Implicit and Explicit Memory for Novel Visual Objects in Older and \Bunger Adults

$Implicit and Explicit Memory for Novel Visual Objects in Older and \Bunger Adults$

Implicit and Explicit Memory for Novel Visual Objects in Older and \bunger Adults

Daniel L. Schacter Lynn A. Cooper Harvard University Columbia University Michael Valdiserri University of Arizona

Two experiments examined effects of aging on implicit and explicit memory for novel visual objects. Implicit memory was assessed with an object decision task in which subjects indicated whether briefly exposed drawings represented structurally possible or impossible objects. Explicit memory was assessed with a yes-no recognition task. On the object decision task, old and young subjects both showed priming for previously studied possible objects and no priming for impossible objects; the magnitude of the priming effect did not differ as a function of age. By contrast, the elderly were impaired on the recognition task. Results suggest that the ability to form and retain structural descriptions of novel objects may be spared in older adults.

Explicit memory refers to conscious recollection of previous 1988; Davis et al, 1990; Hultsch, Masson, & Small, 1991). These experiences, as expressed on recall and recognition tests, latter findings are difficult to interpret, however, because they whereas implicit memory refers to facilitations of performance, may well reflect "contamination" of implicit task performance often referred to as priming effects, on tests that do not require by explicit retrieval strategies, strategies that are more benefi- any conscious or intentional retrieval of previous experiences cial to young than to old subjects (cf. Graf, 1990; Howard, 1991; (Graf & Schacter, 1985; Schacter, 1987). An already large and Light, 1991; Schacter, Bowers, & Booker, 1989; Schacter, Kihl- ever-growing body of research has demonstrated that explicit strom, Kaszniak, & Valdiserri, in press). and implicit memory can be dissociated by numerous experi- Whatever the reasons for discrepancies among existing stud- mental manipulations and that implicit memory is often ies, it seems clear that a great deal remains to be learned about spared in brain-damaged amnesic patients with severe impair- the nature and extent of implicit memory abilities in the elderly. ments in explicit remembering (for reviews, see Richardson- In the present article, we extend research on implicit memory Klavehn & Bjork, 1988; Roediger, 1990; Schacter, 1987; Shima- and aging into a previously unexplored domain: priming of mura, 1986). novel, three-dimensional visual objects. We have developed an The explicit-implicit distinction is of considerable interest experimental paradigm for examining this issue in a series of from the perspective of cognitive aging. Although it is well- recent studies (Cooper, Schacter, Ballesteros, & Moore, 1992; known that age-related memory deficits can be observed on Schacter, Cooper, & Delaney, 1990; Schacter, Cooper, Delaney, numerous explicit memory tests, a number of recent studies Peterson, & Tharan, 1991). The paradigm makes use of draw- have indicated that age effects can be attenuated or even elimi- ings that depict unfamiliar structures such as those displayed in nated on various implicit memory tests (for review, see Graf, Figure 1. Half of the drawings represent structurally possible 1990; Howard, 1991; Light, 1991). Thus, for example, old and objects that could exist in the three-dimensional world. The young subjects have shown comparable priming effects on tests other half represent structurally impossible objects whose sur- of word completion (Light, Singh, & Capps, 1986; Howard, Fry, faces and edges contain ambiguities and inconsistencies that & Brune, 1991), word identification (Light & Singh, 1987), would prohibit them from existing as actual three-dimensional reading (Moscovitch, Winocur, & McLachlan, 1986), and pic- objects. Subjects initially study drawings of both types of ob- ture naming (Mitchell, Brown, & Murphy, 1990). By contrast, jects for several seconds and are then given explicit, implicit, or age-related priming deficits have been documented in other both memory tests. Explicit memory is assessed with a stan- experiments on some of the same tasks (cf. Chiarello & Hoyer, dard yes-no recognition memory task in which studied and nonstudied objects are presented, and subjects indicate whether they remember studying an object previously. Implicit This research was supported by National Institute on Aging Grant 1 memory is assessed with an object decision task in which stud- RO1 AGO8441-01 and by Air Force Office of Scientific Research ied and nonstudied objects are flashed briefly (typically for 100 Grant 90-0187. We thank Darlene Howard and two anonymous re- viewers for comments concerning an earlier version of the article and ms or less), and subjects decide whether each object is possible Dana Osowiecki for help with preparation of the manuscript. or impossible. Priming on this task is indicated by more accu- Correspondence concerning this article should be addressed to rate object decisions about studied than nonstudied drawings. Daniel L. Schacter, Department of Psychology, Harvard University, 33 A number of experiments have shown that significant prim- Kirkland Street, Cambridge, Massachusetts 02138. ing is observed on the object decision task and have delineated 299 300 D. SCHACTER, L. COOPER, AND M. VALDISERRI

mation in the elderly is clearly needed (cf. Schacter, Delaney, & Merikle, 1990). Note also that Howard and Howard (1992) have reported evidence of intact implicit learning of nonverbal information in elderly adults using a different type of task that involves learning to respond to a repeated spatiotemporal sequence of lights (e.g., Nissen & Bullemer, 1987). A second advantage of the object decision paradigm is that it allows us to address the important question of whether priming effects in the elderly depend on, or reflect the activation of, preexisting memory representations of target items. Because familiar words and objects are represented in memory before the experiment, it can be argued that priming in experiments using such materials reflects the temporary activation of old, preexisting knowledge. Our possible and impossible objects, however, do not exist in memory before the experiment, so priming is necessarily based on newly formed representations. As noted earlier, Howard and Howard (1992) have shown that elderly subjects can learn a novel spatiotemporal sequence. Evi- dence bearing on priming of new versus old information in the elderly has been reported in experiments by Howard et al. (1991) that examine implicit memory for newly acquired associations between unrelated words. Using a paradigm developed by Graf and Schacter (1985; Schacter & Graf, 1986), they found Figure 1. Sample of objects used in our experiments. (The drawings that elderly subjects showed normal priming of new associa- in the upper row depict possible objects that could exist in three-di- tions under some experimental conditions and impaired prim- mensional form. The drawings in the lower row depict impossible ing of new associations under other conditions. Thus, the status objects that contain structural violations that would prohibit them of priming of novel information in the elderly requires further from actually existing in three-dimensional form. See text for further investigation and clarification. explanation.) A third reason for using the object decision paradigm with elderly adults is that we have developed some relatively well- specified ideas about the locus of the observed priming effects. several of its properties. Specifically, our studies indicate that On the basis of the findings that object decision priming re- object decision priming (a) is observed for possible but not for quires encoding of global object structure, does not benefit impossible objects, (b) depends on encoding information about from semantic encoding, and transfers across study-test the global structure of the object at the time of initial study, (c) is changes in object size and reflection, we have argued that such