Memory &. Cognition
1992.20(4),4t3-423
Working-memory mediation of adult age
differences in integrative reasoning
TTMOTHY A. SALTHOUSE
Georgia Institute of Technolagy,Atlontq Georgia
Three research methods were used to inveetigate the hypotheeized mediational influence of
working memory on age-related differencee in integrative ieasoning. Reeulte from all three pro
cedureswere consietentwith the-hypothesisbecause(1) statietical control ofan index ofworking
memory attenuated the age differences in reasoning accuracy, (2) young adults were more accurate than older adults in a measure reflecting the preservation oflinformation during procegsing, and (3) yorrng adults performing the task with a concunent memory load exhibited i qualitative pattern of performance similar to that of older adults performing thetask without a concurr€nt
memory load.
Although there has recently been considerableinterest
in working memory as a possible mediator of adult age
differencesin cognition (for reviews, see Light, l99l;
Salthouse, 1990; Stine & Wingfield, 1990), rhe amounr
of evidence directly relevant to the mediational role of
working memory is still quite limited. The research reported in this article was therefore designedto use three
investigative procedures to examine the hypothesis that
working memory functions as a mediator of the agerelated differences in at least some cognitive tasks.
The existence of negative relations between age and
measuresof fluid or processaspectsofcognition has been
well documentedon the basisof researchdating from the
early decadesof this century (see Salthouse, l99lb, for
a review). Despite a considerableamount of research,no
completely satisfactory explanation of these age-cognition relations is yet available. However, in the last few
years there has been growing interest in the role of working memory as a proximal (i.e., assessedat the time of
testing) mediator of age differences in at least some measuresof cognitive functioning. One of the reasonsfor the
enthusiasmabout explanations based on working memory is that the construct of working memory seemsmore
amenable to operationalization than do other relatively
general constructs such as attentional capacity. That is,
if one conceptualizesworking memory as involving the
simultaneous storage and processing of information, then
it presumably can be measuredby tasks in which there
are both storageand processingrequirements.For example, the two tasks used to operationalize working memory in the current project, computation spanand reading
This research was supported by NIA Grant R37 AG06826. I would
like to thank J. Jackson and A. Kersten for assistance in testing subjects, and the members of the Cognitive Aging Group at Georgia Tech
(R. Babcock, J. Earles, C. Hereog, A. Mattina, W. Rogen, B. Rypma,
and A. Smith) for helpful comments on an earlier draft of this manuscript. Corrcspondence should be addrcssed to T. A. Salthouse, School
of Psycholog, C.rcorgiakstitrte of Technologr, Adanra, CA 308324170.
span,involved subjects'retentionof digit or word information while concurrently carrying out processingconcerned with solving arithmetic problems or answering
sentence-comprehensionquestions.
The focal cognitive task in this project was integrative
reasoning involving abstract verbal materid. A typical
problem is illustrated in the top panel of Figure l. Prob.
lems can vary in the number of premisesdescribing relations between two terms, but dl evenrually end with a
question asking what will happento one term if a specified changeis introduced in another term. An advantage
of this particular task is that problem diffielty (as rcflected
by decision accuracy) can be systematically altered by rnanipulation of the number of premises presented prior to
the question, presumably because demands on working
memory are increasedby the additional requirementsfor
the storage and coordination of information associated
with more premises.
The tlree investigative proceduresused in this project
were all designed to examine the hypothesis that agerelated differences in the integrative reasoning task are
at least partially attributable to age-associatedreductions
in some aspectof working memory. The statistical control procedure tests the prediction that the magnitude of
the age differences should be greatly reduced if people
of different ages are statistically equated with respect to
their working-memory ability. Becauseworking npmory
involves the preservation (storage) of information during
processing, the experimental analysis procedure examines
the implication that older adults should be less accurate
than young adults at maintaining relevant information
while engagedin the performance of the task. And finally,
if a low level of working nrcmory can be consideredanalogous to a concurrent memory load, then the panern of
performance exhibited by older adults should be qualitatively similar to that found in young adults who perform
the task while also remembering other information. This
expectation is examined in the simulation procedure.
413
Copyright 1992 PsychonomicSociety, Inc.
414
SALTHOUSE
relatively narow and closely linked to particular qpes
of information and specific kinds of processingoperauons.
R and S do the OPPOSITE
The Salthouse (l99la) studies included two distinct
Q and R do the SAME
working-memory measures, but the group-administration
whatwill happento S? format may have created a spurious associationbetween
lf Q INCREASES,
the working-memory and reasoningmeasuresbecauseof
factorsunrelatedto working memory (e.g., time restrictions necessitatedby group testing). An attemptwas made
(1 Relevant,
1stposition)
to minimize the possibility of an artifactual relation beG and H do the SAME
tween the working-memory and reasoning measuresin
the present study by administering the tasks by meansof
F and G do the OPPOSITE
what will happento H? computers. This allowed research participants to spend
lf G DECREASES,
as much time as desired in each phase of the workingmemory tasks and to respond at their own pace in the
reasoning task.
(RecognitionProbe, 1st position)
If working memory is important for cognitive tasksbeD and E do the SAME
cause it allows information to be preserved while other
information is being processed,then one should expect
E and F do the OPPOSITE
*** D and E do the SAME***
to find better preservation of information during the performance of a cogritive task among people wtnse workingmemory systems are highly effective than among people
Figure l. Illustration of sample problems in the integrativewhose working-memory systemsare less effective. This
reasoning task.
prediction can be tested by using versions of the experimental analysisprocedure to evaluatethe availability
Statistical control procedures have been used in two of information presentedearlier in an ongoing cognitive
earlier research projects with this same integrative- task. Information availability can be examined with a vareasoningtask. Salthouse,Mitchell, Skovronek, and Bab- riety of different methods, but the critical point is that
cock (1989) administered the reasoning task and the the evidence for age differences in working memory is
computation-spanworking-memory task to 120 adultsbe- derived while the subject is actively engagedin the pertween 20 and 80 years of age. Multiple-regression equa- formance of a cognitive task and not from a separatetask
tions predicting reasoningaccuracyrevealedthat age was deliberately designedto assessworking memory. In the
associatedwith an R' of .278 when consideredalone. but terminology of Salthouse(1990), measuresobtainedwith
the R' value for age was reduced to only .l 19 after par- the experimental analysis procedure are within<ontext
tialing the variance associatedwith the working-memory measuies, whereas those typically used in the statistical
measure.Two additional studies,eachinvolving over 220 control procedure are out-of-context measures.
