Interrelations of Age, Visual Acurty, and Cognitive Functioning

Transcription

1 J ournl of Gerontology : PSYCH OLOCICAL SC I ENCES 1996, Vol.5lB, No.6, P3l7-P330 Copyright 1996 by The Gerontologicl Seiety of Arcric Interreltions of, Visul Acurty, nd Cognitive Functioning Timothy A. Slthouse, Holly E. Hncock, Elizbeth J. Meinz, nd Dvid Z. Hmbrick School of psychology, Georgi Institute of Technology. It hs recently been suggested thot Ihrge Foportion of the ge-relted influences -h^ on,nn! menr.res of cognitive functioning h medited through singk common Jctor. Thi hypothesis brrn suppoied by the disioviry tht much of the ge'relred vrince in diflerent cognitive mesures is shred, nd is not iiitinct or-independent. Thr1yerlier results were replicted in this proiect, nd il ws lso discovered tht mesures of corrected visul cuity i processing speed shre very-lrge proportion of the ge-reltedvrince in mcsures of working memory, ^roiiotin1" lerning' nd concept identifiction. The pprent imptiction is tht the commonfcir tht f,pers n iontribute to ge'relted dffirences in m-ny.cognitive mesures is quite brod nd my refuit reltivefy'generl reduction in centrl nemous system functioning. pecent reserch hs estblished tht ge-relted inr\ fluences on mny different cognitive vribles re not independent, but insted thtl0%o or more ofthe ge-relted vrince is shred with other vribles (Slthouse, l99}b, 1994b, 1996). This finding suggests tht dult ge differences in cognition re not exclusively ttributble to tskspecific processes but insted re determined t lest prtilly by broder or more generl fctors. Vritions in these brod fctors re unlikely to be responsible for ll of the observed ge differences in cognitive functioning, but it is importnt to ssess nd understnd the contribution of nv generl fctors tht might exist becuse the role of morl specific fctors cnnot be ccurtely determined unless the generl influences re first tken into considertion. One pproch tht cn be used to investigte the nture of the hypothesized common or generl fctor is to determine which vribles "ge together" in the sense tht they shre lrge portions of their ge-relted vrince. Tht is, to the extent tht vrible is found to hve considerble overlp of its ge-relted vrince with the ge-relted vrince in other vribles, then it cn be inferred to be either cuse or consequence of the hypothesized common fctor. For exmple, number of studies hve exmined mesures of how quickly simple comprison or substitution opertions cn be executed. Nerly everyone chieves perfect ccurcy in these tsks if enough time is llowed, nd thus performnce is usully ssessed in terms of how quickly the tsks cn be completed. Becuse mesures of performnce in tsks of this type hve been found to shre'75vor more of the ge-relted vrince from vriety of cognitive mesures, speed of processing hs been postulted to be centrlly involved in the hypothesized common fctor (Slthouse, 1993, 1994b, 1994c, 1996, I996b). Recently, however, Lindenberger nd Bltes (1994) hve reported tht mesures of sensory bility lso shred lrge proportions of ge-relted vrince with severl mesures of cognitive functioning in smple of dults between 70 nd 103 yers of ge. Furthermore, the reltions they reported were pprently not merely consequence of difficulty registering the stimuli, becuse similr ptterns were evident with mesures from three different sensory modlities - vision, hering, nd blnce. Among the possibilities discussed by these uthors ws tht the sensory nd cognitive mesures were relted becuse they were both indictors of the hypothesized common fctor tht hs been postulted to contribute to dult ge differences in mny mesures of cognitive functioning. The gol of the current project ws to investigte the role of sensory bility on ge-cognition reltions in helthy smples of dults from younger ge rnge - between pproximtely 18 nd 80 yers of ge - thn the smple studied by Lindenberger nd Bltes (1994). (See Appendix, Note I ). Only mesures of ner visul cuity were exmined becuse Lindenberger nd Bltes (1994) found similr reltions with mesures from ech sensory modlity, nd vision is the esiest sensory modlity to ssess. Moreover, visul cuity ws ssessed while the individuls were wering their norml corrective lenses, becuse Lindenberger nd Bltes (1994) found tht this mesure exhibited stiong reltions both with ge nd with mesures of cognitive functioning. Note tht, becuse vision is ssessed when the reserch prticipnts were wering corrective lenses, everyone might hve been expected to hve close to optimum cuity if the opticl corrections were fully effective in remediting ny visul defects. However, the reserch literture contins mny reports of ge-relted declines in corrected visul cuity (e.g., Burg, 1966; Chpnis, 1950; Fozrd, 1990; Gittings & Fozrd, 1986; Pitts, 1982). There is some difference of opinion s to the primry fctors responsible for the ge-relted cuity loss, becuse Kline nd Schieber (19S5, p. 3l) clim tht "Much of the slight to moderte loss in sttic visul cuity ccompnying norml ging ppers to be due to chnges in the optic medi of the eye," wheres Wele (1982, p. 167) suggests tht opticl fctors re responsible for only some of the declines in visul cuity, with the rest ttributble to loss of neurl cells. When cuity is ssessed t reltively close viewing distnces, s ws the cse in the present studies, reductions in the effectiveness of P3r7

2 P3l8 SALTHOUS ET AL. ccommodtion probbly lso contribute to negtive reltions between ge nd visul cuity becuse of decresed bility to focus on ner objects. Regrdless ofthe resons for the ge-relted declines in corrected ner visul cuity, however, the visul cuity mesure is of interest if it is lso relted to mesures of cognitive functioning becuse it might then be nother reflection of the hypothesized common fctor. The primry nlyticl strtegy in this project involved prtitioning the vrince mong ge. vision. nd cognitive vribles to determine how much vrince is shred in vrious combintions. The gol ws to find out which vribles "ge together" by, in effect, exmining the correltions between the ge-relted effects on different vribles. Tht is, the ge-relted effects cn be expressed s the squre of the correltion (i.e., the covrince), nd then the degree of independence of the reltions between ge nd different vribles cn be exmined by inspection of the overlp of the ge-vrible covrinces. Commonlity nlysis (Pedhzur, 1982) ws the principl method used to ccomplish the vrince prtitioning. When there re two predictors (e.9., ge nd vision) of mesure of cognitive functioning, three vrince proportions re of interest in commonlity nlysis. Two of these proportions represent unique contributions of ge nd of vision, respectively. They cn be computed with hierrchicl regression procedures nd correspond to the increment in Rt ssocited with one predictor vrible fter the vrince in the other predictor vrible hs been controlled. The estimtes therefore represent the vrince in the criterion vrible ssocited with one predictor tht is independent of the other predictor. These unique vrince estimtes would be expected to be high if most of the influences of the predictor were distinct from the other predictor, but they would be expected to be low if most of the influences were shred. The third vrince estimte represents the common vrince