Controlled and Automatrc Forms of Memory and Attention: Process Purity and the Uniqueness of Age-Related Influences

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1 Jumal J Gercntlgy: PSYCHOLOGCAL 997. Vl.528. N.5-P216 P228 SCENC'S Cpyright 1997 by The Cerntl!:ical Sciet! famerica Cntrlled and Autmatrc Frms f Memry and Attentin: Prcess Purity and the Uniqueness f Age-Related nfluences Timthy A. Salthuse,' Jeffrey P. Tth,r Hlly E. Hancck,r and Jhn L. Wdard' 'Schl f Psychlgy, Gergia nstitute f Technlgy. ' Department f Neurlgy, Emry University. Estimates f cntrlled and autmatic prcesses hypthesized t underlie perfrmance in a memry task and in an attentin task were derived fr 1 15 participants frm 18 t 78 years f age using the prcess-dissciatin prcedure. Participants als perfrmed speed and neurpsychlgical tests that were suspected t he negatively rclated t age. Prcess estimates shwed gd reliabilfu (frm.76 t.98), and the qualintive distinctin between prcesses t'as supprted by the verall pattern f cnelatins an ng measures. Hwever, nly estimated autmatic prcesses exhibited unique variance, as they were either weakly related r unrelated bth t perfrmance n the ther tests and t each ther. Estimates f the cntrl prcesses, in cntrast, shared cnsiderable variance with measures frm ther tests, and there were n unique, r independent, age-related effects n these measures. The results highlight the need t distinguish between prcess purity and the uniqueness f age-related influences in accunting fr age differe nc e s in c gnitin. l\ fost measures f cgnitive perfrmance can be as- Vlsumed t reflect a mixture f several theretical prcesses. This is a ptential prblem ifne is interested in assessing the relatins amng measures, r between cgnitive measures and ther variables, because the bserved relatins culd be attributable t nly sme f the prcesses r t all f them. Fr example, if Measure is determined by theretical prcesses A and B, then any relatin between Measures and2 culd be due t prcess A, t prcess B, r t bth prcesses. dentifying the specific prcess(es) respnsible fr the relatin is imprtant, particularly if prcesses A and B are thught t be differentially affected by variables f interest, such as age. n cmparing relatins amng measures. it is als imprtant t be sensitive t the issues f sample size and reliability. Sample size needs t be cnsidered because the precisin f an estimated relatin (i.e., the narrwness f the cnfidence interval) is inversely related t the size f the sample. Reliability als cannt be neglected because if the reliability f a measure is lw, then there is little systematic varianie in that measure available t be assciated with ther measures. This is f particular cncern with difference scres (such as priming measures) because the reliability f such scres is ften lwer than that f either f the cnstituent scres (e.g., Chen & Chen, 1983, p. 69). A primary gal in this prject was t examine theretical prcess estimates frm tw different tasks t determine their relatins with each ther, with chrnlgical age, and with a variety f ther cgnitive measures. The relatins amng prcess estimates are interesting because if sme f the estimates are assumed t reflect a similar theretical cnstruct, then ne shuld expect a psitive crrelatin between them. n cntrast, little r n crrelatin wuld be expected between theretical estimates if they were pstulated t reflect different cnstructs. Relatins with individual difference variables such as age are interesting because if it is assumed that mst f the relatins with age are attributable t ne particular prcess (e.g., A and nt B), then relatins wuld be expected between age and estimates f prcess A, but little r n relatin wuld be expected between age and estimates f prcess B. Finally, relatins f the prcess estimates with ther measures f perfrmance are relevant t the issue f the distinctiveness f the hypthesized cnstructs. That is, if tw prcess estimates reflect the same theretical cnstruct, they shuld have a similar pattern f relatins with ther measures; but if they reflects different cnstructs, they shuld exhibit different patterns f relatins with ther measures. When the sample cnsists f a wide range f ages, and several different measures are available frm each participant, it is als pssible t investigate the uniqueness f age-related influences. That is, many cgnitive measures have been fund t be sensitive t age-related effects, but it is usually unclear whether these effects are independent f ne anther. This issue can be imprtant because even if a measure was thught t prvide a pure estimate f a specific theretical prcess, the interpretatin f the agerelated effects n that measure wuld be quite different depending n whether thse effects were unique r were shared with ther measures. Fr example, discvering that mst f the age-related variance in prcess A was shared with ther cgnitive measures wuld be cnsistent with the view that age-related effects n prcess A were simply ne manifestatin f a mre general shared r cmmn factr cntributing t the age-related influences n many measures. f this were the case, then at least with respect t P2t6

2 PROCESS PURTY AND UNQUENESS OF AGE EFFECTS P21l age-related influences, there might be nthing special r unique abut a theretically pure prcess estimate if very little f its age-related influence was independent f the age-related influences n ther measures. Nte that the issue here cncerns the uniqueness r independence f age-related influences n varius measures, and nt the purity r validity f the theretical prcesses the measures are pstulated t assess. That is, examining agerelated effects n a measure in the cntext f age-related effects n ther measures is infrmative as t the uniqueness f age-related influences, but it is nt necessarily relevant t the issue f what the measure actually represents. When a variety f measures is available frm individuals spanning a wide age range, mediatinal relatinships amng the measures can als be investigated t determine which measures, r theretical prcesses, are plausible mediatrs f the age relatins n ther measures. n the present study the Califrnia Verbal Learning Test (CVLD was used as the primary criterin task fr these analyses, with the gal f determining the extent t which different measures might mediate age-related effects n this task. n the past, statistically cntrlling measures f prcessing speed has been fund t reduce the age-related variance n a wide range f cgnitive tasks (e.g., Salthuse, 1996); hence, speed measures will be examined tgether with estimates pstulated t reflect pure measures f different theretical prcesses. n additin, the relative attenuatin f the age-related variance in the theretical prcess estimates and in the speed measures was examined befre and after statistical cntrl f the ther type f measure. The reasning was that the mre fundamental measures shuld prduce the greatest attenuatin f the age-related effects in the ther measures. T btain estimates f theretical prcesses in bth a memry and an attentin task, we used the prcess-dissciatin prcedure (Jacby, l99l; Jacby, Tth, & Ynelinas, 1993), a general analytic technique designed t separate the cntributin f cntrlled and autmatic prcesses t task perfrmance. A stem-cmpletin task similar t that used by Jacby et al. (1993) was used t assess the cntributin f these prcesses t memry perfrmance. Participants were presented with a list f wrds under incidental encding