Irurnul ttl Ctntnrolot\ : PSf CHOI,OGI('AL
1 9 9 6 .V o l 5 l B . N o . ' 1 .P l 6 G P t 7 8
.tC/l!Nat!..!
( t\)\ri(ht 1996 ht Tlu,G.ktnkloqictl tt
irt| t)l Anrri&
Wherein an OrderedSequence
of Variables
Do Independent
Age-RelatedEffectsOccur?
TimothyA. Salthouse
Schtxrl ol'Psychology. Georgia Institutc of Technology.
A series of regression analyses wqs conducted to determine which variables in an ord.eredsequence had signiJicant
oge-related eJfectsal'ter control of'the itnmediately preceding variable in the sequence.I ndepenient age-retatid effects
in these rypes oJ analyses are particularly interesting because they represent age-relatid influences that aii not
nrcdiated through earlier vsriables. A total of 56 analyses are reported with ordered varfubles representing: (a)
snccessivetriols or ssssions in learning; (b) progressively more intervening events during the retentiin interval of a
nctnorl task; (c) suctessively bnger stimulus presentation durations; and (d) increased processing complexiry. In
nost ol the analyses a very large proportion d the age-related effects on later variahles was
fttuni to bi mediarcd
through earlier variahles in the sequence.
possihlcrcusonwhy thcrearc currentlyl'ewtheories
nNE
\ - - l l . r lc o g n i t i v ca g i n gp h e n o r nnea ( s c eS a l t h o u s e1. 9 9I i s
)
that thercis still littlc agrcclncntaboutthe corc phenontena
that ncedto bc cxplained.A ntajorgoal ol'thc currentreport
is to addressthis pnlblcnt by providing a parsintonittus
c l c s c r i p t i oonl ' t h ea g c - c o g n i t i orne l a t i o nisn n c c do f c x p l a n a l i o n . T h a t i s . t h e p r i r n a r yp u r p o s ci s t o s p e c i f y w h e r e
indcpendcnt
and distinctagc-rclatcdinflucnccsappearto be
o p c r a t i n gl.n l i l r n t a t i o o
n l ' t h i st y p c i s r c l c v a n t o w h a tn c e d s
to hc cxplaincd,bccauscscparatcexplanationsmay not be
nccessary
il'thc agc-rclatcdinllucnccson somclncasures
are
rncdiatedthroughthc cl'l'ccts
on othcr nleasurcs.
Figurc I portraysagc-rclatcdct'l'cctsin an ordercdsetol'
variables,with cachvariablepostulatedto be inlluencedby
thc prccedingvariablcin thc scquenccand by age. In other
wtlrds, perlitrmanccon a given variableis hypothesized
to
bc dctcrnrincdby perlirrntance
on the sanrevariablcat an
carlicrpositionin the scquenceas well as by age (secNote
I ). Thc key qucstionin this l'ranrework
is where,or whcn,do
uniqucor indcpendent
age-related
cft'ectsoccur'lOr, stated
Itornthe oppositepcrspcctive,
at what point in a sequence
of
ordcredvariablesarc thc age-relatcd
ef'fectsmerelycarried
by. or nrediatcdthrough,the et'f'ects
on variablesearlierin
the scquence'/
lf indcpendentage-relatcdcf'fbctsare cvident on every
variablcin the scqucnce,thenone could inf-erthat thereare
scparateor spccificage-relatcdinfluenceson eachvariable
that do not completelyoverlapwith the influenceson variablesoccurringearlicrin the sequence.
An clutcomeof this
typc would sugcestthattherearc severaldistinctage-related
influenceson thc variables.The existenceof independent
age-rclated
el'tcctsrlay bc interpreted
as clriginatingfrom a
shiti in the identityof lactorsaff'ectingvariablesat different
positionsin the scquence,
or fiom a shift in whatthe variable
reprcsents
as one nlovcsfiom early to late in the sequence.
Regardless
of thc cause,however,a finding of significant
independent
age-related
ef-fectson severalvariablesin the
sequencewould suggestthe needfbr multipleexplanations
of the age-related
influenceson the variables.In contrast,a
Pl66
discovcrythat nrostol' thc independent
age-related
ef'fects
occurearlyin an orderedsequencc
wouldsuggestthateffects
latcr in thc scquencearc mediatedby the earlier effects.
Bccausc thc nra.jorityof the interestingage-relatedinliuenccsin thiscascwouldoperatcon the initialvariables,an
outcontcol'this typc could bc interpreted
as suggesting
that
cflilrts at cxplanationol' agc-related
eft'ectswould be most
p r o d u c t i v ci t ' d i r e c t e da t t h c i n f l u e n c e o
s c c u r r i n go n t h e
variablcscarly in thc ordercdscquence.
Anultscs
Sirnilar analyticalproccdureswcre used in analysesof
orderedvariablcsrepresentinglearningacrosssuccessive
trialsor scssions.
lirrgettingacrossprogressively
moreintervening events, el'l'ectsof increasedstimulus presentation
tinrc,andel'f'ects
ol'increased
taskcomplexityas reflectedby
the numberof requiredprocessing
operations.Both correlation coefficients,indicatingtotal age-relatedeffects, and
standardized
regression(i.e., semi-partial)coefficients,indicatingdirectage-related
eft'ects,were computedfbr each
variablein the sequence
(seeNote 2). In termsof Figure l,
the directeffectscorrespondto the pathcoefficientsfiom age
to the variable(i.e., pathsri throughr/), the indirectel cts
correspondto the productof the pathsfrom ageto variablenI ( i . e . , a t h r o u g hr ' ) , a n d t h e p a t h sf i o m v a r i a b l en - l t o
variablen (i.e., x throughz), andthecorrelationcorresponds
to the sum of the direct and indirecteffects. In addition,
becausethe relativecontributionof a particularinfluenceis
often more interestingthan merelywhetherthat influenceis
significantlydiff'erentfrom zero, an estimateof the percentageof mediatedage-relatedvarianceis alsoreportedfor each
variable.The estimateis derivedby squaringthecoefficients
correspondingto the total and direct age-relatedeffects,
subtractingthe latterfrom the former, and then dividing that
differenceby the squareof the coefficientrepresentingtotal
age-relatedeffects. To illustrate, if the correlation coefficientwas .5 and the regression
coefficient(i.e., the semipartial correlationfor age after controlling for the previous
variablein the sequence)
was .2, the percentage
of mediated
P161
WHERE ARE AGE-RELATED EFFECTS?
age-related
variancewould be (.5' *.2' )l(.5' ) : .84 ( x 100)
: 84.07c. Finally, the total R2 value for the regression
equation is reportedto indicate the proportion of the total
variancein thecriterionvariablethat is accounted
fbr by age
and the prior variable.
A secondanalysiswas also conductedin each data set
afterexcludingresearchparticipantsin the bottom quartile
on the variablein the sequencewith the highestlevel of
performance.For example, in analysesof learning, the
individualsin the bottomquartileclnthe measureof performancein the last learningtrial would be eliminatedin this
analysis.The rationalewas that the variation acrossthe
orderedsequenceof variablesmight be reducedif some
researchparticipantshad low levels of performanceacross
all variables.This possibilityshouldbe minimizedby eliminatingthoseindividualswith low levelsof performancein
"easiest"
the
conditionin thedataset.However.the pattern
of resultsin thisrestrictedsamplewasnearlyidenticalto that
in the completesample.and thus only the resultsof the
completesampleare reported.
The currentanalyticalproceduresare basedon correlaof proportionsof varianceratherthan
tionsandexaminations
more traditionalanalysesof varianceand examinationsol'
prttmeanlevelsof perlirrmancebecausecorrelation-based
ceduresallow a dcterminationof the relationbetweenvariof the
ables and, more specifically.allow an assessment
degreeto which the age-related
influenceson two or more
variablesare independent.
This lattert'eatureis importantin
the currentcontext because- regardlessof the absolute
levels of perfbrmance- if two variablesare perfectly
shareall oftheir agc-related
correlated,
thenthey necessarily
influencesbecausethe age-rclatedeft'ectson one variablc
can be predictedl'rontthoseon the other variable.Admittcdly. l-cwvariableshavc perl'ectcorrelationswith one another,but it is probablyalsothe casethat f'ewvariablesare
completelyindependcntol' one another.Correlation-based
procedures
arethusneededto determinetherelativeamounts
of common and unique variance,and especiallycommon
variance,in difl'erentcombinaticlns
and uniqueage-related
; a l t h o u s&
e Coon,1994).
o l ' v a r i a b l e(sS a l t h o u s e1. 9 9 4 bS
of memoryor fluid
The datato be analyzedare measures
cognitiveabilitiesobtainedprimarilyfiom studieswith rnoderately large samplesof adults of diftbrent ages. Most
samplesconsistedof adultsfrorn a continuousrangeof ages
rather than two extremegroups such as college students
between lti and 2-5and rctircd adultsbetwccn60 and 75
yearsol'agc. Finally. thc nra.joritv
of thc analysesare based
on clatacollectedin rly laboratorvbecauscthey require
i n f o r m a t i o n o t t v p i c a l l vr e p o r t c di n j o u r n a la r t i c l e s .