not increased—and may even be reduced—by elaborative study priming is mediated by a structural description system (cf. Rid- tasks that greatly enhance explicit memory, and (d) is relatively doch & Humphreys, 1987). The structural description system is unaffected by study-to-test changes in the size and left-right a subsystem of a more general perceptual representation sys- reflection of target objects, even though such changes impair tem (Schacter, 1990, 1992; Tulving & Schacter, 1990) that is recognition memory significantly (Cooper et al, 1992; Schacter, specialized for representing and retrieving information about Cooper, & Delaney, 1990; Schacter, Cooper, Delaney, et al., the global form and structure of objects. By hypothesis, the 1991), but is eliminated by study-to-test changes in picture structural description system does not represent information plane orientation of objects (Cooper, Schacter, & Moore, 1991). about an object's associative and functional properties and is In addition, brain-damaged patients with explicit memory dis- distinct from the episodic memory system that underlies ex- orders have shown normal priming on the object decision task plicit recollection of a specific encounter with an object. Ac- (Schacter, Cooper, Tharan, & Rubens, 1991). cording to this view, priming of possible objects on the object There are several reasons why the object decision paradigm is decision task reflects the establishment, at the time of study, of appropriate for studying cognitive aging. First, most previous novel structural descriptions that preserve information about research on priming and aging has used verbal materials, such global relations among object parts. As noted earlier, our exper- as words or paired associates; there have been few studies that iments have consistently failed to produce significant priming used nonverbal materials. In one such study, Mitchell et al. of impossible objects (e.g., Schacter, Cooper, Delaney, et al, (1990) found that elderly subjects show intact priming of latency 1991). This finding may indicate that it is difficult to form a to name familiar objects despite impaired recognition memory. representation of the global structure of an impossible object However, this task involves a large verbal component. Russo (cf. Hochberg,1968). and Parkin (1991) have reported impaired priming in the el- Independent evidence for the existence of a structural de- derly on a picture fragment completion task, although the au- scription system has been provided by studies showing that thors acknowledged that the impairment may be attributable to brain-damaged patients with object-processing deficits have rel- explicit rather than implicit memory deficits. Given these con- atively intact access to structural knowledge about objects, de- trasting results, further research on priming of nonverbal infor- spite severely impaired access to knowledge of their fvmctiona\ IMPLICIT AND EXPLICIT MEMORY 301 and associative properties (cf. Riddoch & Humphreys, 1987; range = 17-19). Elderly subjects had on average 15.3 years of education Warrington, 1975,1982; Warrington& Taylor, 1978). Moreover, (SD = 2.4), whereas young subjects had on average 12.3 years of educa- evidence from patient studies, as well as from single-cell record- tion (SD = 0.58). On the Wechsler Adult Intelligence Scale—Revised ings and lesion experiments in nonhuman primates, suggests (WAIS-R), old subjects scored higher than did young on the two sub- thatregions of inferior temporal cortex constitute an important scales that were administered: Information (old = 24.6, SD = 2.8; young = 19.2, SD = 5.0) and Vocabulary (old = 62.5, SD = 6.2; young = neuroanatomical basis of the structural description system (for 49.9, SD =7.8). By contrast, on the Wechsler Memory Scale—Revised review, see Plaut & Farah, 1990). We have thus suggested that (WMS-R), old subjects scored more poorly than young on the two this brain region plays a key role in object decision priming subtests that were administered: Logical Memory (old = 36.9, SD - (Cooper et al., 1992; Schacter, Cooper, Tharan, & Rubens, 6.8; young= 55.2, SD = 6.5) and Visual Reproduction (old = 61.9, SD= 1991). Therefore, if intact object decision priming is observed 6.3; young = 75.9, SD = 3.4). in elderly adults, it could be argued that aging spares the ability Materials, design, and procedure. The target materials were the 20 of this system to form new representations of the global struc- possible and 20 impossible objects used by Schacter, Cooper, and De- ture of unfamiliar objects. laney (1990). The objects had been selected on the basis of an earlier study with young subjects that indicated that (a) there was relatively Experiment 1 high agreement about whether they were possible or impossible when subjects were given unlimited time to classify them and (b) unprimed To investigate object decision priming in the elderly, we used performance with brief presentation (i.e, 100 ms) was approximately the basic procedure and materials described by Schacter, 60%-65% correct, thus allowing room for potential priming effects to Cooper, and Delaney (1990). Old and young subjects were ini- be observed. tially exposed to a series of possible and impossible figures such The object drawings were divided randomly into two sets, A and B, as those in Figure 1, and judged whether each object appeared that each contained 10 possible objects and 10 impossible objects. Each to be facing primarily to the left or to the right. The left-right subject studied either Set A or Set B and was later tested on both object sets. The drawings were presented for study and test by a Compaq 386 encoding task was used because it has produced reliable evi- Deskpro computer on the screen of a 12-in Princeton Ultrasync Moni- dence of priming in previous studies (Cooper et al., 1992; tor. They subtended a mean visual angle of 18.4° when viewed from 45 Schacter, Cooper, & Delaney, 1990; Schacter, Cooper, Delaney, cm. The drawings were presented in medium resolution and appeared et al., 1991; Schacter, Cooper, Tharan, & Rubens, 1991). Follow- white against a uniform dark-gray background. ing this study phase, subjects were given either an object deci- The main experimental design was a 2 (age) X 2 (test order) x 2 sion or yes-no recognition task. Finally, subjects who were (object type) X 2 (item type) mixed factorial. The 1st two variables—old given the recognition task first were given an object decision versus young subjects and object decision test first versus recognition task, and subjects who were given the object decision task first test first—were between-subjects factors. The latter two variables— were then given a recognition task. possible versus impossible objects and studied versus nonstudied objects—were within-subjects variables. The experiment was completely counterbalanced so that drawings from Set A and Set B appeared Method equally often as studied and nonstudied objects for both age groups Subjects. Sixteen elderly and 16 young subjects took part in the and in both test orders. experiment. All subjects were paid $10 for their participation. Elderly For all subjects, the first phase of the experiment involved perform- subjects were recruited through sign-up sheets and advertisements that ing the left-right study task. Subjects were told that a series of drawings were posted in local libraries, senior centers, and newsletters on the of unfamiliar structures would appear on the computer monitor and University of Arizona campus. Young subjects were recruited with that their task was to judge whether each drawing appeared to be sign-up sheets that were posted at the University of Arizona. facing primarily to the left or to the right. They were further informed All subjects were native English speakers who performed normally that the drawings were not as simple as they might appear, so that it was on a reading test in which they read aloud from printed passages in important to use the full 5 s to make the left-right judgment. Each standard book type and passed with 80% or greater accuracy a speech object was exposed for 5 s on the computer screen, preceded by a discrimination