Previousresearch(e.g., Salthouse,[rgg, Palmon, &
adults between 20 and 80 years of age who were adMitchell, 190; Salthouseet al., 1989)with the current
ministered the integrative-reasoningtask and two workingmemory tasks, were reported by Salthouse(l99la). The integrative-reasoningtask examined information availabilworking-memory tasks in these studies were group- ity in terms of the contrast between two types of trials.
administered versions of the computation-span and Trials in which all premises are relevant to the decision
(illustrated in the top panel of Figure l) require both memlistening-spantasks (seeSalthouse& Babcock, 1991, for
further description). Resultssimilar to those of Salthouse ory and integration of information. That is, becausethe
et al. (1989) were obtained in both studies.To illustrate, question concerns terms originally mentioned in differvalues of R2 associatedwith age in the prediction of ent premises, information from several premises must be
reasoningaccuracy were .121 and .104 before statistical integrated and coordinated to determine the answer. In
control of a compositemeasureof working memory, but contrast, no information integration is required in trials
were only .015 and .036 after such control. The results in which only one premise is relevant becausethe quesof these earlier studies, therefore, suggestthat a fairly
tion concerns terms mentioned in a single premise. An
large proportion of the age-related differences in the example is illustrated in the middle panel of Figure 1, in
integrative-reasoning task may be mediated by reductions which the question refers to two terms originally related
in working memory. In terms of percentages,the vari- in the first premise. Becausetrials in which all premises
anceassociatedwith agewas reducedby 57 .2%,87 .6%, are relevant require both memory and integration whereas
those with a single relevant premise do not require acrossand 65.4To, respectively, across the three studies.
Although the statistical control procedure can be very premise integration, it has been assumedthat compariinformative. it does have several limitations. For exam- sons of accuracy in t}te two types of trials would be inple, the fact that only a single measureof working mem- formative about the relative importance of memory and
ory was used in the Salthouseet al. (1989) study raises integration processesin the performance of this particuthe possibility that the assessmentof working memory wits lar task.
(All Relevant)
WORKINGMEMORYAND REASONING
In both earlier srudies(Salthouseet al., 1989, lg0),
decision accuracydecreasedas more premiseswere presented, and the magnitude of accuracy decline for trials
with one relevant premise was nearly the same as that for
trials with all relevant premises. Furthermore, the same
generalpatternwas evident in adultsofall ages.Theseresults were interpreted as suggesting that a critical factor
in the variation in accuracy as a function of number of
premises and as a function of adult age rnay be the preservation of information, and not its integration or coordination. That is, the principal determinantof the variations
in reasoning accuracy associatedwith additional premises
or with increasedage appearsto be the ability to maintain previously presentedinformation rather than the ability to integrate information that is available in memory.
As with almost any experimental technique, however,
objections can be raised with respect to how results of
the manipulations are best interpreted. One reservation
about the contrast between one-relevantand all-relevant
trials is that even performanceon one-relevanttrials may
not be a pure measure of information availability, but
might also reflect the ability to transform the format of
the information from the terms "opposite" and ..same"
used in the premises to the terms "increase" and ..decrease" used in the question. Rather than representing
the ability to maintain information without integration,
therefore, accuracy of decisions in one-relevant trials
could reflect the ability to maintain information and to
convert it from one representationalformat to another.
This concern can be addressedby attempting to obtain
a more direct assessmentof information availability in the
form of recognition probes for previously presented
premise information. An example of a probe-recognition
trial used in the current experiment is illustrated in the
bottom panel of Figure l. Notice that the probe is presented in the same format as the premises, and the subject merely has to decide whether it is the same as. or
different from, one of the premises presentedearlier in
that trial. Supplementing the contrast of performance in
one-relevant and all-relevant trials with these recognition
probes should therefore allow a more definitive evaluation of the hypothesis that older adults perform pmrly
on integrative-reasoning tasks becausethey are less likely
to preserve relevant information than are young adults.
Becauserecognition probes provide a more direct assessment of the status of information in memory, a finding
of age differences in measures of probe-recognition accuracy would provide additional support for the inference
that a failure to maintain critical information during processing is an important determinant of age differences in
integrative-reasoning performance.
The principal assumptions underlying the simulation
procedure are that the effects of reduced working-mernory
functioning can be mimicked by various experimental
manipulations, and hence that the pattern of performance
exhibited by young subjects performing the reasoning task
with one of those manipulations should be qualitatively
similar to the pattern exhibited by older subjects perform-
4I5
ing thetaskundernormalconditions.BaddclcyandHitch
(1974;Hitch & Baddeley,1976)havepropoaedrharrequiring subjectsto maintaina concurrentmemoryload
reduceseffective working-memoryfunctioning because
someaspectsof working memory havcto bc devotedto
preservingthetask-irrelevant
memory-loadinformation.
