A cornparison of serial position effects in implicit and explicit word-stern cornpletion

Transcription

1 Psychnmic Bulletin & Review (2), A crnparisn f serial psitin effects in implicit and explicit wrd-stern crnpletin BARBARA M. BROOKS City University and Gldsmiths Cllege, Lndn, England In this study I examined a further pssible dissciatin between implicit and explicit memrywhether implicit memry prduces serial psitin effects that are similar t thse fund in explicit memry. When implicit wrd-stem cmpletin and explicit wrd-stem cued recall were cmpared, nly the explicit test shwed significant primacy and recency effects. The explicit test was sensitive t the rder in which stimuli wrds were encded, but the implicit test was nt. This dissciatin between implicit and explicit memry prvides further evidence that cnscius retrieval prcesses were nt invlved in the implicit test. In their review f implicit memry, Rediger and McDermtt (1993) stated that "Althughexaminatin f serial psitin effects has guided research abut ther issues in the study f memry, wrk n implicit memry is a clear exceptin at this pint in time" (Rediger & McDermtt, 1993, p. 115). Referring specifical1y t primacy effects, they nted that "the v1uminus implicit memry literature is almst mute n the issue as t whether a primacy effect exists n any imp1icit memry test" (Rediger & McDermtt, 1993, p. 115). The general cnsensus f pinin is that primacy effects arise frm either mre rehearsal (e1abrative r rte) r greater attentin devted t the first few items in a tbe-rernembered list than t the remaining items (Atkinsn & Shiffrin, 1968; Craik & Lckhart, 1972; Glenberg et al., 1980; Rundus, 1971). There is 1ess cnsensus abut the explanatin fr recency effects. The standard thery is that recency effeets in free reeall ccur beeause subjects ff-lad the cntents f their shrt-term memry prir t retrieving items frm lng-term memry (Craik, 1970; Glanzer & Cunitz, 1966). Indeed, the recency effect disappears when a subject is asked t cunt backward fr 30 sec befre recalling a list f wrds (Glanzer & Cunitz, 1966). Dubts abut this explanatin arse when Bjrk and Whitten (1974) reprted a lng-term recency effect, which ccurred when 12 sec f distractr task preceded the presentatin f each study item. This lng-term recency effeet survived a 20-sec retentin interval in which the same distractr task was perfrmed. Presumably, any items in shrt-term memry wuld have been displaced during this perid. A number f explanatins fr the lng-term reeency effeet have been prpsed. They include the stra- I am grateful t Jhn Gardiner fr bis valuable advice befre I started this study and in the preparatin f this rnanuscript. I als thank Ruth Campbell, Felicia Gershberg, Rs Java, Henry Rediger, Dan Schacter, Rss Tasker, and an annymus reviewer fr helpful cmments. Address crrespndence t B. Brks, Psychlgy Department, Gldsmiths Cllege, University f Lndn, New Crss, Lndn SE14 6NW, England. tegic use f shrt-term memry (Pltrck & MacLed, 1977), the distinctiveness f the mst recent items in a well-rdered series (Bjrk & Whitten, 1974; Glenberg et al., 1980), and retrieval using rdinal infrmatin (Baddeley & Hitch, 1977; fr a brief review see Greene, 1986). Althugh they differ in their explanatins, ne assumptin that all these theries make is that serial psitin effects reflect cnscius retrieval f studied items. If this assumptin is crrect, serial psitin effects shuld nt ccur in implicit memry tests that assess indirect memry fr a study episde. Implicit memry tests d nt require subjects t cnsciusly refer back t that episde and shuld nt reflect any evidence f effrtful retrieval. Fr example, a variable such as levels f prcessing, which manipulates the extent f cnscius recllectin in nrmal subjects, prduces a significant effect in explicit but nt in implicit memry tests (see Rediger & McDermtt, 1993, fr a review). There have been nly fur studies investigating whether primacy r recency effects ccur in implicit memry tasks. The first, by Slman, Hayman, Ohta, Law, and Tulving (1988, Experiment 1), indicated the existence f a recency effect and a single-item primacy effect in primed wrd-fragment cmpletin. Hwever, a clser examinatin fthe experimental prcedure in that study reveals that wrd-fragment cmpletin invlved bth effrtful and autmatic memry prcesses. The instructins t the subjects stated that they were t "try t cmplete each fragment with a study-list wrd" (Slman et al., 1988, p. 227). It is pssible that the effrtful cmpnent f the task was respnsible fr the serial psitin effects btained. In the secnd study, McKenzie and Humphreys (1991) fund a significant recency effect in implicit wrd-stem cmpletin. Their subjects cmpleted significantly mre wrd sterns in an immediate test than they did in a delayed test. Hwever, this recency effect is different frm the shrt-lived recency cmpnent fthe serial psitin curve, which disappears if a subject is asked t cunt backward Cnvrizht 1994 Psvchnmic Sciety, Inc. 264