in the criterion vrible tht is shred between the two predictors, nd is not unique to either. It is computed by subtrcting the estimte of the unique contribution of predictor on the criterion vrible from the totl effects ofthe predictor on tht vrible. In the current context, this estimte of shred vrince cn be interpreted s the contribution ofthe hypothesized common or generl fctor on the ge-relted effects in the criterion vribles. An extension of commonlity nlysis proposed by Slthouse (1992b, 1994b) ws lso used to express the rtio of shred to totl ge-relted vrince in the form of correltion coefficient. The trditionl Person productmoment correltion reflects the squre root of the rtio of shred to totl vrince for ll of the vrince in the vribles, nd the prtil correltion controlling for ge conesponds to the squre root of the shred to totl geindependent vrince in the vribles. In contrst, the qusi-prtil correltion is the squre root of the rtio of the shred to totl ge-relted vrince. It will be high if much of the reltion between the vribles is becuse of common fctor ssocited with both vribles nd with ge, nd it will be low if most of the ge-relted influences re unique. Commonlity nd qusi-prtil correltion nlyses were conducted both with cognitive mesures nd with speed mesures s the criterion vribles. Speed mesures re interesting becuse previous reserch hs reveled tht speed mesures shre lrge proportion of the ge-relted vrince with mny cognitive mesures (e.g., Bors & Fonin, 1995; Bryn & Luszcz, 1996;' Grf & Uttl, 1995; Hertzog, 1989; Lindenberger, Myr, & Kliegl, 1993; Nettelbeck & Rbbitt, 1992; Slthouse, 1992, 1993, 1994, 1994c, 1996, 1996b; Schie, 1989, 1990). Anlyses from three seprte dt sets re reported in this rticle. Two dt sets were from studies conducted for other purposes, but some of those dt were menble to the present nlyses becuse the prticipnts spnned wide ge rnge nd mesures of visul cuity nd speed were obtined from every prticipnt. The other tsks in these studies were not trditionl cognitive tsks nd thus only the speed mesures from those studies re reported here. The third dt set is from new study with the sme four speed mesures s in Studies I nd2 nd lso three mesures of working memory nd mesures from n ssocitive lerning tsk nd from concept-identifi ction tsk. Studies I nd 2 The purpose of the nlyses in the initil two studies ws to investigte the role of vision on the reltions between ge nd reltively simple mesures of processing speed. Of prticulr interest ws whether strong negtive reltions between ge nd corrected ner visul cuity would be found in smples of helthy dults between pproximtely l8 nd 80 yers of ge nd the degree to which the ge-relted vrince in the mesures of processing speed ws shred with the ge-relted vrince in the vision mesure. METHoD Subjects. - Prticipnts in these studies consisted of 77 nd 127 dults, respectively, in Studies I nd 2. Descriptive chrcteristics of the prticipnts re summrized in Tble l, where it cn be seen tht nerly ll of them reported themselves to be in good to excellent helth. (More detils bout the prticipnts re provided in the complete reports of these studies; Slthouse, Hmbrick, Luks, & Dell, in press; Meinz & Slthouse, 1996). Procedure. - Visul cuity ws ssessed by mens of ner-vision eye chrt held t distnce of pproximtely 30 cm in room with norml (uncontrolled) mbient illumintion. The chrt (Scle Typogrphice Birkhuseri, Birkhuser Verlg, Bsel) contined both Lndolt C nd two-digit number stimuli in 10 different font sizes conesponding to Snellen cuity rtios of.l to 1.0. The ssessment consisted of sking reserch prticipnts to red the numbers or stte the direction of the gp in the C with ech type of stimulus, first with the left eye covered nd then gin with the right eye covered. The Snellen rtio corresponding to the smllest font size t which this could be ccomplished with fewer thn two errors out of the 8 to l6 items t ech font size ws identified s the visul cuity estimte. Prticipnts used ny corrective lenses they hd vilble during the testing,

3 VI SI ON -C OGN ITI ON RELATI ON S P319 Tble l. Chrcteristics of Prticipnts in Studies I nd 2 Study I Study 2 Vrible Men SD r Men SD r n Vo Femle Eduction Helth Rting I Helth Rting 2 Helth Stisfction Helth-Relted Limittions Crdiovsculr Surgery Hypertension Medictions Hed Injury 't'1 l; t2' l l)_ / l l 15.5 Neurologicl Tretment - Right Eye - Left Eye Synonym Vocbulry Antonym Vocbulry Perceptul Speed Letter Comprison Pttem Comprison Rection Time Digit-Digir Digit-Symbol o o.25 o '7 o.22 o l8.l' * l0 -.56* -.62* * -.54*.35* M 0.5' r' ). t t@.t-i-) ll -. ll.32* * y'vote.' Eduction is number of yers of forml eduction completed, nd Helth Rting, Helth Stisfction, nd Helth-Relted Limittions re rtings on 5-point scle where lower numbers indicte better helth. Responses to the Crdiovsculr Surgery, Hypertension Medictions, Hed Injury, nd Neurologicl Tretment items were Yes/No, nd thus the mens conespond to the proportion of individuls reporting positive response. scores re the verge of the Snellen rtios for the number nd Lndolt C stimuli. Scores in the Vocbulry nd Perceptul Speed tests re number of items correct, nd scores in the Rection Time tsks re in msec. *P <.ol..tl.06 _.46* -.43*.42*.5'7* but we hve no informtion bout the recency, or ccurcy, of their opticl correction. Although this prticulr visul cuity test hs not been widely used in the United Sttes, it hs severl dvntges for the current purposes. First, nd most importnt, the test is from the sme set of cuity tbles used by Lindenberger nd Bltes (1994) nd Bltes nd Lindenberger (1995, in press), nd therefore we cn exmine the replicbility of their results with very similr ssessment instrument. Second, unlike mny cuity tests, two types of stimulus (2- digit numbers nd Lndolt C) re presented, nd therefore it is possible to determine whether the results re specific to prticulr type of stimulus. Third, the stimuli re clibrted in equl Snellen rtios from 0.1 to 1.0 in steps of 0.1, nd thus there is wide rnge of sensitivity within the norml popultion. And fourth, the cuity estimtes from this test were found to correlte.91 with the estimtes from more trditionl visul cuity test (i.e., the Lighthouse Ner Visul Acuity Test, Modified ETDRS with Slon Letters) in smple of 19 individuls. Two of the speed tsks were dministered with pper-ndpencil procedures. The letter comprison tsk consisted of the presenttion of pirs of three, six, or nine letters, with pproximtely hlf of the pirs differing in the identity of one letter. The prticipnt ws instructed to write n "S" (for sme) or "D" (for different) on line between the numbers of the pir nd to work s mny of the items s possible within 30 sec. The pttern comprison test ws very similr except tht the pirs consisted of ptterns composed of three, six, or nine line segments. Ech test begn with pge contining severl smple items, nd then ws dministered in two seprtely timed (30 sec) sections. The score in ech section ws the number of items mrked correctly minus the number of items mrked incorrectly, nd the verge of the two scores served s the primry performnce mesur9. The digit-digit nd digit-symbol rection time tsks were dministered on computers. Trils in ech tsk consisted of the presenttion of code tble t the top of the computer screen nd pir of probe items in the middle of the screen. In the digit-digit tsk, the code tble contined nine pirs of identicl digits nd hence ws superfluous, but in the digitsymbol tsk, it contined nine digits ech pired with different symbol. Probe items consisted of pirs of digits in the digitdigit tsk nd pirs of digit nd symbol in the digit-symbol tsk. Reserch prticipnts were instructed to press the " 1" key on the keybord if the members of the probe pir were the sme (i.e., either physiclly identicl in the digitdigit tsk or ssocitionlly equivlent in the digitsymbol tsk), nd to press the "2" key on the keybord if the members of the pir were different. A prctice block of l8 trils preceded the experimentl block of90 trils in ech tsk. Becuse ccurcy verged over 95Vo, the medin rection time served s the primry mesure of performnce in these tsks. No constrints on viewing distnce were imposed in ny

