Copyright 2001 by the American Psychological Association, Inc.
O278-7393/O1/S5.OO DOI: 10.1037//0278-7393.27.5.1131
Journal of Experimental Psychology:
Learning, Memory, and Cognition
2001, Vol. 27, No. 5, 1131-1146
Source Memory in Older Adults: An Encoding or Retrieval Problem?
Elizabeth L. Glisky, Susan R. Rubin, and Patrick S. R. Davidson
University of Arizona
Source memory has been found to be more affected by aging than item memory, possibly because of
declining frontal function among older adults. In 4 experiments, the authors explored the role of the
frontal lobes (FLs) in source memory, the extent to which they may be involved in the encoding and/or
retrieval of source or context, and the conditions under which the source memory deficit in older people
may be reduced or eliminated. Results indicated that only a subset of older adults show deficits in source
memory, namely those with below average frontal function, and these deficits can be eliminated by
requiring people at study to consider the relation between an item and its context. These results provide
convincing evidence of the importance of frontal function during the encoding of source and suggest that
older adults with reduced FL function fail to initiate the processes required to integrate contextual
information with focal content during study.
As people age, their memories for recent events tend to become
less precise, less well specified. Although they may know that a
particular event occurred or have knowledge of a particular fact,
they may be less likely to recollect where or when the event took
place or how they acquired their knowledge of it. This latter kind
of memory, which seems to be especially susceptible to the deleterious effects of aging, has been referred to as source memory.
Although source memory has sometimes been narrowly defined as
"the episodic source from which a specific item was acquired (e.g.,
from a person, a book, or television)" (Schacter, Kaszniak, Kihlstrom, & Valdiserri, 1991, p. 559), it can also be more broadly
construed to include any aspects of context—perceptual, spatiotemporal, affective, social—that are present when an event occurred (Johnson, Hashtroudi, & Lindsay, 1993). As such, it is often
contrasted with item or fact memory or with memory for the
content of an experience. Such a broad definition of source,
however, raises the further question of exactly how context should
be distinguished from content (for discussion of this issue, see Van
Petten, Senkfor, & Newberg, 2000). In a general sense, content is
what is perceived as focal, either as a result of experience or as a
result of specific instructions. Context is what is perceived as
nonfocal. In most experimental studies of source memory, the
item-source relation is determined by the many-to-few mapping of
items to sources: many words are spoken in one of two voices, are
Elizabeth L. Glisky, Susan R. Rubin, and Patrick S. R. Davidson,
Department of Psychology, University of Arizona.
This research was supported by National Institute on Aging Grant
AG14792, by the McDonnell—Pew Program in Cognitive Neuroscience,
and by the Flinn Foundation. We thank Amanda Dawson for statistical
assistance, Shelly Barkley, Erica Nielsen, Jamie Ouellette, Gina Patriarca,
and Alysha Teed for help in data collection, and Kelly Murray and Jason
Worrell for neuropsychological testing.
Correspondence concerning this article should be addressed to Elizabeth
L. Glisky, Department of Psychology, P.O. Box 210068, University of
Arizona, Tucson, Arizona 85721. Electronic mail may be sent to
glisky @u.arizona.edu.
printed in one of two fonts, or are either perceived or imagined. In
the present article, we adopt the broad definition of source and
operationally define it in terms of the many-to-few mapping.
A number of studies have shown that source memory is generally affected by aging more than fact or item memory (Brown,
Jones, & Davis, 1995; Ferguson, Hashtroudi, & Johnson, 1992;
Henkel, Johnson, & DeLeonardis, 1998; Mclntyre & Craik, 1987;
Schacter et al., 1991; Spencer & Raz, 1995; Trott, Friedman,
Ritter, & Fabiani, 1997; Trott, Friedman, Ritter, Fabiani, &
Snodgrass, 1999), but the reasons for the differential effects are
unclear. One hypothesis is that source memory relies to a greater
extent on the integrity of the frontal lobes (FLs), and the FLs are
particularly likely to be affected by aging (Coffey et al., 1992; Raz,
2000; Raz et al., 1997). This hypothesis has been supported by
findings in patients with focal frontal lesions (Janowsky, Shimamura, & Squire, 1989; Johnson, O'Connor, & Cantor, 1997),
who were found to make more source memory errors than normal
control participants concerning the place and time that facts were
acquired, despite their equivalent memory for the facts themselves.
Also, studies of source memory in amnesic patients have demonstrated that those patients who show deficits on tests of FL function are more likely to exhibit impaired source memory performance (Schacter, Harbhik, & McLachlan, 1984; Shimamura &
Squire, 1987), whereas those without frontal impairment perform
normally on source tasks, despite their severe impairment on tests
of fact memory. Recent studies measuring event-related potentials
in source memory tasks with normal individuals have also supported a special role for the FLs in source memory relative to item
memory (Johnson, Kounios, & Nolde, 1997; Senkfor & Van
Petten, 1998; Trott et al., 1997; Trott et al., 1999; Van Petten et al.,
2000; Wilding & Rugg, 1996), as have studies using event-related
functional magnetic resonance imaging (Nolde, Johnson, &
D'Esposito, 1998). There are, however, contrary findings. For
example, Kopelman (1989) noted in a list discrimination task with
amnesic Korsakoff patients that the probability of correct list
identification was unrelated to the amount of FL atrophy or to
performance on tests of frontal function, but it was related to
1131
1132
GLISKY, RUBIN, AND DAVIDSON
performance on standard tests of item memory. Similarly, Shoqeirat and Mayes (1991; also Mayes, Meudell, & MacDonald,
1991) found no correlation between memory for spatial location
and performance on FL tasks in amnesic patients but instead found
an association between spatial location memory and item memory
(see also Kopelman, Stanhope, & Kingsley, 1997).
Studies of healthy older adults have also produced conflicting
findings. Several investigators have reported that the performance
of older individuals on source memory tasks is correlated with
their performance on tests of FL function and is uncorrelated with
their performance on tests of fact or item memory (Craik, Morris,
Morris, & Loewen, 1990; Glisky, Polster, & Routhieaux, 1995;
Parkin, Walter, & Hunkin, 1995). Other researchers, however,
have not obtained this relation. For example, Spencer and Raz
(1994) found that some kinds of source memory were not predicted by FL tests (see also Degl'Innocenti & Backman, 1996;
Johnson, DeLeonardis, Hashtroudi, & Ferguson, 1995) but were
correlated with fact recall. Recently, Henkel et al. (1998) reported
in a source monitoring experiment that source accuracy, although
correlated with performance on frontal tasks under some conditions, was also correlated with performance on tasks usually associated with functions of the medial temporal lobes (MTLs)—
standard tests of item memory—under other conditions. They
suggested that explanations that assigned source memory processes solely to the FLs were too simplistic and that source
memory tasks may share processes or features with item memory
tasks in some circumstances (see also Johnson et al., 1993). Nevertheless, as noted above, disproportionate source memory deficits
have generally not been found in patients with damage confined to
MTL structures (Milner, Corsi, & Leonard, 1991; Schacter et al.,
1984).
Reasons for the somewhat variable results with respect to the
brain regions implicated in source memory may stem from materials used, task demands, and individual differences among participants. So, for example, studies grouped under the rubric of source
memory have required people to make a range of judgments about
the context in which an event occurred, including when and where
it happened, whether it was heard or seen, perceived or imagined,
in what voice it was spoken or font it was written, and numerous
other questions about the contextual features of a particular episode (for reviews, see Johnson et al., 1993; Kausler, 1994; Spencer
& Raz, 1995). Encoding instructions have also varied, as have the
formats of the memory tests used, and in many cases frontal
function has been assessed on the basis of just one or two "frontal"
tasks. Participants in the studies have often been brain-injured and
older individuals, who are notably variable in behavior and neurophysiology. It is therefore not surprising that different outcomes
have been obtained across experiments. Yet,despite this variability
there is now considerable consensus that the FLs are in some way
involved in source memory.
The interesting questions now concern the processes involved in
memory for source or context, the extent to which these are
qualitatively or quantitatively different from those required for
item or fact memory, and the exact role that the FLs play in these
processes. More generally, interest focuses on how multiple attributes of an event are encoded, linked together, stored, and later
retrieved, and what brain regions are involved in these different
aspects of memorial processing.
Source memory tasks are virtually always more difficult than
item memory tasks, requiring the retrieval of additional detail and
the use of more complex decision processes. So, for example, if
one heard a sentence spoken in a particular voice, memory for the
sentence might be achieved without knowledge of the voice, and
recognition might be accomplished on the basis of a simple familiarity judgment. However, memory for which voice spoke that
particular sentence would require retrieval of the sentence, of the
voice, and of information linking the two in a particular spatiotemporal context. Although a source recognition decision might
still be made on the basis of familiarity, the judgment is almost
certainly more difficult than item recognition, requiring an evaluation of the familiarity of an item-source pair rather than of the
item alone. In many source recognition tasks, this judgment requires discrimination among highly confusable alternatives, each
with high and equivalent levels of familiarity (i.e., alternative
sources have been presented equally often during the experiment),
making the task particularly difficult. Such difficult decision processes may require the FLs.