Leurrtittg,
Sonreol'thc most interestingsctsol'orderedvariablesare
t h o s ed c r i v c dl l ' o n rs t t c c c s s i lter i a l sr t r s c s s i o nisn a l e a r n i n g
s i t u a t i o nT
. h a t i s . i n t h c s c d a t a s c t s t h e v a r i a b l e si n t h e
scquenccreprescntnreusurL'\ol pcrlirrntanceat progresc r t r a i n i n go n t h c s a m et a s k .
s i v el y g r e a t c lrer c l s o l ' p r a c t i c o
S e v e r adl a t as c t sa r ca r a i l a b l ci n u h i c h t i v c t t r m o r et r i a l s
have been prcsentedwith thc satncstitttulusnraterials.A
numbeo
r 1 ' s t u d i ehsa v ci n v o l v c da n a s s o c i a t i vl ce a r n i n gt a s k
in which the rcsearchparticipantuas rcquiredto determine
w h i c hp a i r so l ' i t c n r sc. o n s i s t i nogl c o t n b i n a t i o nosf s y m b o l s ,
l e t t e r s ,o r d i g i t s . w c r c a s s o c i i r t cw
d ith cach othcr. The
in this task has involvcdthe displayof a
typical proceclure
s i n g l es t i r l u l u si t c r no n t h c l c l ' to l ' t h cc o r n p u t esrc r c c na. l o n g
w i t h t h c c n t i r cs c to l r c s p o n sac l t c r n a t i v cosn t h c r i g h to f t h c
s c r c e nA
. l i c r t h c p a r t i c i p a nstc l c c t c da r c s p o n s cb. y m o v i n g
an arrow in l'rontof'onc ol' thc rcsponsealternativcs,f'cedback was prcscntcdto indicatcthc corrcct rcsponse.The
<ll'stimulusterms
is thc pcrccntage
measureol'perlirrrnancc
(l'roma sct ol'cithcr lirur or six) with corrcctresponses
on
c a c hs u c c e s s i vt cr i a l .
Typical data l'ronrthis task arc illustratedin Figure 2,
which portraysresultsavcragcdacrossthreediff'erentsetsof
s t i r r u l i f ' r o r nS t u d y 2 i n S a l t h o u s c( 1 9 9 . 5 a )A. l t h o u g ht h e
samplcin this study consistcdol' adultsl'roma continuous
rangcol'agcs,the rcscarchparticipantswcrc classificdinto
threegroupsto portraythc agc and trial cl'l'cctsin a single
figurc. N<lticcthat althoughthc thrce agc groupsstartedat
nearlythc sarnclcvcl, thc at.nountol' improvemcntacross
succcssivc
trials was snrallerlilr older adultsthanlirr young e ra d u l t s .
analyscsol'thesedata,of the data
Rcsultsl'romsequential
l'rornsimilar tasksin other studies.and ol data fiom maze
learningand liee recall tasksarc sumnrarizedin Table I .
Also includedin Table I aredataI'rorna nrentalsquarinstask
Young
(n=35)
+
Middlo
(n=34
otd
(n=17)
fr
6 6 0
o
-o
C)
o)
6 a
o
C
o
o
o
(L
L e a r n i n gT r i a l
g i r e c t ( e . g . . p a t h sa t h r o u g hd )
F i g u r e l F r a m e w o r kl i r r i n v e s t i g a t i n d
a n d i n d i r c c t( c . g . . a - x , b - y , c t c . ) r e l a t i t t n sb c t w e e na g e a n d a n o r d e r e d
s e o u e n co
e l c o s n i t i v ev a r i a b l e s .
Figure 2. Mean percentagecorrect on six successivelearninc trials in
( 1 9 9 5 a ,S t u d y2 ) t h r e ea g eg r o u p s ,S a l t h o u s e
P1 6 8
SALTHOUSE
Table l. Correlationsand PathCoefficientsfor RelationsBetweenAge and Measures
of Time or Accuracyon SuccessiveLearningTrials
Source
t0
PairedAssociateLearning
'Iri
( 1 9 9 4 a )S
Salthouse
. tudy I
n=239
( .12)
Correlation
( - .l 2 )
P a t hc o e f t i c i c n t
% Mediated
o
Total R'
.oI
( 1 9 9 4 a )S
Salthouse
. t u d y2
n - 125
( - .l 5 )
Correlation
( .15)
Path coetficient
(,
% Mcdiated
'fotal
R2
.02
al/B lock/Session
72.6
.64
93u
.
.70
-.42
(-.04)
99.I
.7U
,.30
(-.04)
98.).
.61
-.30
G.07'
94.6
.65
(-.09)
92.4
.6tt
( - . l l J)
-.29
.).9
t1
a<
1a
25.7
.21
-.3.+
.29
2't.2
.71
-.44
-.ll
1l
-.40
(-.02,
99.r.t
.tt5
)1
(0.00)
100
.'14
( 1 9 9 5 a )S
Salthouse
, tudy I, Digit-Lcttcr
n-170
Corrclation
Path coel'licient
% Mediatcd
'Iotal
R2
( - .r 4 )
( - . l . +)
0
02
-.26
1t
t4.lJ
.l0
( 1 9 9 - 5 aS
Salthouse
) .t u d y l . S y m b o l - S y m b o l
rt = 170
-.26
(-.07)
Correlation
1/
P a t hc o e l l i c i c n t
1.t)7)
(,
7 Mediatcd
l4.t.t
'fotal
R'
.(x)
.14
-.3|
. l-5
76.6
.39
-.26
( .01J)
90.5
.39
(.0u)
lto.2
.17
4 1. 6
.25
- . 4t
.28
53..1
.3tt
-.21t
(-.04)
91t.0
.36
6 1. 3
.16
1t.6
. 5|
-.3tt
( - .l 4 )
l,t6.4
.56
(.03)
99 I
.62
.31
( .10)
92.'t
.76
.42
( . lr )
93.1
.78
1 l
.35
-.llJ
.4-5
at
S a l t h o u s c( 1 9 9 5 a 1S, t u d y2
n
-ll9
Corrclation
Path coel'licient
% Mediated
(-.04)
(-.04)
0
.(x)
li)ral R,
-.3.1
-.33
5.lJ
.21
Maze Learning
Trial/B lock/Session
( I 9 9 5 a ) Study2
Salthouse
rt = t{6
(.05)
Correlation
(.05)
Path coellicient
% Mediated
t,
Total R2
.00
( - .r 8 )
( .19)
.09
(-.21)
(- l-5)
69.I
.49
r
)51
1-.03)
9tt.6
.61
( .26)
(, 07)
92.tt
.64
G.271
(.05)
96.6
.71
Free Recall
Trial/Block/Session
S a l t h o u s eF. r i s t o e ,& R h e e( 1 9 9 6 )
n -259
Correlation
Pathcoefticient
% Mediated
Total R'
-.38
-.3tt
0
.t4
-.47
-.28
64.5
.43
-.43
-.09
95.6
.60
.45
I t
92.9
.66
.41
(-.06)
97.9
.64
Mental Squaring
Session
C h a r n e s s& C a m p b e l l( 1 9 1 3 8 )
n =4t1
Correlation
Path coefficient
o/cMediated
T o t a lR 2
.50
.50
0
.15
.56
(.ls)
92.8
.82
.57
( 07)
98.5
.88
.61
(.0u)
98.3
.92
.62
(.04)
99.6
.95
( conlrnuesne,\tpage)
WHERE ARE AGE-RELATED
P169
EFFECTS?
Tablc | . Correlationsand PathCoefficientsfbr RelationsBetweenAge and N{easurc'
of Timc or Accuracyon SuccessiveLearningTrials (continuetll
Sourcc
t
2
3
4
-
5
6
7
f
i
e
t
0
Visual Search Varied Mapping
S u c c e s s i v2e4 0 - t r i a lB l o c k s
C o o p c r( 1 9 9 3 )
n - tl9 Y. t3tiC)
Correlation
P a t hc o e l f i c i c n t
% Mcdiatecl
lirtal R'
.66
.66
0
.11
.51
(-.09)
100+
.tt7
.53
(-.02)
100+
.93
.51
( .01)
100+
.94
S u c c c s s i v6e( X ) - t r i aBl l o c k s
R o g c r se t a l . ( l 9 t ) 4 )
n - l0 Y.70o
Corrclation
P a t hc o c fl i c r c n t
7 Mediatcd
'Iotal
R2
.10
.1(l
0
.49
.6u
(.01)
99.9
.92
.65
( .01)
l ( X )+
.93
.61
(.07)
9U.9
.91
.66
(.01)
99.1t
.94
V i s u a lS c a r c h- C o n s i s t c nM
( apping
S u c c e s s i v2e4 0 - t r i a lB l o c k s
( ' ( x ) p c r( 1 9 9 - 1 )
rr - ll9 Y. ult o
Corrclation
P a t hc o c l f i c i e n t
% Mcdiatcd
'l'otal
R'
.-56
.56
0
.l I
.57
(.0-5)
99.2
.91
.57
(.04)
99.5
.93
.5u
(.02)
99.9
.96
.5li
(.02)
99.9
.96
.61
.12
96.4
.90
.(rl
(-.01)
l ( X )+
.95
.61
1t)2)
99 9
.9-5
.60
(.02)
99.9
.95
.62
(.04)
99.6
.96
S u c c e s s i v6c( X ) - t r i aBl l o c k s
R o g c r sc t r l . ( 1 9 9 . 1 )
n - l0 Y.70o
(irrrclation
P a t hc o c l ' f i c i c n t
% Mediatcd
'lirtal
R2
.75
.75
(\
.56
.7lt
.l3
9 1. 2
.95
. I JI
.Olt
99.0
.9]
.t t l
.l0
9t1.5
.91
.lt2
(.01)
99.9
.91
M e n r o r yS e a r c h- C o n s i s t e nM
t apping
S u c c c s s i v 2e 4 0 - t r i a lB l o c k s
C o o p c r( 1 9 9 3 )
n -u] Y,lJ7o
Corrclation
Pathcoclficient
% Mediarcd
'lotul
R2
.55
.-55
0
.30
.59
.13
9 5 .|
.u5
.57
(.01)
99.9
.93
.61
.0u
98.3
.94
.66
.ll
9 1. 2
.95
Nolt,: Valuesin parcntheses
are not signilicantly(2 < .0 I ) dil'lerentlionr zero. A dashindicatesthat therewas an increasein thc age-relatedvarianceatier
c o n t r o lo l t h e o r i o r v a r i a b l ei n t h e s e u u e n c e .
reportedby Charnessand Campbell(lgtt|) and data fiom
visualand memorysearchtasksreportedby Cooper(1993)
and Rogers,Fisk. and Hertzog(1994) (sce Note 3). The
Charnessand Campbelldatacorrespondto the meantimes
ncededto squaretwo-digitnumbers(Class4 problemsin the
tcrnrinologyof the authors)acrosstive successivc
sessions.