4 P320 SALTHOUS ET AL. of the tsks. However, the visul ngles t viewing distnce of 45 cm were pproximtely two degrees for the letter comprison nd pttern comprison stimuli, nd four degrees for the digit-digit nd digit-symbol stimuli. RESULTS AND DISCUSSION - Reltions The visul cuity scores with the Lndolt C nd with the two-digit number stimuli were highly correlted with one nother (i.e., r's >.7), nd thus the verge of the two scores ws used s the visul cuity estimte for ech eye. The vision scores cross the two eyes were lso modertely to highly correlted with one nother (r :.82 in Study l, r :.49 in Study 2), nd thus the verge cross the two eyes ws used s composite vision score (see Appendix, Note 2). Estimted relibility of the composite vision score ws computed by determining the prtil correltion between the scores for the two eyes controlling for ge nd then boosting tht vlue by the Spermn-Brown formul. The resulting estimtes were.87 in Study I nd.59 in Study 2. Becuse the results of the nlyses reported below were very similr with the visul cuity score in ech eye serving s the vision mesure, the ggregtion cross eyes primrily serves to increse the relibility of the vision mesure (see Appendix, Note 3). Figure I portrys the reltions between ge nd the composite vision mesure in Studies I nd 2. It is pprent tht there were strong negtive ge reltions on the corrected ner-vision cuity mesure in smples rnging from l8 to 80 yers of ge. Regression nlyses reveled tht the qudrtic (gesqured) term ws significnt in both Study I nd Study 2 nd ws responsible for n dditionl6.6vo of the vrince in Study I nd n dditionl 3.0Vo of the vrince in Study 2. Seprte nlyses on the subgroups bove nd below the medin ge indicted tht the nonliner effects were ttributble to smller ge reltion t older ges. Neither the gender min effect nor the interction of X Gender ws significnt in either study. The influence of helth mesures on the reltion between ge nd vision ws exmined by conducting principl components nlysis on the eight helth mesures (see Tble l), nd then controlling the vrince in the component scores before exmining the reltionship between ge nd vision. The principl components nlysis of the helth vribles in Study I indicted tht two components hd eigenvlues greter thn 1.0. The first component hd high lodings on ll helth vribles except for reports of hed injury nd of tretment for neurologicl disorders nd ws correlted.29 with ge. The second component hd high lodings on the hed injury nd neurologicl tretment vribles nd ws correlted with ge. The R2 ssocited with ge in prediction of the composite vision index ws.379, nd this ws reduced to.293 fter control of fctor I nd to.376 fter control of fctor 2. In Study 2 the principl components nlysis reveled three components with eigenvlues greter thn l. The first hd mjor lodings from the self-rted heth vribles, the second hd high loding from the crdiovsculr surgery vrible, nd the third hd high loding from the report of neurologicl tretment vrible. Correltions of ge with the components were.05, -.01, nd -. 10, respectively. The ge-relted vrince in the composite vision mesure ws.510, nd it ws reduced to.507 fter control of the first component; it ws reduced to.509 fter control ofthe second Study 1 Study o 0.8 (6 E o f o c o Y = q, 12= o o o \. \ -.. \.... \.. \ \.... \... \. \ -. \ o y-1.t (X), r2.:.\ Chronologicl Chronologicl 80 Figure l. Reltion between composite visul cuity score nd ge in Studies I nd 2. Ech point represents different individul.

5 VI S I O N -C OGN ITI ON RE LAT I O N S P32l component, nd it incresed to.516 ftercontrol of the third component. The results of the nlyses just described suggest tht the observed reltions between ge nd vision re not medited by poorer helth, t lest s helth is ssessed with the reltively crude self-report mesures in these studies. Similr nlyses with control ofthe vrible ofyers ofeduction lso resulted in little reduction of the ge-ielted vrince in the composite vision mesure. Tht is, fter the mount of eduction vrible ws sttisticlly controlled, the R, for ge ws reduced from.379 to.37 in Study I, nd from.510 io.479 in Study 2. -Speed Reltions The initil nlysis on the speed mesures consisted of computing correltions, prtil correltions, nd qusi_ prtil correltions between pirs of speed mesures. In Study I the bsolute mgnitude of the correltions rnged from.34 to.65, the rnge for the prtil correltions ws.24 to.59, nd the rnge for the qusi-prtil correltions ws.71 to.86. In Study 2 the rnges of the bsolute vlues were.27 to.63 for the correltions,.10 to.54 for the prtil correltions, nd.58 to.91 forthe qusi-prtil correltions. The reltively lrge vlues of the qusi-prtil correltions indicte tht substntil proportion of the shred vrince between pirs of speed vribles ws lso relted to ge. However, it should be noted tht one reson the qusi-prtil correltions re lrger thn the other correltions is tht ll of the ge-relted vrince ws relible, wheres some of the totl vrince nd of the ge-independent vrince ws due to error nd hence ws not systemtic. A composite speed index ws creted by subtrcting the verge z-score for the digitdigit rection time nd digir symbol rection time mesures (r :.65 in Study I nd r =.50 in Study 2) from the verge z-score for the letter comprison nd pttern comprison mesures (r :.49 in Study I nd r :.63 in Study 2). Note tht the subtrction reflects the fct tht the rection time mesures re scled in time per item, wheres the comprison mesures re scled in items per time. This composite speed index served s n dditionl speed mesure in the subsequent nlyses. Influence of on -Speed Reltions Tests for the x interction were conducted by entering the cross-product term fter the ge nd vision term's in the multiple regression equtions with the five speed mesures s criterion vribles. Only one of the interction tgrms (i.e., on Digit Symbol Rection Time in Study 2) ws significnt t the specified (cr :.Ol) significnce level, nd therefore there is little evidence tht the reltions between vision nd speed vried s function of ge. Tble 2 contins commonlity estimtes of the proportions of vrince in the speed mesures ssocited with different predictors. Note tht the proportion of vrince in the speed mesures unique to vision ws ner zero for ll five speed mesures. This indictes tht there ws little geindependent reltion between vision nd speed nd implies tht lmost