It may also be the case that the FLs are not just involved in
source memory per se but are recruited for any difficult or novel
memory tasks that cannot be easily handled by well-wom routines
(Shallice, 1982). Considerable evidence implicates the FLs in
recall tasks (for a review, see Wheeler, Stuss, & Tulving, 1995),
which are typically more difficult than recognition tasks and
usually require a search process not always necessary for recognition. Similarly, remembering aspects of experience, such as new
voices or fonts, may be more difficult than remembering the
meaning of words and sentences and thus may require more
controlled processing. Even in recognition tasks, retrieval of context may be needed if familiarity assessments fail to yield an
unambiguous result. When memory retrieval is not simple or
effortless, as in many free recall and source memory tasks and also
in difficult recognition tasks, the FLs may be required to formulate
and initiate search strategies and engage in complex decision
processes concerning the outcome of the search (Moscovitch,
1994).
Although the FLs may have a special role to play during
memory retrieval, they may also be involved at encoding, particularly for the encoding of nonfocal information like source or
context (Craik & Jennings, 1992). Central aspects of an episode,
such as the meaning of a sentence, may be processed rather
automatically, limiting the need for frontal involvement. Peripheral information, however, may require more controlled frontal
processing to ensure that it is attended, adequately encoded, and
represented in memory. In many source memory experiments,
participants' attention is directed toward the primary content information. Contextual features may therefore be ignored. There is
some evidence to suggest that source memory deficits may be
eliminated in older adults when attention is directed specifically to
the source (Naveh-Benjamin & Craik, 1995), but failure to reduce
such deficits through attentional manipulations has also been reported (Schacter, Osowiecki, Kaszniak, Kihlstrom, & Valdiserri,
1994). It may be, as suggested by Naveh-Benjamin and Craik
(1996), that older adults exhibit a trade-off between memory for
item and source such that they process one at the expense of the
other. Failure to take account of more than one aspect of a stimulus
may be particularly likely in older adults with frontal dysfunction.
1133
SOURCE MEMORY IN OLDER ADULTS
Finally, for source memory tasks, it is not sufficient to encode
an item and its context independently; the two must be linked. The
source memory question is not, "Did you hear this voice in the
experiment?," but rather, "Which of the voices that you heard in
the experiment spoke this particular sentence?" To answer the
latter question, content and context (i.e., sentence and voice) must
be integrated at encoding, and information about their cooccurrence must be stored in memory. Integrative encoding processes may depend on the FLs (Stuss & Benson, 1986; Wheeler,
Stuss, & Tulving, 1997). Alternatively, the binding of multiple
components of a stimulus event into an integrated trace may be a
function of the MTLs (Chalfonte & Johnson, 1996; Cohen &
Eichenbaum, 1993; Cohen, Poldrack, & Eichenbaum, 1997; Henkel et al., 1998; Kroll, Knight, Metcalfe, Wolf, & Tulving, 1996).
Further, it may be that both brain regions are needed for successful
coding and storage of an entire event: The FLs are needed to
initiate and carry out the control processes to ensure that all aspects
of an experience are encoded; the MTLs are needed to ensure that
these various attributes are bound together and reregistered in the
memory storage system.
The present series of experiments was designed to investigate
the nature of the role of the FLs in source memory, specifically the
extent to which the FLs are implicated in the encoding and/or
retrieval of source or context information. In a previous source
memory experiment with older adults (Glisky et al., 1995), we
found a double dissociation between item and source memory such
that older adults with below average frontal function showed an
impairment in memory for the voice that spoke a sentence (i.e.,
source memory) relative to adults with above average frontal
function, but they showed no impairment in memory for the
sentence itself (i.e., item memory). However, those adults with
below average performance on MTL tests showed a relative impairment of item memory but not of source memory. Although
these findings were suggestive of a special role for the FLs in
source memory, the nature of that role was not explored.
The present experiments examined that role more fully by
including comparisons with young adults, by extending the findings to different domains of item and source information, and by
manipulating the focus of attention during encoding. We also
increased the size of the normative group on which neuropsychological functioning of the older adults was based to ensure greater
reliability of our FL and MTL measures. Still, our measures of FL
and MTL function are based, at this point, solely on neuropsychological, not neuroanatomical, evidence, and so they provide only
indirect indication of the involvement of specific brain regions. We
note that, although the tests that generate the composite scores
have been found to be sensitive to dysfunction of the FLs and the
MTLs, most of them require several cognitive processes and may
rely on multiple brain structures. Nevertheless, factor analyses
suggest that the tests contributing to each factor share a common
variance that is not shared by the tests in the other factor. Our
composite measures may therefore be more stable than the individual test measures that have often been reported in the literature
and may be more likely to reflect two independent processes. We
also do not mean to imply that these factors represent the only
functions subserved by these brain regions, but rather that they
reflect one of many functions that may involve these brain areas.
In the following experiments, we focus particularly on the role that
the FLs play in memory for the context of an event.
Experiment 1
Source memory judgments are virtually always more difficult
than item memory judgments, and for this reason it is possible that
the involvement of the FLs in source memory tasks reflects their
difficulty rather than any specific memory processing component.
In our earlier experiment (Glisky et al., 1995), the source task
required memory for an unfamiliar voice—a relatively difficult
memory task. If the FLs are involved when memory encoding and
retrieval processes are nonroutine (Shallice, 1982), then they may
be required for remembering novel voices whether these constitute
source information or represent the primary focal content of an
experience. In the present experiment, the stimuli for the item
memory task were unfamiliar voices, each speaking one of two
sentences. If the FLs are involved in all difficult memory tasks,
then we would expect that our low-frontal older adults would be at
a particular disadvantage on the difficult item task. However, if
there is something special about source memory that requires
frontal involvement, then we would expect that our low-frontal
performers would be impaired, as they were previously, on the
source or context memory task, which in the present study required
memory for the particular sentence that each voice spoke.
Method
Participants. The participants in all of the experiments reported in this
article were selected from a larger pool of healthy, community-dwelling
adults over the age of 65, who had been characterized on the basis of their
neuropsychological test performance within 2 years of experimental testing. Each individual in the pool has been assigned two scores, one representing relative performance on a group of tests associated with FL
function and the other representing relative performance on a group of tests
thought to represent MTL function. The tests contributing to the FL factor
include: number of categories achieved on the modified Wisconsin Card
Sorting Test (Hart, Kwentus, Wade, & Taylor, 1988), the total number of
words generated in a word fluency test, using initial letters F, A, and 5
(Spreen & Benton, 1977), Mental Arithmetic from the Wechsler Adult
Intelligence Scale—Revised (WAIS-R; Wechsler, 1981), Mental Control
from the Wechsler Memory Scale—Revised (WMS-R; Wechsler, 1987),
and Backward Digit Span from the WMS-R. The tests contributing to the
MTL factor include Logical Memory I, Verbal Paired Associates I, and
Visual Paired Associates II (all from the WMS-R) and the Long-Delay
Cued Recall measure from the California Verbal Learning Test (Delis,
Kramer, Kaplan, & Ober, 1987). These tests were grouped according to the
results of two factor analyses: (a) an exploratory principal factors analysis
of data from 48 older adults, which was reported in Glisky et al. (1995),
and (b) a confirmatory factor analysis of data from a separate group of 100
older adults. (Variance attributable to age was removed from test scores
prior to the factor analyses.) Both analyses produced two uncorrelated
factors and the same factor structure. The composite scores for each
individual represent average z scores for those tests loading on each factor,
relative to either the 48- or 100-member normative groups (depending oh
when the experiment was conducted). Scores in the 100-member normative
group are distributed such that 34 are above the mean on both factors, 26
are below the mean on both factors, 18 are above the mean on the FL factor
and below the mean on the MTL factor, and 22 are above the mean on the
MTL factor and below the mean on the FL factor (see Glisky et al., 1995,
for information about the 48-member group). Factor scores for participants
1134
GLISKY, RUBIN, AND DAVIDSON
for Experiment 1 were based on the 48-member group, and for all other
experiments, they were based on the 100-member group. In all of the
experiments reported in this article, the high- and low-FL groups differed
significantly on their composite FL scores but not on their MTL scores,
whereas the high- and low-MTL groups differed on MTL scores but not on
FL scores.
For the present study, 32 older adults were selected from the pool, 8
from each of the four neuropsychological groups. They received monetary
compensation for their participation. Characteristics of each group are
presented in Table 1. Separate one-way between-subjects analyses of
variance (ANOVAs) indicated that there were no differences in age,
education, or scores on the Mini-Mental Status Examination (MMSE;
Folstein, Folstein, & McHugh, 1975) as a function of neuropsychological
group (all Fs < 1.20). (The probability of a Type I error was set at .05 for
all statistical comparisons.) There were also no significant differences in
scaled scores from either the Vocabulary subtest of the WAIS-R, F(3,
28) = 2.15, MSE = 5.15, or the Similarities subtest of the WAIS-R, F(3,
28) = 2.50, MSE = 3.10. Twenty-four young adult undergraduates (age
range = 18-40, M = 19.9, SD = 4.6) at the University of Arizona
volunteered to participate to fulfill a course requirement. The scaled score
on the Vocabulary subtest was significantly lower in young adults
(M = 9.0, SD = 1.7) than in older adults (M = 13.4, SD = 2.4), F(l,
53) = 56.60, MSE = 4.60.