The Cooperdata representnteanreacti()ntinreslor varied
and consistentmapping conditionsin visual or memory
searchtasks acrosssuccessivesets of 240 trials, and the
Rogcrsct al. datarcflcctnreanreactiontimesacrosssuccessivc sessions
consistingof 600 trialseach(seeNote 4).
the total
The first row in eachdataset(Table l) represents
age-related
efl'ectson thevariable,in the form of thecorrela-
tion coefticientwith age.The secondrow containsthedirect
or independent
age-related
et'fbcts.in the firrm of the standardizedregression
coeflicienttirr agcwhenbothageandthe
prior variablein the sequencewere usedas predictorsin il
sinrultaneous
regression
equation.The third row portraysthe
percentage
of the total agc-rclatcdvariancein the variable
that is rnediatedthroughthe eff'ectson the previttusvariable
in the sequence.Finally, the firurth row representsthe
proportionof total variancein the variablethat is predicted
by ageand. for variablcsotherthanthc lirst in the sequence,
thc pritlr variable.
The nrostimportantp()intt()noteaboutthedatain Table I
is that even though the magnitudeof the total age-related
P1 7 0
SALTHOUSE
eff'ectsremainsapproximatelyconstantin many of the data
sets.thereis a decrease
in the dircctage-related
effects,and
a concomitantincreasein the rnediatcdage-related
effbcts,
acrosssucccssivetrials or sessions.For example,tbr the
S a l t h o u s(e1 9 9 5 aS
) t u d y2 d a t as e ti l l u s t r a t eidn F i g u r e2 , t h e
age correlationsin trials 2 through6 rangedfiom .32 to
.42, but the perccntage
of mediatedeft'ectsincreased
from
lcssthan6% on trial 2 to over90'h on trials4 through6. This
patternsuggeststhat distinct and independentage-related
cif'ectsarc evidentprirnarilyat carly stagesin learning,and
thata Iar-{eproportionof'thcage-related
effectson Iatertrials
arc rlediatcdthroughthe efl'ectson earliertrials.
Althoughthe majorityof thedatain Table I correspond
to
accuracylcvcls on single trials acrossscvcral stimulusresponsepairs in a given task. the data l'ronrthe Charness
a n d C a m p b e l l( l g t i | ) , C o o p e r( 1 9 9 3 ) , a n d R o g e r se t a l .
(1994)studiesarc basedon meanslitr ntuchlargernumbers
o f t r i a l s( i . c . . 3 U l i r r C h a r n e s &
s C a r n p b e l l l,g t J t J2; 4 0 l b r
Coopcr. 1993;and 600 firr Rogerset al.. 1994).The very
sinrilarpatternin the analysesof thosedataprovidessorne
generalizability
to the int'erencc
that ntanyof the age-related
influencesin sirnplelcarningtasksare apparentfairly early
i n t h e l e a r n i n gs i l u a t i o n .
Althoughlargeproportionsol'the age-related
ell'ectswere
nrediated,and thc indcpendentage-relatcdinfluencesdecrcascdacrosssucccssivetrials, severalol'thc dircct ager c l a t c di n l l u e n c e so n l a t c r t r i a l s o r s e s s i o n sw e r e s i g n i ficantlydil't'crentlronr zero. Becausethis irnpliesthat thc
agc-relatcd
cft'ectson thosevariables wereunique, or at least
distinct l'ronrthc ef'l'cctscarriedthroughearlier variables,
theywarrantspecialattcntionevenil'thentagnitudes
of thosc
el'l'ects
are srnallrelativcto the ntediatcdcll'ects.Unlilrtunately. thc patternol' significantindepcndcntage-related
cl'l'ectsin thesedata is not vcry systernatic.and thus it is
diflicult to identil'ya trendotherthanthatalreadymentioned
in which tlirccr cl'lc'ctstlecrcasc.anct intlireci el'lccrsincrease,acrosssuccessivctrials or sessions.For example,
significantindepcndentage-related
ef'fectsoccurredon the
sccond.lirurth. and fifih 240-trialblocks in the consistent
mappingrnemorysearchtask in the Cooper(1993) study,
suggestingthat distinctage-related
inUuences
were operating throughoutlearningin this task. However,the specific
naturcof thoseinfluences.and why they appearto be absent
on the third 240-trialblock. cannotbe deternrinedfiom the
currentanalyses.The issueof how independent
age-related
cftectson later variablesin an orderedsequencernight be
investigated
is consideredin the GeneralDiscusston.
Lug Eflects
Anothertype of orderedvariableconsistsof measures
of
accuracyas a functionof the numberof eventsintervening
betweenthe presentation
and test of the relevantinfbrmation. Becauseit is the lossratherthanthe gainof infbrmation
that is of interestin this context.analysesof performance
as
a function of the nuntber of interveninsevents can be
considered
to reflectforgetting.or the conierseof learning.
Severalstudieshave been conductedwith a continuous
associative
memorytaskin which the stimulusand response
terms keep changing,and the researchparticipantis occasionally asked to report which responseterm was most
recentlypresentedwith a specificstimulusterm. Typical
datafrom comparisonsof lag manipulations,consistingof
the numberof eventsinterveningbetweenthe presentation
and testof the relevantinformation,can be illustratedwith
resuftsfiom Study I of Salthouse(1994a).Stimuli in this
study consistedof letter-digitpairs. and on diff'erenttrials
either0, I , 2, or 3 otherstimulus-response
pairsintervened
betweenpresentationand test of the critical pair. Mean
levelsof accuracyat each lag tbr three age groups in this
studyareportrayedin Figure3.
Resultsof sequentialanalysesof lag effectsin this and
othersimilarstudies are summarizedin Table 2. Noticethat
in many of thc datasctsthe agecorrelations,
corresponding
to thetotalage-related
eff'ects,aresmall.althoughtheywere
moderatelylarge in the Salthouse(1995b)study. In most
cases.howevcr. the direct age-relatedeff'ectstend to decrease,and the mediatedet-tectstend to increase.with
increasedlag. This patternimplies that most of the agerelatedef'lbctsat longerlagsare mediatedthroughthe ef-fects
at shorterlags. A similar strongmediationalinfluencehas
a l s ob e e nf b u n d i n s t u d i e sw i t h o n l y l a g so f 0 a n d I ( i . e . ,
K e r s t e n& S a l t h o u s c1, 9 9 3 :S a l t h o u s et ,9 9 4 a ) .
Thc amount ol' relevantdata on larr manioulationsis
clcarly limited. and the magnitudesof tte total age-related
el'f'ects(and proportionso1' total varianceexplained)are
r c l a t i v c l ys r n a l l .N e v e r t h c l c s st h
. e a v a i l a b l ed a t a s u g g e s t
that most ol' thc age-related
diff'erences
in firrgettingoccur
within thc lirst one or two items afier the infirrmationis
prcsentedbecauscthere are little or no independentagerelatcdel'l'cctson longer lags. Il'confirmed in additional
studies.this patternwould imply that explanationsmay be
nccdedonly lilr thc age-rclatedinlluences<lnmeasuresof
pcrlirrrnancc
with rclativclyshortlagsbetweenprescntation
and test becauscthc efl'ectsat longer lags appearto be
nrcdiatedthroughthoseat shorterlags.
Stirnulus
PrcsentutionTimc
An orderedsequence
ol'variablescan also be createdby
nranipulatingthe amount ol' time that relevant stimulus
infirrmationis displayed.That is, the stimuluspresentarion
Young
(n=83)
+
Middle
(n=85)
o
o
old
ln=72)
I
o
o
o)
s
c
o
o
L
^
O
^
U
0
1
2
3
- TestLag
Presentation
Figure3. Meanpercentage
correctwith0 to 3 stimulus-response
pairsbetweenpresentation
andtestfbr threeagegroups,Salthouse
StudyI ).
11994a,
WHERE ARE AGE-RELATED EFFECTS?
Pl7l
Table2. Correlations
and PathCoefhcients
lbr RelationsBctweenAge and Accuracy
on Difl'crentLags Bctween Prescntationand Test
Young
(n=39)
+
otd
(n=39)
a
90
o
o
i
Source
3 8 0
o
o-)
o
E
C o n t i n u o u sA s s o c i a t i v eM e n x r r y
S a l t h o u s (e1 9 9 3 ) .S t u d y I
tt - 246
(-.ll)
Corrclation
( . l l )
Pathcocfticient
% Mediatecl
o
'lirtal
R,
.0|
( 1 9 9 3 ) .S t u d y2
Salthouse
r - 25li
Correla(ion
. 16
-. l6
P a t hc o e l f i c r c n t
% Mediated
0
'lirtal
R,
.03
4l.ll
.22
-.20
( .0u)
1J4.0
.26
( 1 9 9 4 a )S
Salthouse
. tudyI
rt : 240
-.35
Correlation
-.35
P a t hc o e l f i c i e n t
7 Mcdiated
0
'Iotal
R,
. ll
-.23
(-.03)
9tt.I
.l-r
( .t6)
(-.06)
1t5.9
.21
-.56
.54
(-. l-5)
9t.3
.6|
( I995b)
Salthouse
r - 50Y.50O
Correlalion
l ) a t hc o e l l i c i en t
7 Metliatctl
-lirtal
R,
.51
.-52
0
.27
-.21
( .l6)
42.0
.10
.21
-. l9
|li.l
.ll
-.24
-. il3
.26
18.1
.5(r
o
(L
0
s00
1,000
1,500
2,000
2,500
Stimulus Presentation Duration (msec)
F - r g u r c : 1M. c a n p c r c c n t a g ceo r r c c ti t sa l u n c t i 0 n0 l s t i r n u l u sp r c s c n t l t t i ( ) n
t i n r el i r r ( w o a g c g r o u p s .K e r s t e na n d S : r l t h o u s(c1 9 9 - l ) .
