts. They argued that to some extent the
latter question is not really clinically important given that expanded retrieval prac-
tice does indeed work for memory-impaired patients. Clearly, one would agree
with this statement on an individual patient basis, where the goal of treatment is to
enhance memory for important personal information. It is evident from the litera-
ture that having memory-impaired individuals engage in an expanded retrieval
strategy does improve memory performance under a variety of situations, at least
relative to baseline (no treatment) performance (Camp, Bird, & Cherry, 2000).
Furthermore, one can see how the gradual expansion of recall attempts with the
initial accompanying retrieval success would be relatively easy to implement in a
clinical setting or in a home setting by caregivers (McKitrick & Camp, 1993).
However, from a theoretical perspective, it is also critical to examine the proper-
ties of the most effective spacing of retrieval practice to enhance long-term reten-
tion. This research could also provide evidence for designing the best intervention
strategies for memory-impaired individuals.
A SUPERIOR FORM OF SPACED RETRIEVAL? 95
RE-EXAMINATION OF THE EVIDENCE FOR THE
BENEFITS OF EXPANDED RETRIEVAL OVER EQUAL
SPACED RETRIEVAL: BACK TO THE LABORATORY
As reviewed in the previous two sections, there is clear evidence that expanded
retrieval practice has considerable potential in both educational and applied set-
tings. The question that we will now turn to is an examination of how much of this
evidence is speciﬁc to “expanded” retrieval. This of course depends on what is the
appropriate baseline. As in Landauer and Bjork’s (1978) original paper, we believe
the appropriate baseline to be a comparably matched equal interval schedule. In
this way, one can directly investigate if there is an additional beneﬁt of expansion
over mere spacing. For these studies, we are forced to return to the laboratory
where more control of critical variables is available.
In one of the most comprehensive studies in this area, Cull, Shaughnessy, and
Zechmeister (1996) explored the beneﬁts of expanded retrieval over uniform spa-
cing in a series of ﬁve experiments. They compared the expanded schedules of
1-5-9, with the equal interval schedule of 5-5-5, and included a 0-0-0 massed
presentation condition, as a baseline to measure the beneﬁt of spacing on a later
ﬁnal recall test. As shown in Table 6.2, the results generally support the beneﬁt of
expanded retrieval over equal interval conditions. Experiments 1 and 4 produced
reliable expanded retrieval beneﬁts compared to an equal interval condition,
whereas the results from Experiments 2 and 3 were in the same direction, but did
not reach signiﬁcance. Experiment 5 produced near ceiling effects in both spaced
conditions. Somewhat surprisingly, the comparison of the equal interval condition
to the massed condition did not consistently produce spacing effects. A test for the
spacing effect was not directly provided for Experiments 1 and 2, and in Experi-
ments 3 and 4, these two conditions produced identical performance. Only, their
ﬁfth experiment provided strong evidence for a spacing effect, but this experiment
did not provide evidence for an expanded retrieval effect, because of ceiling
Cull (2000, Exp. 1) provided a direct follow-up study to the initial Cull et al.
TABLE 6.2 Results from Cull et al. (1996), and Cull (2000) Studies
Experiment Presentation schedule
1-5-9 5-5-5 0-0-0
Cull et al. (1996)
1. Test only .33 .23 .17
2. Test only .27 .18 .11
3. Test only .34 .28 .28
4. Test only .72 .59 .59
5. Test–study .91 .91 .62
Cull (2000, Exp. 1)
Test only .38 .34 .18
Study only .27 .29 .14
Test–study .48 .49 .19
THE FOUNDATIONS OF REMEMBERING96
(1996) study. He included the same three spacing schedules used in the ear-
lier Cull et al. study, along with three different types of study. In essence, his
ﬁrst experiment included three different experiments, as these conditions were
between participant manipulations. In the study-only condition, the cue and
response item of a paired associate were both presented on each repetition for 8 s.
In the test-only condition, the cue for retrieval was presented on each occasion for
8 s. In the study–test condition, the cue was presented for 6 s for retrieval, followed
by the response item for 2 s. As shown in Table 6.2, Cull did not obtain an advan-
tage for the expanded over the equal interval condition in any of these conditions.