Materials. A large number of voices, both female and male, were
recorded speaking two sentences that were equated for speaking time:
"Clouds are expected to move in from the west later this afternoon,
increasing the likelihood of rain overnight," and "Stock prices fell
sharply in heavy trading today, reflecting the uncertainty in the trade
negotiations." Voices were selected to be as distinctive as possible and
included both young and old voices and voices with accents. Recording
was done using Soundedit software (Farallon Computing Inc., Berkeley, CA) and a Macintosh Hex computer. Voices were rated for distinctiveness by an independent group of 12 undergraduates, and three
sets of 12 voices—half female and half male—were constructed such
that all three sets had relatively high and equivalent ratings of distinctiveness. Two 12-item lists served as study lists, and a third 12-item list
served as distractors for the item recognition test. In each list, half of
the voices spoke one sentence and half of the voices spoke the other
sentence. There were two versions of each of the lists such that the
voices that spoke one of the sentences in one version spoke the other
sentence in the alternate version, and these were counterbalanced across
participants in groups. The three lists were also counterbalanced across
participants such that each list served equally often as a study list for the
item test, a study list for the source test, and distractors for the item test.
An additional two voices occurred at the start of each study list to
absorb primacy effects. All study and test materials were presented by
a Macintosh Quadra 610 computer using SuperLab (Cedrus Corporation, San Pedro, CA).
Procedure. Two study-test sessions were conducted. The first was
always the item memory test (i.e., memory for the voice) and the second
was the source-context memory test (i.e., memory for the particular
sentence that was spoken by the voice). Pilot data indicated no differences as a result of test order or whether the memory test was incidental
or intentional as long as an orienting task was used. In the first study
session, participants listened to one 12-item list of voices that was
presented three times in a different random order. After they heard each
voice, participants made a judgment on a 4-point scale, ranging from 1
(very unlikely) to 4 (very likely), concerning how likely it was that each
voice would be heard on the radio. No mention was made of a subsequent memory test. Following a 2-min interval in which people were
engaged in conversation while the test program was being loaded on the
computer, a two-alternative forced-choice (2AFC) recognition memory
test for the voices was given. Each of the 12 target voices was presented, speaking either the same sentence as at study or the other
sentence. The distractor voice was a novel voice of the other gender,
which spoke the other sentence. The interstimulus interval was 500 ms.
Voices were presented at test in a different random order for each
participant, and the order in which target and distractor voices were
heard was counterbalanced across items. Participants were asked to
press the appropriate key (7 or 2) to indicate whether they had heard the
first or the second voice at study, without regard to the particular
sentence that was spoken. They had unlimited time to respond.
Following a 15-min break, during which participants engaged in an
unrelated task, a second study session was administered, which was identical to the first except it had a new list of 12 voices. The recognition
memory test in this case was a 2AFC test for the sentence that each voice
spoke. Each of the 12 voices that had been heard during study was
re-presented at test, speaking each of the two sentences in a 2AFC format.
The participants' task was to indicate, by pressing a key on the computer
keyboard, which sentence the voice had spoken in the study phase. Voices
were presented in a different random order for each individual, and the
order in which the two sentences were heard was counterbalanced across
items.
Finally, all participants were given a voice discrimination test to ensure
that their sensory and perceptual abilities were adequate to detect similarities and differences in voices. Each individual heard 16 pairs of novel
Table 1
Characteristics of Older Adults as a Function of Neuropsychological Group in Experiment 1
HighFL function
High MTL
function
Low FL function
Low MTL
function
High MTL
function
Low .MTL
function
Variable
M
SD
M
SD
M
SD
M
SD
Age (years)
Education (years)
MMSE
Vocabulary8
Similarities'
FL scoreb
MTL scoreb
71.8
14.5
29.0
14.8
11.3
.56
.49
4.4
2.1
1.1
2.3
1.5
.55
.33
70.6
15.3
29.1
13.5
12.1
.58
-.64
3.5
2.4
1.4
2.2
2.0
.43
.52
70.8
14.5
28.1
13.4
11.1
-.39
.36
4.5
1.3
1.4
2.9
1.4
.40
.29
73.3
15.1
28.6
11.9
9.8
-.58
-.66
5.4
3.0
0.9
1.5
2.1
.45
.64
Note. FL = frontal lobe; MTL = medial temporal lobe; MMSE = Mini-Mental Status Examination.
* Scaled scores from the Wechsler Adult Intelligence Scale—Revised (Wechsler, 1981). b z scores (see text).
1135
SOURCE MEMORY IN OLDER ADULTS
voices speaking one of two sentences. The voices and sentences were
different from those heard in the main part of the experiment. Participants
were required to say whether the voices in each pair were the same or
different. For half of the pairs, the same voice spoke both sentences; for the
other half of the pairs, a different voice spoke each sentence. The two
sentences were always different.
Table 3
Proportion of Items Correctly Identified in the Item Memory
Task and Source Memory Task as a Function of
Neuropsychological Group in Experiment 1
FL function
Low
High
Results
On the discrimination task, all participants obtained a score of at
least 12 out of 16, with a mean score of 15.1 for young adults
and 14.2 for older adults. This difference was significant,
t(54) = 3.29, SE = 0.28, but both groups were close to the ceiling.
There were no significant differences among the four groups of
older adults.
Table 2 presents the proportion of items correctly identified in
the two memory tests as a function of age. Older adults were
impaired relative to young adults in both item memory (i.e.,
memory for voice) and source memory (i.e., memory for the
sentence), and both age groups scored higher on the item memory
test than on the source memory test. A 2 X 2 mixed ANOVA of
the number of items correctly recognized, with age as the betweensubjects factor and type of memory test as the within-subject
factor, confirmed a main effect of age, F(l, 54) = 19.64,
MSE = 3.57, a main effect of type of memory, F(l, 54) = 14.53,
MSE = 2.73, and no interaction. There was also a strong samedifferent effect such that voices that spoke the same sentence at
study and test were more likely to be identified correctly than
voices that spoke a different sentence. This same-different effect
appeared to be larger in younger than in older adults. A 2 X 2
mixed ANOVA, with age as the between-subjects factor and same
versus different as the within-subject factor, revealed a main effect
of age, F( 1,54) = 8.98, MSE = 1.77, a main effect of same versus
different sentence, F(l, 54) = 21.50, MSE = 1.00, and a marginally significant interaction, F(l, 54) = 2.86, MSE = 1.00,p = .10.
Analysis of the simple main effects of age indicated that younger
adults outperformed older adults in the same condition, F(l,
54) = 13.20, MSE - 1.22, but not in the different condition, F(l,
54) = 1.70, MSE = 1.55.
The top half of Table 3 shows the mean proportion of items
recognized correctly in the voice memory task as a function of
neuropsychological group. There were no differences among
groups. A 2 X 2 between-subjects ANOVA, with FL group and
MTL group as the two factors, indicated no main effects (Fs < 1)
and no significant interaction, F(l, 28) = 1.84, MSE = 3.33. A
MTL function
M
SD
M
Overall
SD
M
SD
.15
.14
.15
.70
.70
.17
.13
.12
.13
.12
.60
.59
.14
.11
Item memory task
High
Low
Overall
.19
.12
.16
.75
.68
.71
.66
.73
.69
Source memory task
High
Low
Overall
.68
.64
.66
.13
.08
.10
.52
.55
.54
Note. FL = frontal lobe; MTL = medial temporal lobe.
subsequent analysis that added the same-different factor as a
within-subject variable (see data in Table 4) showed that all groups
of older adults demonstrated an equivalent advantage for voices
that spoke the same sentence at study and at test, F(l, 28) = 3.82,
MSE = 1.33. The same-different variable did not interact with
group.
The bottom half of Table 3 shows results from the source
memory task (i.e., memory for the sentence that each voice spoke)
as a function of neuropsychological group. As supported by a
2 X 2 between-subjects ANOVA, high-frontal older adults outperformed low-frontal adults, F(l, 28) = 8.88, MSE = 1.86. In
fact, the low-FL group did not perform significantly above chance
(i.e., .50), 1(15) = 1.24, SE = 0.35. There were no differences in
performance as a function of MTL function, and the two factors
did not interact (both Fs <1). An additional analysis compared the
high-FL group with the young group and found a nonsignificant
Table 4
Proportion of Voices Correctly Identified as a Function of
Whether the Voice Spoke the Same or a Different Sentence at
Study and at Test in Experiment 1
FL function
High
Table 2
Proportion of Items Correctly Identified in Each TwoAlternative Forced-Choice Recognition Memory Test as a
Function of Age in Experiment 1
Young
MTL function
Old
Memory
M
SD
M
SD
Voice (item)
Same
Different
Sentence (source)
.83
.93
.73
.74
.17
.14
.23
.15
.70
.75
.65
.60
.13
.20
.18
.12
High
Same
Different
Low
Same
Different
Overall
Same
Different
Overall
Low
M
SD
M
SD
M
SD
.77
.73
.22
.20
.73
.58
.22
.25
.75
.66
.21
.23
.73
.63
.25
.12
.77
.69
.20
.14
.75
.66
.22
.13
.75
.68
.23
.17
.75
.64
.20
.20
Note. FL = frontal lobe; MTL = medial temporal lobe.
1136
GLISKY, RUBIN, AND DAVIDSON
difference, F(l, 38) = 3.25, MSE = 2.71. Finally, there was no
significant correlation between performance on the item memory
and source memory tasks among older adults (r = .01) or younger
adults (r = .28, p = .18).