ll of the reltion between vision nd speed ws ttributble to the ge vrition. The estimtes of the vrince unique to ge rnged from 46 to 66Vo of the totl ge-relted vrince in Study l, nd from 38 to6l%o in Study 2.The percentge ofthe totl gerelted vrince common to vision verged 43Vo instudy I nd 53Vo in Study 2. It cn therefore be concluded tirt pproximtely hlf of the ge-relted vrince in the current speed mesures is shred with mesure of ner-vision cuity. Although only bout 5O7o of the ge-relted influences on speed were shred with the vision mesure, it is nevertheless importnt to note tht there were strong negtive reltions between ge nd corrected ner-visul cuity. nd moderte correltions between the visul cuity meisure nd speed mesures obtined under high visibility conditions. The next study ws therefore conducted to determine whether similr, or possibly even lrger, reltions of vision would be evident with mesures from higher-order cognitive tsks. Study 3 Previous reserch hs indicted tht processing speed is mjor fctor in the ge reltions on ny cognitive mesures (e.g., Bors & Forrin, 1995; Bryn &Luszcz,1996; Grf & Uttl, 1995; Hertzog, 1989; Lindenberger, Myr, & Kliegl, 1993; Nettelbeck & Rbbitt, t992; Slrhouse, 1992, 19i3, 1994, 1994c, 1996, I 996b; Schie, I 989, I 990). The question of interest in this study ws whether the ge-reited vrince tht is shred with speed is unique or whether it is lso shred with mesures of vision. If the lffer is the cse, this would suggestht common fctor reflecting reltively brod centrl nervous system functioning my be responsible for the medition of ge-relted cognitive differences. The tsks dministered in this study consisted of the sme four speed tsks used in Studies I nd Z nd, in ddition. three working memory tsks nd two tsks ssessing higherorder cognitive functioning. Two of the working memory tsks, reding spn nd computtion spn, hve been used in severl previous studies (Slthouse & Coon, 1994; Slthouse & Meinz, 1995). The zbck tsk ws bsed on tsk originlly described by Ky (in Welford, 1958) nd Kirchner (1958). It consisted of the presenttion of series of rndomly selected digits with the prticipnt sked to report the digits n bck in the sequence. Vlues of n equl to 0, l, nd 2 were used in this study. The two higher-order cognitive tsks were ssocitive lerning (Slthouse, 1994) nd computer-dministered version of the Wisconsin Crd Sorting Test (WCST; Heton, Chelune, Tlley, Ky, & Curtiss, 1993). These prticulr cognitive tsks re of specil interest becuse both yield mesures ofpersevertion responses tht hve been found to increse in frequency with incresing ge. Although the increse in persevertion responses with incresed ge seems well estblished, prticulrly for the WCST, there re two importnt questions bout this phenomenon. First, re persevertion mesures from different tsks highly conelted, s would be expected if they reflect common construct? And second, re the ge differences in persevertion responses medited by ge-relted differences in working memory, s might be expected if they re ttributble to filure to effectively process feedbck informtion (cf., Slthouse, 1994)2 It should be possible to nswer these

6 P322 SALTHOUS ET AL. Tble 2. Commonlity Estimtes for Speed Mesures, Studies I nd 2 Criterion Predictor Unique to Unique to Common to & Totl Studyl(n:77) Letter Comprison Pttern Comprison DigirDigit Rection Time r Digit-Symbol Rection Time Composite t Study2(n: 127) Letter Comprison to. 133 Pttem Comprison t42.t l6l Digit-Digit Rection Time Ag" t Digit-symbol Rection Time.t t Composite l)-, -z)j questions with dt from study in which the prticipnts performed bttery of working memory nd ssocitive lerning tsks in ddition to the WCST. The dt in this study were exmined with two sets of commonlity nlyses. The first set of nlyses ws identicl to those in Studies I nd2, with ge nd vision s predictors of the speed mesures. The second set of nlyses involved three predictors (i.e., ge, vision, nd speed) ofthe working memory nd cognitive mesures. The gol in these nlyses ws to determine whether the ge-relted vrince shred with speed nd cognition ws the sme s the ge-relted vrince shred with vision nd cognition. If so, then this result would be consistent with the common fctor interprettion. If not, then seprte speed nd vision influences on the ge differences in cognition would presumbly need to be postulted. METHOD Subjects. - The smple consisted of 197 dults between l8 nd g2yers ofge. None ofthe individuls hd prticipted in either of the previous studies. Descriptive chrcteristics of the prticipnts re summrized in Tble 3, where it cn be seen tht most of the prticipnts reported themselves to be in good to excellent helth, nd hd ttended college for n verge oftwo to three yers. Procedure. - All prticipnts performed the following sequence of tsks in single session of pproximtely two hours. The tsks included letter compiuison' pttern comprison, synonym vocbulry, ntonym vocbulry, digitdigit rection time nd digirsymbol rection time (in counterblnced order), sentence spn, computtion spn, nbck with n equl to 0, l, nd 2 (in counterblnced order), computer-dministered WCST, nd ssocitive lerning. The letter comprison, pttern comprison, digit-digit rection time, nd digitsymbol rection time tsks were identicl to those dministered in Studies I nd 2. The sme vocbulry tests from the erlier studies were lso used in this study nd consisted of 10 four-lterntive multiple choice items for both the synonym nd ntonym tests. The reding spn nd computtion spn tsks were identi-

7 VI SI ON -C OGN ITION RELATI ON S P323 Tble 3. Chrcteristics of Prticipnts in Studv 3 Group Vrible I _59 60_ 92 r n Vo Femle Eduction Helth Rting I Helth Rting 2 Helth Stisfction Helth-Relted Limittions Crdiovsculr Surgery Hypertension Medictions Hed Injury Neurologicl Tretment Visul Acuity - Right Eye Visul Acuity - Left Eye Synonym Vocbulry Antonym Vocbulry (6.4) 64.2 r4.8 (2.3) 2.0 (0.e) 2.2 (0.9) 2.3 (0.8) 1.5 (1.0) 0 (0) 0.03 (0.17) 0.04 (0.21) 0.09 (0.29) 0.69 (0.22) 0.'72 (0.20) s.3 (2.8) 4.8 (3.0) 68 s0.5 (6.0) 61.8 ts.t (2.3) 2.1 (0.9) 2.3 (0.8) 2-4 (O.7) 1.7 (0.8) 0.01 (0.12) 0.16 (0.37) 0.t2 (0.32) 0.09 (0.2e) 0.4s (0.23) o.46 (0.2t) 6.8 (3.0) 6.1 (3.4) (7.0) (3.2) 2.0 (0.9) 2.3 (0.8) 2.3 (0.8) 1.8 (0.9) 0.13 (0.34) 0.37 (0.49) 0. l l (0.32) 0 (0) 0.35 (0. ls) 0.34 (0.16) 1.3 (2.9) 6. r (3.3) Nole.' Eduction is number of yers of forml eduction completed, nd Helth Rting, Helth Stisfction, nd Helth-Relted Limittions re rtings on 5-point scle where lower numbers indicte better helth. Responses to the Crdiovsculr Surgery, Hypertension Medictions, Hed lnjury, nd Neurologicl Tretment items were Yes/No, nd thus the mens conespond to the proportion of individuls reporting positive response. icores re the verge of the Snellen rtios for the number nd Lndolt C stimuli. Scores in the Vocbulry tests re number of items correct. *p <.ol ll.o4.20*.29*.39*.ll -. l5 *.59* -.62*.29*.16 cl to those used in erlier studies by Slthouse nd Coon (1994) nd Slthouse nd Meinz (1995). Ech consisted of prctice set of trils followed by two experimentl blocks with different items in ech set. Trils in the reding spn tsk involved the presenttion of short sentence ccompnied by question nd three lterntive nswers. The reserch prticipnt ws instructed