test consisting of repeating words and phrases spoken fixation point. The task began with presentation of 5 practice items, by the experimenter from the Boston Diagnostic Aphasia Examina- followed by presentation of the 10 possible and 10 impossible target tion Repetition subtest (Goodglass & Kaplan, 1983). In addition, all items in a different random order for each subject. subjects were individually interviewed to rule out those with a history Half of the subjects in each age group were then given the object of any of the following: alcoholism or substance abuse; recent myocar- decision task, whereas the other half were given the recognition task. dial infarction or chronic cardiovascular disease; cerebrovascular acci- For the object decision test, subjects were instructed that they would dent; present or previous treatment for acute or chronic psychiatric be exposed to a series of briefly displayed drawings. They were in- illness; syphilis; brain damage sustained earlier from a known cause formed that some of the drawings represented valid, possible three-di- (e.g., hypoxia); chronic renal, hepatic, pulmonary, or endocrine dis- mensional objects that could exist in the real world, whereas other ease; uncontrolled chronic hypertension; primary systemic illness; drawings represented impossible figures that could not exist as actual metabolic or drug toxicity; primary degenerative brain disorders (e.g., objects in the real world. It was explained that their task was to decide Alzheimer's, Parkinson's, or Huntington's disease); and cancer. In ad- whether each object was possible or impossible. Several practice ob- dition, no subjects were admitted to the experiment who had a score of jects of each type were then shown to the subjects. They were informed 11 or greater on the Geriatric Depression Scale (Scogin, 1987; Yesavage that all possible objects must have volume and be solid, that every et al, 1983) or who had subscale scores that were two or more standard plane on the drawing represents a surface on the object, that all sur- deviations above the mean for older adults on the Brief Symptom Inven- faces can face in only one direction, and that every line on the drawing tory (Hale, Cochran, & Hedgepeth, 1984). represents an edge on the object. The experimenter explained the im- Mean age of elderly subjects was 69.4 years (SD = 6.4, range = 63- possibilities in sample objects and answered questions as needed. 81), whereas mean age of young subjects was 18.2 years (SD = 0.54, Subjects were also instructed to respond with a personal computer 302 D. SCHACTER, L. COOPER, AND M. VALDISERRI

(PC) mouse that they controlled with their preferred hand; they were formance for nonstudied items was at the chance level for el- told to press the left key when they thought that the object was possible derly adults (.48), whereas it was over .60 for young subjects. and the right key when they thought that the object was not possible. Second, and more important, both old and young subjects Administration of instructions required about 2 min. showed priming of possible but not of impossible objects, and The object decision test then began with presentation of 10 practice items, 5 that had appeared as practice items at study and 5 that were the overall magnitude of the observed priming effect was vir- new, followed by the 40 critical drawings in a different random order tually identical in the two groups. Third, comparison of perfor- for each subject. Each drawing was presented for 100 ms, preceded by a mance in the object decision first and second conditions indi- fixation point and followed by a darkened screen. cated that the appearance of an item on the recognition test did For the recognition test, subjects were told that they would be shown not produce consistent priming in either group, although there a further series of drawings, some of which had just been exposed were trends for test priming in individual conditions. during the encoding task, and some of which had not been exposed An analysis of variance (ANOYA) revealed a main effect of previously. Subjects were instructed to use the mouse and to press the item type (studied vs. nonstudied), F(\, 28) = 4.88 (MS, = .027, left key if they remembered seeing the object during the encoding task and the right key if they did not remember seeing the object previously. p < .05), indicating that object decision accuracy was higher for As on the object decision task, 10 practice drawings (5 old and 5 new) studied than for nonstudied drawings, and a significant inter- were presented before the 40 critical drawings, and about 2 min action between item type and object type (possible vs. impossi- elapsed between the end of the study list and the appearance of the ble), F(l, 28) = 4.50 (MS, = .024, p < .05), indicating that prim- first critical drawing. Objects remained on the computer screen for 6 s ing was observed for possible but not for impossible objects. A until subjects made their recognition response. significant main effect of age was also documented, F(\, 28) = After the conclusion of the initial tests, subjects who had been given 10.14 (MS, = .076, p < .01), showing that the object decision the object decision test were given the recognition test, and subjects task was more difficult for the old than the young. More impor- who had been given the recognition test were given the object decision tant, however, the interaction between age and item type did task. Instructions and procedure were the same as described previously. For subjects who were given the recognition test after the object not approach significance, F(\, 28) < 1, thus confirming that decision test, and hence had received some exposure to all objects, it old and young showed similar amounts of priming, and age did was emphasized that a yes response should be made only when they not enter into any other significant interactions (all Fs < 2.05). remembered seeing a drawing during the study task. After the conclu- The main effect of test order was not significant, F(l, 28) < 1, sion of testing, all subjects were debriefed about the nature and pur- nor did test order enter into any significant interactions (all pose of the experiment. Fs < 2.05). The foregoing analyses suggest that both old and young sub- Results jects showed significant priming for possible objects. To test this more directly, we performed separate 2x2 ANOVAs for old Object decision. Table 1 displays the proportion of correct and young on the results for possible objects only, with item object decisions by young and old subjects. Several points about type (studied vs. nonstudied) as a within-subjects factor and these data should be noted. First, the object decision task was test order as a between-subjects factor. For the elderly, the AN- quite difficult for the old subjects: Baseline object decision per- OVA showed a significant main effect of item type, F(l, 14) = 4.81 (MS. = .026, p < .05), and no other effects (Fs < 1). The same pattern was observed for the young, except that the main Table 1 effect of item type was only marginally significant, F(l, 14) = Object Decision Performance for Studied and Nonstudied 4.16(Afifc=.027, p=.06). Objects as a Function of Age, Object Type, Although the foregoing analyses appear to indicate that ob- and Test Order in Experiment 1 ject decision priming is spared in the elderly, the fact that baseline levels of performance differed in the old and young sug- Old Young gests the need for some interpretive caution. To address the Test order/ issue, we performed an additional analysis in which we sub- item type P I M P I M tracted the proportion of correct object decisions for nonstud- First ied possible and impossible objects from the proportion of S .65 .43 .54 .71 .63 .67 correct object decisions for studied possible and impossible ob- NS .49 .46 .48 .61 .56 .59 jects. An ANOVA on these priming scores revealed nonsignifi- S-NS .16 -.03 .06 .10 .07 .08 Second cant main effects of age and test order and a nonsignificant S .69 .40 .55 .80 .63 .71 Age X Test Order interaction (all Fs < 1). Thus, even with base- NS .60 .36 .48 .66 .69 .68 line differences subtracted, there was no evidence