If this assumptionis corr€c.t,and if a major faclor contributing to the agedifferencesin reasoningperforrnarrce
is a diminishedworking nrcmoryamongolder adultsrelative to young adulS, then the patternsof perforrnancc
for older adultsshouldbe expectedto be very similar to
thosefor young adults performing the task with a concurrent memory load. Bottr groups shorld have lower
levels of performancethan young adults without I concurrrentnpmory l@d, ard thc panernof pcrfornrala differerrcesbetweenyoung adults and old aduls should
resemblethat berweenyoungadultswith and without the
concurrentmemoryload.
The major limitation of the simulationapproachis that
directquantitativecomparisons
aregercrally rn nEaningful when there is no basisfor speci$ing the correspondencebetweena particular numberof yearsof agc differenceanda given amountof concurrentmemoryload.
Qualitativecomparisonsevaluatedwith rcspoct!o a common refererrcegroup are also complicatcdbecauscimpairmentsin performancesan be producedin a variety
of different ways. Confidenccthat the simulationis accuratethustendsto increasein proportionto the nnmber
and patternof correspondences
that can be establishcd.
Fortunately,the reasoningtaskinva*igatcdin this pmject
allowsserreralpossibleconmstsbetweendrepcrfmrrance
of older adultsandthat of youngadultswith a corrcurrent
memoryloadby comparingeachagainstthc pcrformance
of youngadultswith rcspectto ( I ) ttle effectof additional
premiseson decisionaccuracy,(2) trc pofiernof utrry
ofone-relevanttrials relativeto all-relevantfials, (3) thc
patt€rnof accuracyof orrc-relevanttrials asa fuirctionof
the serialpositionof the relevantpremise,and(4) thepattern of accuracyof recognition-probetrials as a function
of the serial position of the relevantpremise.
To summarize,if an important factor contributing to
adult age differencesin integrativereasoningis an agerelatedreductionin working npmory, thenorp wouldexpect (l) substantialattenuationofthe agedifferenccsin
reasoningafter statisticalcontrol of measuresof working memory, (2) significantly lower accuracyfor older
adultscomparedwith youngadultsin measuresof information availability obtafuredwhile subjecSare engaged
in theperformanceof thetask,and(3) a qualitativelysimilar patternof performancefor older adultsard for young
adultsperforning thetaskwith a concurrentrrcrnory led.
The study describedbelow was designcdto test eachof
thesepredictions.
In additionto the primary focus on working npmory,
there was also a secondaryintercst in the role of percepual-comparisons@ as a potential mediatorof the
agedifferencesin both reasoningand working memory.
Previoussodies have revealedthat statisticalcontrol of
416
SALTHOUSE
an indexofperceptuals@ greatlyattenuated
theagedifferencesin measuresof reasoningand working memory
(Salthouse,
l9la; Salthouse
& Babcock,l99l). However, the samepaper-and-pencil
measuresof perceptualcomparisonspeedwere usedin all of the earlier studies,
andconsequentlythe generalizabilityof this result is not
yet known. Two computer-administeredmeasuresof
perceptual-comparison
speedbasedon the Digit Symbol
SubstitutionTest (Salthouse,1992)were thereforeemployedto examinethe influenceof perceptualspeedon
the relationsbetweenageand performanceon both the
reasoningand working-memorytasks.
METHOD
SubJccts
Characteristics of the three samplesof adults who participated
in this project are summarized in Table l. Older adults were
recruited from ncwspaperadvertiscmentsand referrals from other
participantsand were paid a nominal fee for their participation. Both
samplesof young adults were college studentswho received extra
credit in psychology courses for their participation. It is apparent
in Table I that the three groups were sirnilar with respectto averageyearsof edrcation ard self-ratedtrealth,ard thus any age-related
differences in the performance rneasuresare unlikely to be confounded with differences in at least these characteristics.
hocedure
All participants performed four tasks, in the sameorder, before
the reasoningtask. The first task, digit-symbol, was a computeradministeredversion of the WAIS-R Digit Symbol SubstitutionTest
(Wechsler, l98l). Displays in this task consistedof a code table
associatingdigits and symbolsand a singletest stimulusconsisting
of a digit-symbol pair. The code table remained constant across
trials, but the identity ofthe digits and symbols in the test stirnulus
varied from trial to trial. The task was to press the / (slash) key
on the keyboard as rapidly as possible when the digit and symbol
in the test stimulus matchedaccording to the code table and to press
tlrcZkey on the keyboard when they did not match. The digit-digit
task was very similar but had no symbols. The code table was therefore uninformative in this task becausethe decisions were to be
made on the basis of the physical identity of the pair of digits. In
both tasks,a practiceset of 18 trials was followed by an experimenal
set of 90 trials. Becauseaccuracy was greater than 95% in both
tasks for all three groups, the median time per responsein the experimental trials served as the dependent measure.
The two working-memory tasks required subjects to remember
information while also carrying out specified processing. The tobe-rememberedinformation in the reading-span task was the last
word in the sentenoe,and the processingconsistcdof selectingwhich
of three alternatives was the corr@t answer to a simple question
about the sentence.The to-be-rememberedinformation in the computation spantask consistedofthe secod digit in an arithnreticproblem, and the processingconsistedof selecting which of three alternatives was the correct answer to the problem. Materials in both
tasks were identical to thosc described in Salthouseand Babcock
(l9l). Each successiveitem (scntenceor arithmaic problem) could
be viewed ai long as desired, and the subjectswere allowed as much
time as neededto type their recall responses.A trial consisted of
the presentationof the designatednumber of senteircesor arithmetic
problems followed by an anempt to recall the last items from all
of the presentedsentencesor arithmetic problems in the order in
which they were pres€nted. Spanswere determined by the longest
sequenccin which the target items were recalled correcdy and the
processing was performed without mistakes on at least two of the
three trials. A practice phase with trials containing sequencesof
up to three items preceded the experimental phase in each task.