( .03)
(0.0|)
t(x)+
.01
N o t r . V a l u c si n p a r e n t h c s casr c n o t s i g n i l i c a n t l y( 2 . : . 0 1) d i l l e r e n tl r o n r
z c r o .A d a s hi n d i c a t c st h i r tt h e r ew a sa n i n c r e a s ei n t h e a g e - r c l a t evda r i a n c c
r l ( e r c ( ) n t r oo
l l ' t h c p r i o r v a r i a b l ci n t h e s e o u c n c c .
tinre can be varied, and then the level of accuracydeterm i n e da t c a c h v a l u eo l ' t i m e . T h i s p r o c e d u r e
can be illustratedwith datal'roman unpublishedstudyby Kerstenand
( 1 9 9 3 ) ,i n w h i c h 3 9 y o u n g a d u l r sa n d 3 9 o l d e r
Salthouse
adultspertormeda continuousass()ciative
memorytaskwith
letterstimulianddigit responses,
and lagsbetweenpresentation and test of either 0 or I stimulus-response
pair. The
prcsentationduration of the letter-digitpair was varied
acrosstrial blocksfirst liom slow to fastduratir)ns.
and then
fiom lastto slow durations.Mean levelsof accuracyat each
durationaveragedacrosslags0 and I fbr the two agegroups
areportraycdin Figure4.
Results of sequential analyses of the Kersten and
Salthouse( 1993)data,of datafrom threeother associarive
memorystudies,andof datatiom a seriallettermemorytask
with recallof 5 lettersin eitheroriginalorderor alphabetic
order(Salthouse
& Coon, 1993),aresummarized
in Table3.
Although the patternis somewhatvariable,it appearsthat
independentage-relatedeffectsoften occur for presentation
timesup to 500 msec,but not consistently
for longerpresentationtimes.To the extentthatthis is an accuratecharacterization of the results,independentand distinct age-related
influences
may operateprimarilyon measures
within thefirst
500 msec of processingfbr some tasks.A broaderrangeof
tasks should be examined to explore the limits of this
suggestion.but at leaston the basisof the availabledata,
distinctexplanations
fbr age-related
influencesappearto be
neededlargelylirr measureswith relativclyshortpresentation durationsbecausemostol'thc age-related
ef'fbctson the
nrcasurcs
at longerclurations
arc ntediatedthroughthc shortdurationlneasures.
Complc.rittEllects
A linal sct o{' ordcred variablcscan be derived fiom
contrastsof' diff'erentlevels <ll'complexitywithin the same
t a s k .N u m e r r ) ucso l n p a r i s o nesx i s tw i t h t w o l e v e l so l ' c o m p l e x i t y ,w h i c h t y p i c a l l yi n v o l v ca c o n t r a sbt e t w e e nc o n d i tions with and without an additionalhypothesized
processing rcquircmcnt.Contrasts
ol'thistypecanbc illustratedwith
dataliom two pairsot'tasksrcccntlyadministered
to a total
o t ' 6 2 5 a d u l t sa c r o s st h r e cs t u d i e s( i . e . , S a l t h o u s e1, 9 9 - 5 a ;
S a l t h o u s eF, r i s t o e ,& R h e c , 1 9 9 6 ; S a l t h o u s e& M e i n z .
1 9 9 5 ) . ' I h ct a s k sw c r ct o c o p yd i g i t s( D i g i t C o p y )o r t o f i r s r
subtract2 l'ronrthe digits befirrecopying them (Subtract
Two). and to copy symbols(SymbolCopy) or to first rotate
the symbolsby 90 degreesbelirrecopyingthem (Rotation).
Eachtask was perli)rmedtwice. and the perti)rmance
measurewas the numberof itemsansweredcorrectlywithin 30
sec.Reliabilities.estimatedby boostingthetest-retest
correlationby thc Spearman-Brown
fbrmula,were high firr each
m e a s u r e( i . e . . D i g i t C o p y : . 9 6 . S u b t r a cT
t wo : .95,
S y m b o lC o p y : . 9 6 . R o t a t i o n: . 9 - 5 ) .
The most inlitrn.rative
analysesfbr the presentpurposes
are thc contrastsbetweenthe age correlationand the standardizcdregressioncoefhcientfitr age firr the measurefrom
the presumablymorecomplcxtask.Thc correlationwith age
tbr the subtractionmeasurewas .26, but the regression
coefficient,indicatingthe director unmediatedageef'fects,
wasonly .04. This patternis consistent
with a recentfinding
by Salthouse
andCoon (1994).in that rnost(i.e.,91 .60/o)
<tf
the age-relatedvariancc in the subtractionmeasurewas
sharedwith simplermeasures.
However,somewhatdifferentresultsareevidentin other
two-variablecomplexitycomparisons.
For example,the age
correlationfirr the rotationmeasurewas .31, and the regress i o nc o e f f i c i e nwt a s . 1 6 . i n d i c a t i n g
t h a ts o m e( i . e . , 7 3 . 4 o / o ) ,
but not all, of the aqe-related
effbctsin therotationtaskwere
SALTHOUSE
Pt]2
Durations
Table 3. Correlationsand path Coefficicntsfbr RelationsBetweenAge and Accuracyat Difterent Stimulus Presentation
Duration(msec)
Presentation
Source
ContinuousAssociativeMemorY
150
S a l t h o u s c( 1 9 9 4 a ) .S t u d y I
n -240
Corrclation
Pathcocl'ticicnt
% Mediatcd
lirtal R'
(
(
300
l4)
l4)
{- l 5 )
( l0)
()2
55 6
l1
250
5(X)
t,
( 1 9 9 4 a )S
. t u d Y2
Salthouse
n -125
Correlation
Pathcrnl'ticient
(,?Mcdiated
T o t a lR 2
14
1t
t,
(Xr
(.20)
( .05)
9l l1
.39
I(XX}
S a l t h o u s c( 1 9 9 5 b )
r - 50Y.50o
C\rrrclation
Pathcocl'licicnt
% Mediatcd
lirtal R'
-.62.
.62
t,
.lu
450
-.28
.2{)
49.0
.31
750
( - . 0 2)
96.'7
..+I
| 5(X)
5It
t.t2
t96
2(X)
4(X)
SelfPaced
( . l l )
.54
(
SellI)aced
.19
(.()2)
0
I( X ) . +
.4tt
,.21
5ll 7
.35
66'7
296
11
11
t0
-.34
.14
tt3.0
4q
(0.(x))
| (x).0
t6)
92 4
ll
Ir.l
.t 9
-.30
( .12)
u4.0
( .14)
.-56
( .13)
946
.61
K c r s t c n& S a l t h o u s (c 1 9 9 3 )
a - -19Y.39o
( .22)
C o r r cl a t i o n
)1\
|
P a t hc o c ll i c i c n t
0
7 Mcdixted
'lirtal
05
R'
750
600
(-.221
713.1
.52
.45
(- Il)
94.0
.61
-.41{
(.11)
1J7.5
.62
I( X X )
| 5(X)
.50
( .17)
tttt.4
.61
( 06)
9u2
45
6l
2250
3l
(.02)
l ( x ) . 0+
59
L c t t c rM e n r r r r y
S a l t h o u s c& C t x r n( I 9 9 - l ) S t u d y 2
O r i g i n a lO r d e r
n - Jl'l Y, 3fJo
st
Corrclation
P a t hc o c l t i c i e n t
t)
7 Mcdiated
'lirtal
.21't
R'
A l p h a b c t i cO r d c r
a - 3uY.3lto
.59
Correlation
-.59
P a t hc o c l f i c i c n t
(,
% Mediated
'l'otal
R2
<()
.29
75.lt
.5lJ
lJ(X)
-.49
(.07)
9t3.0
.59
.,+lt
( - . 1 1)
.513
u7.,1
131.4
.69
^ a
I 6(X)
(
47
l6)
IJIJ 4
52
OL
8't.1
.69
N o t r , :V a l u c si n p a r e n t h c s easr c n o t s i g n i f i c a n t l y( 7 r< . ( ) l ) d i l l c r e n tl r o n l z e r o .
apparentlymediatedby the cl'l'cctsin thc copyingtask' This
patterncould be intcrpretcdas indicating that therc arc
agc-rclatedinflucnccson thc prospccilicand indepcndent
with rotation,in additionto thosc-ilssociccssesassociated
a t c dw i t h s y m b o lc o p y i n g .
i n v o l v e sa
A n o t h e rt w t l - v a r i a b lceo m p l c x i t yc o m p a r i s o n
working
with
words
or
digits
span
li)r
ol
memory
contrast
m c m o r ys p a ni n v o l v i n gt h e s a m et y p e< l l ' m a t e r i abl 'u t w i t h
participantalsorcquircdto carryout Pr()ccssing
the research
questionsaboutsentences
suchas answeringcomprehension
or perli)rntingsimple arithmcticopcrations.Becausethe
sanic tasks were perli)rnredin both studies repofled in
Salthouscand Babcock( 199I ), the rclevantdatawerc combincd acrossthe two stuclicsto produce a total of 460
Thc agecorrelationwith the listening
researchparticipants.
span mcasurcwas -.49, and the standardizedregression
cocl'ficicntfirr age was -.29. indicatingthat 65.0%'of the
agc-relatedvariancein the working menlory measurcwas
throughthe sintplespanmeasure.Corrcsptlnding
mediatecl
were -.44 and
valucs li)r thc colrputation span lllcasurL-
WHERE ARE AGE.RELATED EFFECTS?