of an age-re- S-NS .09 .04 .07 .14 -.06 .03 lated deficit in object decision priming. It is also worth noting M that priming was intact in the elderly when it was analyzed with S .67 .42 .55 .76 .63 .70 NS .54 .41 .48 .64 .63 .64 an absolute score, as discussed earlier (i.e., studied minus non- S-NS .13 .01 .07 .12 .00 .06 studied items), or as a proportional score. With respect to the latter measure, the elderly showed about a 24% increase in ob- Note. S and NS cell entries indicate proportion correct object deci- ject decision accuracy for studied relative to nonstudied possi- sions; S - NS is the priming score for each condition. P = possible objects; I = impossible objects; S = studied objects; NS = nonstudied ble objects (i.e., .67 vs. .54) and a 15% increase overall (i*., .55 vs. objects. .48). Young subjects showed about a 19% increase for studied IMPLICIT AND EXPLICIT MEMORY 303 relative to nonstudied possible objects (.76 vs. .64) and a 10% tional increases relative to baseline. By contrast, explicit mem- increase overall (.70 vs. .64). ory for novel objects was impaired in elderly adults. Recognition. Table 2 shows data from the yes-no recogni- The overall pattern of results is consistent with the idea that tion test, which are displayed in terms of hits (yes responses to cognitive aging spares the ability to form novel structural de- studied objects), false alarms (yes responses to nonstudied ob- scriptions of unfamiliar objects and that age-related deficits in jects), and corrected recognition scores (hits - false alarms). In memory for novel objects are confined to explicit memory. contrast with their normal levels of priming, elderly adults' ex- However, each of the age groups in Experiment 1 was composed plicit memory for novel objects was considerably less accurate of a relatively small number of subjects (n = 16), and it is conceiv- than that of the young, as indicated most clearly by the able that our failure to detect age differences in priming is attrib- corrected recognition scores. Although the hit rates for the el- utable to a small sample size. This possibility seems unlikely, derly were in some conditions quite comparable with those of because (a) there were no age differences in magnitude of prim- the young, they showed consistently elevated false-alarm rates, ing (as opposed to a trend that did not reach significance be- thus producing impaired recognition performance. Corrected cause of small sample size) and (b) the sample size was adequate recognition scores for possible objects were higher than for im- to allow detection of significant differences in recognition per- possible objects in both old and young, and performance was formance. Nevertheless, it would be desirable to examine ob- somewhat worse for both age groups when the recognition test ject decision performance with a more sensitive experiment was given after the object decision test than when it was given that includes larger groups of old and young subjects. first. Another potential difficulty with Experiment 1 was that the An ANOVA was performed on the corrected recognition impossible objects we used, which were drawn from our first scores of old and young subjects. The analysis revealed signifi- study (Schacter, Cooper, & Delaney, 1990), were less than ideal: cant main effects of age, F(l, 28) = 8.34 (M$ = .094, p < .01), When pilot subjects in Schacter, Cooper, and Delaney (1990) and object type, F(l, 28) = 5.57 (M$. = .038, p < .05), and a were given unlimited time to classify drawings as possible or nonsignificant main effect of test order, F(l, 28) = 1.04 (MS^ = impossible there was only 87% agreement about the impossible .094). No interactions approached significance (all Fs < I). objects, compared with 99% agreement for possible objects. Moreover, the priming data for this set of impossible objects showed marked fluctuation across experimental conditions Discussion (Schacter, Cooper, & Delaney, 1990), and some fluctuations of this kind can be noted in Table 1. We have subsequently devel- The major result of Experiment 1 was that elderly adults oped a set of impossible objects with 99% intersubject agree- showed normal implicit memory for novel objects on the object ment that yields more stable patterns of results (Schacter, decision test: Old and young both exhibited priming for possi- Cooper, & Delaney et al., 1991). It would be desirable to deter- ble objects and no priming for impossible objects. The magni- mine whether elderly adults exhibit normal priming when these tude of the priming effect was virtually identical in the old and stimuli are used. young whether it was assessed in terms of absolute or proper- We attempted to address the foregoing issues by changing several features of Experiment 1. To determine whether age differences in priming could be observed with a more sensitive Table 2 experimental design, we doubled our sample size to include 32 Recognition Performance for Studied and Nonstudied Objects subjects in each age group and gave all subjects the object deci- as a Function of Age, Object Type, and Test Order sion test before the recognition test. We included this latter in Experiment 1 change because there were some (nonsignificant) trends for test priming in Experiment 1, and we wanted to provide as strong a Old Young test as possible of the hypothesis that older adults show normal Test order implicit memory for objects that appeared only during the item type P I M P I M study episode. To reduce and, we hoped, eliminate any prob- First lems that might be attributable to the object set, we replaced S .75 .54 .65 .68 .70 .69 the impossible objects from Experiment 1 with the set devel- NS .46 .44 .45 .20 .34 .27 oped by Schacter, Cooper, Delaney, et al. (1991). Finally, we also S-NS .29 .10 .20 .48 .36 .42 Second used a briefer object decision exposure duration for young sub- S .56 .49 .53 .68 .56 .62 jects (50 ms) and a longer one for old subjects (250 ms) in an NS .38 .44 .41 .33 .24 .29 attempt to produce more closely comparable levels of baseline S-NS .18 .05 .12 .35 .32 .33 performance in the young and old. M S .66 .52 .59 .68 .63 .66 NS .42 .44 .43 .27 .29 .28 S-NS .24 .08 .16 .41 .34 .38 Experiment 2 Note. The corresponding proportions for NS are false-alarm rates, or proportion of nonstudied objects called old. The corresponding pro- Method portions for S are hit rates or proportion of studied objects called old. P = possible objects; I = impossible objects; S = studied objects; NS = Subjects. Thirty-two old and 32 young subjects participated in the nonstudied objects. experiment. They were recruited and paid in the same manner de- 304 D. SCHACTER, L. COOPER, AND M. VALDISERRI

scribed for Experiment 1. In addition, inclusion criteria for the elderly Table 4 were the same as described previously for Experiment 1. Recognition Performance for Studied and Nonstudied Objects Mean age of elderly adults was 70.9 years (SD = 7.0, range = 60-81), as a Function of Age and Object Type in Experiment 2 whereas mean age of young subjects was 19.9 years (SD = 1.8, range = 17-25). Elderly subjects had on average 13.9 years of education (SD = Old Young 2.9), and young subjects had on average 13.8 years of education (SD = 1.4). On the WAIS-R, old subjects scored slightly higher than young on Item type P I M P I M the Information subscale (old = 22.5, SD = 3.6; young = 21.9, SD = 3.1) and the Vocabulary subscale (old = 56.0, SD = 8.8; young = 55.8, SD = S .64 .64 .64 .86 .66 .76 NS .41 .47 .44 .31 .29 .30 6.6). On the WMS-R, old subjects scored more poorly than did young S-NS .23 .17 .20 .55 .37 .46 subjects on both Logical Memory (old = 39.8, SD = 7.2; young = 57.5, SD= 5.4)and Visual Reproduction (old-56.1,SD= 7.7; young =64.8, Note. The corresponding proportions for NS are false-alarm rates, or SD = 2.8). proportion of nonstudied objects called old. S - NS is the corrected Materials, design, and procedure. All aspects of materials, design, recognition score for each condition. The corresponding proportions and procedure in Experiment 2 were identical to Experiment 1, with for S are hit rates or proportion of studied objects called old. P = the following exceptions: With respect to materials, the impossible possible objects; I = impossible objects; S = studied objects; NS = objects were the 20 used and described by Schacter, Cooper, and De- nonstudied objects. laney et al. (1991), with 99% agreement rates during unlimited viewing. Schacter, Cooper, and Delaney et al. (1991, Experiment 4) also equated possible and impossible objects for overall size, whereas the objects ble and impossible objects, the absolute magnitude of the prim- used in Experiment 1 were not systematically equated for size. We used ing effect (.06) was identical in old and young subjects. the size-equated objects in this experiment. An ANOV\ revealed a main effect of item type (studied vs. With respect to design and procedure, we used the same left-right nonstudied), F(\, 62) = 8.06 (MS, = .031, p < .01), confirming encoding task as in Experiment 1. In Experiment 2, however, subjects that overall object decision accuracy was increased by study-list were given two exposures to the study list and hence performed the exposure. There was also an interaction of Item Type X Object left-right judgment task twice for each object. In a previous study with Type (possible vs. impossible), F([, 62) = 13.18 (MS, = -024, p < young subjects, it was found that number of study exposures did not .001), confirming that priming was observed for possible but affect the magnitude of priming on the object decision task. The target not for impossible objects. A main effect of age was observed, objects were presented in different random orders on the two study trials. On the object decision test, drawings were exposed for 250 ms to F(l, 62) =31.79 (M5JL = .050, p < .001), indicating that the elderly adults and 50 ms to young subjects. For all subjects, the object object decision task was generally more difficult for the old decision test was given before the recognition test. than the young. More important, the Age X Item Type interaction was negligible (F < 1), thereby indicating that the overall Results magnitude of the priming effect did not differ in old and young. However, there was an unexpected three-way interaction of Object decision. Table 3 displays the results of the object Age X Object Type X Item Type, F(l, 62) = 6.64 (MS. = .024, p < decision task. The data for nonstudied items indicate that over- .05). The interaction reflects the fact that elderly adults showed all baseline performance for elderly subjects remained lower more priming for possible objects than did the young, whereas than for the young. Nevertheless, elderly adults still showed the old showed a trend for negative priming of impossible ob- robust priming. Indeed, the absolute magnitude of priming for jects that was not observed in the young. possible objects was actually somewhat larger in the old (. 17) We performed t tests to determine which of the priming ef- than in the young (.09). However, the elderly also showed a fects were individually significant. Both old, /(31) = 3.58, and trend for negative priming of impossible objects—their object young, r(31) = 2.46, showed significant priming for possible decision performance was .06 less accurate for studied than objects (p < .05), whereas the apparent trends for negative nonstudied objects—whereas the young showed a weak trend priming of impossible objects in the old, t(31) = 1.14, and posi- for priming of impossible objects. Thus, combined across possi- tive priming of impossible objects in the young, f(31) = 0.98, both failed to achieve significance. Thus, although the three- way interaction may indicate some differences between patterns of priming in old and young, it is important to emphasize Table 3 that the overall accuracy of object decision performance was Object Decision Performance for Studied and Nonstudied increased similarly by study-list exposure in old and young. Objects as a Function of Age and Object Type in Experiment 2 Because baseline differences between old and young were Old Young observed, we performed an additional analysis in which we subtracted the proportion of correct object decisions for non- Item type P I M P I M studied possible and impossible objects from the proportion of S .60 .47 .54 .75 .65 .70 correct object decisions for studied possible and impossible ob- NS .43 .53 .48 .66 .61 .64 jects. No age differences were observed (t< 1). In addition, it is S-NS .17 -.06 .06 .09 .04 .06 worth noting that, as in Experiment 1, elderly subjects exhibited normal levels of priming whether absolute or proportional Note. S and NS cell entries indicate proportion correct object deci- priming scores are considered. sions; S - NS is the priming score for each condition. P = possible objects; I = impossible objects, S = studied objects; NS = nonstudied Recognition memory. The recognition data, displayed in Ta- objects. ble 4, are relatively clear-cut: Elderly adults showed less accurate IMPLICIT AND EXPLICIT MEMORY 305 explicit memory, as indicated by corrected recognition scores, the probability of making a correct object decision is uncorre- than did the young for both possible and impossible objects. lated with the probability of making a correct recognition judg- Elderly subjects' hit rate was depressed and false-alarm rate was ment (Schacter, Delaney, & Merikle, 1990). Stochastic indepen- elevated relative to young subjects in all conditions, although dence between priming and explicit memory has been ob- hit rates differed only slightly for impossible objects. An AN- served in a variety of experimental situations (cf. Hayman & OVA was performed on the corrected recognition scores and Tulving, 1989; Hintzman & Hartry, 1990; Tulving, Schacter, & revealed a highly significant effect of age, F(l, 62) = 20.87 Stark, 1982). With respect to the present data, if elderly subjects (MS, = . 119, p < .001), and a significant main effect of object rely more on familiarity than do the young to make object type, F(l, 62) = 7.95 (MS, = .063, p < .01). The Age X Object decisions, we might expect them to show dependence between Type interaction was not significant, F(l, 62) =1.61 (MS, = priming and recognition under conditions in which young sub- .063). jects show stochastic independence. We examined the relation between object decision and recog- General Discussion nition performance in Experiments 1 and 2, focusing solely on studied possible objects (because only these objects showed In two experiments, elderly adults exhibited spared priming priming). To assess independence-dependence between prim- of novel objects despite impaired explicit memory for the same ing and recognition, we used Yule's Q, a special case of Good- objects. Priming in the elderly, as in the young, was observed for man and Kruskal's (1954) gamma correlation that applies to possible but not for impossible objects. Our data thus extend the analysis of data from 2x2 contingency tables (see Hayman findings of preserved implicit memory abilities in elderly & Tulving, 1989). Q measures the strength of the relation be- adults to the domain of novel three-dimensional objects, and tween two variables and can vary from — 1 (negative association) they confirm previous reports that the elderly can show implicit to +1 (positive association), with 0 reflecting complete inde- memory for newly acquired information without a preexisting pendence. We constructed 2x2 tables in which each cell corre- memory representation (Howard et al., 1991; Howard & How- sponded to one of the four possible joint outcomes of subjects' ard, 1992). responses to particular items on the object decision and recogni- These conclusions must be qualified to some extent by the tion tests: correct on both tests, correct on object decision and lower levels of baseline object decision performance in old than incorrect on recognition, incorrect on object decision and young subjects in both experiments; it would be desirable to correct on recognition, or incorrect on both tests. We then com- find intact object decision priming under conditions in which puted Q values using procedures outlined by Hayman and baseline performance rates are statistically indistinguishable Tulving. between older and younger subjects. As noted