The reasoning task was first described, then administered in a
practice block of seventrials. Two experimental blocks of63 trials
each were then presented.All participants received the sametrials
in the samesequence.Forty-five ofthe trials were normal reasoning trials, and l8 were recognition-probetrials. Across the two
blocks there were an equal number of increase (or satne) and decrease(or diferenr) trials for eachof the five combinationsof number and type ofpremises(i.e., l-1, 2-1,2-2,3-1, and 3-3, where
Tsble I
Mesns gnd Standard Deviationsfor Variables in the Three Samples
young
Young-Memory Load
ord
N
3
Proportionfemales
30
.53
0
.50
SD
Age
Health
Education
20.l
1.5
t4.2
DS time
DD time
CSpan
RSpan
Reas. acc.
Probe acc
l.l3
0.53
4.4
2.9
79.1
7'7.3
1.0
0.7
l.l
30
.30
SD
68.2
t.7
t4.5
0.14
l.9l
0.05
0.77
2.1
2.2
1.5
1.9
ll.l
59.9
r5.2
6.4
SD
5.'l
0.9
2.2
20.3
1.6
1 4 I.
1.5
0.6
1.3
0.36
0.27
t.7
1.6
9.2
12.2
l.l9
0.53
4.7
3.3
63.6
68.6
0.19
0.(X
1.8
1.8
l1.8
15.6
Note-Health is self-rating on a scale where I = excellent and 5 = poor. Education
is self-reported years of formal education completed. DS time is time in seconds in
digit-symbol task. DD time is time in seconds in digit-digit task. CSpan is the span
in the computation-spantask. RSpan is the span in the reading-span!ask. Reas. acc.
is percentagecorrect in the normal-reasoning trials. Probe acc. is percentagecorrect
in the probe-recognition trials.
WORKINGMEMORYAND REASONING
the first digit refersto the total numberof premisesand the second
digit to the number of relevantpremises).All types of trials, including the recognition-probetrials, were rurdomly intermixed
within the experinrntal block, but all participantsreceivcdthe sanre
random s€quence.
Premiseswere presentedsequentiallyfor 4 seceach. The ques_
.
tion remainedvisible until the subject'sresponse(Z for incriase,
/ [slash] for decrease),but the instructionsemphasizedthat the responsesshould be made as rapidly as was consistentwith maximum accuracy.
Recognition-probetrials were identical to the reasoningtrials except that the recognition probe replaced the question requiring an
increase or decreasedecision. One half of the probe trials had the
samepremiseasone ofthose pres€ntedearlier in the trial, and one
h4f
!"d a premise that differed from an earlier prcmise by a reversal of the original relation (e.g., a premise with a sanrerelation
was changed to one with an opposite relation). Decisions that the
premise was identical to onc pr€sent€dearlicr were communicated
by pressingthe / (slash)key, and decisionsthat the premts€was
different were communicatedby pressingthe Z key.
Trials for the subjectsin the concurrent-memory-load
condition
were preoded by the presenadon of a sct of five randomly sclected
digits. The subjectsviewed the digits for 4 sec, after which thc first
display of the reasoningtask was prescnted.Immediatelyfollowing_thedecisionresponseto the reasoningqucstionor recognition
probe, the subjectwas askedto recall the five digits in rhe order
in which they were presentedby typing them on the computerkeyboard. Performance in the reasoning tasks was only analyzed for
trials.in which the subjectswere correct on the digit recall. This
includedl0l trials for the averagesubject,with a raige acrosssub.
jects of 4E to 125.
REST.JLTS
Statistical Control Analyscs
Multiple-regression
analyseswereconductedto examine the statisticalcontrol predictionsofattenuatedagerelationson the measureof reasoningaccuracyaftei partialing the varianceassociatedwith working memory.
Becausemeasuresof informationavailability, in the form
of probe-recognition
accuracy,andof perceptualspeed,
from thedigit-symbolanddigit-digit tasl$, wer€obtained
from eachparticipant,thesemeasureswere also entered
into theregrcssionanalyses.Compositenreasures
of working memoryand perceptualspeedwere createdby averagingthe e scoresfrom the measuresin the computation
spanand readingspantasksto createa working-memory
compositeand averagingthe e scoresfrom the mqNures
in the digit-symbl and digit-digit rasks to create a
perceptual-speed
composite.(Correlationsbetweenthe
measuresin the total sampleafter partialingout agewere
.38 betrveen
the two working-memorymeasures
and .56
betweenthetwo perceptual-speed
measures.
Theremaining correlations,
againafterpartialingage,were -.0g
betweencomputationspanand digit-symbol, -.07 be_
tweencomputation
spananddigit-digit, -.16 between
readingspananddigit-symbol,and -.O$ betweenreading
spanand digit-digit.) Resultsof the regressionanalysei
basedon the completesamplesof youngandold aOutts,
andof youngadultswith andwithouta Concurrent
mem_
ory load,are summarized
in the top panelof Table2.t
417
Entriesin the first columnof Table2 referto the cumulativeR2afterthevariablein thatrow andtheimnrcdiately precedingrows had beenenteredinto the regression equation.Valuesin the secondcolumnindicatethe
incrementin Rr whenthc variablein that row is added
to the regressionequation.The valuesin thethird column
are F ratiosevaluatingthe statisticalsignificanccof the
initial R'or theincrementin Rr associated
with theadded
variable.Finally, the entriesin the fourth columnindicatethe perc€ntage
by which thegroupdifferenccswere
attenuated
by satisticalconrol of theprecedingvariables.
For example,thediffererrcebetweenth€ initial R! for age
of .479andthe incrementin Rr for ageafter controlling
the influenceof workingmemoryof .248is .23I , whicfi
correspondsto an att€nuationof 4t.2%.