instructins and later were presented with a series f wrd-stems (e.g., tru ) crrespnding t the previusly presented (ld) wrds as well as unstudied (new) wrds. Accmpanying each test stem was a respnse instructin (OLD r NEW), which indicated t participanrs whether they were t include r exclude previusly presented wrds. Fr the nclusin (OLD) cnditin, participants were t cmplete each stem with a previusly presented wrd r, if they culd nt remember a studied wrd, t cmplete the stem with the first wrd that came t mind. The nclusin cnditin is similar t a traditinal cued recall task, but with instructins t guess when recllectin fails. n the Exclusin (NEW) cnditin, the participants were t cmplete each stem with a wrd that had nt been presented befre; that is, they were t generate nvel cmpletins fr the stems. As in the nclusin cnditin, if the individual culd nt remember a previusly presented wrd (and thus did nt knw what wrd t avid). he r she was t cmplete the stem with the first wrd that came t mind. Fr bth cnditins the primary dependent measure was the prbability f respnding with previusly presented wrds. The ratinale underlying these tw cnditins is that memry perfrmance reflects the cntributins f bth cnsciusly cntrlled recllectin and mre autmatic. invluntary effects f memry. Autmatic mnemnic prcesses are hypthesized t increase the prbability f respnding with ld wrds in bth the nclusin and Exclusin cnditins, whereas recllectin is hypthesized t increase r decrease this prbability depending n test instructins. By casting these cnditins int equatins (essentiallr. a thery f perfrmance), ne can cmbine perfrmance in the tw cnditins and thereby derive separat estimates f the cntrlled and autmatic prcesses. Frmally, the prbability f using ld wrds in the nclusin cnditin is equal t the prbability f recllectin (C) plus the prbabilir\ rhar rhe ld respnses will autmatically cme t mind ra r u,hen recllectin is unsuccessful (l-c). Thus, p(ldllnclusin) = C + A(l-C). Fr the Exclusin cnditin. in cnrrasr. ld wrds shuld nly be used when they cme t mind autmatically (A) in the absence f recllectin ( l-cr. hecause successful recllectin wuld act t exclude prer iuslr presented wrds. Thus, p(ldlexclusin) - A( l{t. Cmbining these equatins, mnemnic cntrl (recllectinr is estimated as the difference between perfrmance in thc' nclusin and Exclusin cnditins (C = nclusin-erclusin). Given an estimate f C, ne can algebraicallv derire an estimate f autmatic mnemnic prcesses [e.g. A = Exclusin / (l-c)1. The thery and assumptins underlying the prcessdissciatin prcedure have been discussed extensively in the literature (see Jacby, l99l; Jacby et al., 1993: Jacby, Begg, & Tth, in press; Reingld & Tth, 1966: Tth, Reingld, & Jacby, 1994, 1995b); we refer the interested reader t these surces. We shuld nte, hwever. the central assumptin underlying the abve equatins; namely that cntrlled and autmatic prcesses make independent cntributins t perfrmance. Supprt fr this assumptin cmes frm experiments shwing invariance in ne parameter (e.g., A) acrss levels f a variable assumed t selectively affect the prcesses indexed by the ther parameter (C). T date, variables prducing this pattern in stem- r fragment-cued recall include age (Jacby, Jennings, & Hay, 1996), divided attentin (Jacby et al., 1993), and levels-fprcessing (Tth et al.,1994). The cnverse pattern (invariance in C acrss change in A) has als been shwn (Hay & Jacby, 1996). n the present study we used the equatins described abve t estimate cntrlled and autmatic mnemnic prcesses fr each research participant. T assess reliability f these estimates, each participant studied and was tested n tw different sets f (intermixed) wrds. A nvel aspect f the present study cncerned the testing cnditins under which mnemnic estimates were btained. A ptential prblem with the inclusin/exclusin instructins is their cmplexity (Graf & Kmatsu, 1994). T ensure parricipants' understanding f instructins, mst previus prcess-dissciatin studies have used highly trained examiners in a ne-n-ne testing sessin; hwever, this strateer ir labr intensive and limits the cnditins under which rhe

3 P218 SALTHOUS ETAL. prcedure can be emplyed. As part f a larger effrt t increase the generallty f the prcedure (see Hay & Jacby, 1996; Jacby, Jennings, & Hay, 1996), we autmated all aspects f the experiment n cmputer (i.e., stimulus presentatin, instructins, and respnse cllectin) and had the test administered by relatively naive examiners. T estimate cntrlled and autmatic prcesses in the attentinal dmain, we used a spatial S-R cmpatibility task mdeled after Tth et al. (1995a). n this task, lefr (<) r light-pinting (>) arrws were presented in the middle, left, r right prtin f a cmputer screen, and participants were instructed t make left- and right-handed respnses that crrespnded t the arrw's directin (e.g., a right-handed respnse t the presentatin f '>'). Previus wrk has shwn that, analgus t Strp interference, participants are unable t avid prcessing f the irrelevant dimensin (the arrw's spatial lcatin) as shwn by faster reactin times (RTs) when the arrw's directin and spatial lcatin are cngruent (e.g., a right-pinting arrw n the right side f the screen) as cmpared with when they are incngruent (e.g., a righrpinting arrw n the left side f the screen). Tth et al. (1995a) hypthesized that perfrmance in this task culd be described as reflecting tw independent influences, cntrlled prcessing f stimulus frm (i.e., arrw directin) and autmatic prcessing f spatial lcatin. Similar t the strategy used fr cued-recall, they develped equatins fr perfrmance n cngruent and incngruent trials that were used t derive separate estimates f spatial (S) and frm (F) prcessing. Specifically, they hypthesized that the prbability f a crrect respnse n cngruent trials is equal t the prbability that spatial prcessing directs respnding, plus the prbability f respnding n the basis f frm when spatial lcatin des nt direct respnding; that is, p(crrectlcngruent) = S + F(l-S). Crrect respnding n incngruent trials, in cntrast, shuld nly ccur when respnding is based n frm and nt spatial lcatin; thus p(crrectlincngruent) = F(l-S). Subtracting the prprtin crrect n incngruent trials frm that n cngruent trials prvides an estimate f spatial prcessing (S = cngruent-incngruent). Given S, an estimate f frm prcessing can be derived algebraically [F = incngruentl(l-s)1. As with cued-recall, the central assumptin underlying the equatins fr this attentin task is that spatial and frm prcesses make independent cntributins t perfrmance. Tth et al. (1995a) fund supprt fr this assumptin with the discvery that a manipulatin f the prprtin f cngruent trials influenced spatial, but nt frm, prcessing estimates (see als Lindsay & Jacby, 1994). Additinal evidence fr the validity f the estimates was prvided by shwing that frm, but nt spatial, estimates accurately predicted bserved perfrmance n arrws presented at fixatin (neutral trials) where spatial prcessing is minimal. Nte that, unlike mst attentin tasks in which RT is the primary dependent measure, Tth et al. (1995a) used a deadline prcedure t btain prprtinal data apprpriate fr use with the prcess-dissciatin equatins. That is, they required participants t respnd within 500 ms after stimulus presentatin t allw assessment f the accuracy f perfrmance. n the present study we did nt use respnse deadlines because f the well-established relatins between age