2 SERIAL POSITION EFFECTS AND IMPLICIT MEMORY 265 fr 30 sec befre recalling a list f wrds (Glanzer & Cunitz, 1966). In a mre relevant previus study, Rybash and Osbme (1991) investigated serial psitin effects in free recall, implicit wrd-stem cmpletin, and explicit wrd-stem cued recall. Their results indicated that all three tests prduced a significantrecency effect, but nly free recall prduced a significant primacy effect. Since n details abut presentatin rders were included in the methdlgy, it may be inferred that all f their subjects were presented with the study wrds in the same rder. The first few wrds may have been less memrable r less easily cmpleted than the remaining wrds, negating any pssible primacy effects in all but the free-recall test. Sirnilarly, the last few wrds may have been mre memrable r mre easily cmpleted, prducing a spurius recency effect in the cued-recall and wrd-stem cmpletin tests. The significant recency effect in the wrd-stem cmpletin and cued-recall tests was surprising because the test sheet cntained 48 wrd sterns, and any recency effects wuld presumably have disappeared befre the relevant wrd sterns were cmpleted. The latest study t investigate serial psitin effects in implicit wrd-stem cmpletin was perfrmed by Gershberg and Shimamura (in press). In tw f three experiments they fund transient primacy effects in implicit wrd-stem cmpletin, which nly ccurred when the first half f the wrd sterns tested were analyzed separately. They als fund transient recency effects in ne f three experiments. It shuld be nted, hwever, that they did nt find cnsistent primacy effects in an explicit test f wrd-stem cued recall, nr did they find cnsistent recency effects in an immediate wrd-stem cued-recall test r even in an immediate free-recall test. There is therefre clearly a need fr evidence f serial psitin effects in explicit tasks in cnjunctin with effects-r a lack f them-in implicit tasks. The purpse f the present study was t prvide reliable evidence as t whether serial psitin effects exist in implicit wrd-stem cmpletin. An explicit test f wrd-stem cued recall was included, in which the test stimuli and study instructins were identical t the implicit test and nly the test instructins differed. The results f these tw tests therefre fulfilled the retrieval intentinality criterin f Schacter, Bwers, and Bker (1989) and culd be directly cmpared. Any differences in the results wuld be attributable t the different test instructins. EXPERIMENT 1 Experiment 1 was devised t investigate whether a primacy effect exists in an implicit wrd-stem cmpletin test. Wrd sterns were cmpleted under explicit r implicit test instructins, but allther aspects fthe study were the same. The rder f presentatin f wrds was rtated s that any significant results wuld be reliable and nt cntaminated by differences in wrd memrability r ease f cmpletin. The serial psitins f target wrd sterns cmpleted in the tw tests were cmpared t see whether there were any differences in the effects btained. Methd Subjects. Thirty-six students frm City University, Lndn, and Gldsmiths Cllege, University f Lndn, age range years, participated in the experiment. They were randmly allcated t tw grups f 18 subjects each, and were tested either individually r in pairs. Design and Materials. The design factrs were test (implicit vs. explicit) and serial psitin; test was cnducted between subjects, and serial psitin was cnducted within subjects. The stimulus material cmprised 36 cards. Printed n each card in capitalletters was a six-ietter nun; these wrds were selected frm materials prepared by Java (1991; Java & Gardiner, 1991). The first three letters f each wrd frmed the initial wrd stern f at least six wrds fund in the Cncise Oxfrd Dictinary. The 36 cards were randmly allcated t tw sets f 18 wrds. During the curse f the experiment, the tw card sets were cunterbalanced s that when ne set was presented as target wrds, the ther set frmed the lure wrds. The cards within each set were sequentially numbered frm The sequential rder f each set fcards was kept cnstant during the curse f the experiment, but the psitinal rder varied. Each set f cards was advanced by tw numbers after it had been presented nce in the implicit and nce in the explicit memry task. This prcedure resulted in each wrd's appearing nce in every ther serial psitin. The test rder was held cnstant in the frm f ne test sheet f 40 three-ietter wrd sterns, printed in capitalletters in tw clumns. The first 4 wrd sterns were filler items, fllwed by wrd sterns frm bth sets f wrds, listed in a pseudrandm rder with n mre than 3 cnsecutive wrd sterns frm ne set. Prcedure. The subjects were randmly assigned t either the implicit r explicit test grup and were tested either individually r in pairs. Bth grups received the same preliminary instructins-t try t mernrize