Journal of Gerontology: PSYCHOLOGICAL SCIENCES Copyright 1995 by The Geromological Society of America 1995, Vol. 50B, No. 3, P162-P17O Adult Age Differences in Perceptually Based, But Not Conceptually Based Implicit Tests of Memory Brent J. Small, David F. Hultsch, and Michael E. J. Masson Department of Psychology, University of Victoria. Implicit tests of memory assess the influence of recent experience without requiring awareness of remembering. Evidence concerning age differences on implicit tests of memory suggests small age differences in favor of younger adults. However, the majority of research examining this issue has relied upon perceptually based implicit tests. Recently, a second type of implicit test, one that relies upon conceptually based processes, has been identified. The pattern of age differences on this second type of implicit test is less clear. In the present study, we examined the pat- tern of age differences oh one conceptually based (fact completion) and one perceptually based (stem completion) implicit test of memory, as well as two explicit tests of memory (fact and word recall). Tasks were administered to 403 adults from three age groups (19-34 years, 58-73 years, 74-89 years). Significant age differences in favor of the young were found on stem completion but not fact completion. Age differences were present for both word and fact recall. Correlational analyses examining the relationship of memory performance to other cognitive variables indicated that the implicit tests were supported by different components than the explicit tests, as well as being different from each other. N RECENT years, there has been a great deal of interest in tasks rely on the semantic meaning of the study items and I implicit tests of memory (Graf & Masson, 1993; Lewan- less upon the perceptual characteristics of the items. The dosky, Dunn, & Kirsner, 1989). Unlike explicit tests of memory tasks Blaxton used were constructed so each type of memory (e.g., recall and recognition), which directly ask task, explicit or implicit, would require either conceptual or subjects to use their memory to retrieve past information, perceptual processing. The results indicated that perfor- implicit tests require only that subjects perform an assigned mance on the memory tests did not correspond to the type of task without reference to particular prior events. With im- memory task but rather to the type of processing required by plicit tests, memory is revealed as a facilitation or change in each of the tasks. Specifically, performance on the conceptu- task performance that is attributable to exposure to informa- ally based tasks was greatest when the semantic meaning of tion during a previous episode (Jacoby & Dallas, 1981). For the study words was processed. On the other hand, perfor- example, in the word stem completion task, subjects are mance on the perceptually based tasks was greatest when the required to complete a word stem with the first word that perceptual characteristics at study matched those at test. comes to mind (e.g., CON ). Prior presentation of a Blaxton concluded that distinctions cannot be made simply valid completion for a stem enhances the probability of its on the basis of whether a task employs implicit or explicit generation, implying a form of memory for the initial pre- test instructions. The nature of the processing operations is sentation. This facilitation of task performance is called critical in determining performance. priming (Schacter, 1987). The distinction between conceptually driven and percep- Much of the early work with implicit tests of memory tually driven implicit tests of memory has interesting impli- centered on dissociations from explicit tests of memory. For cations for age differences in memory performance. The example, whereas explicit tests typically benefit from deep pattern of age-related effects in implicit tests of memory is and elaborative semantic encoding, the magnitude of prim- one of small differences in favor of younger subjects. Often ing effects on some implicit tests are insensitive to the levels these differences are not statistically significant (Light & of processing manipulation (Graf & Mandler, 1984; Singh, 1987; Light, Singh, & Capps, 1986; Mitchell, 1989; Hashtroudi, Ferguson, Rappold, & Crosniak, 1988). Simi- Russo & Parkin, 1993), but in some studies they are reliable larly, amnesics exhibit severe deficits on explicit tests of (Chiarello & Hoyer, 1988; Howard, Heisey, & Shaw, 1986; memory, but their performance on implicit tests is often Hultsch, Masson, & Small, 1991; Rose, Yesavage, Hill, & similar to normal subjects (Cohen & Squire, 1980; see Bower, 1986). One factor that may be responsible for Shimamura, 1986, for a review). inconsistent age-related effects in implicit tests of memory is Recently, dissociations have been observed among im- the potentially small magnitude of any existing age differ- plicit tests of memory themselves (Blaxton, 1989; Wither- ences. For example, Hultsch et al. (1991) found the age- spoon & Moscovitch, 1989). Blaxton compared perfor- related effect in stem completion accounted for roughly mance on two explicit and two implicit tests of memory. The 2.5% of variance, whereas the age effect in word recall tasks used were classified into conceptually based or percep- accounted for approximately 9% of variance. Therefore, tually based tasks. Perceptually based tasks rely on process- studies based on sample sizes of 30 or so subjects per age ing the physical features of the presented stimulus in order to group may not have sufficient power to consistently detect perform the tasks. On the other hand, conceptually based small age effects. A recent meta-analysis suggests that P162 AGE DIFFERENCES IN IMPLICIT MEMORY P163 insufficient statistical power may be the reason inconsisten- analysis, Perruchet and Baveux (1989) obtained a factor cies in results have been observed. Light and La Voie (1993) structure in which two perceptually based implicit tests compared age differences on a number of implicit tests (stem completion, perceptual clarification) loaded on a fac- including word stem completion, word fragment comple- tor with free recall and recognition, whereas two other tion, and perceptual identification. They found small, but perceptually based implicit tests loaded on a factor of their reliable, age differences in implicit test performance. Meta- own. However, subjects in the study were warned of im- analyses achieve great statistical power because they pool pending memory tests prior to initial encoding of the target the results of studies, thus combining subjects from different items, and this may have contributed to the use of explicit experiments to achieve a larger effective sample size. memory strategies when performing some of the implicit Although it might be tempting to conclude there are small tests of memory. On the other hand, Mitchell (1989) found age differences in implicit tests of memory, the majority of that measures associated with a perceptually based implicit tasks used to examine this question have been perceptually test (naming repeatedly presented pictures), loaded on a based. The few studies that have employed conceptually factor that was distinct from two other factors, characterized based implicit tests have found no evidence of reliable age as episodic and semantic memory. Although this finding differences in performance. Light and Albertson (1989) might be suggestive of a distinct implicit memory factor, the observed no age differences in performance when a category implicit measures of memory were based on response time generation task was used as the implicit measure, despite and might reflect a processing speed factor. statistically significant age differences on the explicit corol- In the Hultsch et al. (1991) study we examined the lary of category generation, category cued recall. Similarly, patterns of relationships among implicit tests (stem comple- Rabbit (1982, 1984) failed to find age differences in implicit tion), explicit tests (word, text, and fact recall), and a memory when a category judgment task was used. Although number of cognitive ability variables in a sample of young both sets of experiments failed to find age differences in (19-36 years), middle (55-69 years), and older (70-86 performance, they also employed relatively small sample years) adults. The cognitive ability variables included mea- sizes. Therefore, it is unclear whether the results indicate age sures of verbal speed, working memory, verbal ability, and invariance on conceptual implicit tests or reflect relatively reading comprehension. Results indicated that although the low statistical power to detect the small age differences in explicit tests of memory intercorrelated highly, correlations performance. between implicit and explicit tests were not statistically sig- Given the uncertainty regarding the existence of age nificant. Moreover, examination of the correlations of the differences on conceptually based implicit tests of memory, cognitive ability measures with stem completion showed one of the goals of this study was to provide an unusually that, of the 14 variables examined, there was only one sig- powerful test for an age-related effect. In order to increase nificant relationship (a correlation of .17 between stem power, we used a very large sample of subjects from three completion and reading comprehension in the middle-aged age groups. Two implicit tests of memory, one conceptually group). In contrast, multiple