earlier, however, the elderly showed normal priming using both absolute and In Experiment 1, we performed these analyses separately for proportional measures. Nevertheless, the fact that older adults' the recognition-first and object-decision-first conditions. baseline object decision performance was at chance levels in When the recognition test was given first, we observed independence between recognition and object decision for both old both experiments, whereas young subjects consistently per- 2 formed at above-chance levels for nonstudied items, raises the subjects, Q = +.07, x (l, N = 80) < 1, and young subjects, Q = 2 possibility that the two groups may have performed the object +.02, x (l, N= 80) < 1, in conformity with previous findings in decision task differently. For example, young subjects may have recognition-first test conditions (Schacter, Cooper, & Delaney, based their responses on access to specific information about 1990; Schacter, Cooper, Delaney, et al., 1991). By contrast, when object structure, whereas the elderly may have responded more the object decision test was given first, young subjects showed 2 on the basis of global familiarity with an object, tending to call significant (p< .01) dependence, Q = +.59, x 0, N= 80) = 7.28, an object possible when it seemed familiar. and old subjects showed a similar, albeit nonsignificant, trend 2 Responding on the basis of global familiarity would tend to for dependence, Q= +.34,x (l, #= 80)= 2.02. In Experiment produce positive priming of possible objects and negative prim- 2, where the object decision test was always given before the ing of impossible objects. The three-way interaction of Age X recognition test, significant dependence was observed for the 2 2 Item Type x Object Type noted in Experiment 2 is consistent old, Q = +.27, X (l, N = 320) = 4.75, and young, Q = +.45, X (l, with this hypothesis. However, the difficulty with this idea is #=320) = 8.22. that elderly adults showed an entirely normal priming effect in The independence between object decision and recognition both experiments even when object decision performance was performance in the recognition-first condition replicates ear- collapsed across possible and impossible objects—that is, they lier findings with young subjects and extends them to the el- showed a normal increase in the accuracy of object decision derly. However, the consistent evidence for dependence in the performance. If they had been responding on the basis of global object-decision-first condition is somewhat puzzling. A rather familiarity, there should have been a reduced increase in the similar pattern of results was reported by Tulving et al. (1982), overall accuracy of object decision performance for studied who found independence between recognition and priming on items. a word fragment completion test when the recognition test was Another way to address this issue is to examine the relation given first, but observed dependence between the two tasks between object decision and recognition performance in the when the fragment completion test was given first. The latter old and young. More specifically, in previous research we found result was attributed to the fact that subjects who completed a that priming of possible objects exhibits stochastic indepen- fragment correctly received an additional exposure to it, dence from recognition memory for the same objects—that is, thereby increasing the likelihood of subsequent recognition. In 306 D. SCHACTER, L. COOPER, AND M. VALDISERRI our study, however, a correct response on the object decision showed intact priming of possible objects, as well as the finding task did not result in an extra exposure to the object. that they showed no priming of impossible objects. As noted It is thus not entirely clear how to explain the asymmetrical earlier, we have suggested that lack of priming for impossible pattern of dependence-independence that we observed. Analy- objects reflects computational constraints on the structural de- ses of stochastic independence involve a variety of complex scription system, that is, the difficulty of representing the issues (cf. Hayman & Tulving, 1989; Hintzman & Hartry, 1990; global shape of an impossible object. To the extent that object Shimamura, 1985), and further exploration of this asymmetry decision priming in the elderly depends on the structural de- would require careful attention to these issues. The important scription system, it should be subject to the same constraints as point for the present purposes, however, is that the observed are observed in young adults. However, the fact that elderly patterns of independence and dependence were quite similar in adults' baseline performance on the object decision task was old and young. Thus, the contingency analyses do not support less accurate than that of the young raises the possibility that the idea that old subjects relied on a different kind of informa- the structural description system is not entirely spared by ag- tion to make object decisions than did the young. ing; as noted earlier, the elderly might tend to rely more on Because the baseline performance of elderly adults was lower global familiarity and less on access to structural information than that of the young subjects, we cannot rule out unequivo- when making object decisions. cally the possibility that elderly adults rely more on familiarity Alternatively, because object decisions are based on ex- and less on access to information about object structure than tremely brief stimulus exposures, older adults' poor baseline do the young when making object decisions; the matter clearly performance may be attributable to a more general problem of warrants further investigation. It should also be noted, how- slowed information processing (Cerella, 1985; Salthouse, 1985) ever, that the low level of baseline object decision performance that affects a variety of systems, impairing performance on a by elderly subjects creates problems for any attempt to account range of tasks that involve brief stimulus exposures. By this for preserved priming and impaired recognition in terms of latter view, the structural description system would be subject task difficulty. That is, it is often tempting to argue that demon- to the same sort of slowing that most other perceptual-cogni- strations of impaired explicit memory and preserved implicit tive systems are but is otherwise intact and computes novel memory in elderly adults indicate that explicit tasks are in some structural descriptions normally. general sense more difficult than implicit tasks and are thus Although we cannot settle the issue on the basis of available disproportionately affected by a general cognitive impairment associated with aging (cf. Light, 1991; McDowd & Craik, 1988; data, there is some evidence suggesting that elderly adults have Schacter, Kaszniak, Kihlstrom, & Valdiserri, 1991). However, specific difficulties representing the three-dimensional struc- given that the object decision task was quite difficult for elderly ture of objects. Cerella, Milberg, and Plude (1991) found that adults—so difficult that their overall baseline performance was elderly subjects performed poorly on a pattern perception task at chance levels—one cannot readily appeal to an easy implicit that required discriminating among objects on the basis of their task as the basis for preserved priming. Instead, it is necessary three-dimensional structure, but performed normally on asimi- to put forward hypotheses about specific processes or systems lar task that involved processing of two-dimensional features. that are spared or impaired by cognitive aging. They suggested that the elderly form a "low resolution" three- As noted earlier, we have argued that object decision priming dimensional model of target objects. These observations raise depends to a large extent on the structural description system, a the possibility that the structural description system is not en- perceptual representation subsystem that handles information tirely spared by aging and that a specific impairment in this or about the global form and structure of objects independent of some similar system