- . 3 1 . r e f l e c t i n g5 0 . 4 % r n e d i a t e da g e - r e l a t evda r i a n c e .I n
bothcases,therefbre.it appearsthatsome.but not all, of the
agc-rclatcd
ef'fbctsin the mureconrplexmeasurcweremediatedby thc cl'l'ects
on the simplermeasure.
just describedindiAlthoughseveralof the cornparisons
cate that distinct and independentage-relatedinfluences
sometinresoccur on m()rL'c()mplex cognitive measures,
qualitativeand quantitativeaspectsof cornplexityare c()ntbundedin thesecomparisons.
That is. in eachol'thesecases
thc nrorecomplexconditioncan be viewedas involvingnot
only dif'l-erent
processingoperations.but also more operations.Becauscthis makcsit difficult to dcternrinewhetherit
is the specilicadditionaloperation.as opposedto any additionaloperation.that is responsible
lirr the observcdefl'ects.
it is desirableto evaluatewhetherindependent
agc-related
i n f l u e n c c sa l s o o c c u r w h c n c o m p l e x i t yi s i n c r e a s e d
only
quantitativcly.by the requiremcntto pcrlirrnr additional
o p e r a t i o nosl ' t h es a m et y p e .B e c a u sqeu a n t i t a t i vvca- r i a t i o n s
of cornplexitylorm an orderedsequence,
thedataareamenable to thc sanlc typcs ol' scquentialanalyscson ordered
variablcsconductcdon the learning,lirrgetting.and presentationtirnc data.
Thc rclcvant comparis<lns
can bc illustratedwith clata
fiorn a paper-lilldingtaskin which cornplcxitywas nranipul a t c db y v a r y i n gt h c n u n r b cor l ' l i r l d sd i s p l a y c d
p r i o rt o a h o l e
p u n c h .T h e s cd a t a . l i o r n a s t u d y b y S a l t h o u s cM
. itchcll.
Skovronck.and Babcock( l9l't9).arc portraycdin Figurc5.
R c s u l t so l ' s c q u c n t i aal n a l y s c so l ' t h e S a l t h o u s cc t a l.
( l 9 t J 9 )d a t a .a n d o l ' d a t a l ' r o ma v a r i c t yo l ' t a s k si n v o l v i n g
dil'f'crcntrnanipulations
ol' complexity.are sunrtnarizcdin
Tablc4. An initialpointto noteaboutthc cntries in Tablc4 is
that thc corrclationswith agc do not alwaysincrcascacross
s u c c c s s i vlcc v e l so l ' c o r n p l c x i t y a
. s n r i g h tb c c x p e c t e db y
what has bccn terrncd thc age-cornplcxityphenomcnon
( S a l t h o u s c1, 9 9l ) . T h i s r r a y b c p a r t l y a t t r i b u t a b l teo t h c
i n c l u s i o no l ' s o r n e( p a r t i c u l a r loyl d e r )p a r t i c i p a n twsh o h a v c
relativclylow perlilrnrance
acrossall levclsol'cornplcxity.
However, the ovcrall pattcrn was sirnilar in analyscsrestrictedto individualsin thc too 75lc <'tl'thedistributionon
YOUng
(n=40)
+
Mrddle
(n=40)
otd
(n:10)
O
0)
o
O
O
o
6
c
o
o
o
o-
1
2
3
4
Numberof PaperFoldingOperations
Figure-5.MeanpercL-ntagc
correctas a tunctionol numberof recluired
et al. ( 1989).
Salthouse
papcr-lirlding
operations
lirrthreeagegroups.
Pl13
the rneasure
fiom the lowestlevelof complexity,and hence
this is not theentirereasonfbr the failureto find strongerage
relationswith greatercomplexityin thesedata.
Inspcctionol'Table 4 revealsa mixtureof outcomes.In
s o m c d a t a s e t s( e . g . . m e n t a la r i t h r n e t i cm
, e m o r ys e a r c h .
v i s u a ls e a r c h d. i g i t s y r n b o ls u b s t i t u t i o n n
) .e a r l ya l l o f t h e
age-related
varianceon morecomplexmeasures
seemsto be
mediatedthrough the measuresat the sirnplcr levels of
complexity.Closerinspectionof the dataindicatesthat this
patternappearsto hold lirr most of the analyseswith responsetime measures.
of the numberof
and with nreasures
i t c m sc o r n p l c t e idn a t i x e dt i r l e . I n c o n t r a s td, a t as e t sw i t h
percentagecorrect or other ilccuftrc) nreasuresappcar to
have less mediationof the agc-rclatcdetfbcts on more
complexvariablesthroughthc agc-rclated
on simpler
et'f'ects
variables.Both ol'these patternsare evident in the papertirldingtasksbccauscaccuracywas thc dcpcndentmeasurc
in the first. second,and fifth data scts, but the dependcnt
rneasurcin thc thircland lilurth datasctswas thc numberof
correctresponscs
in a spccifiedtime. Noticc that the degrec
ot' mediationof'the age-related
efl'ectswas snrallerin the
lirrrnerdatasctsthanin the latter.
T o t h e e x t c n t h a tt h c d i s t i n c t i o nb c t w c e nt i n r ea n d a c c u racy variablcsis nrcaningl'ul.scparatcagc-rclatcdcxplanat i o n sn r a yb c n c c d c cl li r r s u c c c s s i vlcc v c l so l ' c o n t p l c x i t yi n
t a s k sw i t h a c c u r a c yn l c a s u r c sb u t n o t i n t a s k sw i t h t i r n c
nrcusurcs.Onc possibility is that accuracyrneasuresare
nrorcscnsitivcto cumulativccrr()rsintroducedby dclicient
lirnctioningol' working nrcnr()ryncccssarylirr rnaintaining
s l ' p r o c se s i n g( c . g . .S a l t h o u s c1, 9 9 2 ) .
i n t c r r n c d i ap
t cr o d u c t o
d i t h i n r p a i r m c n t isn
a n d t h a t i n c r c a s c da g c i s a s s o c i a t cw
working nrclllory.The significitntindcpcndcntage-rclated
inllucnccson thc largcrsel sizc conclitionsin the consistent
n r a p p i n gn r c n r o r ys c a r c ht a s k i n t h c C r x r p e r( 1 9 9 3 )s t u d y
bccauscthc
nray also bc consistentwith this interpretation
working nrcnr()ryinvolvcrnentis prcsunrablylargcr when
in rncmory.
nrorctargctitcrnshavcto bc nraintained
(l cttcruI D i.s<'
ussi t ttt
s sut.nnrarizcd
above
Thc nra.jorinrplicationof'thc analyse
i s t h a to n l y a r e l a t i v e l ys r n a l ln u r l b c ro l ' d i s t i n cat g e - r e l a t e d
causall'actorsappearneccssaryto accountfirr a largeproporlatedvirrianccin rnanycognitivenleasures.
tion ol'thea-rlc-re
Statedsornewhatdif'tcrently.separate
and distinctexplanain which significant
tions are not retluiredtilr all nreasurcs
havcbeenreportedbecausemuch of
age-related
diff'erences
rnay be mediated
the age-related
eft'ectson thcscnreasures
througheff'ectson rneasurcs
that occurearlierin an ordered
sequence.
ln all but one of thc data sets with paired associate
learning.mazc lcarning,and fice recalltasks.over 907cof
varianccwas mediatcdby the fburth expothc age-related
surc to the rnaterials.and over 90% of the age-related
varianccwas mcdiatedfrom the secondvariableon in the
mentalsquaring.visual search.and memory searchtasks.
The trend in the lag analyscswas not as clear, perhaps
becausethe total age-relatedcffects, representedby the
in
correlationcoefficient,werenot very large.Nevertheless,
(i.e..