As noted earlier, Cull also explored more educationally relevant manipulations in
three additional experiments. None of these experiments afforded any beneﬁt of
expanded retrieval over a comparable equal interval condition.
Carpenter and DeLosh (2005, Exp. 2) have recently investigated face-name
learning under massed, expanded (1-3-5), and equal interval (3-3-3) conditions.
This study also involved study and study and test procedures during the acquisition
phase. Carpenter and DeLosh found a large effect of spacing, but no evidence of a
beneﬁt of expanded over equal interval practice. In fact, Carpenter and DeLosh
reported a reliable beneﬁt of the equal interval condition over the expanded
retrieval condition. Although Carpenter and DeLosh did report a reliable (20%)
beneﬁt of expanded retrieval during the acquisition phase, they did not break this
down by each retrieval event to determine the size of the difference at the last
retrieval event in the expanded condition.
In addition to studies with healthy young adults, there have been two recent
studies that have explored the beneﬁts of expanded retrieval with healthy older
adults and early stage Alzheimer’s disease. Balota et al. (2005) compared a massed
presentation condition (0-0-0-0-0-0) with an equal interval (0-0-3-3-3) and an
expanded retrieval schedule (0-0-1-3-5). Because this study included healthy
young adults, older adults, and individuals with Alzheimer’s disease, who have
quite a wide range of memory ability, Balota et al. had subjects engage in two
massed retrieval attempts before each of the three schedules to insure all groups
were off the ﬂoor in their ﬁnal recall performance. The results of performance
during the acquisition phase are shown in Figure 6.2. Here one can see that the
expanded retrieval condition indeed produces a beneﬁt over the equal interval
condition that persists until the last retrieval event for all groups of participants.
Hence, because performance on the last retrieval event reﬂects longer mainten-
ance of the memory in the 0-0-1-3-5 condition than the 0-0-3-3-3 condition, one
would expect a beneﬁt to persist in the ﬁnal cued recall tests. This was not what the
results indicated. Speciﬁcally, as shown in Figure 6.3, all three groups produced
large spacing effects in a ﬁnal cued recall test; however, there was no evidence of a
reliable difference between the expanded and equal interval conditions for any of
the groups. Moreover, the lack of a difference in ﬁnal recall between the expanded
and equal interval condition was replicated in two subsequent experiments, in
which corrective feedback was given to participants. Hence, the Balota et al.
results converge nicely with the recent Cull (2000) and Carpenter and DeLosh
(2005) studies and extends this pattern to both healthy older adults and individuals
with early stage Alzheimer’s disease.
A SUPERIOR FORM OF SPACED RETRIEVAL? 97
Of course, one might be concerned that the Balota et al. (2005) and Carpenter
and DeLosh (2005) study used the 3-3-3 and 1-3-5 comparison. Logan (2004)
conducted a comprehensive study that compared three schedules of retrieval
practice in healthy young and older adults, i.e., 0-0-0 versus 1-2-3 versus 2-2-2;
0-0-0 versus 1-3-5 versus 3-3-3; 0-0-0 versus 1-3-8 versus 4-4-4. An important
additional contribution of the Logan study is that she also included both an
FIGURE 6.2 Mean proportion correct during the acquisition phase for the Young (top
panel), Old (middle panel) and DAT (bottom panel) individuals, as a function of spacing,
and retrieval attempt from Balota et al. (2005, Exp. 1).
THE FOUNDATIONS OF REMEMBERING98
immediate and a delayed retention interval. The retrieval schedule did not modu-
late the difference between expanded and equal spaced retrieval and so we will
collapse across these schedules here. As shown in Figure 6.4, Logan obtained
beneﬁts of expanded retrieval over equal interval during the acquisition phase for
both the young and the older adults. This acquisition advantage was retained on an
immediate ﬁnal cued recall test, at least in older adults. However, after a 24 hour
delay between acquisition and ﬁnal test, the advantage for items practiced on an
expanding schedule compared to an equal interval schedule was lost in both age
groups. In fact, memory was signiﬁcantly worse for expanded items compared to
equal interval items in younger adults. Thus, the ﬁndings from Logan imply that
when an expanded retrieval advantage is found, it may be short-lived, compared to
comparable equal interval spacing.