and speed f prcessing (e.g., Salthuse, 1996). nstead, we used an RT versin f the task and used pst hc deadlines t analyze the prbability fa crrect respnse at successive time intervals. This strategy allwed us t examine bth RT and accuracy as a functin f age and t recnstructhe time-curse f bth bserved behavir (i.e., perfrmance n cngruent, incngruent, and neutral trials) and prcess estimates (S and F). Reliability f the prcess estimates was assessed by administering three separate blcks f lfi) trials, each blck cntaining all trial types. n rder t examine the age relatins n the estimates f cntrlled and autmatic prcessing in the cntext f age relatins n ther variables, all participants perfrmed several additinal cgnitive tasks that were hypthesized t be related t age in varying degrees. Several cmputer-administered and paper-and-pencil speed tasks were used t assess highly age-sensitive perceptual speed abilities, and tw fluency tasks were used t assess perfrmance in situatins where bth speed and wrd knwledge might be relevant. A spatial test f line rientatin was administered because it was assumed t reflect right hemisphere functining, which has been hypthesized t decline with increasing age; the Trail Making Test was administered because it is smetimes pstulated t be sensitive t frntal lbe functining, which has als been hypthesized t decline with age. Finally, an episdic memry task was administered t prvide an agesensitive measure f verbal memry that culd functin as a criterin measure in sme f the analvses. Mers Participants Of the 124 adults examined, cmplete data were btained frm l15 between 18 and 78 years f age. Participants were recruited frm appeals t grups and acquaintances. The primary criteria fr inclusin in the study were that the individual had t be in reasnably gd health, had t have cmpleted at least years f educatin, and was nt currently a student. Descriptive characteristics f the sample are sununarized in Table l. [Nine participants were excluded because f incmplete data. Tw participants in the stem cmpletin task skipped 25% r mre f the trials, apparently because they kept the ENTER key depresse during the presentatin f the test items. The data frm anther individual were lst because the cmputer was inadvertently tumed ff in the middle f the stem cmpletin task. Six participants in the arrw task used a reversed stimulus-respnse mapping (i.e., they cnsistently made left-handed respnses t right-pinting arrws, and vice versa), and hence their data were deleted frm the analyses. Three ther participants had missing data but were kept in the verall sample. One had missing data n the digit symbl RT test, and that value was replaced with an estimate predicted frm the individual's age and scre n the digit-digit RT test. One individual each had missing data n the CVLT recgnitin measure and the Judgment f Line Orientatin Test, and in bth cases the mean f the age grup was used as the estimate fr the missing value.l Prcedure T maximize cnvenience fr the participants and t facilitate recruiting, mst f the testing was cnducted in the

4 PROCESS PURTY AND UNQUENESS OF AGE EFFECTS P2t9 N Age Va Female Educatin Health (l = excellent,5 - pr) Satisfactin Rating Limitatins Cardivascular surgery (7) Bld pressure medicatins (7) Head injury (7) Neurlgical treatment (7) Vcabulary (n. crrect ut f l0) Synnym Antnym CVLT (n. f items crrect) List A Trial Trial2 Trial 3 Trial 4 Trial 5 List B mmediate free recall mmediate cued recall Delayed free recall Delayed cued recall Recgnitin (n. crrect) Arrw Neutral RT Cngruent RT lncngruent RT Frm 500 ms Space 5fi) ms Stem cmpletin p(ldlinclusin) p(ldlexclusin) p(passlld-incl) p(passlld-excl) p(passlnew-incl ) p(passlnew-excl) Cntrlled estimate Autmatic estimate Reactin time (ms) DDRT DSRT Paper-and-pencil speed (n. items/sec) SD Cpy SD Cpy 2 XO cmparisn XO cmparisn 2 Letter cmparisn Letter cmparisn 2 Pattem cmparisn Pattern cmparisn 2 Fluency (n. items in 60 sec) VF-C VF-F VF-L VF-animals VF-furniture VF-vegetables Judgment f Line Orientatin Trail Making (n. secnds) Trail A Trail B Table l. Descriptive Characteristics f Research Participants and Summary Measures f perfrmance Age Grup l Age Cnelatin (4.8) 57.5 ls.5 ( l.7) 2.4 (O.s) 2.2 (O.8) 1.4 (0.6) 0 s.0 (22.1) s.0 (22.t) 2.s (1s.8) 5.s (2.9) 4.9 (2.9) 7.9(1.9) t.s (2.4) t.3 (2.6) t2.s (2.4) 12.8 (2.7\ 7.0 (2.4) l1.9 (2.8) t2.s (2.4) 12.2 (2.8) 12.6 (2.6) t4.9 (t.2) 434 (64) 434 (79) 47t ('74).688(.259).136(.122).543(.094).234(.r81).088(.093).r0e(.092).22t(.t92).098(.099).309(. l 94).299(. l 83) 665 (r0l) 1428 (186) l.6e (0.3s) 1.70 (0.31). r8 (0.24) 1.22 (O.24) 0.38 (0.08) 0.33 (0.08) 0.64 (0. l4) 0.58 (0.12) 16.2 (4;7) 14.9 (4.2) 15.0 (4.r) 20.6 (5.1) 12.e (2.8) 13.8 (3.3) 12.7 (1.7) 21.0 (4.6) s3.6 (20.3) (5.1) 50.0 ts.2 (2.s) 2.2 (O.8) 2.3 (0.e) l.s (0.8) (37.0) 2.6 (16.2) s.3 (22.6) 6.3 (2;7) 5.2 (3.t) 6.6 ( 1.6) e.6 (2.3) t.4 (2.s) l 1.3 (2.3) fi.1 (2.3) 6.s ( r.e) r0.6 (2.8) l r.8 (2.5) 10.8 (2.8) t2.0 (2.s) r4.0(l.7) 4ee (61) 49s (64) 55 l (74).403(.26e).221(.t20).480(.096).236(. l s3).085(.089).t2(.124).2w (.174).r0l(.124).24s(.188).284(. l 50) 744 (95) 1693 (280) t.s9 (.32) 1.62 (0.29) 1.03 (0.31) l.0e (0.32) 0.33 (0.09) 0.3r (0.08) 0.56 (0.11) 0.s4 (0.09) 14.9 (4.9) 13.7 (4.6) 1,3.4 (3.3) 18.8 (s.7) 12.3 (3.4) 14.0 (3.9) 12. (2.2) 26.2 (7.e) 66.1 (21.3\ 69.2 (5.1) 51.4 l s.3 (2.6) 2.0 (0.8) 2.r (r.0) 1.8( 1.0) l3.s (34.7) 43.2 (s0.2) 2.7 (t6.4) 8.1 (27.'7) 8.1 (2.2) 6.6 (3.2) 6.2 (2.t) 8.2 (2.6) 9.4 (2.7) t0.t (2.1) 10.7 (2.8) 6.4 ( 1.8) 8.4 (3.3) 9.7 (3.0) e.0 (3.2) 9.6 (2.8) t3.2 (2.t) 600 ( l 42) 565 ( l 23) 66t (147). l 83 (.236).24s (.143).464(.1 l3).255(.1r3).108(. r 14).ll4(.138).232(.226).103(.159).239(.184).277(.123) 92O (22s) 20'16 (4s6) l.3 l (0.31) t.3'7 (0.26) 0.87 (0.16) 0.90 (0.20) 0.27 (0.09).23 (O.t2) 0.46 (0.r0) 0.44 (0.10) 14.8 (s.2) 14.6 (4.7) l3.s (4.9) r7.1 (4.6) 11.8 (3.3) r4.0 (3.3) r2.1 (2.3) 32.9 (10.s) 87.2 (36.6\ -rt _ *.41* -.07.il.40*.24* -.35* -.38* _.40* _.40* -.t] -.45* _.41* -.44* -.43* -.41*.59*.52*.62* * -.30* -.M l+ -.0'7.58*.65* -.4'7* -.49* -.46* -.52* -.41* -.5 1* _.47* Ntes: CVL = Califmia Verbal lrarning Test; RT = reactin time; DDRT = digirdigit reactin time; DSRT = digit-symbl reactin time; VF = verbal fluency *p < l _.26* -. l l3.53*.46+

5 P220 SALTHOUS ETAL. participants' hmes. The testing sessin was preceded by a shrt descriptin f the tasks, and written infrmed cnsent was then btained. The sessin lasted between 1.5 and 2 hurs, depending n the individual's pace and desire fr breaks. All participants received the tests in the fllwing rder: backgrund questinnaire, SD cpy, XO cmparisn, letter cmparisn, pattern cmparisn, synnym and antnym vcabulary, digit-digit RT, digit-symbl RT, arrw RT, stem cmpletin, CVj, letter and categry verbal fluency, Judgment f Line Orientatin, delayed prtin CVLT, and Trail Making Test Parts A and B. The backgrund questinnaire cntained a variety f questins abut health status and educatin (Table l). Speed tests. - The letter cmparisn and pattern cmparisn tests were identical t thse used in earlier studies (e.g., Salthuse, 1996). These paper-and-pencil tests cnsist f pairs f 3, 6, r 9 letters (letter cmparisn) r line segments (pattern cmparisn), with ne-half f the pairs differing in ne element. The task fr the participant was t decide whether the tw members f the pairs were the same r different, and t write the letter S (fr same) r D (fr different) between