to use the rrow keys on the keybord to position n row in front of the correct nswer to the question while lso remembering the lst word in the sentence. After selecting the nswer to the questions, prompt ppered, requesting the prticipnt to recll the trget words by typing them on the keybord. The number of sentences (nd to-be-remembered words) incresed to mximum of nine s long s the prticipnt ws correct on both the comprehension question nd the recll on t lest two of the three trils t ech list length. The spn estimte ws the lrgest number of items t which the prticipnt ws correct on both the comprehension nd the recll on t lest two of three trils. The computtion spn tsk ws very similr to the reding spn tsk, except tht it consisted of rithmetic problems insted of sentences, nd the items to be remembered were digits insted of words. The nbck tsk involved the presenttion of sequence of l0 to 12 (i.e., n + 10) digits on the computer screen with the prticipnt instructed to type the digit 0, l, or 2 items bck in the sequence. Ech digit ppered for 1.5 sec, nd the pproprite response hd to be entered within tht intervl to be counted s correct. Prticipnts received prctice in ech of the three conditions (i.e., n : 0, l, nd 2) before performing totl of six trils in ech condition, with the conditions presented in counterblnced order (i.e., 0-l-2-2-l-O). The n : 0 condition ws primrily control condition becuse there ws no storge requirement when the digit to be typed ws currently on the screen. Performnce could be less thn mximum (l00vo) in this condition becuse of confusion bout the instructions nd/or difficulty in locting the response keys nd responding within the 1.5-sec intervl. The influence of these fctors on performnce in the other conditions ws exmined by computing the residuls in predictionof then: I nd n:2 scoresfrommultiple regression eqution fter controlling for the n : 0 score. However, becuse these residuls were highly correlted with the rw scores (i.e.,.83 for n : I nd.90 for n : 2), only the rw scores were used in subsequent nlyses. A computer-dministered version of the Wisconsin Crd Sorting Test ws used to presenthe WCST. (The computer progrm ws developed by John L. Woodrd, who kindly llowed us to use it in this study). The stndrd version of this test consists of set of four stimulus crds nd I 28 response crds, which re to be sorted into the pproprite stimulus ctegory ccording to principles (i.e., on the bsis of color, form, nd number) tht hd to be discovered, nd which chnged throughout the test. Insted ofpresenting the stimulus nd response items s crds, in the computerdministered version they were displyed s boxes on the computer screen. A response crd ws sorted into the pproprite ctegory by typing number from I to 4 corresponding to the stimulus item below which the response crd should be plced. The response crd then ppered underneth the stimulus crd nd both uditory (i.e., tones of different frequencies) nd visul (i.e., "Right" or "Wrong") feedbck ws presented. The two mesures of primry interest in this test were the number of ctegories (out of mximum of six) successfully completed, nd the percentge of persevertive errors in which the prticipnt continued to respond to previous ctegory fter the sorting principle hd chnged. The ssocitive lerning tsk ws very similr to the tsks

8 P324 SALTHOUS ET AL. described by Slthouse (1994). An initil prctice block with two pirs of stimuli ws presented, followed by two blocks of six trils ech with six symbol pirs s stimuli. Trils in the tsk consisted of the presenttion of single stimulus item on the left of the screen nd column of six response items on the right of the screen. The response ws selected by using rrow keys to position n ilrow in front of the designted response item, fter which feedbck ws presented in the form of n uditory signl nd visul highlighting of the correct response term. A vriety of detiled performnce mesures cn be derived from this tsk (see Slthouse,1994), but the two of primry interest in this study were the percentge of correct responses nd the percentge of persevertion responses in which the sme incorrect response to stimulus ws repeted on successive trils. As in Studies I nd 2, prticipnts viewed the stimuli without constrints; therefore viewing distnce ws not controlled. However, visul ngles for the trget stimuli t viewing distnce of 45 cm were pproximtely 4 degrees for the items in the digit-digit, digit-symbol, nd ssocitive lerning tsks, 2 degrees for the chrcters in the reding spn nd computtion spn tsks, l4 degrees for the digits in the nbck tsk, nd 6 degrees for the individul symbols nd 24 degrees for the "crds" in the computer-dministered WCST. RBsulrs AND DISCUSSIoN Reltions Mens, stndrd devitions, ge correltions nd estimted relibilities of the performnce mesures re summrized in Tble 4. All vribles were significntly relted to ge except for the WCST persevertive error mesure, nd the relibility estimtes were ll in the moderte rnge except for the ssocitive lerning persevertive erors mesure. Becuse the WCST ws dministered only once, no relibility estimtes could be computed for the mesures in this tsk. The ge reltionships on the mesures of performnce in the ssocitive lerning tsk were similr to those from two studies reported in Slthouse (1994) where the ge correltions were -.41 nd -.30 for the percentge correct mesure nd.36 nd.20 for the persevertion elror mesure. The ge reltions on the WCST mesures in this study were smller thn those in recent study (Slthouse, Fristoe, & Rhee, 1996) using the trditionl crd version ofthe test. Tht is, in the erlier study the ge correltions were -.41 for the number of ctegories mesure nd.43 for the persevertion mesure. It is not cler whether the smller ge reltions in the current study re ttributble to differences in the formt ofthe test, to smple differences, or to fctors relted to the other tests dministered prior to the WCST. Other mesures from the ssocitive lerning tsk nd the WCST were lso exmined. Unlike erlier studies (Slthouse, 1994), the mesure of percentge forgetting in ssocitive lerning hd low (r :.10) nd nonsignificnt correltion with ge in this smple. The percentge of conceptul level responses in the WCST hd correltion of -.20 with ge, but it ws lrgely redundnt with the other WCST mesures becuse it ws correlted.91 with the number of ctegories mesure nd -.80 with the percentge of persevertion errors mesure. The correltion between ge nd the WCST persevertion Vrible Tble 4. Performnce Mesures in Studv 3 Group l r Estimted Relibility' Perceptul Speed Letter Comprison Pttem Comprison Rection Time Digit-Digit Digit-Symbol Working Memory Computtion Spn Reding Spn NBck 0-Bck l-bck 2-Bck Associtive Leming Vo Conect 7o Persevertion Error Wisconsin Crd Sorting Test Number of Ctegories 7o Persevertion Error 10.5 (2.9) 18. l (3.6) 698 (148) l30l (317) 3.9 (2.2) 2.6 (r.4) 84.7 (18.s) 66.8 (33.7) 42.r (29.0) 40.3 (16.3) 13.4 (8.4) 4.o (2.2) 20.3 (12.6\ 8.8 (2.9) 15.s (3. l) 786 (l9l) rs72 (329) 3.7 (2.0) 2.3 (l.l) ^14.o (22.4) s'7.r (28.'t) 34.9 (22.7) 30.9 (13.4) 18.6 (e.6) 3.6 (2.2) 20.0 (11.2) '7.3 (2.6) 13.2 (3.6) 852 (184) l80s (476) 3.0 (2.2) 2.0 (1.2) 6t.3 (21.9) 51.9 (31.5) 32.4 (22.6) 30.3 (1s.5) l7.7 (8.5) 2.7 (2.t) 24.0 (r2.o) "Estimted relibility is computed by boosting the prtil coneltion (controlling for ge) between the scores on the two dministrtions of the test by the Spermn-Brown formul. *p < x -.54* *.21* -.23* _.41* -.25* -.20* -.33*.25* -.23* t)