The Logan results are particularly intriguing in light of a recent study by
Karpicke and Roediger (2005). These investigators compared massed (0-0-0),
equal interval (5-5-5), and expanded (1-5-9) retrieval conditions for paired associ-
ates (vocabulary GRE practice items, such as sobriquet–nickname) in both an
FIGURE 6.3 Mean ﬁnal cued recall performance as a function of group and spacing
schedule from Balota et al. (2005, Exp. 1).
FIGURE 6.4 Mean ﬁnal cued recall performance as a function of group, spacing sched-
ule, and retention interval from Logan (2004).
A SUPERIOR FORM OF SPACED RETRIEVAL? 99
immediate 10 minute delayed, and 48 hour delayed cued recall test. The results
indicated that again both spaced schedules produced better performance than
the massed schedule at both retention intervals. More importantly, there was
evidence of a beneﬁt of the expanded condition over the equal interval condition
in the immediate test, but the equal interval condition produced a clear beneﬁt
in the delayed recall test. This later pattern was replicated in a second study in
which feedback was provided after each testing event, although the immediate
test performance was limited by ceiling problems. Hence, the short-term gains of
expanded over equal interval retrieval found in both the Logan (2004) and
Karpicke and Roediger (2005) studies were either eliminated or turned into
long-term losses in a delayed testing condition.
The results of the current review lead us to conclude that, as expected, spaced
practice produces considerable beneﬁts in learning compared to massed practice;
however, the additional beneﬁts of expanded practice over equal interval practice
have not been well substantiated in recent research. We ﬁnd the lack of a beneﬁt
of expanded retrieval quite intriguing, because the acquisition phase data (when
measured) clearly indicate that participants are at higher levels of retrieval success
over a longer retention interval in the expanded condition than in the equal inter-
val condition. For example, at the last retrieval event during the acquisition phase
of the Balota et al. (2005) study, subjects correctly retrieved 16% more items in
the expanded retrieval condition than in the equal interval condition, even though
at this last retrieval event, the expanded retention interval was ﬁve items, and the
equal interval was three items. Clearly, one would expect such a beneﬁt to either
persist or increase during a ﬁnal recall test. However, there was no beneﬁt in the
ﬁnal cued recall performance of expansion. Moreover, the results from Logan
(2004) and Karpicke and Roediger (2005) indicate that one can either eliminate or
actually reverse any acquisition beneﬁt of expanded over equal interval retrieval
when tested at a 1 or 2 day retention interval.
Why might the beneﬁts of expanded retrieval over equal interval retrieval
observed during the acquisition phase be lost in a later cued recall test? One
simple possibility is that long-term retention is simply a function of the average
amount of spacing. Since this is equated in the equal interval and expanded condi-
tion, there is, on average, no effect. A more intriguing possibility is that there are
counteracting inﬂuences, as a function of retention interval. Speciﬁcally, it is
indeed beneﬁcial to maintain high levels of retrieval success during acquisition,
but there is a potential cost of maintaining these high levels, i.e., a loss of one of
the spaced intervals. Consider for example, the 1-3-5 schedule compared to the
3-3-3 schedule. The initial retrieval event during acquisition in the expanded
condition occurs after only one intervening item. In some sense, one could
argue that the 3-3-3 condition involves three functional spaced events during
acquisition, whereas, the 1-3-5 condition only involves two spaced events during
THE FOUNDATIONS OF REMEMBERING100
As noted earlier, one theoretical account of the spacing effect is encoding
variability theory, which nicely handles the intriguing spacing by retention interval
interaction. This framework may also be relevant to the expanded vs equal interval
spacing results. Speciﬁcally, although expanded retrieval does indeed produce
higher performance during the acquisition phase, this beneﬁt may be lost in longer
delays, precisely as any beneﬁt of massed spacing is relatively short lived. The
notion is that the equal interval condition will on average involve three distinct
encoding events, whereas, as noted above, the expanded condition on average
will involve two distinct encoding events. Because long-term retention is a reﬂec-