contributes to the elderly's low level of their associative and functional properties and that may de- baseline performance on the object decision task. pend critically on regions of inferior temporal cortex (Cooper et If this line of reasoning is correct, it immediately raises the al., 1992; Schacter, 1990, 1992; Schacter, Cooper, & Delaney, question of why the elderly showed normal priming on the ob- 1990; Schacter, Cooper, & Delaney, et al., 1991; Schacter, ject decision task. One possibility is that the left-right encod- Cooper, Tharan, & Rubens, 1991). Explicit memory for objects ing task constrains processing sufficiently so that the elderly are and other materials, by contrast, requires an episodic or declar- guided to form normal structural descriptions of target objects. ative memory system that encodes and retrieves multiple kinds By contrast, in the Cerella et al. (1991) study, the task was rather of information (e.g., contextual, semantic, or perceptual) that open-ended (subjects had to classify an object as one of two render an object distinctive and likely depends on limbic struc- types under conditions in which no explicit classification rules tures, such as the hippocampus, as well as regions of frontal were provided, and they had to uncover the rules themselves); cortex (cf. Schacter, 1987; Squire, 1987; Tulving, 1983). Thus, elderly subjects may have had difficulties detecting relevant one possible interpretation of the present results is that the aspects of three-dimensional structure on their own. Thus, ability of the structural description system to compute new under the relatively constrained conditions of our experiment, representations of unfamiliar objects is spared by aging, the elderly may have been able to form normal structural de- whereas the ability of the episodic-declarative system to link scriptions of target objects. these representations to contextual information, or to allow An alternative possibility, consistent with Cerella et al. conscious access to them, is impaired by aging. (1991), is that the structural description system is impaired Consider first the possibility that a spared structural descrip- with aging and that the elderly might exhibit subtle priming tion system underlies object decision priming in the elderly. deficits under appropriate conditions. For example, we noted This result is consistent with the finding that older adults earlier that object decision priming in young subjects is little IMPLICIT AND EXPLICIT MEMORY 307 affected by study-test changes in object size and reflection, References thereby suggesting that the structural descriptions underlying Bartlett, J. G, Strater, L., & Fulton, A. (1991). False recency and false priming are relatively abstract representations of relations fame of faces in young adulthood and old age. Memory & Cognition, among object parts (Cooper et al., 1992). Perhaps elderly sub- 79,177-188. jects do not form abstract structural representations and hence Cerella,! (1985). Information processing rates in the elderly. Psycholog- would not exhibit such size- and reflection-invariant priming. ical Bulletin, 98, 61-83. Similarly, we have found that priming on the object decision Cerella, J., Milberg, W P., & Plude, D. J. (1991). Two and three dimen- task persists with little change over a 1-week delay (Schacter & sional pattern perception in elderly adults. Manuscript submitted for Cooper, 1992). If the structural description system is in some publication. way impaired by aging, the deficit might be expressed by faster Chiarello, C, & Hoyer, W J. (1988). Adult age differences in implicit decay of priming over time. More generally, however, we must and explicit memory: Time course and encoding effects. Psychology and Aging, 3, 358-366. remain cautious about the conclusion that priming of novel Cooper, L. A., Schacter, D. L., Ballesteros, S., & Moore, C. (1992). Prim- objects is entirely normal in the elderly until further data are ing and recognition of transformed three-dimensional objects: Ef- available from a range of experimental conditions. fects of size and reflection. Journal of Experimental Psychology: Several points should also be noted about the age-related defi- Learning, Memory, and Cognition, 18, 43-57. cit in explicit memory for novel objects that was observed in Cooper, L. A., Schacter, D. L., & Moore, C. (1991, November). Orienta- both experiments. Deficits in recognition of nonverbal mate- tion affects both structural and episodic representations of 3-d objects. rials in the elderly have been reported previously, but most of Paper presented at the Annual Meeting of the Psychonomic Society, San Francisco. these studies have involved pictures of familiar objects or every- Davis, H. P., Cohen, A., Gandy, M., Colombo, P., VanDusseldorp, G., day scenes, and the deficits are sometimes observed only under Simolke, N., & Romano, J. (1990). Lexical priming deficits as a func- rather circumscribed conditions (e.g., Huppert & Kopelman, tion of age. Behavioral Neuroscience, 104, 288-297. 1989; Park, Royal, Dudley, & Morrell, 1988; Pezdek, 1987; Till, Goodglass, H., & Kaplan, E. (1983). Assessment of aphasia and related Bartlett, & Doyle, 1982). However, several studies have re- disorders. Philadelphia: Lea & Febiger. ported age-related impairments in recall and recognition of Goodman, L. A., & Kruskal, W H. (1954). Measures of association for novel nonverbal materials, including abstract geometric de- cross classification. Journal of the American Statistical Association, signs (Riege & Inman, 1981; Rybarczyk, Hart, & Harkins, 1987) 49, 732-764. and unfamiliar faces (Bartlett, Strater, & Fulton, 1991). Graf, P. (1990). Life span changes in implicit and explicit memory. Bulletin of the Psychonomic Society, 28, 353-358. As Bartlett et al. (1991) pointed out, age differences on yes- Graf, P., & Schacter, D. L. (1985). Implicit and explicit memory for new no recognition tasks are frequently (though not always) ex- associations in normal and amnesic patients. Journal of Experimen- pressed in terms of elevated false-alarm rates by elderly sub- tal Psychology: Learning, Memory, and Cognition, 11, 501-518. jects, with little or no age-related differences in hit rates. We Hale, W D, Cochran, C. D., & Hedgepeth, B. E. (1984). Norms for the observed this pattern for possible objects in Experiment 1, elderly on the Brief Symptom Inventory. Journal of Consulting and when the recognition test was given first; in fact, old subjects Clinical Psychology. 52, 321-322. exhibited a slightly higher hit rate than did young subjects. How- Hayman, C. A. G, & Tulving, E. (1989). Contingent dissociation be- ever, the elderly showed lower hit rates and false-alarm rates tween recognition and fragment completion: The method of trian- gulation. Journal of Experimental Psychology: Learning, Memory, than did the young for impossible objects in the recognition- and Cognition, 15, 228-240. first condition and also when the recognition test was given Hintzman, D. L., & Hartry, A. L. (1990). Item effects in recognition and after the object decision test in Experiments 1 and 2. It is not fragment completion: Contingency relations vary for different sub- clear why elderly adults exhibited normal hit rates with possible sets of words. Journal of Experimental Psychology: Learning, Mem- objects in the recognition-first condition but not otherwise; ory, and Cognition, 16, 955-969. given the small number of subjects per condition in this experi- Hochberg, J. (1968). In the mind's eye. In R. N. Haber (Ed.), Contempo- ment, interpretive caution is required. As Bartlett et al. noted, rary theory and research in visual perception (pp. 308-331). New both normal and impaired hit rates have been observed in stud- York: Holt, Rinehart & Winston. ies that have used yes-no recognition procedures in studies Howard, D. V(1991). Implicit memory: An expanding picture of cog- with elderly adults. nitive aging. In K. W Schaie (Ed.), Annual review of gerontology and geriatrics (pp. 1-22). New York: Springer. Although our experiments were not designed to illuminate Howard, D. V, Fry, A. F, & Brune, C. M. (1991). Aging and memory for the nature of the