Discussion
The voice memory task in the present experiment was an extremely difficult task. Although only 12 voices were presented and
they were repeated 3 times, older adults were able to identify only
70% of the voices in a 2AFC test. Recognition memory in young
adults was also well off the ceiling (83%). Despite the difficulty of
the item memory task, however, there was no hint that older adults
with below average FL function were impaired relative to those
with high FL function. It is therefore not the case that the FLs are
involved in all difficult or nonroutine memory tasks. Instead, once
again, the results implicated the FLs in memory tasks that require
the encoding and retrieval of source or context information. Thus,
there seems to be something qualitatively different about the kinds
of processes required for source memory relative to item memory—at least in the experimental paradigm used here. This conclusion was further supported by the lack of correlation between
performance on the two kinds of memory tasks. It should also be
noted that the frontal effect is unlikely to be attributable to IQ
differences: The groups were equivalent in Vocabulary and Similarities scores from the WAIS-R.
A hint concerning what component of memory processing may
be particularly dependent on FL function comes from results of the
same-different manipulation. In Table 4, it can be seen that the
older adults with low FL function showed a same-different effect
that was roughly equivalent to that of the high-FL group. When the
voice spoke the same sentence at test as at study, both frontal
groups benefited equally. This finding suggests that information
about the conjunction of the voice and sentence was encoded
during study by both groups. Those in the low-FL group, however,
were unable to make use of that information. When asked explicitly to discriminate between two possible conjunctions, the low-FL
participants' recognition of the correct sentence was at chance.
Two possible explanations of these findings may be considered.
First, it may be that both groups encoded the conjunction equally
well, but the low-FL group had a problem at retrieval. The two
sentences that were presented in the 2AFC memory test were very
familiar, both having been presented many times during the experiment. Thus, a recognition decision could not be made on the
basis of familiarity of the sentence alone. Instead recognition
would likely require retrieval of the specific voice-sentence pairing. Those people with diminished FL function may not have
initiated a search for the conjunction information and may therefore have had little relevant data on which to base their decision.
Second, the problem may lie in the decision process itself such that
individuals with low FL function may have difficulty evaluating
retrieved information, particularly when it requires discrimination
among highly confusable alternatives.
Although the finding of a same-different effect in the low-FL
group seems to implicate a retrieval problem in source memory, it
does not entirely rule out an encoding difficulty. People with
reduced FL function may engage in less elaborate or less thorough
encoding processes, focusing on central information to the detri-
ment of the peripheral or contextual detail. Nevertheless, they may
encode some of the context, perhaps enough to make the target
voice more familiar, particularly when re-presented in the same
context, yet not enough to support the kind of explicit retrieval
required by the source memory task (cf. Naveh-Benjamin & Craik,
1995).
Overall, older adults showed a much smaller benefit of the
repeated context than young adults, a 9% advantage compared
with a 20% advantage, respectively (see Table 2), and this finding
extended across all neuropsychological groupings of older people.
Young people appeared able to take advantage of the repeated
context to benefit item recognition in a way that older adults could
not. We suspect that with repeated presentations of a voice speaking the same sentence, components of the voice that are involved
in that specific voice-sentence pairing may be strengthened. This
may serve to enhance memory for the voice when it is heard again
at test speaking the same sentence. Evidence from pilot testing is
consistent with this interpretation. When 16 voices were presented
only once, young people showed only a 9% advantage for the same
compared with the different condition. It was only with repetition
that the enhanced same-different advantage emerged. Also, in the
present study, the item memory performance of younger adults
was superior to that of older adults only in the same condition.
Two possible explanations for this age-related same advantage
come to mind. First, with repetition, younger adults may have
developed a strategy that focused on specific voice-sentence features. Older adults may not have used this strategy, although to the
extent that such strategies are dependent on frontal function, we
might have expected the high-FL group to engage a similar strategy. Perhaps with more repetitions they would have. Alternatively,
the failure to benefit from repetition may reflect poorer voice
discrimination abilities among older adults. Although voice discrimination was high in all participants, there was a small but
significant advantage for young adults, which may have been
sufficient to allow them but not older adults to detect voice
features that were specific to a particular sentence. A correlation
between discrimination and the size of the same-different effect
was not significant, however (r = .21). In addition, a reanalysis of
the data including only those participants who scored at least 15
out of a possible 16 on the discrimination task (16 older adults
and 20 young adults) showed exactly the same pattern of effects.
Nevertheless, a more sophisticated analysis of auditory discrimination abilities might have revealed deficits among the older adults
that were not detectable in the current study.
One puzzling aspect of the findings in this study was the
complete absence of an effect of MTL function in the item memory task. In a previous study (Glisky et al., 1995) in which
sentences were the focal targets, we found a significant effect of
MTL function on item memory. There was no hint of such an
effect in the present study. Although we postulated that our MTL
factor reflected some basic memory process that would span
materials, three of the four tests that contribute to the factor are
verbal. It is possible therefore that the composite score reflects
primarily verbal memory and not a more global measure of memory functioning, or that memory for novel voices relies on different
processes than those needed on standard neuropsychological tests
of memory (cf. Winograd, Kerr, & Spence, 1984).
1137
SOURCE MEMORY IN OLDER ADULTS
Table 5
Characteristics of Older Adults as a Function of Neuropsychological Group in Experiment 2
Low FL function
High FL function
High MTL
function
High MTL
function
Low :MTL
function
Low MTL
function
Variable
M
SD
M
SD
M
SD
M
SD
Age (years)
Education (years)
MMSE
Vocabulary"
Similarities'1
FL score"
MTL scoreb
72.8
14.5
29.7
12.8
11.3
.62
.76
4.8
3.3
0.5
2.8
1.9
.65
.39
15.5
28.5
13.0
11.0
.37
-.80
5.4
2.9
1.6
3.5
4.6
.36
.48
73.0
15.0
28.0
12.6
11.2
-.36
.34
8.1
2.5
0.6
3.2
2.9
.16
.20
70.5
14.0
29.3
11.4
9.6
-.44
-.59
3.2
2.5
0.5
1.5
1.8
.45
.46
Note. FL = frontal lobe; MTL = medial temporal lobe; MMSE = Mini-Mental Status Examination.
a
Scaled scores from the Wechsler Adult Intelligence Scale—Revised (Wechsler, 1981) and the Wechsler Adult
Intelligence Scale—III (Wechsler, 1997). b z scores (see text).
In summary, the principal findings of this first experiment
discount the possibility that the FLs are involved in all memory
tasks that are novel and difficult. Instead, it appears that there is
something special about source memory tasks that requires the
input of the FLs. The question of interest, then, is whether the
source memory problem experienced by older adults with compromised FL function lies at encoding, retrieval, or both. Before
pursuing this question, we decided first to test the generality of our
findings with a different set of materials.
Most source memory studies have focused on memory for
perceptual features of linguistic stimuli, such as the voice, the font,
or the modality in which words or sentences are presented. Few
studies have examined nonlinguistic, visuospatial materials, and
the findings from those studies have been conflicting. Spatial
memory has usually been associated with MTL rather than FL
function. For example, Kopelman et al. (1997) reported that memory for spatial context was impaired in patients with temporal lobe
lesions but not in FL patients. Parkin et al. (1995) found no
correlation between spatial location memory and a selected group
of frontal tests in normal older adults. Thus, memory for spatial
context may rely on different processes than perceptual or linguistic context. We proposed to create a visuospatial analogue of our
voice-sentence experiments in order to test whether the effects that
we have observed reflect general memory principles applicable
across stimulus domains or whether they are specific to the verbal
domain.
Experiment 2
In this experiment, the materials consisted of a series of photographs portraying different chairs located in one of two rooms. The
item memory task required memory for visual objects (i.e., the
chairs), whereas the source memory task required memory for the
location of the objects. If source memory effects are independent
of the materials used but instead depend on the nature of the
memory task (i.e., source memory as opposed to item memory),
we should once again find that older adults with reduced FL
function are impaired relative to the high-FL group on memory for
the location of the chairs, despite equivalent memory for the chairs
themselves.
Method
Participants. Twenty-four older adults were selected from the pool, 6
from each of the four neuropsychological groups created by combining
high and low FL and MTL function. They each received monetary compensation for their participation. Characteristics of each group are presented in Table 5. The groups did not differ in age or education (Fs < 1).
There was a significant difference between groups in MMSE, F(3,
20) = 3.84, MSE = 0.91. Newman-Keuls tests indicated that the group
with high performance on both factors scored significantly higher than the
low-FL/high-MTL group, but as can be seen in Table 5, all groups were
near the ceiling and there was little variance in performance. The IQ
measures in this study were obtained from different versions of the WAIS
across individuals. We report mean scaled scores for the Vocabulary and
Similarities subtests, derived from the performance of 21 of the 24 participants on the WAIS-R or the WAIS-HI (Wechsler, 1997). Two other
participants had scores from the WASI (Wechsler Abbreviated Scale of
Intelligence, 1999), but we could not convert those to the same scale.1
There were no differences in either of these measures as a function of
group (all Fs < 1). The young adult group consisted of 24 undergraduates
(age range = 17-30, M = 20.5, SD = 3.1) at the University of Arizona
who volunteered to participate to fulfill a course requirement. The scaled
score on the Vocabulary subtest was significantly lower in young adults
(M = 8.8, SD = 2.1) than in older adults (M = 12.5, SD = 2.7), F(l,
43) = 27.40, MSE = 5.70.