9 V I S I ON -C O GN ITI O N RELATI ON S enor mesure ws smll (r :.09), nd the persevertive mesures from the ssocitive lerning nd WCST tsks were wekly relted to ech other (r :.16). The low correltion between the two persevertion mesures provides little evidence for common persevertion construct. Speed ndworking Memory Tble 5 contins correltions, prtil coneltions, nd qusi-prtil correltions for the speed nd working memory mesures. In ll cses, the product-moment correltions, representing shred totl vrince, were somewht higher thn the prtil correltions, representing shred igeindependent vrince. The qusi-prtil correltions, repielgnling shred ge-relted vrince, were consistently the highest. This pttern indictes tht the vribles shred lrge proportion of their ge-relted vrince, but much smller proportions of their totl vrince or of their geindependent vrince. Composite speed nd working memory vribles were formed for lter nlyses. The composite speed mesure ws creted by subtrcting the verge of the z-scores for the digirdigit rection time nd digit-symbol rection time mesures from the verge of the z-scores for the letter comprison nd pttern comprison mesures. The composite worklng memory mesure ws formed from the verge of the z-scores for the four working memory mesures. In both cses, higher scores in the composite mesures corre_ sponded to better performnce. Hierrchicl regression nlyses were next conducted with the working memory mesures s the criterion vribles nd ge nd the composite speed mesure s predictors. The ge-relted vrince in the working memory mesures ws significntly greter thn zero for ll mesures when ge ws the only predictor, but it did not differ significntlf from zero when ge ws considered fter control of the composite speed mesure. For exmple, the proportions of ge-relted vrince for the composite working memory mesure were.084 for ge lone, nd.000 for the increment in R2 ssocited with ge fter control of the speed index. These results re very similr to those from severl erlier studies in which processing speed hs been postulted to medite ge-relted influences on untimed mesures of working memory (e.g., Slthouse, 1992; l994d; Slthouse & Bbcock, t99t; Slthouse & Meinz, 1995). Tble 6 contins the results of hierrchicl regression nlyses with cognitive mesures s the criterion vribles nd ge nd the composite speed nd composite working memory mesures s predictor vribles. Notice tht there ws substntil reduction in the ge-relted vrince ofech criterion vrible fter control of the composite working Tble 5. Correltions Between Speed Mesures nd Between Working Memory Mesures, Study 3 Vribles Digit-Digit-DigirSymbol Digit-Digit-l-etter Comprison Digit-Digit-Pttem Comprison Digit-Symbol-L,etter Comprison Digit-Symbol-Pttem Comprison [ftter Comprison-Pttern Comprison Computtion Spn-Reding Spn Computtion Spn-Nbck- l. Computtion Spn-Mck- I Reding Spn-Mck-l Reding Spn-Mck-2 Mck-l-Mck-2 Person Correltion & l,.41, Prtil Correltion.63 _.JU J '76 Qusi-Prtil Correltion t).71.'t Tble 6. Increment in R' Associted with Successive Predictors in Hierrchicl Regression Anlyses, Study 3 Associtive [,emine Eqution I 2 Predictors Working Memory 7o Conecl.108*.279*.033* 7o Persevertion Responses.062*.124*.024 No. of Ctegories Achieved.055*.231x.010 7o Persevertion Responses *.000 *p <.ol. Speed Speed Working Memory.165* *. l3l*.0r9.069* *.062* * *.080*.001

10 P326 SALTHOUS ET AL. memory mesure. However, the reduction of ge-relted vrince ws lso considerble fter control of the composite speed mesure, nd the residul ge-relted vrince ws nerly the sme fter control of only the speed mesure s fter control of both the speed nd working memory mesures. The finding tht lrge proportion of the ge-relted vrince in mesures of working memory nd higher-order cognitive functioning from tsks without time limits is shred with simple mesures of processing efficiency is consistent with the results of numerous recent studies (e.g., Lindenberger et l., 1993; Slthouse, 1992, 1993, 1994, 1994c.1996). - Relqtions The estimted relibility of the composite vision mesure, computed in the sme mnner described in Studies I ndz, ws.80. The reltion between ge nd the composite vision mesure is portryed in Figure 2, where it cn be seen tht the prmeters of the regression eqution were very similr to those in Studies I nd 2. Tests of the qudrtic ge trend, of the gender min effect nd of the x Gender interction indicted tht none were significnt. The influence of helth mesures on the ge-vision reltions ws exmined in the sme mnner s in Studies I nd2. The principl components nlysis on the eight helth mesures yielded three components with eigenvlues greter thn 1.0. The components, defined in terms of the vribles with the highest lodings (nd the correltions of the components with ge), were: self-rtings (.14), crdiovsculr (.41), nd neurologicl (-.14). The ge-relted vrince (i.e., R'ssocited with ge) in the vision mesure ws.405 no.e (d o 6 U) ^ Y=.934_.009,r2= o l O - o }.. - r O - \.... \..\..t.. \.. \ - o \ - o..f o \ o \ - l \ o - \-. o - \ oo- o \ o -Q o o- --o o o Chronologicl Figure 2. Reltion between composite visul score nd ge in Study 3. Ech point represents different individul. - when ge ws the only predictor nd ws.385 fter control of the self-rting component,.327 fter control of the crdiovsculr component, nd.299 fter control of the neurologicl component. There ws some reduction in the reltions between ge nd vision fter control of the helth vribles, prticulrly fter control of the vrince in mesures of reports of hed injury nd tretment of neurologicl disorder. However, this is somewht different pttern thn tht observed in Study I nd my simply reflect smpling vrition. There ws little reduction of the ge-relted vrince in the composite vision mesure fter control of the number of yers of eduction (i.e., from.405 to.401). Influence of on -Speed Reltions Tests were conducted for the interction of x on the speed vribles, but the interction ws not significnt for ny speed mesure. As in Studies I nd 2, therefore, there is little evidence tht the reltion between vision nd speed vries s function of ge. Tble 7 contins the commonlity estimtes for the speed criterion mesures. Note tht there ws reltively little vrince shred between vision nd speed tht ws independent of ge, but tht bout one third of the totl ge-relted vrince in speed ws independent of vision. The estimtes of the common influence in this study were somewht lrger thn those in the erlier studies, but the overll pttern is generlly similr to tht in Studies I nd2. Influence of nd Speed on -Cognition Reltions Interctions of x nd x Speed were exmined in multiple regression equtions with the working memory nd cognitive mesures s the criterion vribles. None of the interctions were significnt for ny of the cognitive criterion vribles, nd thus there is no evidence tht the reltions between vision nd working memory or between vision nd the cognitive mesures vry ccording to ge. Tble 8 contins results of the commonlity estimtes with ge, vision, nd speed s predictors of the cognitive mesures. Notice tht very similr pttern ws evident with ll mesures. The unique contribution of ge ws quite smll, nd most of the ge-relted vrince ws shred with both vision nd speed. These results re consistent with the erlier findings tht lrge percentge of the ge-relted vrince in mesures of working memory nd of higher order cognition is shred with mesure of speed (lso see Tble 6). However, the previous findings re extended by the discovery tht vision is lso component of tht fctor. An verge of lmost 89Vo of the ge-relted vrince in the working memory nd cognitive mesures ws shred with both vision nd speed. Structurl Eqution Model The finl nlysis exmined the fit of structurl eqution model with single common fctor postulted to medite the ge-relted influences on ll speed nd cognitive vribles' Severl of the mesures were trnsformed (i.e., the reciprocls of the digirdigit nd digirsymbol rection time vlues were multiplied by 10,000, nd the nbck nd ssocitive lerning percentge correct vlues were divided by l0) to