the members f the pairs as quickly as pssible. Tw separate administratins f each test were presented with 30 secnds allwed in each administratin. Fr ease f cmparisn with ther variables, the scres were cnverted t the number f items cmpleted per secnd. Tw simpler paper-apd-pencil tests were designed t assess presumed cmpnents f the cmparisn tests. n the XO cmparisn test the items cnsisted f pairs f letters that were either bth X, bth O, r an X and an O. As in the ther cmparisn tests, the participant was instructed t classify the pairs as same r different as quickly as pssible by writing the letter S r the letter D between the tw members f the pair. This test was assumed t require a very elementary type f cmparisn, f a single element, relative t the letter cmparisn and pattem cmparisn tests, which cntained multiple elements. The SD cpy test cnsisted f clumns f blank lines adjacent t clumns f the letters S and D intermixed. The task fr the participant was t cpy the indicated letter as rapidly as pssible n the blank line. This test was assumed t invlve sme f the same sensry and mtr requirements f the cmparisn tasks but withut any requirement fr cmparisn. Each f these tests was administered twice with 30 secnds allwed fr each administratin. The scres in each test were the number f items cmpleted per secnd. The digirdigit and digit-symbl RT tasks have been used in numerus recent studies (e.9., Salthuse, 1996) and cnsist f a chice RT respnse t a pair f items presented in the middle f the cmputer screen. n the digit-digit task the items were digits, and in the digit-symbl task the tp item was a digit and the bttm item was a symbl. n bth versins a cde table was presented at the tp f the screen, but in the digit-digit versin it merely cnsisted f identical digits, whereas in the digirsymbl versin it cntained pairs f digits and symbls. The task fr the participant was t decide, as rapidly as pssible, whether the pair f items presented was the same r different, either accrding t physical identity (digit digit) r accrding t crrespndence in the cde table (digit symbl). Same respnses were indicated by pressing the / key, different respnses by pressing the Zkey. A practice blck f 18 trials preceded the test blcks f 27 trials each in bth the digirdigit and digit-symbl versins f the task. Average accuracy was greater than 95V in bth f the tasks and was nt significantly crrelated with RT; perfrmance in each task is therefre summarized in terms f the median RT in millisecnds (ms). Vcabulary tests. - The vcabulary tests were identical t thse used in several earlier studies (e.g., Salthuse, 1993), and cnsisted f l0 five-altemative multiple-chice synnym items and l0 five-alternative multiple-chice antnym items. Five minutes were allwed fr the cmpletin f the tw parts f this test. The scres were the numbers f wrds answered crrectly in each part f the test. Anw Task. - Stimuli in the arrw task cnsisted f right- (>) and left- (<) pinting arrws presented alng the medial-hrizntal axis f the cmputer screen in ne f three lcatins: left, right, r center. Trial-type (cngruent, incngruent, neutral) was defined by the relatinship between the lcatin and directin f each arrw: Fr cngruent trials, the directin and lcatin f the arrw dented the same respnse (e.9., a left arrw n the left side f screen); fr incngruent trials, directin and lcatin dented ppsite respnses (e.9., a left arrw n the right side f screen); and fr neutral trials, the arrw was presented in the center f the screen and had n apparent spatial displacement (relative t the fixatin pint). n each f three blcks participants respnded t 100 cnsecutive trials cnsisting f 40 cngruent, 40 incngruent, and 20 neutral trials. Trial types ccurred randmly within each set f l0 trials s that, althugh trial type culd nt be predicted frm trial t trial, the prprtin f trial types was cnsistent thrughut testing. Participants were instructed t sit a cmfrtable distance frm the cmputer screen. At a distance f 50 cm, each arrw subtended a visual angle f apprximately l.l" square and, fr cngruent and incngruent trials, appeared apprximately 8" t the left and right f fixatin. Prir t testing, participants read instructins and were shwn visual examples f the arrws and trial types. nstructins stressed bth speed and accuracy. The test began immediately after a practice blck f 50 trials. Each trial began with a fixatin pint (asterisk) presented in the center f the screen fr 250 ms. mmediately upn its remval, an arrw was presented fr apprximately 90 ms. Participants respnded by pressing the Z key fr left-pinting arrws and the / key fr right-pinting arrws. Respnse timing began at arrw nset and cntinued until a respnse was made. After a respnse was detected, the screen was cleared and remained blank fr secnd, at which time the fixatin pint fr the next trial was presented. Stem cmpletin task. - Critical stimuli in the stemcmpletin task cnsisted f 120 five-letter wrds, mstly nuns, ranging in frequency frm t 200 (Kucera & Fran-

6 PROCESS PURTY AND UNQUENESS OF AGE EFFECTS P22l cis, 1967). The wrds were divided int three sets (1-3), and each set was further divided int tw subsets (A and B) f 20 wrds each (mean frequency f the six subsets frm 28.8 t 31.9). Tw f the sets (1 and 2) were used as studied wrds. Stems crrespnding t all f the critical wrds were presented at test under either inclusin (subsets la, 2A, and 3.A) r exclusin (lb,2p, and 38) instrucrins. As is cmmn in individual difference research, all participants received the same items fr a given cnditin t avid cnfunding experimental treatment with the characteristics f participants. Hwever, the presentatin rder f items at study, and within cnditins at test, was randmized fr each participant. n additin t the 120 critical wrds, there were 16 buffer wrds (8 primacy, 8 recency), 2 f which were used as examples in the test instructins (see belw). Wrd stems were created by replacing the last tw letters in each wrd with tw underscres. The wrd stems were unique within the set f critical wrds, and each had at least tw cmpletins. All aspects f the task were presented n cmputers and were self-paced. Study instructins infrmed participants that a list f wrds wuld be presented that they were t rate fr pleasantness n a scale f t 5 ( = mst unpleasant and 5 = mst pleasant). They were tld that their ratings shuld be based n the meaning f the wrds, but that we were interested in their first impressin, s they shuld make their ratings quickly. N mentin was made f the subsequent memry test. Study wrds remained n the screen until the participant respnded by pressing ne f the number keys (frm t 5) n the keybard. Once an apprpriate key was pressed, the next wrd was autmatically presented after a blank-screen delay f secnd. Test instructins were presented immediately fllwing study. Participants were infrmed that their memry wuld be tested fr wrds presented in the pleasantness-rating task using wrd-stems ["the first three letters f five-letter wrds fllwed by tw dashes (e.g., pea )"1. They were als tld that, in additin t wrd stems, the message OLD r NEW wuld appear abve each stem, and that they were t respnd differently depending n this message: f the message is OLD yur jb is t cmplete the stem with a wrd presented in the pleasantness task; that is, try t cmplete the stem with an ld wrd. f the message is NEW yur jb is t cmplete the stem with a wrd that was NOT presented in the