Materials. Photographs were taken of a large number of different
office chairs that were situated in the psychology department at the University of Arizona. Each chair was photographed in one of two distinct
locations: a laboratory office cubicle and the department lounge. The
photographs were then scanned into monochrome format using an HP
ScanJet Hex. Thirty-two chairs, half appearing in each of the two locations,
were selected at random for the item memory test. Sixteen of these were
1
Scores on the WASI are age scaled. Scores on the WAIS-R cannot be
converted to age-scaled scores for adults over the age of 74. Therefore, we
report scaled scores from the WAIS-R and the WAIS-DI, which were
available for the majority of the participants.
1138
GLISKY, RUBIN, AND DAVIDSON
used during the study phase and 16 served as distractors during the
recognition test. These two 16-item sets appeared equally often as targets
and distractors across participants. A different set of 12 chairs, half in each
of the two locations, served as targets for the source memory test. There
were two versions of each of the three lists such that the chairs that
appeared in one room in one version appeared in the other room in the
alternate version, and these were counterbalanced across participants in
groups. An additional two chairs occurred at the start of each study list to
absorb primacy effects and at the start of each test list to serve as practice
items. All study and test materials were presented by a Macintosh Quadra
610 using SuperLab (Cedrus Corporation, San Pedro, CA).
Procedure. Two study-test sessions were conducted. The first was
always the item memory test (i.e., memory for the chair) and the second
was the source-context memory test (i.e., memory for the room in which
the chair appeared); pilot data indicated no differences as a result of test
order. In the first study session, participants viewed one set of 16 chairs,
which were presented one at a time for 3 s each. Participants were asked
to make a judgment on a 4-point scale, ranging from 1 (very uncomfortable) to 4 (very comfortable), concerning how comfortable each chair was
likely to be. They had unlimited time to respond. No mention was made of
a subsequent memory test. Following a 2-min interval in which people
were engaged in conversation while the test program was being loaded, a
2AFC recognition memory test for the chairs was given. Each of the 16
target chairs was pictured at test either in the same room as at study or in
the other room. The distractor chair was a novel chair that had been
photographed in the other location. The two choices were presented sequentially (to maintain equivalence to the voice study); each remained on
the screen for 3 s, with a 500-ms interstimulus interval, and participants
were required to press key 1 or 2 to indicate whether they had seen the first
or the second chair at study, without regard to its studied location. Chairs
were presented at test in a different random order for each participant, and
the order in which target and distractor chairs were seen was counterbalanced across items.
Following a short break, a second study session was administered, which
was identical to the first except with the 12-item list of chairs. The
recognition memory test in this case was a 2AFC test for the location in
which the chair had initially appeared. Each of the 12 chairs that had been
seen during study was shown at test in each of the two rooms in a 2AFC
format. The two choices were presented sequentially for 3 s each, and the
participants' task was to indicate, by pressing a key on the computer keyboard,
in which room the chair had appeared in the study phase. Chairs were
presented in a different random order for each individual, and the order in
which the two locations appeared was counterbalanced across items.
Results
Table 6 presents the proportion of items correctly identified in
the two memory tests as a function of age. Older adults were
Table 6
Proportion of Items Correctly Identified in Each TwoAlternative Forced-Choice Recognition Memory Test as a
Function of Age in Experiment 2
Young
Old
Memory
M
SD
M
SD
Chair (item)
Same
Different
Room (source)
.77
.78
.76
.64
.11
.16
.15
.16
.66
.66
.67
.54
.14
.21
.16
.15
impaired relative to young adults in both item memory (i.e.,
memory for chair) and source memory (i.e., memory for the room
in which the chair appeared), and both age groups scored higher on
the item memory test than on the source memory test. A 2 X 2
mixed ANOVA of proportion correct, with age as the betweensubjects factor and type of memory test as the within-subject
factor, confirmed a main effect of age, F(l, 46) = 12.60,
MSE = 0.02; a main effect of type of memory, F(l, 46) = 18.20,
MSE = 0.02; and no interaction. There was no same-different
effect (F < 1); chairs were equally well remembered whether they
were re-presented in the same room as at study or in a different
room.
The top half of Table 7 shows the mean proportion of chairs
recognized correctly in the item memory task as a function of
neuropsychological group. There were no significant differences
among groups. A 2 X 2 between-subjects ANOVA indicated no
main effect of the FL factor (F < 1); no significant effect of the
MTL factor, F(l, 20) = 2.96, MSE = 0.02; and no interaction
(F < 1). A subsequent analysis that added the same-different
factor as a within-subject variable showed no main effect and no
interactions associated with this variable (Fs < 1).
The bottom half of Table 7 shows results from the source
memory task (i.e., memory for the room in which each chair was
located) as a function of neuropsychological group. The data
indicate that high-frontal older adults outperformed low-frontal
older adults on this task, but this difference was not reliable, F(l,
20) = 1.38, MSE = 0.02. There was also no effect of the MTL
factor (F < 1) and no significant interaction, F(l, 20) = 1.36,
MSE = 0.02. However, the high-FL group was the only group that
performed significantly above chance, f(ll) = 2.11, SE = 0.04.
The high-FL group also did not differ significantly from the young
group, F(l, 34) = 1.50, MSE = 0.02, whereas the low-FL group
did, F(l, 34) = 5.53, MSE = 0.03. Finally, there was no
correlation between performance on the item memory and
source memory tasks among older adults (r = -.02) or younger
adults (r = .01).
Discussion
The pattern of results in the present experiment was roughly
consistent with previous findings, although the frontal effect on the
source memory task was not significant in this study. Nevertheless,
the effect was in the predicted direction, with the high-FL group
performing at a higher level than the low-FL group. The overall
levels of performance on the source memory task were rather low,
however, and so the failure to find a significant difference between
the two frontal groups may be attributable to a floor effect. As in
the previous study, the low-FL group failed to perform better than
chance on the source task and was impaired relative to young
adults, whereas the high-FL group performed at above chance
levels and was equivalent to young adults.
On the item memory task, there were no differences between the
high and low groups in either neuropsychological category. Although the lack of a frontal effect on item recognition is not
surprising—we have not found such an effect in any of our
studies—the failure to see an effect of MTL function on item
memory was unexpected, even though we failed to obtain that
effect in Experiment 1. We speculated that our MTL composite
1139
SOURCE MEMORY IN OLDER ADULTS
Table 7
Proportion of Items Correctly Identified in the Item Memory
Task and Source Memory Task as a Function of
Neuropsychological Group in Experiment 2
FL function
MTL fiinction
M
High
Low
Overall
.60
.71
.66
Overall
Lowi
High
SD
M
SD
M
SD
.19
.11
.15
.61
.71
.16
.11
.17
.15
.16
.56
.53
.15
.14
Item memory task
.14
.12
.14
.63
.72
.67
Source memory task
High
Low
Overall
Note.
.56
.60
.58
.15
.11
.13
.56
.46
.51
not be supported. It may be that voice and sentence information are
well integrated at the level of the stimulus, whereas object and
location information are more likely to be separate (Troyer, Winocur, Craik, & Moscovitch, 1999). Thus, in the case of chairs in
rooms, the background spatial context may have been only weakly
encoded, if at all, and not well linked with the target item, particularly in the low-FL group. The poor source memory performance
of that group may therefore be attributable to an encoding problem.
To rule out the possibility that people were failing to take account
of the source information at study, we decided to conduct another
experiment using an orienting question that focused attention on
the relevant information during encoding. When the memory test
was to be an item test, participants were oriented to the item, but
when the test was a test of source, people were oriented to the
relation between the item and its context. Thus for both the item
and the source task, the orienting question was task relevant.
Experiment 3
Method
FL = frontal lobe; MTL = medial temporal lobe.
score may be primarily verbal, although it does include a test of
visual-cued recall. It also does not include any recognition measures. It is possible, therefore, that the processes required for 2AFC
recognition memory are different from those required by the recall
tasks included in our composite measure. Consistent with this
notion, Aggleton and Shaw (1996) found that patients with damage
confined to the hippocampus were unimpaired on the Warrington
Recognition Memory Test (Warrington, 1984), a 2AFC test, and
Pickering (1999) reported that performance on 2 AFC recognition
tests did not fit a familiarity signal detection model. Both of these
findings suggest that the processes involved in 2AFC recognition
memory may be different than those on other memory tasks. We
plan to explore more fully the differences among various item
memory tasks in a further series of experiments.
In the present experiment, there was no memory advantage
when chairs were re-presented in the same room at test as at study.