Becausesomesubjectshad an averageaccuracyvery
close to chance,the analyseswere repeatedaftcr omitting subjectswith lessthan80%correctresponscs
on the
reasoningtrials with only onepremise. This is an arbitrary
criterion, but it doesensure.that
the levelof understanding and degreeof motivationwas sufficientlyhigh thar
the task could be performedwith moderateaccuracyin
the simplestcondition.Thesedata, bascdon 26 young
adults, 16older adults,and 12 youngadultswith a concurrentmemoryload, are displayedin the bottompanel
of Table2.
Three points should be noted about the resultsof the
analysesinvolvingthe groupsof youngadultswithouta
concurrentmemoryloadandold adults.The first is that
therclativeannuntof afienuation
(i.e.,48.2% in thcconplet€sarnpleand32.4% in the restrictedsample)of the
age-associated
varianceafter control of working memory
is similar to that foundin the previousstudiesusingthe
statisticalcontrolprocedure(e.g., Salthous€
et al., 1989;
Salthouse,
l99la).
The secondpoint is that the reduction in age-related
varianceassociatedwith control of the probe-accuracy
rneasureis approximatelythe sanreasthatassociated
with
theworking-memory
(i.e., 49.3%vs. 48.2% in
measure
the completesample)and that the additional reduction
when both measuresare controlled simultaneouslyis
rathersmall(i.e., to 61.8%).This suggcsts
that,ar least
with respectto theage-related
differerrceson reasoningaccuracy, the two variablesare not in&pendentbut instesd
have a certain amountof straredor common variance.
Finally, it can be seenthat statistical control of the
perceptual-speed
measure,either by itself or in combination with other variables,resultedin an attenuationof
the age-relatedvarianceby 80% togO%. The apparent
implication is that a large proportion of the age-related
differences in this reasoningtask is mediatedby agerelatedreductionsin speedofprocessing,as indexedby
the perceptual-speed
measures.
Resultsfrom the contrastsof young adults with and
without a concurrentmemory load are presentedin Table 2 primarily for purposesof comparisonwith the age
contrasts. Notice that unlike the differences between
4I8
SALTHOUSE
Table 2
Results of Hierarchical RegressionAnalyses on Average ReasoningAccuracy
Young vs. Old
Young vs. Young-Memory
Percent
Attenuated
Increment in R
N
Load
Percent
Attenuated
Increment in R'
All Subjects
2'l.4*
Group
.479
53.28*
.321
Working memory
Group
.283
.531
34.41*
30.12*
48.2
.009
-346
551
0.77
29.41*
Probe accuracy
Group
.396
.639
.243
62.50*
38.2't*
49.3
.461
.617
156
68.56*
23.191
51.4
Working memory
Probe accuracy
Group
.283
.463
.&6
.180
.1 8 3
44.74*
28.35*
28.92*
61.8
.009
.461
.622
.l6l
I.31
67.01*
23.87*
49.8
Perceptual speed
Group
.46
.547
.081
58.55r
1 0 . 2*1
8 3 .I
.100
.370
.210
9.08*
24.38*
15.9
Percepoal speed
Probe accuracy
Group
.46
.605
.67
.1 3 9
.062
78.22*
23.36*
10.43*
87.1
.100
.480
.626
.380
.t46
15.03*
56.77*
21.86*
54.5
Percepoal speed
Working memory
Group
.46
.529
.582
88.9
.100
.r 0 l
.382
.001
.281
9.09*
0.06
25.q*
t2.5
Perceptual speed
Working memory
kobe accuracy
Group
.M
.529
.620
.67|
89.4
.100
.l0l
.480
.629
.001
.379
.t49
t4.87*
0.10
56.l3*
22.03*
53.6
Group
.426
29.72*
.t47
Working memory
Group
.tu
.r22
.472
.288
13.62*
2t.261
12.4
.2' to
.148
6.03
7. 2 8
Probe accuracy
Group
. t66
. 5l 7
.351
I3.38*
28.451
17.6
.312
.48
.136
20.33*
8.88*
'1
.5
Working memory
Probe accuracy
Group
.184
.254
.531
.070
.277
14.94*
5.67
22.44*
35.0
.122
.34
.482
.222
.138
8.25*
14.94*
9.31*
6.1
Perceptual speed
Group
.451
.490
.039
34.52*
3.03
.o94
36.1
Perceptual speed
Probe Accuracy
Croup
.451
.525
-5&
.o'74
.039
36.49t
4.36
2.M
.2n
.rt'l
5.33
4.30
90.8
.361
.M
.244
.105
7.6*
16.02*
6.86
28.6
94.r
.l17
.2N
.305
.083
.105
5.89
4.t9
5.28
93.0
.tl7
.2ffi
.3U
.494
.063
.053
.063
.091
.051
62.3t4
8.43*
7.10
'17.93*
10.54*
15.28*
8.64*
.452
-5.0
Subjects Satisfying Accuracy Criterion
Percepoal speed
Working memory
Group
.451
.505
.530
Perceptual speed
Working memory
Probe accuracy
Group
.451
.505
.547
.5't7
.054
.425
.054
.u2
.030
39.32*
6.45
3.43
39.46*
4.'t2
3 . 7|
2.62
6.35
.lt7
90.8
.083
.184
.l l0
7.95*
5.59
12.33r
7.16
-0.l
I
I
25.2
*P < .ol.
young and old adults, the performance differences associated with the memory-load condition were not substantially attenuatedby statisticalcontrol of the workingmemory or perceptual-speedvariables. This is to be expected becausethe two young adult groups were very similar in these out-of-context measures(cf. Table l).