the one datasct with moderatelylargeagecorrelati<lns
Salthouse,1995b),clver 907o of the age-relatedvariance
I
I
I
Pt74
SALTHOUSE
Table4. Correlations
and PathCoefficicntsfor RelationsBetwecnAge
and Mcasuresof Time or Accuracyat Successive
ComplexityLevels
Conrplcxtty
)
Source
f ' a p c rF o l c l i n t - f a s k( N u n t b e ro f F o l t l s )
S i t l t h o u s c( l 9 t i t i ) . S t u d \ I
r r - l ( X ) Y . l ( X )o
Colre lrtion
Path coel licient
f 1
I Mctliatctl
'Rrtal
Rl
_..r9
-.llt
.lu..s
_.i I
(-. t.+)
7 9. 6
.05
-.13
-.l6
76.-5
37
S a l t h o u s cc l i l I . ( l ( ) u 9 )
rr
|l0
Correlrtion
_..19
-..51
-..s-l
I)ath coel licicnt
li l\Ictliatcd
'I'otal
Rl
. -19
t,
.t 5
..r|
.20
6.+.+
lt5.lt
.)i
\h
-.5lt
-.22
IJ5.6
.61
Sallhousc ( l()91). Studr' I
r - lllJ
(,
.(X)
S a l l h o u s(cl ( ) 9 1 ) .S t u d r ' l
rr - ll.l
Cirrrcla(ion
.-+.1
l)tlh cocllicicnt
.-1-]
'ri Mctliatctl
0
'I'otal
Rr
. lft
S a l t h o u s c( l ( ) 9 - l ) .S t u d r 'I
rr
l](r
('orrclirtion
.J]
I ) i r l l rc o c l l i c i c n t
.17
(l Mcdiltctl
0
'l'otal
Rr
.ll
( .16)
(.01)
G c o n r e t r i cA n a l o g i e sT a s k ( N u r n b er o l ' E l e m e n t s()L t n t i n u t , t l )
S a l t h o u s (c1 9 9 2 ) .S t u d y I
n :228
Correlation
P a t hc o e l t i c i e n t
'l Mediated
T o t a lR 2
-.3,1
-..11
.-50
-.3'+
-lu
.lt
0
92.u
u7.0
.lt
.t35
.76
S a l t h o u s (e1 9 9 2 ) .S t u d y2
n - ::\
-.1.+
Correlation
P a t hc o e l f i c i e n t
.3.1
'l Mediatcd
0
T o t a lR r
.12
-.tu
-.ll
-.211 ( .t0)
66.0
90 li
.-5
I
.29
S a l t h o u s&
c C o o n ( 1 9 9 4 ) .S t u d y2
ri - 40Y.'10o
Corrclation
.76
11
.64
P a t hc o el ' l i c i e n t
(.0-s)
(.20)
.76
.l Mcdiatcd
0
99.5
90.2
lirtal ftr
.5lt
.rJ9
.57
( .|])
(.(x))
t ( x+)
t(x).0
.-sL-58
ll
(.(x))
( .il)
(.02)
|( x ) . 0 t ( x+
)
.t.s
..17
..ll
( l.l)
l.i.l.-s
.tt
. . 1|
.11
69.9
.trJ
I n l c l r i r t i v c R c a s o n i n g l ' l r s k ( N L r r r r h c ro l l ) r c r r r i s c s )
Salthousct rl. ( 191.19)
rr
Il0
( ' o r r cl a ti o n
l ) i r t hc o c l l i c i c n t
.21
rri Mcdiirtctl
0
'l'()tal
Rr
.01
S a l l h o u stcl 9 9 l ) . S t L r d l
rr - llll
( ' o r r cl a ti o n
P a t hc o c l l i c i c n t
'/ Mcclirtcd
'l'otrl
Rr
rl
. .16
-.15
ul.6
il
.59
-.59
0
.-15
.+9
.51
.t6
7-s.0
..s7
.;1.+
(.01)
99.5
.Ot)
..1|
- t5
1t6.6
.60
(.07)
9tt.6
.17
S a l t h o u se
c r a l . ( 1 9 9 . 5 )S. r u d yl
S c q u e n t i aAl n t h n r c t i cp c r l i r r n t e da l o n e
rr - lll
.16
Corrclation
5(r
1l
.36
.14
.15
P a t hc o c ll i c i c n t
(.()9)
4()
(.0-l) (.01)
7 Mcdiatcd
0
l-5..1 l(X)+
99.3
99.9
'Iirtal
Rr
.lL.16
.jl
6l.r
.til
S c q u c n t i aAl r i l h r r r c t i cw i t h c o n c u r r e nnt t e t r r o r yl o a d
rt - lll
Corrclation
72
.6.5
.16
..16
.llt
P a t hc o e l i c i e n t
( . l l ) ( . 1 0 )
l2
( l l )
( . o l )
7 Mcdiated
0
9 1. t
l(x)+
94..1
l(x)+
'fotal
Rr
5l
.6e
.61
.69
.6ti
.6-l
.16 (.0t)
( .0.1)
.17
9 1. 6
.11
.19
-.39
-.)1
6 1 .|
..1-5
-.31
( - . 0 9)
92.1
..+0
S a l t h o u s (e| 9 9 2 ) . S t u d y I
rr = l2ll
( .t 5 )
Corrclatiot)
(- l5)
P a t hc t r l ' l i c i en t
? Mcdiated
0
T o t a lR r
.0l
( | 9 9 2 ) , S r u d y,
Salthouse
n =)23
Corrclation
P a t hc o e l l i c i c n t
'Z Mediarcd
0
'Iotal
Rl
.31
(-.12)
( .01)
99.3
.54
.30
( .il)
u6.6
.n
(-.I l )
( .02)
96.1
61
( - . I - 5)
(.04)
1 0 0+
..r7
Memory SearchTask (Nunrbcrof Mentorv Set ltents)
( i c o r n e t r i cA n r l o g i c sT a s k ( N u n t b c ro l E l c n t c n t s )
S a l t h o u s c( l g l t l t ) . S t u d \ I
r
l ( X )Y . l ( X )o
Corrclation
.ltt
I ) a t hc o c l l i c i c n t
.18
rri Metliatcd
0
'lirtal
Rr
.0li
.63
(.l0)
97.-s
.t3I
C u b eA s s er n b l yT a s k ( N u r t r b eor l F o l d s )
.+.1
.ll
-+80
.-ll
S a l t h o u s c{ 1 9 9 1 t .S t u d _2" Corrclttiol)
l ) u t hc o c l l i c i c n l
(ri Mrdiatcd
'fotrl
Rr
2
M e n t a lA r i t h n t e t i c( N r . r n r b eorf O n c r a t i o n s )
('ot-rc lat ion
[)rth cocl licicnl
'l Mcdiutcd
'lirtal
Rr
Cornplexitl,'
Source
-.52
-.3-5
-5.1.7
.5 I
S a l t h o u s (e1 9 9 3 ) .S t u d y2 - L e r t e r s
rt : 2-58
Correlation
.39
..+l
.42
..11
Pathcoel'ficient
(.o7) (.04) (.01)
.-19
7 cM e d i a t e d
0
97.1
9 9 .|
99.9
TotaR
l 2
.15
.81
.lJ9
.89
S r l t h t r u s(cl q g . l ) .S t u J yI - D i g i r s
n - 25tl
Correlation
..11
.12
.14
.11
Path coellicient
( 0-l)
( - . 0 1)
.41
.06
? Mediated
0
99.5
9 8 .I
t 0 0+
T o t a lR ,
.17
.90
. 9|
.90
( ('ont utu( s n e.tl pu ge )
WHERE ARE ACE-RELATED
P1 7 5
EFFECTS?
Table 4. Correlationsand PathCoefhcientsfor RelationsBetwccn Age
and Measuresof Tinre or Accuracy at SuccessiveComplexity Levels (tontinued)
Cornplcxity
Complexity
Source
Source
V i s u a lS e a r c h- C o n s i s t e nM
t apping
( N u r n b e ro l D i s p l a vS e t I t e n r s )
D i g i t S y m b o l( N u n r b e ro l P a i r s )
S a l t h o u s (e1 9 9 3 ) .S t u d y I
n -216
Clorrelation
['ath coel'ticient
% Mediated
'li)tal
R'
.5 I
.5 |
0
.26
.59
.23
rJ4.
tt
.72
.61
.59
(.04)
.06
99.5
99.0
9l
.94
( N u n r b er o l ' R e l a t i o n s )
G c o m et r i c M a t r i x R e a s o n i n g
S a l t h o u s c( 1 9 9 3 ) .S t u d y I
n =246
Correlation
-.1.1
P a t hc o c l f i c i e n t
o
% Mediated
.12
T o t a lR 2
(.(D)
9l.tl
.63
Path coellicient
% Mediated
Total R'
f<
-.1.1
1J4.0
.46
.29
-. l9
5 7 .I
.40
11
(.0u)
Itu.9
11
l s k ( N u r n b c ro l R c l a t i o n s )
C c o n r c t r i cA n a k r g i c s ' a
S a l t h o u s (el 9 t t t { ) .S t u d y I
r t - l ( X )Y . l ( X )o
C o r r cl a t i o n
P a t hc o e l t i c i e n t
7 Mcdiatcd
'li)tal
Rl
. ):
(,
.l0
-.16
-.19
12.1
.39
.4r{
. . 1I
5lt.l
.41
-.54
. 3|
67.0
.4n
V i s u a lS v n t h e s i s ' l ' a s(kN u m b c ro l F r a n t c s )
( 1 9 u 1 3S
Salthouse
) .t u d y I
n - l ( X )Y . l ( X ) ( )
.71
Corrclation
P a t hc o e l l i c i c n t
.21
o
7 Mediatcd
T o t a lR 2
.08
.71
11
Correlation
( .0.1)
P a t hc o c l t i c i e n t
.71
% Mediated
t,
| ( x )+
'Iirtal
R2
59
.91
L a t e i n P r a c t i c c( T r i a l s2 4 0 1 - 3 ( X X ) )
.u3
.ti3
Corre lation
l<
S p a t i a lR o t a t i o nT a s k ( N u n r b e ro l 9 0 - d e g r e eR o ( a ( i o n s )
( 1 9 9 - l ; .5 1 x 1 y2
Salthouse
rr - 25lt
Correlation
[)athcoel'licient
'/r Mcdiated
'lirtal
R2
Rogerset al. ( | 99.1)
n =70Y.70O
(Trialsl-600)
Earlyin Practice
f |
(-.16)
42.0
.0u
1l
.21
'1.1.1't
.25
V i s u a lS c a r c h- C o n s i s t e nM
t apping
( N u m h e ro l D i s p l a yS c t l t em s . t
Coopcr( 1993)
rr - ll9 Y. titto
('frialsl-2.10)
[:arlyin Practice
.5-5
.5'7
.-5.1
Correlation
(.0.+)
Path coel'ficient
.57 (.02)
0
100+
99.5
% Mediated
. 32
.94
.95
Total R2
L a t e i n P r a c t i c e( ' l ' r i a l s2 l 6 l - 2 4 ( X ) )
.61
Correlation
.63
6l
Path cocflicient
{.01)
'Z Mediatetl
99.9
0
l - o t a lR 2
..10
.91
.60
(.01)
99.9
.94
l6
l9
72 I
-t5
0
.10
.12
( .(X))
l(x+
)
.96
.lJ|
.lJO
(-.05)
(. 0 1 )
t(x+
)
999
.97
.96
V i s u a lS e a r c h- V a r i c dM a p p i n g
( N u n r b c ro l l ) i s p l a yS c t l t e m s )
C t x r p c r( 1 9 9 - 1 )
rr - tl9 Y. fJlto
L,arlyin Practicc('l'rials | 240)
.66
.65
Correlation
.65
(.04)
(.01)
Pathctrcllicient
.66
'/. Mcdiated
0
99.9
99.6
'lirtal
R?