Thus, the retrieval explanation, which seemed the most likely
interpretation of the source memory deficit in Experiment 1, could
Participants. Twenty-four older adults, 6 from each of the four neuropsychological groups created by combining high and low FL and MTL
function, were selected to participate in this experiment. They each received monetary compensation for their participation. Characteristics of
each group are presented in Table 8. There were no significant differences
among groups in age, F(3, 20) = 2.25, MSE = 22.00, or MMSE, F(3,
20) = 2.37, MSE = 1.62. There were, however, differences in education,
F(3, 20) = 5.38, MSE = 6.31, and in the scaled scores from the Vocabulary
and Similarities subtests of the WAIS-R, F(3, 19) = 8.50, MSE = 4.68,
and F(3, 19) = 3.98, MSE = 3.76, respectively. Post hoc comparisons
using Newman-Keuls tests indicated that older adults who were low on
both FL and MTL factors had significantly less education than both
high-FL groups. On the Vocabulary subtest, the group that was high on
both factors scored significantly higher than all other groups; on the
Similarities subtest, the high-high group scored significantly higher than
the low-low group. Twenty-four young adult undergraduates (age range =
17-23, M = 19.5, SD = 1.9) at the University of Arizona volunteered to
participate to fulfill a course requirement. The scaled score of the young
adults on the Vocabulary subtest (M = 8.8, SD = 1.7) was significantly
lower than that of the older adults (M = 12.6, SD = 3.1), F(l, 45) = 27.40,
MSE = 6.10.
Table 8
Characteristics of Older Adults as a Function of Neuropsychological Group in Experiment 3
High FL function
High MTL
function
Low FL function
Low'.MTL
function
High MTL
function
Low MTL
function
Variable
M
SD
M
SD
M
SD
M
SD
Age (years)
Education (years)
MMSE
Vocabulary*
Similarities*
FL score"
MTL scoreb
69.8
18.0
29.5
16.0
13.3
.68
.54
3.4
2.1
0.8
2.2
2.2
.45
.35
74.7
17.3
28.5
12.2
12.5
.68
-.49
6.2
3.2
1.1
1.0
2.2
.31
.30
70.5
14.3
27.7
12.2
11.3
-.54
.33
2.1
1.5
1.4
2.3
1.2
.34
.20
75.5
12.8
28.0
9.6
9.6
-.62
-.38
5.9
3.3
1.7
2.9
2.1
.16
.31
Note. FL = frontal lobe; MTL = medial temporal lobe; MMSE = Mini-Mental Status Examination.
* Scaled scores from the Wechsler Adult Intelligence Scale—Revised (Wechsler, 1981). b z scores (see text).
1140
GLISKY, RUBIN, AND DAVIDSON
Materials and procedure. The same materials and procedure were used
in Experiment 3 as in Experiment 2, except for the orienting questions
during study. In the first study session, participants were asked to make a
judgment on a 4-point scale concerning how comfortable each chair was
likely to be. Their attention was thus focused on item information, as in the
previous studies. The memory test that followed was a 2AFC recognition
memory test for the chairs.
During the second study session, participants were asked to make a
judgment concerning how well each chair fit in the room. This question
was designed to encourage integration of the chair and the room, ensuring
that the participants encoded the particular conjunction that they would
have to recognize at retrieval. The recognition memory test that followed
was a 2AFC test for the location in which the chair had initially appeared.
Results
Table 9 presents the mean proportion of items correctly identified in the two memory tests as a function of age. Older adults,
although still impaired relative to young adults in item memory,
were no longer impaired in source memory. Both age groups
scored higher on the item memory test than on the source memory
test. A 2 X 2 mixed ANOVA, with age as the between-subjects
factor and type of memory test as the within-subject factor, confirmed a main effect of age, F(l, 46) = 7.02, MSE = 0.02; a main
effect of type of memory, F(l, 46) = 17.50, MSE = 0.02; and a
significant interaction, F{\, 46) = 6.87, MSE = 0.02. There was a
marginal same-different effect, F(l, 46) = 2.75, MSE = 0.02,/> =
.10; chairs were somewhat better remembered when they were
re-presented in the same room at test as at study.
The top half of Table 10 shows the mean proportion of chairs
recognized correctly in the item memory task as a function of
neuropsychological group. There were no differences among
groups. A 2 X 2 between-subjects ANOVA indicated no main
effect of the FL factor, F(l, 20) = 1.67, MSE = 0.02, no main
effect of the MTL factor, and no interaction (Fs < 1). A subsequent analysis that added the same-different factor as a withinsubject variable again showed a marginal effect, F(l, 20) = 2.83,
MSE = 0.03, p = .10, but did not show any interactions associated
with this variable (Fs < 1.5).
The bottom half of Table 10 shows results from the source
memory task (i.e., memory for the room) as a function of neuropsychological group. The difference between high- and low-frontal
older adults that was present in Experiment 2 is no longer evident
in Experiment 3. In fact, there was a significant reversal of the
previous effect with the low-FL group now performing at a higher
level in source memory than the high-FL group, F(l, 20) = 5.73,
Table 9
Proportion of Items Correctly Identified in Each TwoAlternative Forced-Choice Recognition Memory Test as a
Function of Age in Experiment 3
Young
Old
Memory
M
SD
U
SD
Chair (item)
Same
Different
Room (source)
.83
.84
.82
.65
.11
.16
.14
.18
.68
.72
.64
.64
.15
.17
.20
.12
Table 10
Proportion of Items Correctly Identified in the Item Memory
Task and Source Memory Task as a Function of
Neuropsychological Group in Experiment 3
FL function
High
MTL function
M
Low
SD
M
Overall
SD
M
SD
.14
.18
.16
.66
.70
.14
.16
.10
.17
.14
.65
.63
.11
.14
Item memory task
High
Low
Overall
.67
.77
.72
High
Low
Overall
.58
.58
.58
.16
.10
.14
.65
.64
.64
Source memory task
Note.
.07
.09
.08
.72
.67
.69
FL = frontal lobe; MTL = medial temporal lobe.
MSE = 0 . 0 1 . There was also no effect of the MTL factor and no
significant interaction (Fs < 1). Neither the low- nor the high-FL
groups differed significantly from young adults (Fs < 1.7), and all
groups performed significantly above chance. Finally, there was
no correlation between performance on the item memory and
source memory tasks among older adults (r = —.09), but there was
a significant correlation among younger adults (r = .45).
Discussion
The source memory deficit that was present in the low-FL group
in Experiment 2 was completely eliminated in Experiment 3. The
change in the encoding question, which required participants to
attend to the relation between the chair and its visuospatial context
rather than just to the chair alone, benefited the low-FL group
selectively. The performance of the young adults and the older
adults with high-FL functioning was unaffected by this manipulation. This finding suggests that young people and older people with
high-FL functioning engaged these integrative encoding processes
spontaneously, whereas those in the low-FL group did not. Nevertheless, the older adults with reduced FL functioning were able
to encode the chair-room conjunction when instructed to do so,
and their source memory performance benefited accordingly. This
interpretation of the source memory deficit places the locus of the
deficit at encoding rather than at retrieval. It appears that without
instruction, older adults with below average FL functioning do not
initiate the appropriate processes to ensure that the relation between an object and its spatial location is encoded (cf. Craik &
Jennings, 1992). When the encoding processes are supported by an
appropriate orienting question, however, they appear able to
achieve a well-integrated encoding that can be readily discriminated from similar alternatives at retrieval.
This encoding explanation appears at odds with the retrieval
explanation suggested by Experiment 1. However, there may be
trade-offs between encoding and retrieval. So, for example, when
encodings are poor, as might be the case in people with low-FL
1141
SOURCE MEMORY IN OLDER ADULTS
functioning in the absence of appropriate orienting tasks, frontal
control processes at retrieval might be relatively more important.
However, when encodings are task relevant, as in the source
memory condition of Experiment 3, frontal retrieval processes
might be relatively less important.
Alternatively, the effectiveness of the integrative orienting task
may depend on materials. The encoding of words spoken by a
voice may be more automatic than the encoding of the location of
an object. Thus, an integrative encoding question that ensures that
the relation between an item and its context is processed may be
more important with visuospatial materials than with auditoryverbal materials. In Experiment 4, therefore, we tested the generality of the encoding effect with auditory-verbal stimuli.
In Experiment 3, as in the other experiments, we failed to find
any effect of the MTL factor on memory for items. Again, we have
no explanation for this result except to suggest that forced-choice
recognition tasks may rely on different processes than those tapped
by our factor scores. In this experiment, there is clearly an agerelated deficit in recognition of visual stimuli that is unaccounted
for by either of our neuropsychological composites.
An unexpected finding in Experiment 3 was the significant
correlation between item and source memory among young adults
but not among old adults. In Experiments 1 and 2, item and source
memory were uncorrelated in both age groups, consistent with the
view that the two memory tasks rely on different processes. It is
possible, however, that the integrative orienting question, designed
to link item and context, enabled or encouraged young adults to
use similar mechanisms or processes for both tasks. Older adults,
however, may have continued to rely on different processes for the
two tasks. In Experiment 4 we attempted to replicate the findings
of Experiment 3, using the auditory-verbal stimuli from
Experiment 1.
Experiment 4
Experiment 3 suggested that at least part of the problem in
source memory for older adults with reduced FL function is a
failure to encode the relation between an item and its spatiotemporal context. To test the generality of this effect with auditory-
verbal materials, we repeated Experiment 1, changing the orienting
question so that it focused people's attention on the aspects of the
stimuli that were relevant to the following memory test. When the
memory test was for the voice (i.e., the item in this experiment),
participants were oriented to the item; when the memory test was
for the sentence the voice spoke, participants were oriented to the
conjunction between the voice and the sentence. We know from
the results of Experiment 1 that all groups encoded the relation
between the voice and the sentence. It is possible, however, that
such encoding was relatively weak, sufficient to support the samedifferent effect in item memory but not sufficient to enable the
low-FL group to retrieve the context at test. Given the results of
Experiment 3, we predicted that the addition of the relevant encoding task would strengthen the encoding with respect to the
item-source relation and again eliminate the source memory deficit in the low-FL group.