Analyses of Information Availability
Accuracy in the reasoningtask as a function of the number of presentedpremises is displayed in Figure 2. The
top panelcontainsthe datafrom all subjects,andthe bottom panelpresentsresultsfrom the subsetof subjectsin
eachgroupwith accuracyof at least80% on trials with
only one premise. Notice that accuracydecreaseswith
morepremisesandthat the absolutelevel of performance
is very similar for trials with one relevantpremiseand
for trials in which all premiseswere relevant.The analysisof variance(ANOVA) results,summariz€din Table 3,
confirm that the main effects of group and number of
premiseswere siSnificantbut that the relevanceeffect
WORKINGMEMORYAND REASONING
eral waysin whichaverageaccuracycouldhavedecreas€d
with the pres€ntation
of additionalpremises.For example, accuracymight haveremainedinvariantfor either
the first or the last premisein the trial but declinedon
otherpremises,or it mighthavedeclinedneadyuniformly
acrossall premisepositions.The results,displayedin Figure 3, indicatethat the secondcharacterization
is more
accurate.That is, for all threegroups,accuracywaslower
with more premisesregardlessof the serial positionof
the relevantpremise.Furthermore,youngadultswithout
a concurrentmemoryload were alwaysmore accurate
nt
thanweresubjectsin the othertwo groups.Resultsof the
o
ANOVAs with agegoung, old) andpremiscgpe (i.e.,
o
l-1,2-1,2-2,3-1,3-2,arf,3-3,wherethefirstandsec0.4
ond
digitsrefer to numberof premisesand positionof
Young
Old Young- Mom. Load
relevantpremise,respectively)'asfactorsaresummarized
c
A lRl e l 6 / . + + +
o
in Table4. Of particularinterestis theabsence
l Rslev. ----;--of anage
x premisetype inrcractionin both the analysisbasedon
all of the dataand in the analysisbasedon the datafrom
n
the restrictedsample.Virtually identicalrcsultswereevi0.9
dentin theanalysescontrastingthetwo youngadultgroups
distinguished
by the presence
or absence
of a concurrent
0.8
memoryload.
Figure 3 also contains probe-recognition accuracy
o.7
ploaed as a function of serial position of the probcd
prcmise.Thegeneralpatterncloeelyrcsemblesthatof the
one-relevantreasoningtrials exceptwhen the trials containednvo premises,wherethe older adultsandttrcyoung
adults with a concunent memory load were somewhat
more accuratein thc recogrition trials than in thc reasoning trials. Results of the age grorrp x premise type
ANOVAs similar to thosecondrrctedon the accurrcy of
'
t
2
3
one-relevantreasoningtrials are summarizedin Table 5.
Numberof Premises
The major point to be emphasizedfrom thesc&u is that
the agediffererce in recognitionaccuracywaseliminated
by restricting the sampleto subjectswith accuracyof at
Figure 2. Accuracy in trials with all premisesrelevlnt to the do'
least 80% in the reasoningtrials with a single premise.
cision or with only onc premisc rrlevant to the decision es a function of the number of prcsented premises. The top penel prcsents To verify that the elimination of the agedifferenceswas
data from all subjects, and the bottom poml showsdala from sub'
not simply attributableto the reducedpower associated
jects with at least t0% accuracy on trids with a single prcmise.
with a smallersamplesize,an analysisof covariancewith
accuracyin one-premisereasoningtrials asthe covariate
wasalso conductcd.The agegroup main effect wasalso
(i.e., one relevant vs. all relevant) was not significant.
not significantin this analysis[F(1,57) = 0.85, MS, =
primary
patterns
The
difference betweenthe
in the top 131.061,thusconfirmingthe resultsfrom the restrictcd
andbonompanelsofFigure 2 is that in the bottompanel sampleanalysis.
the differencesbetweenthe youngandold groupsappear
to increaseasadditionalpremisesarc presented.This pat- Qualitative Sinituity of Age end
tern wasverified in the ANOVA asthe interactionof age Concurrent-Memory-Loed Contrests
group X numberof presentedpremiseswas significant
Inspectionof Figures2 and 3 and Tables3, 4, and 5
in the data from the restrictedsample.With this single reveals that the performanceof all three groups was
exception,the resultsfrom the analysesinvolvingthecon- qualitatively very similar. This is evidentin the declines
trastbetweenyung adultswith ad witlrut theconcurrcnt- in accuracywith additionalp,remises,
in the neadyequivamemory-loadrequirementweresimilar, particularly with lent levels of accuracyfor one-relevantand all-relevant
respectto t}teabsence
ofinteractionsinvolvingthegroup trials, andin the serial-positionfunctionsfor one-rclevant
factor.
reasoningtrials and for probe-recognitiontrials. StatistiAccuracywas also analyzedon one-relevanttrials as cal supportfor this similarity is evidentin the generalab.
a functionof the serialpositionof the relevantpremise. senceof inleractionsinvolving the group variable in the
Theseanalvseswere of interestbecausethere were sev- ANOVA resultssulrunarizedin Tables3, 4, and 5.
L
I
I
419
,l
420
SALTHOUSE
Young
Young - Mem. Load
otd
0.9
o.7
o
o
t
o
0.5
0.4
()
Reasoning
Recognition
c
9
o
E
I
(L
r
o.s
0.8
o.5
0.4
Premise Position
Figure 3. Accuracy in reasoning trials with one relevant premise and in recognition-probe
trials asa frmction of the serial pmition of the rehvant or probed premise.The top panel prcsents
data from all subjects, and the bottom panel shows data from subjects with rt le{st ffi% sccuracy on trisls with a single prcmisc.