elderly's recognition deficit, further investiga- new associations: Direct versus indirect measures. Journal of Experi- tions of the issue could be pursued profitably in connection mental Psychology: Learning, Memory, and Cognition, 17, 779-792. with studies that investigate the nature of elderly adults' struc- Howard, D. V, & Howard, J. H. (1992). Adult age differences in the rate tural descriptions of novel objects, as discussed earlier. It would of learning serial patterns: Evidence from direct and indirect tests. be of great interest to determine whether recognition memory Psychology and Aging, 7, 232-241. deficits are related to, or produced by, low resolution structural Hultsch, D. F, Masson, M. E. X, & Small, B. J. (1991). Adult age differ- descriptions, or whether recognition impairments are attribut- ences in direct and indirect tests of memory. Journal ofGerontology: Psychological Science, 46, 22-30. able to processes occurring outside of a fully intact structural Huppert, F. A., & Kopelman, M. D. (1989). Rates of forgetting in nor- description system. Although we currently favor the latter alter- mal ageing: A comparison with dementia. Neuropsychologia, 27, native, experiments that explore this issue—however they turn 849-860. out—should enhance the understanding of how cognitive aging Light, L. L. (1991). Memory and aging: Four hypotheses in search of affects both implicit and explicit memory. data. Annual Review of Psychology, 42, 333-376. 308 D. SCHACTER, L. COOPER, AND M. VALDISERRI

Light, L. L., & Singh, A. (1987). Implicit and explicit memory in young ory for unfamiliar objects depends on access to structural descrip- and older adults. Journal of Experimental Psychology: Learning, tions. Journal of Experimental Psychology: General, 119, 5-24. Memory, and Cognition, 13, 531-541. Schacter, D. L., Cooper, L. A., Delaney, S. M., Peterson, M. A., & Light, L. L., Singh, A., & Capps, J. L. (1986). Dissociation of memory Tharan, M. (1991). Implicit memory for possible and impossible and awareness in young and older adults. Journal of Clinical Experi- objects: Constraints on the construction of structural descriptions. mental Neuropsychology, 8, 62-74. Journal of Experimental Psychology: Learning, Memory, and Cogni- McDowd, J. M., & Craik, F. I. M. (1988). Effects of aging and task tion, 17, 3-19. difficulty on divided attention performance. Journal of Experimen- Schacter, D. L., Cooper, L. A., Tharan, M., & Rubens, A. B. (1991). tal Psychology: Human Perception and Performance, 14, 267-280. Preserved priming of novel objects in patients with memory dis- Mitchell, D. B., Brown, A. S., & Murphy, D. R. (1990). Dissociations orders. Journal of Cognitive Neuroscience, 3,118-131. between procedural and episodic memory: Effects of time and ag- Schacter, D. L., Delaney, S. M., & Merikle, E. P. (1990). Priming of ing. Psychology and Aging, 5, 264-276. nonverbal information and the nature of implicit memory. In G. H. Moscovitch, M., Winocur, G., & McLachlan, D. (1986). Memory as Bower (Ed.), The psychology of learning and motivation (Vol. 26, pp. assessed by recognition and reading time in normal and memory- 83-123). San Diego, CA: Academic Press. impaired people with Alzheimer's disease and other neurological Schacter, D. L., & Graf, P. (1986). Effects of elaborative processing on disorders. Journal of Experimental Psychology: General, 115, 331- implicit and explicit memory for new associations. Journal of Experi- 347. mental Psychology: Learning, Memory, and Cognition, 12, 432-444. Nissen, M. J., & Bullemer, P. (1987). Attentional requirements of learn- Schacter, D. L., Kaszniak, A. W, Kihlstrom, J. F, & Valdiserri, M. ing: Evidence from performance measures. Cognitive Psychology, 19, (1991). The relation between source memory and aging. Psychology 1-32. and Aging, 6, 559-568. Park, D. C, Royal, D., Dudley, W, & Morrell, R. (1988). Forgetting of Schacter, D. L., Kihlstrom, J. F., Kaszniak, A. K., & Valdiserri, M. (in pictures in young and older adults. Psychology and Aging, 3, 94-95. press). Preserved and impaired memory functions in elderly adults. Pezdek, K. (1987). Memory for pictures: A life-span study of the role of In J. Cerella, W Hoyer, J. Rybash, & M. Commons (Eds.), Adult visual detail. Child Development, 58, 807-815. information processing: Limits on loss. San Diego, CA: Academic Plaut, D. C., & Farah, M. J. (1990). Visual object representation: Inter- Press. preting neurophysiological data within a computational framework. Scogin, F. (1987). The concurrent validity of the Geriatric Depression Journal of Cognitive Neuroscience, 2, 320-343. Scale with depressed older adults. Clinical Gerontologist, 7, 23-30. Shimamura, A. P. (1985). Problems with the finding of stochastic inde- Richardson-Klavehn, A., & Bjork, R. A. (1988). Measures of memory. pendence as evidence for the independence of cognitive processes. Annual Review of Psychology, 36, 475-543. Bulletin of the Psychonomic Society, 23, 506-508. Riddoch, M. J., & Humphreys, G. W (1987). Visual object processing in Shimamura, A. P. (1986). Priming effects in amnesia: Evidence for a optic aphasia: A case of semantic access agnosia. Cognitive Neuropsy- dissociable memory function. Quarterly Journalof'Experimental Psy- chology, 4,131-186. chology, 38A, 619-644. Riege, W H., & Inman, V (1981). Age differences in nonverbal mem- Squire, L. R. (1987). Memory and brain. New York: Oxford University ory tasks. Journal of Gerontology, 36, 51-58. Press. Roediger, H. L., III. (1990). Implicit memory: Retention without re- Till, R. E., Bartlett, J. C., & Doyle, A. (1982). Age differences in picture membering. American Psychologist, 45,1043-1056. memory with resemblance and discrimination tasks. Experimental Russo, R., & Parkin, A. J. (1991). The influence of divided attention and Aging Research, 8,179-184. ageing on implicit and explicit memory. Manuscript submitted for Tulving, E. (1983). Elements of episodic memory. Oxford: Clarendon publication. Press. Rybarczyk, B. D, Hart, R. P., & Harkins, S. W (1987). Age and forget- Tulving, E., & Schacter, D. L. (1990). Priming and human memory ting rate with pictorial stimuli. Psychology and Aging, 2, 404-406. systems. Science, 247, 301-306. Salthouse, T. (1985). A theory of cognitive aging. Amsterdam: North- Tulving, E., Schacter, D. L., & Stark, H. (1982). Priming effects in word Holland. fragment completion are independent of recognition memory. Jour- Schacter, D. L. (1987). Implicit memory: History and current status. nal of Experimental Psychology: Learning, Memory, and Cognition, Journal of Experimental Psychology: Learning, Memory, and Cogni- 8, 336-342. tion, 13, 501 -518. Warrington, E. K. (1975). The selective impairment of semantic mem- Schacter, D. L. (1990). Perceptual representation systems and implicit ory. Quarterly Journal of Experimental Psychology, 27, 635-657. memory: Toward a resolution of the multiple memory systems de- Warrington, E. K. (1982). Neuropsychological studies of object recog- bate. In A. Diamond (Ed.), Development and neural bases of higher nition. Philosophical Transactions of the Royal Society of London, cognition. Annals of the New York Academy of Sciences, 608, 543- Series B, 298, 15-33. 571. Warrington, E. K., & Taylor, A. M. (1978). Two categorical stages of Schacter, D. L. (1992). Understanding implicit memory: A cognitive object recognition. Perception, 7, 695-705. neuroscience approach. American Psychologist, 47, 559-569. Yesavage, J. A., Brink, T. L., Rose, T. L., Lum, Q, Huang, V, Adey, M., & Schacter, D. L., Bowers, J., & Booker, J., (1989). Intention, awareness Leirer, V O. (1983). Development and validation of a geriatric de- and implicit memory: The retrieval intentionality criterion. In S. pression scale: A preliminary report. Journal of Psychiatric Re- Lewandowsky, J. C. Dunn, & K. Kirsner (Eds.), Implicit memory: search, 17, 37-49. Theoretical issues (pp. 47-69). Hillsdale, NJ: Erlbaum. Schacter, D. L. & Cooper, L. A. (1992). [Long-lasting priming of novel Received July 11,1991 objects]. Unpublished raw data. Revision received November 20,1991 Schacter, D. L., Cooper, L. A., & Delaney, S. M. (1990). Implicit mem- Accepted December 2,1991 •