Method
Participants. Thirty-two older adults were randomly selected from the
pool, 8 from each of the four neuropsychological groups. They each
received monetary compensation for their participation. Characteristics of
each group are presented in Table 11. There were no differences among
groups in age (F < 1), or MMSE, F(3, 28) = 3.20, MSE = 1.72. The
difference in education, F(3, 28) = 4.61, MSE = 5.63, was accounted for
entirely by the high-FL/low-MTL group, which had significantly more
education than all of the others. In this experiment, IQ measures were
obtained from the Vocabulary and Similarities subtests of the WAIS-R or
the WAIS-IH, derived from the performance of 23 of the 32 participants.
Seven other participants had scores on the WASI that could not be
converted to the same scale. There were no significant differences in
Vocabulary, F(3, 19) = 1.90, MSE = 6.65, or Similarities (F < 1). Twenty
four young adult undergraduates (age range = 18-28, M = 20.0,
SD = 2.4) at the University of Arizona volunteered to participate to fulfill
a course requirement. The scaled score on the Vocabulary subtest was
significantly lower in young adults (M = 8.0, SD = 2.2) than in older
adults (M = 11.9, SD = 2.8), F(l, 44) = 27.80, MSE = 6.20.
Materials and procedure. The same materials and procedure were used
in Experiment 4 as in Experiment 1, except for the orienting questions
during study. In the first study session, participants were asked to make a
judgment on a 4-point scale concerning how likely it was that each voice
Table 11
Characteristics of Older Adults as a Function of Neuropsychological Group in Experiment 4
Low FL function
HighFL function
High MTL
function
Low '.MTL
function
High MTL
function
Low MTL
function
Variable
M
SD
M
SD
M
SD
M
SD
Age (years)
Education (years)
MMSE
Vocabulary"
Similarities*
FL scoreb
MTL scoreb
72.9
14.6
29.1
13.7
11.7
.59
.66
5.5
3.3
0.8
2.9
2.1
.27
.40
71.8
17.4
29.1
12.5
9.0
.57
-.58
3.7
1.9
1.1
2.4
2.3
.40
.47
71.6
13.6
28.3
11.0
9.3
-.58
.17
6.2
1.9
1.3
2.2
4.6
.15
.13
71.8
13.5
27.9
10.3
10.0
-.67
-.47
4.1
2.1
1.8
2.6
3.3
.52
.33
Note. FL = frontal lobe; MTL = medial temporal lobe; MMSE = Mini-Mental Status Examination.
1
Scaled scores from the Wechsler Adult Intelligence Scale—Revised (Wechsler, 1981) and the Wechsler Adult
Intelligence Scale—IH (Wechsler, 1997). b z scores (see text).
1142
GLISKY, RUBIN, AND DAVIDSON
would be heard on the radio. Their attention was thus focused on the item
information. The memory test that followed was a 2AFC recognition
memory test for the voices.
During the second study session, participants were asked to make a
judgment concerning how likely it was that each voice would have spoken
that particular sentence. This question ensured that the participants encoded
the specific relation between voice and sentence that they would later have
to recognize at retrieval. The recognition memory test that followed was a
2AFC test for the sentence that the voice spoke.
Table 13
Proportion of Items Correctly Identified in the Item Memory
Task and Source Memory Task as a Function of
Neuropsychological Group in Experiment 4
FL function
High
MTL function
M
Low
SD
Results
M
Overall
SD
M
SD
.19
.15
.18
.68
.73
.19
.14
.15
.17
.15
.65
.64
.13
.15
Item memory task
Table 12 presents the mean proportion of items correctly identified in the two memory tests as a function of age. As in Experiment 3, older adults were no longer impaired in source recognition, given the integrative orienting question. In this study, they
were also not different from young adults in item recognition. Both
age groups scored higher on the item memory test than on the
source memory test. A 2 X 2 mixed ANOVA of number of items
correctly recognized, with age as the between-subjects factor and
type of memory test as the within-subject factor, indicated a
marginal effect of type of memory, F(l, 54) = 3.43, MSE = 3.33,
p = .07, and no other effects. An analysis of the same-different
effect indicated that both young and old individuals were more
likely to identify voices when they spoke the same sentence at test
as at study, F(l, 54) = 41.50, MSE = 0.80.
The top half of Table 13 shows the mean proportion of voices
recognized correctly in the item memory task as a function of
neuropsychological group. Once again, there were no differences
as a function of neuropsychological group: For the main effects,
Fs < 1, and for the interaction, F(l, 28) = 2.28, MSE = 3.96. A
subsequent analysis that added the same-different factor as a
within-subject variable showed all groups were more likely to
identify voices when they spoke the same sentence at test as at
study, F(l, 28) = 24.20, MSE = 0.70. This same-different effect,
however, was enhanced in the high-FL group, as indicated by an
interaction between the same-different variable and the FL factor,
F(l, 28) = 6.42, MSE = 0.70. This interaction is illustrated in
Table 14. There were no other significant effects (all Fs < 1).
The bottom half of Table 13 shows results from the source
memory task (i.e., memory for the sentence that each voice spoke)
as a function of neuropsychological group. The difference between
high- and low-frontal older adults that was observed in Experiment 1 is no longer present (F < 1). There was also no effect of
the MTL factor and no significant interaction (Fs < 1). Neither the
High
Low
Overall
.73
.70
.71
.19
.12
.16
.63
.77
.70
Source memory task
High
Low
Overall
Note.
.67
.63
.65
.12
.13
.12
.63
.66
.64
FL = frontal lobe; MTL = medial temporal lobe.
low- nor the high-FL groups differed significantly from young
adults (Fs < 1), and all groups performed significantly above
chance. Finally, there was no correlation between performance on
the item memory and source memory tasks among older adults
(r = .0009), but as in Experiment 3, there was a significant
correlation among younger adults (r = .40).
Discussion
The results of this experiment replicate the findings of Experiment 3, showing that the source memory deficit associated with
reduced FL function in older adults is eliminated by the presentation of a task-relevant orienting question for auditory-verbal materials as well as visuospatial materials. As in Experiment 3, the
change in the orienting task benefited the low-FL group selectively, providing no improvement in source memory for the young
or the high-FL group. Presumably, those with high FL functioning
spontaneously engaged such integrative encoding processes and so
gained no further advantage from the orienting task. The source
memory problem experienced by those with relatively lower FL
function thus appears to be an encoding problem—a failure to
initiate the appropriate processes required to encode the relation
Table 14
Proportion of Items Correctly Identified When the Voice Spoke
the Same Versus a Different Sentence at Study and at Test as a
Function of Frontal Lobe (FL) Group in Experiment 4
Table 12
Proportion of Items Correctly Identified in Each TwoAlternative Forced-Choice Recognition Memory Test as a
Function of Age in Experiment 4
FL function
Young
Old
Low
High
Memory
M
SD
M
SD
Voice (item)
Same
Different
Sentence (source)
.73
.83
.63
.68
.17
.21
.20
.21
.71
.79
.62
.64
.17
.16
.23
.14
Overall
Study/test context
M
SD
M
SD
M
SD
Same
Different
Overall
.84
.58
.71
.11
.24
.16
.74
.66
.70
.19
.11
.18
.79
.62
.16
.23
SOURCE MEMORY IN OLDER ADULTS
1143
General Discussion
encoded but that it is linked with content. In the present set of
studies, we cannot separate the attentional and integrative aspects
of frontal control. The orienting question that we provided both
focused attention on the source and required people to consider it
in relation to the item. In other studies, however, when attention
was focused on the source without any instruction for people to
relate it to the item (Schacter et al., 1994), source memory deficits
in older adults were not eliminated. Thus, it appears that attending
to contextual information is not sufficient to remediate source
memory deficits. The FLs must also initiate processes to integrate
the item with its context.
The idea that older adults may be deficient at initiating appropriate encoding processes is not new. Craik (1986; 1994) proposed
that failure of self-initiated processing is the principal cause of
reduced memory performance in aging. The present study further
suggests that these self-initiating processes are frontally controlled
and are deficient only in a subset of older adults. Craik (1986;
1994) also suggested that the provision of environmental support
in the form of encoding and retrieval cues should reduce or
eliminate the age-related memory deficit. The integrative orienting
questions in Experiments 3 and 4 clearly played such a supportive
role for adults with reduced frontal function, enabling them to
encode the relation between item and source and thereby perform
normally on the source memory task. The use of recognition tests
may also have provided retrieval support, reducing the need for
search processes at test.
The results of Experiments 1 and 2, which used auditory-verbal
stimuli (i.e., many voices speaking one of two sentences) and
visuospatial materials (i.e., many chairs in one of two rooms),
respectively, expand the domain of source memory studies and
provide further support for the hypothesis that source memory is
particularly dependent on functions associated with the FLs. In
addition, they suggest that the age-related deficits often observed
in source memory tasks are a result not of age per se but of reduced
FL functioning, which occurs in a subset of older adults.