pleasantness task; that is, try t cme up with a new wrd. Regardless f the message (OLD r NEW), if yu cannt remember a wrd frm the pleasantness task that fits int the stem, then just cmplete the stem with the first live-letter wrd that cmes t mind. All f the stems can be cmpleted with mre than ne wrd s try t cme up with a cmpletin fr all f them. Hwever, d nt use plurals r prper nuns. Als, ifthe message tells yu t give a NEW wrd, but all yu can think f is ONE cmpletin that yu are SURE is ld, then it is kay t pass that stem by entering xx. Participants made their respnses by typing in tw letters, which appeared n the screen under the stem's tw underscres, and then pressing the ENTER key. Fllwing test instructins, the cmputer led participants thrugh fur practice test trials. The first tw used stems crrespnding t the last tw buffer wrds in the study list; the last tw practice trials used new stems. The first and third practice trials were nclusin (OLD) trials, the secnd and furth were Exclusin (NEW) trials. Fr each practice trial, the cmputer represented the apprpriate instructins and prvided feedback cncerning the participant's respnses. Fr example, if a participant respnded with a plural wrd, the cmputer infrmed him r her f the errr and presented the test stem again until an apprpriate respnse was prvided. Fllwing practice, the participant was given the ptin f beginning the actual test r repeating the practice phase. N feedback was prvided during the test prper. Test stems were presented in the center f the screen, in large lwer-case letters, and in white against a black backgrund. The nclusin (OLD) and Exclusin (NEW) cues were bright green and bright red, respectively. They appeared 500 ms prir t the presentatin f the test stem and were psitined in the center f the screen just abve the stem. Stems and respnse cues remained n the screen until participants respnded; if l5 secnds elapsed withut a respnse, the cmputer beeped and the message "Please enter a respnse" appeared belw the stem. Once a respnse was entered, the respnse cue fr the next trial (OLD r NEW) appeared immediately. Other tests. - The CVLT (Delis, Kramer, Kaplan, & Ober, 1987) was administered accrding t the instructins in the manual. There are tw lists f 16 wrds each in this test, with fbur wrds frm each list in each f fur categries (i.e., spices, fruits, clthing, tls). The prcedure invlves the presentatin f five immediate free recall trials with List A, ne immediate free recall trial with List B, recall f List A, and cued (by categry) recall f List A. After a 20-minute delay ccupied by ther activities, there was a delayed free recall test f List A, a delayed cued recall f List A, and a delayed recgnitin test fr items frm List A. Tw different types f verbal fluency tests were administered. n the letter fluency tests the participants were allwed minute each t say as many wrds as pssible that began with the letters C, F, and L, with the cnstraint that nne f the wrds shuld be prper nuns. n the categry fluency test they were allwed minute each t say as many wrds as pssible that were members f the animals, fumiture, r vegetables categries. The scre in each test was the number f different wrds prduced that were in the apprpriate categry. The Judgment f Line Orientatin Test (Bentn, Hamsher, Varney, & Spreen, 1983) was administered accrding t the published instructins except that nly the dd-numbered items were presented. This test cnsists f a display f line segments in different rientatins with the participant instructed t select the lines f matching rientatins frm a semicircle f numbered lines. The scre is the number f test lines matched crrectly. This abbreviated frm has been demnstrated t have acceptable reliability and validity (Wdard et al., 1997). The Trail Making Test (Reitan, 1992) was als administered accrding t the published instructins. This test cnsists f tw versins, A and B, and in bth versins the test

7 P222 SALTHOUS ETAL. frm cnsists f ahaphazardly arranged set f 25 circles n a piece fpaper that are t be cnnected as rapidly as pssible. n the A versin f the test the circles cntain the numbers frm t 25, and the circles are t be cnnected in numerical sequence, but in the B versin the circles cntain alternating letters and numbers; thus, the participant has t cnnect the circle with the A circle, the A circle t the 2 circle, the 2 circle t the B circle, etc. Because errrs were very infrequent, the measure f perfrmance in these tests is the time in secnds t cmplete the sequence. Rpsulrs CVLT analyses. - There are many pssible measures that can be derived in the CVLT, but mst have similar relatins t age (Table l) and are nt independent f ne anther. A principal cmpnents analysis was therefre cnducted t identify a parsimnius set f variables fr later analyses. Tw cmpnents were identified with eigenvalues greater than l, the first accunting fr 68.3c/ f the variance, and the secnd accunting fr 9.8% f the variance. All f the variables except List B recall had mderate t high ladings (between.62 and.92) n the first cmpnent, and List B recall was the nly variable with a high lading (>.5) n the secnd cmpnent. Further analyses revealed that the sum f the scres acrss the first five trials in List A was crrelated.96 with the first principal cmpnent scre and nly.15 with the secnd cmpnent scre, whereas List B recall was crrelated.74 with the secnd cmpnent scre and nly.49 with the first cmpnent scre. These tw variables were therefre used t summarize CVLT perfrmance in all subsequent analyses. Arrw analysej. - Tw separate sets f measures were btained in the arrw task. One set cnsisted f the median reactin times (RT) n neutral trials (arrws in the middle f the screen), cngruent trials (e.g., left-pinting arrw n the left side f the screen), and incngruent trials (e.g., leftpinting arrw n the right side f the screen). Means f these medians fr each age grup are presented in Table l, where it can be seen that RTs in each cnditin increased with age. Hierarchical regressin analyses were cnducted t determine whether there was a significant influence f age n cngruent r incngruent RT after cntrl f neutraltrial RT. n neither case was the residual age-related variance significantly different frm zer (i.e., incngruent, AR2 =.005; cngruent, AR' =.002), indicating that there was n relatin between age and either measures f interference (i.e., incngruent relative t neutral) r facilitatin (i.e., cngruent relative t neutral) after verall speed was taken int cnsideratin. The secnd set f measures frm the arrw task was estimates f the prbabilities f spatial- and frm-based respnding. The initial step in these analyses cnsisted f partitining the data accrding t respnse time, and then cmputing the cumulative prbability f a respnse in the neutral, cngruent, and incngruent cnditins fr each 100-ms interval frm 200 t 1000 ms. The results f these cmputatins are displayed in Figure l. Ntice that, as expected, the prbabilities increase with greater time, and c. an E E g - G'. L at, c CL G := - (t,.ct - c. G a 'l Yung! Neutral j + Cnruent --%-. ncngruent "'u"' ,000 Middle F".a.""'""'.El Neutral Cnruent --:a-- ncngruent "'u"' s ,000 rd. 8 " Neutral Cnruent lncngruent ,000 Reactin Time (ms) Figure l. Prbability f a respnse in the neutral, cngruent, and incngruent cnditins in the arrw task as a functin f age grup (yung - l8 t 39, middle = 40 t 59, and ld = 60 t 78) and pst hc resnse deadline.