11 VI SI ON -C OGN ITI ON RELATI ON S P327 Tble 7. Commonlity Estimte for Speed Mesures, Study 3 (n : 197) Criterion [-etter Comprison Pttern Comprison Digit-Digit Rection Time Digit-Symbol Rection Time Composite Predictor Unique to t Unique to.0r t Common to & t96 t Totl obtin similr vrinces of the mesures for the nlysis. A single common fctor with reltions from ge nd to ll of the vribles ws then specified, nd ech vrible ws exmined to determine if it hd significnt reltion directly from ge. The only vribles with direct reltions from ge were the two vision mesures. Despite little ttempt to model reltions mong vribles, except to llow correlted residuls between mesures derived from the sme methods, the model provided modertely good {it to the dt (1, 1df : 591 : ,Std. RMR :.O7,GFI:.89,AGFI:.83, CFI :.94). The model, with significnt pth coefficients expressed in stndrdized form, is illustrted in Figure 3. Generl Discussion Two sets of results from the present studies were rther surprising. The first unexpected results were the strong negtive reltions between ge nd mesure of corrected visul cuity found in three independent smples (Figures I nd 2). The second surprising set of results ws the high proportion of the ge-relted vrince in mesures of speed, working memory, ssocitive lerning, nd concept identifiction tht ws shred with the mesures of vision (Tbles 2, 7, nd 8). Although similr findings were reported by Lindenberger nd Bltes (1994), their smple ws composed entirely of older dults nd even they suspected tht the reltions ofthe sensory mesures would be much reduced in younger smple. (But note tht these reserchers hve recently extended their reserch to wider ge rnge nd found similr results; cf., Bltes nd Lindenberger, 1995, in press). Furthermore, mny investigtors hve screened reserch prticipnts for vision but hve not reported tht lrge numbers of potentil prticipnts were excluded for this reson, nd they still found significnt ge differences in mny cognitive mesures (e.g., Hhn & Krmer, 1995; Hrtmn, 1995; McClley, Bouwhuis, & Juol, 1995; Pul, 1996). This rises the posiibility tht there is something unusul bout the current vision ssessment, nd it is certinly true tht corrected visul cuity ws not mesured under optimum conditions becuse there ws no control over illumintion nd no restrints were used to ensure tht the viewing distnce ws exctly 30 cm. Nevertheless, the mesures were generlly quite relible s evident in the relibility estimtes nd in the strong reltions with other vribles. Moreover, the ge reltions were lso pprently not ttributble to declining helth becuse there ws reltively little ttenution of the reltions between ge nd vision when mesures of self-reported helth were controlled. Of course, the rnge of helth sttus exmined in these studies ws likely quite limited compred to the generl popultion becuse nerly ll of the prticipnts in the current studies reported themselves to be in good to excellent helth. It is lso importnt to note tht there ws little evidence tht the reltion between vision nd either the speed or the cognitive mesures vried s function of ge. This conclusion is dmittedly bsed on cceptnce of the null hypothesis, but becuse the pttern of nonsignificnt interction between ge nd vision ws replicted cross three or more mesures in ech of three independent studies, it cn probbly be treted with some confidence. The reltions involving vision therefore do not seem to be ttributble to visul pthologies emerging only t middle or lte dulthood. Becuse correltions mong ge, mesures of cognitive functioning, nd mesures of visul functioning hve been reported by Clrk (1960) nd Heron nd Chown (1967), the dt from those studies were renlyzed to estimte the mount of ge-relted vrince in their cognitive mesures tht ws shred with the vision mesures. The ssessment of vision in the Clrk (1960) study ws in terms of "ner ccommodtion distnce" but specific detils of the stimuli or viewing distnce were not provided. Anlyses of the correltions in the Clrk smple of 102 dults between 20 nd 70 yers of ge reveled tht this vision mesure shred 58.l%o of the ge-relted vrince with the PMA Resoning mesure nd 50.77o of the ge-relted vrince with the PMA Spce mesure. Heron nd Chown (1961) ssessed

12 P328 SALTHOUS ET AL, Tble 8. Commonlity Anlyses on Cognitive Mesures, Study 3 Speed Criterion : Computtion Spn Unique to Unique to Unique to Speed Common to & Common to & Speed Common to & Speed Common to,, & Speed Totl M ' o o49.M Criterion = Reding Spn Unique to Unique to Unique to Speed Common to & Common to & Speed Common to & Speed Common to,, & Speed Totl Criterion : Nbck-l Unique to Unique to Unique to Speed Common to & Common to & Speed Common to & Speed Common to,, & Speed Totl Criterion : Mck-2 Unique to Unique to Unique to Speed Common to & Common to & Speed Common to & Speed Common to,, & Speed Totl Criterion = Associtive Leming, Percentge Correct Unique to Unique to Unique to Speed Common to & Common to & Speed Common to & Speed Common to,, & Speed Totl Criterion : WCST, Number of Ctegories Unique to Unique to Unique to Speed Common to & Common to & Speed Common to & Speed Common to,, & Speed Totl.000.o t o (Xl t o l4l.o o l l9.l9l 'to UJ).227.o Figure 3. Structurl model with single common fctor mediting the ge-relted influences on ll observed vribles. Numbers re stndrdized coefficients. The vribles were: WCST-NC = number of ctegories chieved in the WCST; AssocPC : percentge correct in ssocitive lerning; NB-2 : percentge correct in the n bck tsk with n : 2; NB- I : percentge correct in the nbck tsk with n : l; WM-N : working memory with number stimuli (i.e., computtion spn); WM-V : working memory with verbl stimuli (i.e., reding spn); DSRT : digit symbol rection time; DDRT : digit-digit rection time; Ptcom : pttern comprison; lrtcom : letter comprison; -R : visul cuity in right eye; nd -L : visul cuity in left eye. visul cuity with Lndolt C stimuli viewed t distnce of 6 meters with both eyes (uncorrected). Anlyses of the relevnt correltions reveled tht, in their smple of 300 mles, 3l.4%o of the ge-relted vrince in the score on the Rven's Progressive Mtrices ws shred with the vision mesure nd tht 46.OVo ws shred in their smple of 240 femles. Neither of these studies reported estimtes of the relibility of the vision mesures, nd