tion of the context at retrieval matching one of the encoding events, the equal
interval condition may produce a beneﬁt in long-term retention, since this
condition affords an additional unique encoding of context. Interestingly, as
noted above, there is already evidence by Logan (2004) and Karpicke and
Roediger (2005) that initial beneﬁts of expansion during a short retention inter-
val turn into losses a day or two later. Thus, although there is the beneﬁt of
expansion in maintaining high levels of performance at increasing delays during
acquisition, the long-term consequence of expansion may produce a decreased
amount of contextual variability, because of the relatively immediate presenta-
tion of the ﬁrst test. Of course, we know that maintaining high levels of retrieval
success during acquisition is not the only variable that is critical to memory
performance, since massed study produces the highest level of performance
during acquisition but the lowest level of performance during a long-term reten-
tion test. Clearly, further work is needed to better understand the balance
between spacing and retention interval in more complex expanded and equal
Although the review of recent empirical work has questioned the beneﬁts of
expanded retrieval over equal spaced retrieval, there are two reasons that may
support the use of expanded retrieval in more applied settings. First, as Camp and
colleagues have nicely demonstrated, this procedure is relatively easy to imple-
ment in a clinical setting. That is, gradually increasing retrieval intervals, while
maintaining success, beneﬁts from feedback driven performance, i.e., providing
positive feedback at increasing retention intervals because of retrieval success.
Alternatively, a priori picking the best spaced retrieval practice schedule may
be relatively difﬁcult to accomplish, especially for someone who is having global
cognitive impairments. Second, and more importantly, maintaining high levels of
retrieval success during acquisition in the face of increasing retention intervals is
likely to be reinforcing for the user. Of course, such reinforcement should ultim-
ately increase the likelihood that individuals will use such a schedule in the future,
and so this is a natural way of nurturing the use of spaced practice. Thus, although
there may be reasons to question the long-term beneﬁts of expanded over equal
interval schedules, there may also be practical reasons to use the expanded retrieval
schedule to implement simple spaced acquisition.
A SUPERIOR FORM OF SPACED RETRIEVAL? 101
Clearly, there is much work to do to better understand the inﬂuence of study
schedules on long-term retention. Comparing different acquisition schedules is a
natural avenue to pursue. Most studies have only used three retrieval attempts,
and the extension to a greater number of retrieval attempts would be likely to
reﬂect the sequence of events in more applied settings, such as in the Camp et al.
studies. Consider, for example, the possibility of comparing an expanded schedule
of 1-2-3-4-5-6-7 with a retrieval schedule of 4-4-4-4-4-4-4. Without feedback pro-
vided, we would expect that in this case the expanded schedule may produce a
beneﬁt over the equal interval schedule, but this is an open empirical question.
Likewise, in addition to exploring different schedules, the inﬂuence of feedback
and the possibility of restudying nonretrieved information are both aspects of
acquisition that typically occur outside the laboratory. With feedback, one might
expect the equal interval condition to possibly produce better performance in the
above example. Finally, as Logan (2004) and Karpicke and Roediger (2005) have
nicely demonstrated, retention interval is critical. In general, what appears to be a
beneﬁt of expanded retrieval during acquisition can be quickly lost and even
reversed at longer retention intervals. In this light, we are reminded of Bjork’s
(1999) arguments regarding the importance of desirable difﬁculties during acqui-
sition, and the counterintuitive observation that variables that produce beneﬁts
immediately on tests sometimes produce losses in long-term retention. Although
there will clearly be constraints on when expansion will and will not produce
beneﬁts over equal interval schedules, the present review makes clear that the
power of spacing is paramount in learning and memory.
Portions of this research were supported by NIA PO1 AGO3991 and P50 AGO5681.
Thanks are extended to Roddy and Jim Nairne for helpful comments on an earlier version
of this manuscript.
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