8 PROCESS PURTY AND UNOUENESS OF AGE EFFECTS P223 there are prnunced age differences such that the functins are shifted t the right with increasing age. t can als be seen that the functins fr the neutral and cngruent cnditins were very similar, but that the functins fr the incngruent cnditins were shifted t the right relative t the ther tw cnditins. The data summarized in Figure were used t cmpute estimates f the prbability f spatial (S) and frm (F) prcessing at each successive respnse time interval frm the equatins presented earlier. The resulting estimates are illustrated in Figure 2. Ntice that F increased mntnically ver time, and that there is a rise fllwed by a decrease in S. There is a large decrease (i.e., shift f the functins tward lnger times) with age in F, but an increase with age in S, particularly in the range between 500 t 700 ms. Because the 500 ms values appear t representhe middle f the range fr all age grups, thse values were used in the subsequent analyses. (Similar patterns f relatins t ther variables were apparent with estimates derived frm deadlines ranging frm 400 t 800 ms). As in the data reprted by Tth et al. (1995a), the theretical distinctin between the tw prcess estimates was supprted by their relatins with bserved perfrmance n neutral (center-arrw) trials that prvide a relatively pure measure f frm prcessing: Crrelatin cefficients predicting neutral-trial perfrmance at 500 ms were.96 fr F and -. l0 fr S. T assess reliability, estimates f spatial and frm prcessing at the 500-ms deadline were cmputed fr each f the three blcks f trials. Using the frmula n(avg. r)/ (l+([n-l]avg. r)), the resulting reliability estimates were.98 fr F (the cntrlled parameter), and.83 fr S (the autmatic parameter). Estimates cmputed separately fbr each age grup were: F, )ung =.96, middle =.96, and ld =.97; S, yung =.80, middle =.7J, and ld =.84. Bth parameters frm the arrw task had mderate t strng crrelatins with age. The crrelatin with F was. '7 E F 0.6 t u E g ,"..a Yung - Fm -----l-- Middls - Fm ----a--- Old - Fm... Y@ng - Spa l/ilddle^- Spae ---r'-\--- Old - Space '... -=R:= AD 300,lO0 50 mo 7OO ,000 Deadline (ms) Figure 2. Estimated prprtin f trials based n frm r spatial lcatin as a functin f age grup (yung = 18 t 39, middle = 40 t 59, and ld = 60 t 78) and pst hc respnse deadline. -.64, indicating that increased age was assciated with a lwer prbability f making a frm respnse prir t the 500-ms deadline. The same pattern was evident at the 400- and 600-ms deadlines as the age crrelatins with these estimates were -.58 and -.53, respectively. The crrelatin between age and S at the 500-ms deadline was.33, indicating that increased age was assciated with a higher prbability f making a respnse based n the spatial lcatin f the arrw. A similar relatin (r =.44\ was evident at the 600-ms deadline, but the relatin was reversed at 400 ms with the crrelatin between age and S being This reversal reflects the different time curses f the spatial estimates fr the three age grups apparent in Figure 2. The results just described suggesthat the relative influence and time-curse f frm and spatial prcesses is qualitatively similar in the three age grups. Mre quantitative cmparisns, hwever, are cmplicated by the increasing respnse times as a functin f age. T determine whether aging had any prcess-specific effects n frm and spatial prcessing, we perfrmed anther analysis in which the functins summarized in Figure 2 were adjusted n the basis f RTs t neutral (center-arrw) trials. Fr this analysis we cmputed an RT fr each participant at the pint where he r she was making 5OV crt ect neutral-trial respnses. This RT was then used as the individual's pst hc deadline fr assessing prbability crect n cngruent and incngruentrials. These prbabilities, in tum, were used t cmpute relative RT estimates f F and S fr each participant using the same equatins described abve. With this methd f cmputing estimates, the crrelatin between age and F was substantially reduced (.05), but the relatin between age and S remained well abve zer (.27). This pattern suggests that age differences in cntrlled (frm) prcessing, but nt in autmatic (spatial) prcessing, are eliminated when verall respnse speed is taken int cnsideratin (see als Spieler, Balta, & Faust, 1996). Stgm cmpletin analyses. - Tw bserved prbabilities were f particular interest in the stem-cmpletin task; the prbability f respnding with an ld item and the prbability f nt prducing a respnse (i.e., "passing"). Age relatins fr each f these measures are summarized in Table 1. Ntice that there was a significant negative age relatin (r = -.30) fr the prprtin f ld items prduced in the nclusin cnditin, but there was n significant age relatin (r = -.04) fr the prprtin f ld respnses in the Exclusin cnditin. There were als n significant relatins between age and the prbability f passing in any f the cnditins. Estimates f mnemnic cntrl and autmaticity were cmputed frm the frmulas described earlier. The means f these estimates fr the three age grups are presented in Table l. Althugh the mean fr the cntrlled prcessing estimate was almst 237 lwer in the ldest age grup than in the yungest, the age crrelatin was nly This weak age relatin was surprising in light f previus studies (e.g., Jacby et al., 1996), and therefre pssible reasns fr the lack f a strnger age relatin were explred. Because vcabulary was psitively crrelated bth with age (r =.34) and with the cntrlled parameter (r =.32), it is

9 P224 SALTHOUS ETAL. pssible that the current sample was biased in favr f high-functining lder adults. ndeed, after cntrlling fr the level f vcabulary, the crrelatin between age and the estimate f cntrlled prcessing changed frm -.14 (n.s.) t -.27 (p <.01). Althugh this finding is interesring, withut additinal infrmatin it is nt pssible t determine whether the apparent discrepancy between the present study and earlier studies is attributable t ur use f a mre select sample f lder adults. T assess reliability, cntrlled and autmatic prcessing parameters were cmputed fr each f the tw sets f items presented in the stem task. Crrelatins were calculated between the tw sets f parameters, and these crrelatins were bsted by the Spearman-Brwn frmula t estimate reliability f the averages acrss the tw blcks. The resulting reliability estimates were.76 fr the cntrlled parameter and.82 fr the autmatic parameter. Estimates cmputed separately fr the three age grups were: Cntrlled, yung -.84, middle =.67, and ld =.76; Autmatic, yung =.88, middle =.87, and ld =.66. Crrelatinal analyses. - Table 2 cntains the crrelatin matrix fr all f the majr variables in the study including age. Values alng the diagnal in parentheses are estimates f the reliability f the variable. f there are separate cnstructs representing cntrlled and autmatic prcesses, the tw measures f the same cnstruct shuld be mderately cnelated with ne anther but either weakly r nt crrelated with measures f the ther cnstruct. nspectin f Table 2 reveals that there was a small psitive crrelatin (r =.26) between the cntrlled estimates frm the stem and arrw tasks, but little r n crrelatin between the tw autmatic prcessing estimates (r =.09). Furthermre, crrelatins between the cntrlled estimate in ne task and the autmatic estimate in the ther task were lw and nt significantly different frm zer (i.e., r = -.16 and r = -.ll). This pattern f results suggests that there is sme crrunnality in the tw measures f cntrlled prcessing, but little verlap in what is being assessed in the tw measures f autmatic prcessing. The relatively large negative crrelatin (r = -.71) between cntrlled and autmatic estimates in the stem task was surprising, especially given the assumptin that these tw prcesses make independent cntributins t perfrmance (see als Curran & Hintzman, 1995). Hwever, it is imprtant t emphasize that althugh the existence f this relatin indicates that the tw parameters are nt independent at the level f individuals, it des nt necessarily indicate that the tw prcesses were nt independent within a given individual. That is, nly if crrelatins culd be cmputed within an individual wuld their magnitudes be relevant t claims abut the independence f the tw prcesses (see Cwan, 1996; Jacby et al., 1997). Several pssible explanatins f the negative crrelatin were explred, but nne prved viable. Fr example, the crrelatin might have been atkibutable t the relatin f each parameter with a third variable such as vcabulary, but statistical cntrl f vcabulary had little effect n the crrelatin (i.e., changing frm r = -.71 t r = -.68). Mrever, the crrelatin between the prbability f cmpleting the stems with ld items in the Exclusin and nclusin cnditins was very lw (r = -.06), and thus it des nt appear that the participants simply ignred the instructins and merely tried t recall as many ld wrds as pssible regardless f the cnditin. As expected, the crrelatins with ther measures were hieher fr the cntrlled estimates than fr the autmatic Table 2. Crrelatins f Mair Variables r '7 9 l0 n t2 13 t t Age 2 Stem-cntrlled 3 Stem-autmatic 4 Arrw-cntrlled (F) 5 Arrw-autmatic (S) 6 Vcabulary 7 DDRT 8 DSRT 9 SD cpy l0 XO cmparisn [rtter cmparisn 12 Pattem cmparisn 13 ktter fluency 14 Categry fluency l5 Judgment fline Orientatin l6 Trails A 17 Trail B t8 cvln-5 19 CVLB Mean SD X -.t4 (;76) -.u -; " (.82) -.11 (.98) (.83) ' M ' t (.87).06 x X s2 (.9s) t t w ' (.e2).43 (.72).47.s2 (.74\ lt ' r2 (.85).49 (.66) x ' N X.50 x (.96) X Ntes: Crrelatins with an abslute value greater than.24 are significantly (p <.01) different frm zer. Values in parentheses alng the diagnal are estimates f reliability. N estimate f reliability was available fr the variables with an X in the diagnal. DDRT = digit-digit reactin time; CVLT = Califrnia Verbal Learnine Test.