DISCUSSION
The results of this study suggestthat there are at leasl
two factors involved in the age differences in integrativereasoning performance. One factor is fairly broad, in that
it affects performance in all conditions of the task and may
reflect lack of understanding, low motivation, or some
type of sensory or motor deficit. It is assumedthat the
influence of this factor can be minimized by eliminating
subjects with low levels of performance in the simplest
trials involving only one premise. The magnitude of the
age differences when the sample was restricted in this
manner was somewhat smaller than that in the complete
sample, but there were only two caseswhere the pattern
ofresults appeareddifferent. One difference occurred in
the analysessunmarized in Table 3, where the interaction
Table 3
Results of Analyses of Variance on ReasoningAccuracy
Young vs. Old
Young vs. Young-Memory Load
df
MS"
dl
MS,
All Subjects
47.50*
658.24
Group
I,58
Numberof premises
Group x number
2,rt6
"
69.87*
2.63
205.45
I ,58
2,1t6
"
Relevance(onevs. all)
Group x relevance
1,58
'
0.60
|.ffi
1 3 5l.9
r,s8
"
Number x relevance
Group x numb€r x relevance
2,t16
"
0.72
0.50
rw.62
2,116
"
Group
SubjectsSatisfyingAccuracyCriterion
I,N
28.29*
363.41
t40.00*
9.69*
125.33
r,37
2,74
"
|,N
"
r.74
1.83
133.0'1
t,3'7
'
2,80
0.65
97.Q
2,'74
"
Numberof premises
Group x number
2,80
"
Relevance(one vs. all)
Group x relevance
Number x relevance
Group x numb€r X relevance
*p < .ol.
'
0.u
2'7.68*
&.14*
0.37
2.93
1.43
1.43
0.36
8| 5.04
t84.98
6.16
107.33*
3.5r
0.70
o.g
2.U
3.20
422.86
133.41
t22.94
125.88
I 14.90
104.59
WORKINGMEMORY AND REASONING
421
Teble4
!fg!Sg!4g!ry5
"lrgryrygg! leasoglg 1gllgy withone.Retevanr
hemise
_ _ I."q!q vt- ry __
df --!---g-L
v.qC '1.-v9rl1C-l49mory
Load
df
F
MS,
All Subjects
Group
l,58
33.93*
765.62
1,58
2 9 . 8 |t
9,61.98
Premisetype
Group x premisetype
5,290
13.851
1.23
3t4.24
5,290
t4.52'
0.46
357.24
Group
1,ltt)
16.39*
590.68
t.3'l
Premisetype
croup x premisetype
5,200
t9.20*
t.22
292.80
5,185
Subjects Satisfying Accuracy Criterion
'P < .ol.
-
8.86i
635.42
15.371
0.92
334.63
Teble 5
rlllnancc
on kobe.Recognirion Accurry
Io{$fl41dry=
_ _Yqlg r. qd
df
F
Group
I,58
Premisetype
Group x premisetype
5,290
Group
l,,to
5,2m
Mi,
All Subjects
9.40*
1139.93
22-t2*
0.66
339.29
L-flg "'. Iguls
__4L_ - J__
{ggg.y l4.a
MS,
1,58
4.77
t422.O7
5,290
22.t6r
t.1l
357.45
Subjects Satis[ing Accuracy Criterion
Premisetype
Group x premiserype
18.62'
o.37
985.06
|.37
288.88
5,185
0.A2
t7:15i
l.l4
t214.24
31 0 . 5 3
tP < .ol.
of age x numberof premiseswas significantin the restrictedsamplebut not in the completesample.This pat_
tern, illustratedin the bonompanelof Figure2, is ionsistentwith earlier findingsof larger agedifferenceswith
a greaternumberof premises(Salthouseet al., 1999,
1990).Inclusionof datafrom subjectswho performedat
or nearchancelevelsin the taskapparentlyobscuredthis
interactionin the analysesbasedon data from the complete sample.
The seconddifference in the results of the complete
sampleand the restrictedsamplewas in the analysisof
probe-recognitionaccuracy,summarizedin Tabli 5. In
this case-,the agedifferenceswere no longer significant
when subjectsperforming poorly in the simplestreasoning problemswereeliminatedfrom theanalyses.This pat_
tern, which is supportedby the absenceof significantige
differencesin the analysisof covariance,suggeststhit,
at leastwhen there is someassurancethat evlryone un_
denands thetaskandis apparentlymotivatedto perform,
young and old adults are equivalent in the aUitity to
preserveuntransformedinformation during processing.
A similar result in a cube-comparison
task was reportA
by Salthouse
ard Skovronek(19y2\,whereit wasconcluded
that agedifferencesin working memoryare pronounced
only whenthe stimulusinformationhasto be manipulated
or transformedin somefashion.This interpretation
may
also apply in the presentstudy becausetransformation
(from same or opposite to increase or decrease) is required with the reasoningquestions,but not with the recognition probes. The tendency for young adults to have
nearly the same accuracy in the one-relevant reasoning
trials and the probe-recognitiontrials (i.e., 79.4% vs.
77.97o) but for older adults to be less accurate in the
reasoningtrials (i.e., 66.7Vovs. 73.6Vo)is also consistent with this interpretation.3
No single set of results is definitive, but the combined
results from three quite different procedures appear fairly
convincing in suggesting that working memory is a major
factor contributing to adult age differences in integrative
reasoning. That is, working memory soemsto be implicated becauseofthe substantial attenuation ofthe age differences after statistical control of an index of working
memory, the presence of age differences in at least some
measures of information availability obtained during the
performance of the task, and the qualitatively similar pattern ofperformance differences between young adults and
old adults and between young adults performing under
normal and under concurrent-memory-load conditions.
Each of these procedures has limitationi, but becausethey
are not the same limitations, confidence in one's inferencesis enhancedwhen the results from each procedure
converge on the same interpretation. It therefore seems
reasonableto conclude that one ofthe causesofadult age
differences in certain cognitive tasks is a limited ability
422
SALTHOUSE
to preserve information during processing, which can be
viewed as a consequenceof an impairment in working
memory.