the wrds they were abut t see. One set f 18 wrds was then shwn t them n cards, ne card at a time fr 2 sec. After 1 subject frm each grup had been presented with the cards in an identical rder, the psitinal rder fthe cards was advanced by 2 wrds (while keeping the sequential rderthe same) befre the cards were presented again. In additin, alternate subjects in each grup received a different set f cards. The subjects were tested irnmediately. In the explicit test, they were instructed t write cmpletins t the wrd sterns f any wrds they culd remember frm the study cards. They were infrmed f the presence f sme lure wrd sterns and were instructed t leave these blank. They were als asked nt t guess cmpletins. In the implicit test, the subjects were asked t cmplete every wrd stern with the first wrd that came t mind. lf a wrd did nt irnmediately cme t mind, they were t leave it blank. They were advised that wrd sterns frm sme study wrds wuld be included in the list, but that they shuld nly cmplete wrd sterns with these wrds if they were the first wrds that came t mind. Three minutes were allwed fr this task. On cmpletin, the subjects in the implicit test were asked whether they had actually cmpleted wrd sterns with the first wrd that came t mind, r whether they had deliberately tried t remember wrds frm the study episde. All the subjects reprted that they had cmpleted the wrd sterns with the first wrd that had cme t mind. Results and Discussin There was a significant priming effect in the implicit memry test (target wrd-stem cmpletin, p =.552; lure wrd-stem cmpletin, p =.197) [t(17) = 9.94]. Since

3 266 BROOKS the level f cmpletin f lure wrd sterns was relatively lw, baseline cmpletin shuld nt have affected any pssible serial psitin effects. Similarly, incrrect cmpletins in the explicit test were very lw (target wrd-stem cmpletin, p =.586; wrng cmpletin, p =.03) [t(l7) = 13.42], indicating that guessing shuld nt have affected serial psitin effects in the explicit test. The results f Experiment 1 are shwn in Table I. A graph f these results, cllapsed acrss three cnsecutive serial psitins t reduce nise and with baseline cmpietin subtracted in the implicit test, is shwn in Figure 1. It appears frm the graph that explicit wrd-stem cued recall prduced a primacy effect, but implicit wrdstern cmpletin did nt. T investigate this interpretatin f the data, a 2 X 2 analysis f variance (ANOVA) was perfrmed with ne between-subjects factr (test; implicit vs. explicit) and ne within-subjects factr (serial psitin; prb ability f recall frm primacy Serial Psitins 1-3 vs. prbability f recall frm asymptte Serial Psitins 7-12). (The chice f these serial psitins as indicatrs f primacy effects and asymptte levels was arbitrary and did nt influence the results.) The ANOVA was perfrmed n the data fr studied items, withut subtracting baselines (i.e., nt the data shwn in Figure 1). The alpha level was set at.05 in all the statistical analyses. The main effect ftest was nt significant [F(1,34) = 1.78, MS e = 0.86], but that f serial psitin was [F(I,34) = 8.59, MS e = 0.39], and there was a significant interactin between test and serial psitin [F(1,34) = 4.73, MS e = 0.39]. Separate ANOVAs were perfrmed between the primacy and asymptte serial psitins frm each test t find the reasn fr this interactin. In the implicit test, the difference between these serial psitins was nt significant [F(l7) = 0.29, MS e = 0.39], but it was significant in the explicit test [F(l7) = 13.11, MSe = 0.39]. Table 1 Percentage f Target Wrds Cmpleted as a Functin f Serial Psitin and Test in Experiments 1 and 2 Serial Experiment I Experiment 2 Psitin Implicit Explicit Implicit Explicit c: ".j:i ~ a. E >.~.s.c ọ.. a.. CO L J Serial psitins -0- Explicit Test --*- Implicit Test Figure 1. Experiment 1: Prbability f cmpletin f target wrds as a functin f serial psitin and test. These results shw a primacy effect in explicit cued recall, but nt in implicit wrd-stem cmpletin. This difference culd nt be attributed t greater variability in the implicit test, since bth tests had identical mean square errr terms. The design f the test sheet in Experiment 1 made it unlikely that a recency effect wuld ccur in either testany pssible recency effects wuld have disappeared during the time it tk the subjects t wrk thrugh the fur filler wrd sterns and intervening wrd sterns. It was therefre necessary t alter the test sheet s that the mst recently seen wrds were presented first in rder t capture any pssible recency effects. EXPERIMENT 2 Because serial psitin recency effects are shrt lived when wrds are encded withut an interplating task (Craik, 1970; Glanzer & Cunitz, 1966), it was necessary t design a new test sheet that wuld prvide an ptimal test fr recency. On this new test sheet, wrd sterns f the wrds n the study cards appeared in the reverse rder, beginning with the wrd stern f the last wrd presented at study.