.11
.94
.96
[ - a t ci n P r a c t i c c( ] ' r i a l s7 ] l 9 6 0 )
Corrclation
.53
.-sl-49
(.0t) ( .0t)
P a t hc o e l l i c i e n t
.5-r
(l Mediatcd
0
9 9 . 9 l ( X+
)
'lotal
R'
.lrJ
.9|
.95
R o g c r sc t a l . ( 1 9 9 , { )
n - lll Y.70o
h , a r l yi n P r a c t i c c( ' l ' r i a l sI ( r ( X ) )
Corrclation
.71
.1|
(-.01)
P a t hc o e l f i c i e n t
.73
(l Mecliatcd
()
l ( X )+
lirtal R'
.-5.1
.96
l . a t ei n P r a c t i c c( ] ' r i a l s2 . 1 0 1l ( X X ) )
75
65
Correlation
P a t hc o e lt i c i c n t
7-5
.I-l
% Mediated
l ( x )+
T o t a lR l
56
.92
.65
( - . o lI
t ( x )+
.9.+
54
' l--l
l ( x )+
.u 9
M e n r o r yS c a r c h C o n s i s t e nM
t apping
( N u n r b e ro l M e n r o r yS c t l t en r s )
Cooper(1993)
n - tl7Y.fl70
L , a r l yi n P r a c t i c e( ' I r i a l s l - 1 4 0 )
Correlation
.52
.-56
P a t hc o e f f i c i e n t
.52
.10
7 Mediated
0
96.1i
T o t a lR 2
.27
.ltg
L a t e i n P r a c t i c e( T r i a l s9 6 1 - 1 2 ( X ) )
6o
Correlation
61
Pathcoetticicnt
.60
It)
(,
% Mediated
94.1
Total R2
16
.91
.-51
(-.(X))
l ( X )+
.92
69
07
99.0
.95
No/<,:Values in parentheses
are not si{nificantly (p < .01) dilfbrent from zero. A dashindicatesthat therewas an increasein the age-relatedvarilnce after
c o n t r o lo f t h e n r i o r v a r i a b l ei n t h c s e q u c n c e .
Pl16
SALTHOUSE
in the lag 2 measurewas mediatedthroughthe measures
fiom shorterlags.A fairly consistentpatternin which 80o/c
varianceon variableswith long
or more of the age-related
presentationtimes was mediatedthrough variableswith
prcscntation
msecwasapparentin the
tinresshorterthan,5(X)
analyscsof the presentationtirne data. The most diverse
resultsoccurred with the complexity manipulations,but
even in this case a median of 95.6c/oof thc age-related
variancein the rneasurcs
ol'the secondcomplexitylevelwas
nrediatedthrough thc measuresat the lowest complexity
level. and a r.nedian
ol'99.0%of the agc-rclatedvariancein
the measuresat thc third complexity levcl was mediated
throughthc mcasuresat the secondcomplexitylevel.
Thc discoveryof substantialmediated.or shared.agerelatcdvariancein theseanalysesis similar to findingsof
largeproportionsol'age-relatedvarianccsharedacrossdil'I'crcntcognitivevariablesin which thereis no a priori basis
t i r r o r d e r i n gt h e v a r i a b l c s( e . g . , S a l t h o u s e1, 9 9 3 , 1 9 9 4 a ,
1 9 9 4 b :S a l t h o u s c t a l . . 1 9 9 4 :S a l t h o u s cF. r i s t o e ,L i n e w c a v c r .& C o o n . 1 9 9 5 ) .l n b o t h s i t u a t i o n st,h e a v a i l a b l e
cvidcncc suggeststhat a surprisinglylargc amttuntof the
agc-relatcdcll'ectson a widc rangeol' cognitivemeasures
can bc accountcdfirr by thc operationol' a relativelysmall
f'actors.
numberot' independcnt
and distinctagc-related
analTwo questionsnaturallycnrergeliom the sequential
y s i s t ' r a r n e w o r kT.h c l i r s t c o n c e r n st h c e x p l a n a t i o o
nf . t h c
age-related
cf'lcctson variablcsthatoccurearlyin an ttrdered
arenot directly
sequcncc.Thc rcsultsol'thecurrcntanalyses
i n t i r r r n a t i vaeb o u tt h i s i s s u c( b u t s e eS a l t h o u s e1. 9 9 3 .f b r
Whatcvcrthe naturcof thesecausal
rclevantspcculations).
lactors. howcvcr, thcy arc presunrablyfairly l'undamental
because
thc currentrcsultsindicatcthattheyarepresentearly
and test,
in learning.with short lags betwecnpresentation
with briel'prcscntation
durations.and at low lcvelsot processingcomplcxity.One importantdirectionltlr future researchshouldbe investigationof the f'actorsthat vary with
ageand arc responsible
filr variationsin measures
ol'simple
processing
efficiency.
The secondqucstionol' interestin sequentialanalyses
concernsthe tactorsresponsiblefbr the independentagerelatedeff'ectson later variablesin the sequence.Because
theseel'f'ects
rcprcsentuniqucage-related
influencesthat arc
distinct l'rornthe inl'luences
on earlier variablesin the sequence,they are not only of interestin their own right, but
may alsobe infirrmativeaboutthe natureof the influences
on
earliervariables.That is, becausethe age-related
influences
on the later variablesare independentof the influences
rnediatedthroughthe earliervariablcs,examinationof these
spccificinf'luences
may contributeto understanding
the nature of the presumablycommoninfluences
fiom which they
aredistinct.
In the analysesreportedabove. independentage-related
effectswere apparenton later variablesin the sequencein
severalof the data sets. For example, independentagerelatedef'tectsoccurred acrossthe first severaltrials in the
pairedassociate
and free recalllearningtasks.Distinctagerelatedinfluenceswere also evident in some. but not all,
blocksof trialsin the consistent
mappingvisualsearchtasks
o f C o o p e r( 1 9 9 3 )a n d R o g e r se t a l . ( 1 9 9 4 ) .( A l s o , s e eN o t e
4.) Independentage-relatedeffectsoccurredfor long presen-
tationtimes when letterswereto be recalledin alphabetical
order, and whcn more processingoperationswere required
with accuracy-based
measures
of perfbrmance.Finally, distinct age-related
influences
wereevidentwith largermemory
set sizes in Cooper's (1993) consistentmapping memory
searchtask,particularlylate in practice.
Independentage-relatedeffectson later variablesin an
orderedsequence
havealsobeenreportedby Kliegl, Smith.
a n d B a l t e s( 1 9 9 0 )i n a s t u d yi n v o l v i n gm e t h o d - o f : l o cmi n e monictrainingin young and old adults.Theseinvestigators
foundsignificantage-related
variancein a measureof pertbrmance in a later sessionafter a measureof serial recall
performance
in an initial sessionwas statistically
controlled.
Furthermore,the age-relatedvariancewas still significant
even when a measureof serialword recall after mnemonrc
i n s t r u c t i o nw a s c o n t r o l l e d .( A l s o , s e e B a l t e s & K I i e g l ,
1992.) A possibleexplanationfor the independentager e l a t e de t t e c t si n t h e l a t e rs e s s i o nos1 ' t h eK l i e g le t a l. ( 1 9 9 0 )
study is that youngeradults.to a greaterextentthan older
adults,wereableto improvethespeedwith which theycould
executethe mnemonicprocedurewith additionalpracticc.In
supportol'this intcrpretation
arethe additionalfindingsthat
mostof the improvementin memoryperti)rmance
occurred
with moderatelyl'astpresentationdurations,and that the
relationbctweenmemory perfirrnrance
and a speedmeasure
( i . e . , D i g i t S y m b o l S u b s t i t u t i o np e r l i r r m a n c ei)n c r e a s e d
acrosssessions.The Kliegl et al. (1990) study is therefilre
instructivein illustratinghow independentage-relatedinfluenceson latervariablesin an orderedsequencemight be
analyzcdand intcrpreted.Not only is it desirableto include
rnanipulations
to cxpklre the sourceof the laterage-related
ef'fects.but othervariablesshouldalsobe assessed
to detect
possiblechangesin the patternof relations.
It is usel'ulto considerthe factorsthat could contributeto
the existenceof uniqueor independentage-related
eff'ects
late in a sequenccof orderedvariables.One possibilityis
that the likelihoodof detectingindependcntefl'ectsvaries
accordingto the type of orderedsequenceunderconsideration. For example.at leasttwo dift'erenttypesof ordered
- gnurinland temporal- can be distinguished.
sequences
Causalsequences
are thosein which the precedingvariable
is logicallyprior to the criterionvariablein thc sensethat it
represents
a constituentol'the criterionvariable.Sequences
composedof variableshypothesized
to correspondto dillbrent levelsof processing
complexity,whereeachsuccessive
level includesthe prior levelsplus an additionallevel, are
examplesol'causalsequences.
in which succesSequences
sive variablesrepresentprogressivelygreateramountsof
processingtime could also be consideredas causalif the
increased
time corresponds
to morecompleteprocessing.A
secondtype of orderedsequence
is temporalor longitudinal
in that successive
representdif'fervariablesin the sequence
at
ent points along a temporalcontinuum.Measurements
differentlevelsof practice,or with variousintervalsbetween
presentationand test (i.e., fbrgetting), are exarnplesof
longitudinalsequences.
Note that causaland temporalsequencesare not mutually exclusive becausea temporal
sequence
variables
could alsobe causal.That is. successive
in a longitudinalsequencecould representsimpler or less
completeamountsof processing(i.e.. causal),or they may
WHEREAREAGE-RELATEDEFFECTS?
involve all of the sameoperationsbut at different levels of
proficiency(i.e., noncausal).
Although it is clearly possiblethat the patternof independent age-relatedinfluencescould vary accordingto the type
ofordered sequence,thereis little evidenceofthis in the data
reportedabove. Instead,the generaltrend seemsto be for
large proportions of the age-relatedeffects to be evident
early in the sequence,regardlessof the nature of the sequence. Nevertheless,the availabledata are not definitive
with respectto this issue,and future researchmay revealthat
the presenceor magnitudeof distinct age-relatedinfluences
variesdependingon the type of orderedsequence.