10 PROCESS PURTY AND UNQUENESS OF AGE EFFECTS P225 estimates. Fr example, the crrelatins with the ttal number f items recalled acrss the first five tnals f the CVLT were.3l and.4l fr the stem and arrw cntrlled estimates, but nly and -.08 fr the stem and arrw autmatic estimates. t shuld be nted that this different pattern f relatins is nt an artifact f lw reliability, because the reliability estimates fr the theretically derived parameters were all between.76 and.98. Cmmn factr analyses. - Many perfrmance measures have mderate relatins with age, and therefre it is useful t examine the independence, r uniqueness, f the age-related influences n each f the measures. One way t assess this is by a single cmmn factr analysis (e.g., Kliegl & Mayr, 1992; Salthuse, 1994). This prcedure cnsists fdetermining what shared age-related influences cntribute t the agerelated effects n each measure, and then identifying the measures with unique (additinal) age-related influences. The fllwing steps were carried ut in ur implementatin [ the single cmmn factr prcedure. First. measures expressed in units f time (i.e., digit-digit and digirsymbl RT and Trail Making Parts A and B) were cnverted t reciprcals such that higher scres represented better perfrmance. Secnd, all measures were pstulated t be related t the cmmn factr, and the cmmn factr was pstulated t be related t age. Measures with n significant lading n the cmmn factr had their measure-cmmn paths deleted tim the mdel, and the remaining measure-cmmn and age-cmmn path cefficients were freely estimated. These parameters were then fixed t the estimated values when determining whether any f the measures had significant direct r independent relatins with age. (Nte that verall fit statistics are nt particularly infrmative in this type f analysis because the fcus here is exclusively n the age-related inlluences n the variables, and patterns f relatins amng variables are ignred.) The results f this analytical prcedure are summarized in Figure 3. The arrws indicate the relatins that were significantly different frm zer, and the numbers cnespnd t standardized regressin cefficients. The mderate t strng ladings f mst measures n the cmmn factr indicate that the measures share substantial amunts f variance with ne anther, and the strng negative relatin between age and the cmmn factr indicates that increasing age is assciated with lwer levels f what the measures have in cmmn. Of particular interest are the relatins invlving the estimates f cntrlled and autmatic prcessing. Ntice that the tw cntrl estimates bth laded n the cmmn factr but had n independent age-related effects, indicating that all f the age-related influences n these measures were shared with ther measures. n cntrast, the autmatic estimate frm the stem task did nt have a significant lading n the cmmn factr, and the autmatic estimate frm the arrw task had a small but negative lading. This pattern suggests that the autmatic estimates are measuring smething that is distinct frm that being measured by the ther variables. Hwever, because the tw autmatic estimates were nt crrelated with each ther (i.e., r =.09), they are apparently nt measuring the same type f autmatic prcessing. AGE "7e - cmmn Stem - Cntrlled Stem - Autmadc ----*.36 Anw - Cntrlled ---->.78 Anw -AutmEtlc -> -.21 DDRT ---->.80 DSRT ---->.83 SamrDlff ----.>.64 XO Cmp. -->.zg Lettercmp. --->.65 Pattem cmp. ----D :D Letter Fluency ---->.48 Categry Fluency ----D.98 JOLO ----D.27 TnllsA ----D.67 Tralls B ----*.73 CVLTA1 ---->.59 cvlt D.29 Figure 3. Results f the single cmmn factr analysis indicating direct and indirect age-related influences n the cgnitive variables. DDRT = digit-digit reactin time; DSRT = digit-symbl reactin time; JOLO = Judgment f Line Orientatin; CVLT = Califrnia Verbal Learnine Test. The letter fluency variable had a unique age-related effect in the ppsite directin f the age-cmmn relatin. This may be attributable t the fact that letter fluency is psitively related t level f vcabulary, which is greater with increased age in this sample (see belw). Mediatinal analyses. - Table 3 cntains the results f the predictin f CVLT perfrmance frm the speed measures and the estimates f cntrlled prcessing. Entries in the first rw crrespnd t the prprtin f variance assciated with age and the standardized regressin cefficient fr age when it was the nly predictr in the regressin equatin. Subsequent rws cntain crrespnding values btained frm hierarchical regressin analyses where the variables in the first clumn were cntrlled befre examining the age re-

11 P226 SALTHOUS ETAL. latins n the CVLT measure. t can be seen that there was a very large reductin f the age-related variance after cntrl f the speed variables. T illustrate, the reductin was 78V after cntrl f the perceptual speed cmpsite (i.e., letter cmparisn and pattem cmparisn), and 9lv after cntrl f the digifsymbl reactin time measure. n cntrast, the reductin was nly l87 after cntrl f the cntrlled reclfectin parameter frm the stem cmpletin task, and 75V after cntrl f the frm parameter frm the arrw task. Finally, Table 4 cntains the results f regressin analyses predicting the age-related variance in the speed variables and the cntrlled-prcessing parameters after cntrl f the ther variables. Ntice that there was a large asymmetry with the cntrlled (recllectin) parameter frm the stem task because statistical cntrl f that parameter reduced the age-related variance in the perceptual speed cmpsite by nly llv (frm.376 t.333), but cntrl f rhe perceptual speed cmpsite reduced the age-related variance in the recllectin parameter by 78V (frm.018 t.004). A similar asymmetry was apparent with the digitsymbl reactin time measure; age-related variance in that measure after statistical cntrl f the recllectin parameter was reduced by nly 8V (frm ), but cntrl f digirsymbl reactin time reduced age-related variance in estimated recllectin by 94V (frm.0l 8 t.001). There was less asymmetry in reductins f age-related variance with the cntrlled (frm) parameter frm the arrw task, perhaps because it is clsely related t speed. T illustrate, cntrl f the perceptual speed cmpsite reduced the age-related variance in the fbrm parameter by TlVa (frm.416 t.119), whereas cntrl f the fbrm parameter reduced the age-related variance in the perceptual speed cmpsite by 78V (frm.316 t.084). Cntrl f the digit-symbl RT measure reduced the age-related variance in the frm parameter by 67V (frm.416 t.136), while cntrl f the frm parameter reduced the age-related variance in the digit-symbl RT measure by 66V (frm.424 t.144). Results frm several ther multiple regressin analyses are als f interest. Fr example, althugh the age-related variance in the digit-symbl RT measure was reduced by SlV after cntrl f the digit-digit RT measure, the residual age-related variance was still significantly greater than zer (i.e., AR' =.082). Statistical cntrl f the SD cpy measure reduced the age-related variance in the XO cmparisn measure by 92V (i.e., AR' =.089, n.s.), and statistical cntrl f the XO cmparisn measure reduced, but did nt eliminate, the age-related variance in the letter cmparisn (i.e., lsv reductin, AR' =.096) and pattern cmparisn (i.e.,21v reductin, M' =.145) measures. Statistical cntrl f the Trails A measure reduced the age-related variance in the Trails B measure by 75V, but the residual age-related variance (i.e., M' =.055) was still significantly greater than zer. Finally, statistical cntrl f the vcabulary measure increased the magnitude f the age relatins n the tw fluency measures, as the crrelatin with age changed frm -.14 (nnsignificant) t -.28 (p <.01) with the letter fluency measure, and it changed frm -. l8 (nnsignificant) t -.32 (p <.01) fr the categry fluency measure. DrscussrN The present study prduced fur new findings f primary interest. First, prcess estimates derived frm the prcess- Table 3. Predictin f Age-Related Variance in CVLT -5 Perfrmance Age alne Age afier: LCPC cmpsite SD XO SD, XO SD, XO, LC/PC cmpsite DDRT DSRT Stem-cntrlled LCPC cmpsite, stem-cntrlled DSRT, stem-cntrlled Arrw-cntrlled (Frm) LC/PC cmpsite, arrw-cntrl led (Frm) DSR anw-cntrlled (Frm).l8t* * * * s.0t8.0(X / Reductin t l ' t ' Nte: The LC/PC cmpsite is the average f the z-scres frm the le! ter cmparisn and pattern cmparisn measures. DDRT = digit-digit reactin time; DSRT = digit-symbl reactin time. Table 4. Predictin f Ase-Related Variance in Speed and Cntr6lled Estimates Arrw LC/PC Cmparisn DSRT Age alne Age after: LCPC cmparisn DSRT Stem Arrw s *.ll9*.136x.378* R'.376x * *.333 E.084* R'.424*.130*.390*.144+.b) Ntes: LCPC cmparisn is average f the z-scres frm the letter cmparisn and pattern cmparisn measures. DSRT = digit-symbl reactin time *p <.01.