4 SERIAL POSITION EFFECTS AND IMPLICIT MEMORY 267 Methd Subjects. Seventy-tw students and staff members frm City University, Lndn, and Gldsmiths Cllege, University f Lndn, age range years, participated in the experiment. They were randmly allcated t tw grups f 36 subjects each, and were tested individually. Design and Materials. The experimental design was similar t that f Experiment I, except the cards were nly advanced by ne wrd after they had been presented t 1 subject frm each experimental grup. This prcedure allwed full cunterbalancing f serial psitins, since every wrd appeared nce in every serial psitin fr each test. The stimuli were als identical t thse f Experiment 1, but the test sheet was designed t capture any pssible recency effects. It cntained 36 three-ietter wrd sterns, printed in capitalletters and equally spaced arund the circumference f a circle; wrd sterns frm each set appeared alternately. The test sheet was cvered by a cardbard circular mask, fixed at the center, with a three-sided cutut n the circumference that allwed ne wrd stern t be viewed at a time. When the mask was rtated in a clckwise directin, the subjects saw wrd sterns frm the study cards, in reverse rder, interspersed by lure wrd sterns. Prcedure. The prcedure was als similar t that fexperiment 1, with the fllwing differences. In Experiment 2, the subjects were all tested individually. The psitinal rder f the cards was advanced by ne wrd instead f tw after presentatin in the implicit and explicit tests. This resulted in each wrd 's appearing nce in every serial psitin. Irnmediately after seeing the study wrds, the subjects were given a test sheet with the mask pen at the lure wrd preceding the last study wrd they had seen. Additinal instructins t mve the mask clckwise fr each wrd stern were given. The subjects were nly allwed t view each wrd stern nce. Results and Discussin In the implicit test, baseline wrd-stem cmpletin was again relatively lw (p =.205) cmpared with target wrd-stem cmpletin (p =.654) [t(35) = 14.16]. Similarly, wrng cmpletins in the explicit test were lw (p =.073) cmpared with target cmpletins (p =.645) [t(35) = 18.44]. The results f Experiment 2 are shwn in Table 1. A graph fthese results, cllapsed acrss three cnsecutive serial psitins t reduce nise and with baseline cmpletin subtracted in the implicit test, is shwn in Figure 2. It appears frm the graph that explicit wrd-stem cued recall prduced a primacy and recency effect, but implicit wrd-stem cmpletin did nt. A 2 x 3 ANOVA was perfrmed n studied items with ne between-subjectsfactr (test; implicit vs. explicit) and ne within-subjects factr (serial psitin; prbability f recall frm primacy Serial Psitins 1-3 vs. asymptte Serial Psitins 7-12 vs. recency Serial Psitins 16-18) t calculate whether there were significant serial psitin effects in the explicit test cmpared with the implicit test. (The chice f these serial psitins as indicatrs f primacy, asymptte, and recency was arbitrary and did nt influence the results.) Neither the main effect f test [F(1,70) = 0.63, MS e = 0.97] nr the main effect f serial psitin [F(2, 140) = 1.44, MS e = 0.51] was significant, but there was a significant interactin between test and serial psitin [F(2,140) = 3.81, MS e = 0.51]. One-way ANOVAs were perfrmed n each test t investigate the reasn fr this interactin. In the implicit test, the main effect f serial psitin was nt significant [F(2,70) = 0.97, MS e = 0.45], but it was significant in the explicit test [F(2,70) = 3.95, MS e = 0.57]. In the 0.8 c '.j:i Q) 0- E 0.6 CJ-,~.0 CO 0.4.0ọ... a.. 0.2' J Serial psitins --0- Explicit Test -*-Implicit Test Figure 2. Experiment2: Prbability f cmpletinf target wrds as a functin f serial psitin and test. explicit test, a paired t test between the primacy and asymptte prbabilities was significant [t(35) = 2.51], as was a paired t test between the asymptte and recency prbabilities [t(17) = 2.60]. These results shw that primacy and recency effects were fund in explicit wrd-stem