The primary focus of the present article, however, is on the
nature of the frontal involvement in source memory, specifically
whether the FLs played a relatively more important role at encoding or retrieval. Although the answer to this question is not
straightforward, the findings of Experiments 3 and 4 provide
convincing evidence of the importance of the FLs for the encoding
of source. When people are given specific instructions to process
the relation between an item and its source or context, age differences in source memory are eliminated as are differences between
the high- and low-FL groups. The performance of the impaired
low-FL group improves, whereas the performance of the normally
performing high-FL group and the young group is unaffected. This
finding suggests that young people and the high-functioning older
adults spontaneously encode the relation between an item and its
context and thus do not obtain any added benefit from the integrative orienting question. However, those with poorer FL function appear not to process that relation unless explicitly instructed
to do so, although they are capable of such processing. The FLs
thus seem necessary to initiate the processes required to encode
contextual information and integrate it with focal content. These
processes may be partly attentional, ensuring an attentional focus
that is broad enough to include the contextual information, and
they may be partly integrative, ensuring not only that context is
It appears not to be the case, however, that the FLs are necessary
for all difficult encoding tasks. In both Experiments 1 and 2, the
item memory tasks were difficult and performance was impaired in
older adults relative to young. Yet there was no hint that this
impairment was related to low-FL functioning: The high- and
low-FL groups performed equivalently on the item recognition
tasks. Rather, the low-FL group seemed not to initiate encoding
activities beyond the processing of the focal stimulus and were
therefore impaired on the task requiring memory for nonfocal
information—the source memory task. By this account, the FLs
are important for initiating processing that is not clearly task
driven or experimenter driven. This characterization of the FLs'
role may also account for the association between source memory
performance and our frontal composite score. Although none of
the tasks comprising the frontal factor are memory tasks, they all
require some degree of nonautomatic, self-initiated processing.
Although the findings from the present experiments strongly
implicate encoding as the locus of the source memory deficit in
people with low FL functioning, they do not rule out the possibility
that the FLs may also play a role at retrieval. In Experiment 1, the
low- and high-FL groups showed an equivalent tendency toward
better item memory performance when the encoding context was
repeated at test. These findings suggest that both groups encoded
the relation between item and context but that the low-FL group
was unable to make use of that information at retrieval. Retrieval
problems of this sort may arise when encoded information is weak
or not relevant to the particular memory task at hand. Under these
circumstances, the FLs may be required to guide a search for
source information at retrieval or to engage decision processes to
evaluate an item-source pairing in the presence of confusable
alternatives. When two sources are both highly familiar, as in the
present experiments and in most studies of source memory, pro-
between an item and its context. Although the present experiment
provides no evidence for a retrieval deficit, as was suggested in
Experiment 1, it does not rule out the possibility that the FLs play
a role at retrieval under some circumstances, particularly when
source information is weakly encoded.
In the present study, there was no age difference in item memory
as there was in Experiment 1, and there were no effects of
neuropsychological group. All groups showed a same-different
effect, exhibiting higher levels of recognition when the voice was
re-presented speaking the same sentence at test. In this study,
unlike Experiment 1, the high-FL group showed a greater advantage of the re-presentation of context than the low-FL group,
suggesting perhaps that, like the young, they developed a strategy
of focusing on specific voice-sentence features. Given that Experiments 1 and 4 were identical with respect to the item memory
task, however, this performance difference across experiments
may reflect individual differences or chance variation.
Of interest, in this experiment as in Experiment 3, performance
on the item memory and source memory tasks was correlated in
the young people but not in the older adults. This finding suggests
that despite the fact that there were no age-related differences in
either item or source memory in Experiment 4, the older adults
may have performed the tasks differently than the young adults.
1144
GLISKY, RUBIN, AND DAVIDSON
cesses that reduce interference from the incorrect alternative may
also be involved. These search, evaluation, and inhibitory processes may break down as the FLs deteriorate with age.
These ideas about the role of the FLs in the retrieval of source
are clearly speculative and are not directly addressed by the
present experiments. Nevertheless, other evidence has suggested a
role for the FLs at retrieval (e.g., Senkfor & Van Petten, 1998; Van
Petten et al., 2000). We suspect that there may be trade-offs
between encoding and retrieval in the extent to which the FLs are
implicated in source memory. When an encoded trace is well
specified with respect to source information, either because of
self-initiated frontal processes or the support of appropriate orienting questions, the FLs may be relatively unimportant at retrieval. However, if the memory trace is poorly specified, as might
be the case for people with reduced FL function and no encoding
support, the FLs may be critical at retrieval. In the present experiments, we have found that we can eliminate the source memory
deficit in older adults with low FL function by using an appropriate
orienting task. We are now beginning further experiments to
determine how we might eliminate the deficit by affecting processing at retrieval.
Although our primary interest in this series of experiments was
in the effect of the FLs on source memory, we also characterized
our older participants in terms of their MTL function. We were
interested in MTL function for two reasons. First, in a previous
experiment (Glisky et al., 1995), we found MTL function to be
predictive of item memory, and so we were interested in replicating that finding with different materials. In the earlier study, the
stimuli for the item memory task were verbal, namely sentences. In
the present experiments, the stimuli for the item recognition tests
were nonverbal, namely voices and chairs. Our failure to find an
effect of MTL function on item memory in the present set of
experiments may reflect the largely verbal nature of our MTL
factor—three of the four tests are verbal. It is possible that some
memory processes are material specific, and that those processes
important for good verbal memory performance are not the same
as those needed for good memory in nonverbal domains. Memory
processes may also be task specific. All of the tests in the composite MTL factor are recall tasks, which may differ in some
fundamental ways from the 2AFC tasks used in the present experiments. Nevertheless, in the earlier sentence-voice experiment, we
did obtain a relation between the MTL factor and 2AFC recognition memory for sentences, and so the factor does seem sensitive
to differences in recognition memory. In three of the four experiments reported here, older adults were impaired in item recognition, an impairment not accounted for by our composites. Thus it
seems likely that our MTL factor score is not an accurate reflection
of global memory function. To explore whether such a global
measure is possible or whether two different composites may be
needed to account for both verbal and nonverbal memory, we are
currently expanding our test battery to include a broader range of
memory tests.
A second reason for including the MTL variable in the present
experiments was to replicate its lack of association with source
memory. In the present experiments, there was no hint of an effect
of MTL function on source memory. Other researchers (Henkel et
al., 1998; Mather, Johnson, & De Leonardis, 1999), however, have
reported correlations between source memory and our MTL com-
posite measure. Henkel et al. (1998) found strong correlations
between MTL functioning and source accuracy in a task that
required older adults to judge whether the referent of a word was
originally perceived as an object or merely imagined. (They also
reported correlations with the FL factor but only when testing was
delayed). Henkel et al. (see also Chalfonte & Johnson, 1996)
suggested that MTL structures are important for binding various
features of complex memories together and that the poorer performance of older adults with low MTL function reflected a binding
problem. Our findings also suggested that some older adults failed
to integrate item and context, but this problem in our experiments
seemed clearly dependent on FL function. Although it seems
possible or even likely that different tasks place different demands
on the functions associated with these two brain regions, methodological differences between experimental paradigms may also
play a role. So, for example, in our experiments the item and
source memory tasks were conducted independently, allowing the
source memory task to be accomplished without access to item
memory. The finding that memories for item and source were
uncorrelated in older adults further suggests that the two tasks
were relying on different processes. In the Henkel et al. experiment, people were asked to make item memory and source memory judgments together (i.e., they indicated whether an item had
been perceived, had been imagined, or was new). Thus, they may
have been encouraged to engage in the same processes and access
the same information for both tasks. The extent to which source
memory relies on MTL function may therefore depend at least
partly on task demands.
A final unexpected finding in these studies was the correlation
between item and source memory that was observed in young
adults—but not in older adults—when they were given the integrative orienting task (but not when given the item orienting task).
There are a number of possible interpretations of this finding, but
at this point all of them are speculative. At the very least, it implies
that even when provided with an integrative orienting question, old
people do not perform the source memory test in the same way as
the young, but nevertheless they are able to achieve equivalent
levels of performance. Further, it suggests that young people may
be flexible in their approach to source memory problems depending on the quality and type of information that they have, whereas
this may be less true for older adults. Finally, our claims that
source memory tasks rely on different processes than item memory
tasks have to be tempered. Although in our experiments with older
adults, we have consistently found item and source memory to be
dissociated with respect to frontal function, it seems reasonable to
suggest, along with Henkel et al. (1998), that under some conditions the two tasks may tap similar processes. The task for future
research is to map out these conditions so that we may gain further
information concerning the cognitive and neural processes that
underlie the encoding and retrieval of both focal and nonfocal
aspects of an event.
Finally, it is worth commenting on the finding that in all of the
studies, the high-FL group of older adults did not differ significantly from young adults in source memory. Thus, source memory
deficits are not an inevitable consequence of aging. In our 100person normative sample of community-dwelling older adults, 52
were categorized above the mean in frontal function; in our current
sample of 212 people, 122 are above the mean. It may, therefore,
SOURCE MEMORY IN OLDER ADULTS
be the case that many older adults do not experience significant
memory declines with age. Failure to take account of these individual differences may mask findings that are important for understanding the deficits that do occur and the reasons for them. The
important differences may not be between young and old adults
but may be between different subgroups of older adults who are
aging differently.
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Received June 14, 2000
Revision received January 5, 2001
Accepted January 17, 2001 •
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