therefore it is possible tht the smller proportions of shred ge-relted vrince thn in the current studies re ttributble to less relible ssessment of vision. It is nevertheless importnt to note tht similr results indicting tht moderte to lrge proportions of the ge-relted vrince in mesures of cognitive functioning re shred with mesures of visul functioning re pprent in other dt sets with different mesures of vision nd cognition. Following Lindenberger nd Bltes (1994), there seem to be three possible interprettions of the reltion between the vision nd cognitive mesures. One possibility is tht visul deficits re responsible for the cognitive deficits becuse individuls with low vision my not be ble to dequtely register the stimuli. Although intuitively resonble, this interprettion does not seem plusible in the current sitution becuse ll stimuli were of high contrst nd reltively lrge in terms of visul ngle. Tht is, the smllest stimuli subtended visul ngles of bout two degrees t typicl viewing distnce nd should hve been esily visible by everyone becuse ll prticipnts hd composite vision scores bove zero. It is lso importnt to note tht there ws little or no reltion between the vision mesures nd either the speed or the cognitive mesures tht ws independent of ge (cf., Tbles 2,'1, nd 8). The influence of vision ws

13 VI S I ON -C OGN ITI ON RELATION S P329 therefore limited to the spects of the speed, working memory, nd cognitive tsks tht were ffected by incresed ge. A second possible interprettion ofthe influence ofvision in these studies is tht the visul ssessment involves cognitive processes. Tht is, reserch prticipnts need to comprehend instructions, to mintin concentrtion, nd to hve t lest minimum level of motivtion to perform well in the visul cuity tsk. Although it is true tht ll these spects re required in the vision test, the cognitive demnds re lmost certinly substntilly less thn those in tsks explicitly designed to ssess cognitive functioning. Ifthe cognitive requirements in the vision test re responsible for the reltions with the other vribles, therefore, very primitive form of cognition must be involved. An interesting, nd testble, impliction of this interprettion is tht the reltions to the cognitive mesures should be gretly reduced or eliminted if the visul ssessments could be obtined with little or no cognitive involvement. A third interprettion of the vision-cognition reltions is tht the visul cuity mesures re nother mnifesttion of common fctor contributing to the ge differences in mny behviorl vribles. This interprettion differs from the first becuse insted of ttempting to ttribute cusl priority to certin vribles, ll of the vribles re considered to be reflections of common fctor tht is relted to both ge nd to the vribles. To illustrte, lthough pth model with vision postulted to medite mny of the ge-relted influences on the other vribles would likely provide good fit to the dt, similr good fits would probbly lso occur for models bsed on ny vribles hving moderte to high lodings on the common fctor. From this perspective, therefore, it my not be prticulrly productive to ttempt to specify the cusl priority mong the vribles with the currently vilble informtion. The key feture of this lst interprettion is tht the common fctor is postulted to contribute to much of the ge-relted influences on wide rnge of cognitive mesures (e.g., Slthouse, 1994b; Slthouse, Fristoe, & Rhee, 1996). The novel contribution of the current studies nd of the studies by Lindenberger nd Bltes (1994) nd Bltes nd Lindenberger (1995, in press) is to suggestht firly bsic sensory functions re lso included within the common fctor. Tht is, the common fctor ppe$ to reflect primitive centrl nervous system functions represented not only by mesures of processing efficiency, but lso by mesures of corrected visul cuity. However, it should be emphsized tht the common fctor is not responsible for ll observed ge-relted effects becuse unique or independent ge-relted influences were evident on the vision mesures in Study 3 (cf., Figure 3), nd independent ge-relted influences hve been found on mesures of memory in other studies (e.g., Slthouset l., 1996). It is interesting to consider the implictions of the hypothesized common fctor for theorist ttempting to ccount for the ge differences observed in mesures of working memory or in cognitive tsk like ssocitive lerning or concept identifiction. The theorist could ttempt to ccount for the observed ge differences in these tsks by focusing on firly specific processes, such s the bility to inhibit irrelevnt informtion, or to shift set when receiving chnging feed- bck. However, the results ofthese nd other recent studies indicte tht there my be no significnt ge differences in the to-be-explined mesures fter the reserch prticipnts re sttisticlly equted on mesures of speed or mesures of ner-visul cuity. These findings imply tht the ge-relted influences on mny cognitive mesures re not independent of the ge-relted influences on mesures of simple processing efficiency nd of corrected visul cuity. This in turn indictes tht the ge-relted effects on the cognitive tsks re not restricted to processes specific to those trget tsks. Limiting the explntory focus to single tsk my therefore result in misleding conclusions bout the fctors responsible for the ge-relted differences in tht tsk. If, s the results of these nd other studies seem to indicte, those differences re not independent of the differences in other tsks, then the theorist my simply be describing one symptom or mnifesttion of much broder phenomenon by concentrting exclusively on the results of single tsk. Although the reserch described bove rises t lest s mny questions s it nswers, it does suggest n importnt priority for future reserch. Tht is, mjor gol should be to explore the nture of the hypothesized common fctor by determining wht other combintions of vribles shre gerelted vrince nd by determining wht vribles hve independent ge-relted influences. The discovery tht mesures of sensory bility pper to be involved in the common fctor lso suggests tht the rnge of vribles to be exmined should be expnded to include noncognitive vribles. ACKNowLETTMENTs This reserch ws supported by NIA Grnt AGR to Timothy A. Slthouse. We would like to cknowledge the vluble contributions of Pul Bltes nd Ulmn Lindenberger in mny phses of this project nd for supplying copies of the visul cuity tests. Address correspondence to Dr. Timothy A. Slthouse, School of Psychology, Georgi Institute oftechnology, Atlnt, GA REFERENCES Bltes, P. B., & Lindenberger, U. (1995). Sensorik und Intelligenz: lntersystemische Wechselwirkungen und Verenderungen im hohen Alter. Akde mi e - J ournl, Bltes, P. B., & Lindenberger, U. (in press). Emergence of powerful connection between sensory nd cognitive functions cross the dult life spn: A new window on the study of cognitive ging? Psychology nd Aging. Bors, D. A., & Forrin, B. (1995)., speed of informtion processing. recll, nd fl uid intelligence. Intelligence, 20, Bryn, J., & Luszcz, M. A. ( I 996). Speed of informtion processing s meditor between ge nd free recll performnce. Psychology nd Aging,6,3-9. Burg, A. (1966). Visul cuity s mesured by dynmic nd sttic tests. 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