12 PROCESS PURTY AND UNQUENESS OF AGE EFFECTS P227 dissciatin prcedure in bth a memry (Jacby et al., 1993) and an attentin (Tth et al., 1995a) task were fund t be reliable, and therefre useful fr individual difference research invlving crrelatins. Secnd, bth cntrlled prcessing estimates were related t many ther measures, but the autmatic prcessing estimates were largely unrelated t these measures and t each ther. Third, althugh the qualitative distinctin between cntrlled and autmatic prcesses was supprted by the patterns f relatins amng variables, we fund little evidence fr a unique age-related influence n the estimates f cntrlled prcessing. Finally, there was a high degree f verlap f age-related variance in the cntrlled prcessing estimates and the measures f simple prcessing speed. We briefly address each f these issues in the fllwing paragraphs. Reliability: - One gal f the present study was t examine the reliability f estimates derived frm the prcessdissciatin prcedure. Assessing reliability is the first step tward mre cmprehensive cmparisns f different perfrmance measures, and is als a prerequisite fr interpreting relatins f the measures t individual difference variables such as age. Previus research with the prcessdissciatin prcedure has shwn that bth aging (Jacby et al., 1997) and brain injury (Tth, in press) may affecr estimates f mnemnic cntrl, but have n effect n estimates f the autmatic prcesses invlved in memry. Hwever, in the absence f infbrmatin abut the reliability f thse estimates. it is cnceivable that autmatic estimates have weaker relatins t variables such as age because they are less reliable than are estimates f cntrlled prcessing. The discvery in this study that bth types f prcess estimates frm a memry paradigm and an attentin paradigm had mderate t high reliability (i.e., frm.76 t.98) makes this artifact-based interpretatin f the different pattems f relatins fr cntrlled and autmatic prcessing estimates unlikely. Distinctiveness f prcess estimates. - A secnd majr finding f the study was that the estimates f cntrlled prcessing were related t many ther measures f perfrmance, while the estimates f autmatic prcessing had weak t nnexistent relatins with these ther measures. This pattern is cnsistent with the view that the cntrlled measures reflect deliberate strategic prcesses that are invlved in many cgnitive tasks, whereas the autmatic measures reflect prcesses that are mre task-specific (Neumann, 1984). The lack f a significant relatinship between the estimates f autmatic prcessing in the memry and attentin tasks (i.e., r =.09) is als cmpatible with the idea that the nature f autmaticity varies accrding t the particular task under investigatin. The clser crrespndence f the cntrlled than f the autmatic measures t ther cgnitive variables was als apparent in the results f the single cmmn factr analysis. That is, Figure 3 illustrates that the cntrlled measures had mderate t high ladings n the factr representing what was cmmn t the ther measures, but there were either weak (and negative) r nnexistent ladings f the measures f autmatic prcessing n the cmmn factr. This pattem is imprtant because the fact that the autmatic measures share little variance with ther measures is cnsistent with the view that they reflect a qualitatively different type f prcessing than that invlved in the ther measures. Uniqueness f age-related influences. - The perspective that cgnitive perfrmance is determined by qualitatively different prcesses is supprted by the evidence just mentined regarding the different pattems f relatins t ther variables fr the estimates f cntrlled and autmatic prcessing. Hwever, there was n evidence in the current study that the age-related influences n the cntrlled measures were unique, in the sense that they were independent f the age-related influences n ther cgnitive measures. Previus research has revealed that a brad range f cgnitive variables has negative relatins t age, but that few f these relatins are independent f ne anther (e.g., Lindenberger & Baltes, 1994; Salthuse, 1994). A similar utcme was evident in this study because variables representing verbal memry, verbal fluency, trail making, and several measures f speed were fund t share large prprtins f their age-related variance. Mrever, as in previus studies. when the variables were examined t determine which f them had unique age-related influences after taking int accunt the relatin between age and what the variables have in cmmn, the independent age-related influences were fund t be few in number and small in magnitude. The new linding in this study is that the estimates f cntrlled prcessing may als share the same set f causal influences as many ther cgnitive measures because there is n independent age-related influence n thse measures in the cmmn factr analysis. Patterns f mediatin - As ne wuld expect when many measures share large prprtins f age-related variance, mediatinal relatins can be pstulated between pairs f measures. Hwever, an interesting implicatin frm the single cmmn factr perspective is that measures with the strngest ladings n the cmmn factr shuld have the greatest impact as ptential mediatrs f the age relatins n ther measures. Examinatin f Figure 3 and Tables 3 and 4 reveals that this was generally the case, as the speed measures tended t have the highest ladings n the cmmn factr and were als the measures which, when statistically cntrlled, led t the greatest attenuatin f the agerelated variance in ther measures. An interesting questin fr which we d nt yet have an answer is whether this pattern is merely a statistical cnsequence f the differential ladings n the cmrnn factr, r whether the measures with the highest ladings are smehw mre central r fundamental t the cmmn factr. Cnclusin. - Many cntemprary measures f cgnitive perfrmance invlve a mixture f theretically distinct prcesses. t is therefre imprtant t disentangle thse prcesses and t identify their separate cntributins t relatins between ther variables such as age. Results frm this study demnstrate that reliable measures f theretically distinct prcesses can be btained frm tw very different cgnitive tasks, and that these estimates have different pat-