Statisticalfactorscould also play a role in the detectionof
independentage-relatedeffectslate in an orderedsequence.
For example, an effect of the same absolutemagnitudeis
more likely to be statisticallysignificantwhen the proportion
of explainedvariancein the variableis high comparedto
when it is low. Furthermore,increasesin the proportionof
explainedvariancecouldoccurbecause
of increased
reliability of the criterion variable (due to the greateramount of
systematicvariance available to be associatedwith other
variables),or becauseof increasesin the magnitudeof the
relationof the variableto the prior variablein the sequence.
Both the reliability of the criterion variableand the strength
of the relationsbetweensuccessivevariablescould therefore
contributeto the detectionof independentage-relatedeffects
in variableslate in an orderedsequence.
Two final f'actorsthat could contributeto the existenceof
independentage-relatedvariance are shifts in either the
natureof the processesrequired in the task, or in what the
variablesrepresent.That is, successivevariablesin the
orderedsequencemay be dependentupon different combinationsof abilities,and age-related
influencesmay be evidenton abilitiesthatbecomeimportantlatein the sequence.
Alternatively, there may not be a shift in the pattern of
influences
on the samevariable.but ratherthe variableitself
may be changingwith respectto what it is measuring.In
other words, early in the sequencethe variable may reflect
one construct, but later in the sequenceit may reflect a
diff'erentconstruct.A possibleexampleis when the ordered
sequenceis composed of measuresrepresentingperformanceat progressivelylongertimes. In this casethe variables at short presentationtimes may primarily reflect processesconcernedwith rapid information processing,but at
longerpresentationtimes the variablesmay reflectwhatever
ability construct is relevant to the particular task being
performed. Examination of the pattern of correlationsbetween variablesat different positions in the sequenceand
measuresof other abilities might allow thesepossibilitiesto
be distinguished.
In conclusion, the framework of conceptualizingwhere
independentage-relatedinfluences occur seems to be a
fruitful perspectivefor understandingwhat needs to be
explained with respectto age-relatedeffects on cognition.
The data setsexaminedaboveare obviously very limited in
many respects,but they nevertheless
raisethe possibilitythat
far fewer explanationsof age-relatedinfluencesare needed
than the number of variables in which age-relatedeffects
have been reported.Not only were few of the independent
age-relatedeffectson later variablesin the orderedsequence
Pt77
significantlydifferent from zero, but even when significant
they were often responsiblefor very small percentages
of the
total age-relatedvariance. Important priorities for future
researchshould thereforebe the explanationof age-related
influenceson the variablesthat occur early in an ordered
sequence,becausethey may be responsiblefor largeproportions of the age-relatedeffects, and of the independentagerelated influenceson variables that occur later in the sequence,becausethey can be viewed as representingdistinct
or unique age-relatedeffects.
AcKNowLEDGMENt
s
This researchwas supportedby NIA Grant R37 AG-06826 to Timothy A.
Salthouse,who can be reachedat Tim.Salthouss(u.'Psych.Gatech.Edu.
I
would like to thank Neil Charness,Brian Cooper, and Wendy Rogers for
sharingtheir data, and for commentson an earlier versionof this article.
Addresscorrespondenceto Dr. Timothy A. Salthouse,School of Psyc h o l o g y ,G e o r g i aI n s t i t u t eo f T e c h n o l o g y ,A t l a n t a ,G A 3 0 3 3 2 - 0 1 7 0 .
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Appendix
| . Thc rcportedanalyscsarcrcstrictcdto first-ordcr( i.e.. inrmcdiatcly prror) autoregrcssion
analyscsrathcr than also including
higher-order
rclationsfi)r two rcasons.I,irst,althoughanalysesof
s c c o n d - o r d (ccr . g . ,v a r i a b l cI o n v a r i a b l c3 ) a n dt h i r d - o r d e(re . g . ,
variablc I on variablc4) rclationsrcvcalcdthat sortrcof thosc
rclationswcrc significantlydil't'cre
nt lionr 0. the incrcrncntsin
proportionsol'total varianccaccountcdlirr wcrc gcncrallyrathcr
snlall. And sccond,inclusionol'additionalnrcdiatcdpathsto thc
critcrion variablctcndcd to rcducc thc ntagnituclcol thc dircct
coclficicntsliorn agc,andthuslhc rcportcdvaluescanbc viewedas
libcral( i.c.. potcntiallylargcrthanthc truc value)estimates
of'the
unnrcdiatcd
agc-rclatcdinflucnccs.
-fhc
2.
standardizcd
rcgrcssioncoct'licicnts
wcrc obtaincdliorn
hicrarchicalrcgrcssioncquationsin which thc cl'lcctsol'agc wcrc
dctcrnrincdlticr control ol'thc prior variablc in thc sequcncc.
'fhcsc
cocl'ficicnts
arc cquivalcnlto what woulclbc obtaincdin a
path analysiswith a nrodcl suchas that illustratccl
in Figurc I in
whichpathswcrc constraincd
to ad.jaccnt
variablcsin thc sequcncc.
-1. Thc sanrcrcscarchparticipants
pcrfi)rmcdin all conditionsol'
thc Ctxrpcr(1993) study. with thc varicd rnappint vrsualscarch
pcrlirrmcdaticr lirurscssions
ol psychorne
tric abilitytcsls.Thc two
scssionsol'thc consistcntmappingvisual scarchtasKwcrc pcrlirrmcdncxt. lirllowcdalicr a transl'crsessionby a scssionwith thc
conslstcntnlapplnglnemoryscarchtask.A rnixcdtlcsignwas also
usedin the Rogerset al. ( 1994)study,with eachsessionconsisting
of 600 trials of thc consistcntmappingtask intermixedwith 600
trialsol'the variedntappingtask.
4. Becausctrialsin the Coopcr( 1993)and Rogerset al. ( 1994)
studieswerepresented
in blocksof 60. the analyseswerc repeated
with meansfbr each 60-trial block as the variablesin the ordercd
sequencc.
In the Cooper( 1993)study,the pathcrrcfficicnts,
reprcsentingdircctor unntediated
agc-related
ef'fccts.weresignificantly
(7r< .0 | ) dillerentlionr zeroonly in block I in the variedmapping
v i s u a ls e a r c hd a t a .i n b l o c k sl . 3 . 5 . l U . 2 1 , 2 5 . 2 9 , 3 t i . a n d4 0 i n
t h ec o n s i s t e nntt a p p i n -vui s u a ls e a r c h
d a t a .a n di n b l o c k sl , 2 , 3 , j ,
l l . 1 3 . l - 5 . 1 7 . a n d l 9 i n t h c c o n s i s t e nmt a p p i n gm e m o r ys e a r c h
data.Thc perccntagc
ol'nrediatcdagc-rclated
varianccwas greatcr
than96% lirr all variahlescxccptthc lirst in the scquencc,and the
variablcrcprcscntingthc first block in lhe sccondscssionof thc
consistcntnrappingvisual scarchtask (i.c., bkrck 2l : 89.2a/c
nrcdiatcd
).
Only -5ol'the 9tl cornparisons
(cxcludingthe first block in cach
task)in thc Ro-uers
ct rl. (1994)clatahad lcssthan 907cmecliatcd
rgc-rclatcdvariancc.Thcsc wcrc thc tirst block of trials in thc
v a r i c dn r a p p i n tga s ko n s c s s i osn2 ( 8 9 . 2 % , 1 ,(3B 2 . O V a4\ .( g 3 . 5 V r , ) .
a n d- 5( t i 6 .l % ) . a sw c l l a sl h c s i x t hb l o c ki n s e s s i o 5n ( i t . 5 . 9 % )p.a t h
coclficicntslirr agcwcrc sirnificantly(p < .0 I ) grcatcrthanzeroin
thc consislcntnrappincvisualscarchtaskoccurrcdon blocks |, 3,
4 . 7 . 1 0 .l t . t 3 . t - 5 t. 7 . 1 t t . 2 0 . 2 1 . 2 3 . 2 - s . 2 7 . 3 1 . 3 2 . 3 1 . 3 5 . 3 6 .
3 t { . 4 0 . 4 1 . 4 2 . . 1 - 5 . 4 6 . :a
1n
7d
. - 5 0 . - I h sc i s n i f i c a n( /rl < . 0 1 )p a t h
ctrclticicntslirr agc in thc varicd nrappingvisual scarch task
o c c u r r eocnl b l o c k sl . 6 , 9 . I | . 2 l . 2 6 . 2 9 , 3 0 . 3 1 , 3 5 . 3 7 . 4 0 , 4 1 ,
12. 16. and ,113.
Alrhoughthcsc pattcrnsarc morc cornplcxthan
thoscin thc analyscsbascdon dataaggrcgatccl
acrossmorctrials,it
ls notcworlhythat in all ctscs thc dircct agc-rclated
cf'l'ccts
corrc_
spondcdto a rclativcly srnall pcrccntagcof'thc total age-rclated
vanilnce.
In ordcr to cxplorc thc gcncralizabilityol' thc phcnomcnonof'
rncdiatctlagc-rclatcdcf'l'ccls.analyscswerc also conductedto
dctcrnrincthc pcrccntagc
ol'nrcdiatcd
agc-rclatcd
varianccliorn the
tirst to thc last trial block in thcscdata scts. Estimatcsf'ronrthc
Coopcr (1993) clatawcrc tlzl..5%lirr consistcntmapping visual
scarch.99 *(I t<>rvaricd nrappingvisual search,and 65.tt% lbr
consrstcnt
nrapplngntcr.nory
search.Estintatcsfrom the Rogersct
al- (1994)datawcrc 16.3(/tl<trconsistcntmappingvisualscarch,
'antl99(/tlirr varied mapping visual search.