The fact that the premises in the reasoning task were
presentedsequentially, and for a duration ofonly 4 sec,
raises the possibility that there was a greater influence
of working-memory or perceptual-spe€dfactors in this
task than in more traditional reasoning tasks. This interpretation is plausible, but it should be noted that similar patterns ofage differences, and attenuationsofthose
differences after statistical control of an index of working memory, were observedin previous studiesin which
the premiseseither were presentedsequentially under selfpacedconditions (Salthouseet al., 1989)or were all presented simultaneously in a paper-and-pencil format (Salthouse, l99la). It therefore seemsunlikely that the results
of the current study have limited generalizability because
of the specific method used to present the stimulus materials.
If it is the case that age-relatedreductions in working
memory play an important role in the age differences in
this, and perhapsother, cognitive tasks, the question immediately arisesas to what is responsiblefor age-related
differences in working memory. Results from other research suggestthat the speedofexecuting relatively simple operations probably contributes to the age differences
in working memory. As an example, Salthouseand Babcock (l9l) found that a large proportion of the age differences in two measuresof working memory were reduced after statistical control of measuresof perceptual
speed, and these findings were replicated and extended
in the studiesreported by Salthouse(l99la). The present
study was not primarily designed to investigate this issue, but some of the results are obviously relevant. For
example, an analysis conducted with the compositeworking-memory measureas the criterion revealed that
the attenuationofthe age-relatedeffects on that measure
'15%,
was nearly
from an R2 of .251 for age when considered alone to a value of .063 after control of perceptual speed. Furthermore, the results summarized in Table 2 reveal that statistical control ofthe perceptual-speed
measures reduced the age differences in reasoning accuracy by an amount larger than that produced by control of working memory and that there was little additional
attenuation of the age differences by also controlling working memory.
In view ofthe apparent importance ofperceptual speed
in mediating the relations between age and performance
in both reasoningand working-memory tasks, it is desirable to consider exactly what is measuredby the tests of
perceptual speed. Of particular concern is the possibility
that becausethe digit-symbol substiotion test involves
nine digit-symbol pairs, it might representmemory factors as much as perceptual-speedfactors. The issue of
what is responsible for age-related differences in the
digit-symbol test was recently investigatedby Salthouse
(19y2).The following results, either basedon original data
or cited from previously published studies reviewed in
that article, led to the conclusion that memory factors were
relatively unimportant determinants of the age-related differencesin digit-symbol performance:(l) age differences
are still evident when all participants have learned the
digit-symbol associationsto a criterion ofperfect recall;
(2) agedifferences either remain constant or increasewith
additional opporrunities to learn the digit-symbol pairs;
(3) young and old adultshave similar serial-positionfunctions when responsetimes to individual items are arnlyznd
according to the position of the digit-symbol pair in the
code table, suggestingthat the code table was searched
in the same manner by both age groups; (a) the age differencesremain constant in relative terms as the number
of digit-symbol pairs, and hence the presumed memory
demands, is varied; (5) young and old adults devote the
same proportion of their responsetime to merely copying the symbols; and (6) adding working memory to the
prediction equation after perceptual speedresulted in little further attenuationof the age differencesin digit-symbol performance. Results supporting an interpretation that
the age differences were largely determined by the speed
at which elementary operations could be executed were
(l) high correlations betweendigit-symbol performance
and performance on other measuresof perceptual speed
and (2) little unique age-relatedvariance in digit-symbol
performance after statistical control of variance in otler
measuresof perceptual speed.
The casefor the current composite measureof perceptual speedas a reflection of speedfactors more than memory factors is even stronger than that for the digit-symbol measure alone because of the inclusion of the
digit-digit measurein the perceptual-speedcomposite. It
is difficult to imagine how memory factors could have
contributed to performance on the digit-digit task in which
sameldifferenrdecisionswere made about pairs of simultaneously presented digits. Of course, other influences
may be operating, but it seemsreasonableto suggeston
the basis of the preceding argumentsthat the perceptualspeedcomposite used in this study probably does reflect
some fairly basic aspectof the speedat which certain kinds
of information can be processed.
One possible interpretation of the relation between speed
and working memory is that working memory has a dynamic quality, perhapssomewhatanalogousto someone
trying to juggle several objects simultaneously. That is,
just as the number of items that can be successfullyjuggled depends on the rate at which they can be caught and
tossed, so might the limits on the number of distinct ideas
that can be kept active (or mentally juggled) in working
memory be set by the rate at which information can be
processed. From this perspective, therefore, working
memory might be interpreted as the set of items currently
active in consciousness,and age differences in working
memory might hypothesized to originate because increased age is associatedwith a reduction either in the
ability to activate new information or in the ability to rnaintain the activation of old information.
The hypothesisthat age-relateddifferences in working
memory might be mediated by reductions in the speed of
executing relevant operationsobviously needsto be con-
WORKINGMEMORYAND REASONING
firmed with additionalevidencefrom convergingproce_
dures.The causeof age differencesin procelsing-speed
must also eventuallybe explained.Nevirtheless, results
from this and other recent studiesseemto suggesta plau_
sible, and testable, interpretation of the caris"esof adult
age.differences in cognition that merits further investi_
gatlon.
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NOTES
l. Interactions involving the group variable with
each predictor vari,
able were also examined to determine whcther the innuclce
of the predictor varied across groups. None of these inre.".tlons
*a" significant
ar the designated(.01) significancelevcl.
2.
thar there are six possiblc premisc typcs becausca
single rel.Note
evant prcmls€ can appear in the first position when on€,
two, or thr@
prcmises are presentcd, in the socond position when
two or three pr€m$€s
are presented, and in the third position only when ihree premrscs
are
presented.
3:
x trial type (one-relevanr reasoning, recognrrron
tn^l-g:_qloup
probe) ANovA on the data from the restricted samples'revealed
thar
the age group.x trial type interaction failed to reachthe
cnt€non significance level [F(l,zlo) : 4.08, MS. = E5.78, p =
.051.
(Manuscript received May 2g, l99l;
revision accepted for publication lanuary 7, lWl.)