cued recall but nt in implicit wrd-stem cmpletin. This difference culd nt be attributed t greater variability in the implicit test, since this test had a lwer mean square errr term than the explicit test. When the results f the tw experiments are cmpared, it is apparent that target wrd-stem cmpletin rates in the implicit tests differed (Experiment 1, P =.552; Experiment 2, p =.654). Since the stimuli and study cnditins were identical, it is prbable that this difference was due t the different test sheets. The absence f fur filler wrd sterns in Experiment 2 may be ne cntributry factr, but a further factr rnight be that in Experiment 2 wrd sterns were presented ne at a time, which was mre sirnilar t the manner in which they were encded. The increased similarity between encding and test cnditins may have prvided mre ptimal cnditins fr retrieval frm implicit memry. A cmparisn f the graphs f the tw explicit tests shws that the primacy effect was higher in Experiment 1

5 268 BROOKS than in Experiment 2. This difference may be because wrd sterns f studied wrds appeared in the reverse rder n the test sheet in Experiment 2. The first wrds encded (frm which the primacy effect is measured) were therefre the last wrd sterns cmpleted, resulting in a lwer primacy effect. GENERAL DISCUSSION There was little indicatin f serial psitin effects in the irnplicit test in either experiment, whereas the explicit test, which was identical t the implicit test in all but the test instructins, shwed a primacy effect in Experiments 1 and 2 and a recency effect in Experiment 2. The lack f serial psitin effects in the implicit tests differed frm the findings f Siman et al. (1988, Experiment 1), discussed in the intrductin. The mst prbable reasn fr this difference was the intentinal use f cnscius retrieval in Siman et al.'s study. The results f the present study als differed frm thse f Rybash and Osbme (1991) and Gershberg and Shimamura (in press), als discussed previusly. The main difference between the three studies was the different methdlgical prcedures used. Fr example, the rder in which the target wrds were presented t the subjects differed between the studies. In Rybash and Osbme's study, all the subjects studied the same list f target wrds in the same rder. In Gershberg and Shimamura's study, each subject studied ne f tw target-wrd lists in ne f tw different rders. In this study, the subjects als studied ne f tw target-wrd lists, but each list was presented in 9 different rders in Experiment 1 and in 18 different rders in Experiment 2. Only by such an extensive rtatin f wrds at encding can differences in wrd frequency and ease f cmpletin f wrd sterns be adequately cntrlled. As weil as prviding evidence fr the lack f serial psitin effects in implicit memry, these results prvide tangible evidence that the testaware subjects perfrmed accrding t instructins in the impl!cit tes!. Ifthey had been using explicit strategies, it is pr?a~le that senal. POSItin effects in the implicit test wuld have been similar t thse In the explicittest... In cnclusin, the finding that implicit wrd-stem cmpletin des nt shw serial psitin effects but that explicit wrd-stem cued recall des, reveals anther dissciatin between tests f implicit and explicit memry and prvides further evidence that cnscius retrieval prcesses are nt invlved in this implicit memry test. REFERENCES ATKINSON, R. C., & SHIFFRIN, R. M. (1968). Human memry: A prpsed system and its cntrl prcesses. In K. W. Spence & J. T. Spence (Eds.), The psychlgy f learning and mtivatin (Vl. 2, pp ). Lndn: Academic Press. BADDELEY, A. D., & HITCH, G. J. (1977). Recency re-examined. In S. Dmic (Ed.), Attentin and perfrmance VI (pp ). Hillsdale, NJ: Erlbaum. BJORK, R. A., & WHITTEN, W. 8. (1974). Recency-sensitive retrieval prcesses in lng-term free recall. Cgnitive Psychlgy, 6, CRAIK, F. I. M. (1970). The fate fprimary items in free recall. Jurnal 0/ Verbal Learning & Verbal Behavir, 9, CRAIK, F. 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