Memory & Cognition 1997,25 (1),11-17

Attention and implicit memory tests: The effects ofvarying attentionalload on conceptual priming

NEIL W. MULLIGAN Illirwis State University, Normal, Illinois

The role of attention during encoding is important to many current accounts of the implicit/explicit memory distinction. Some accounts suggest that implicit memory tests reflect automatic (non-attention­ demanding) encoding processes, whereas other accounts (such as the transfer-appropriate-processing view) suggest that performance on conceptual implicit tests requires attention during encoding. The present study manipulates attention at encoding over several levels (by varying short-term memory load) and examines the effects on the category-exemplar production task (a conceptual implicit mem­ ory test) and its explicit counterpart, category-cued recall. Dividing attention decreased performance on both tests, but in different ways. Mild divisions of attention reduced recall but not conceptual prim­ ing. Strong divisions of attention reduced performance on both tests and, in addition, eliminated con­ ceptual priming entirely. These findings resolve apparently conflicting results in the literature and help to clarify the relationship between attention and performance on implicit memory tests.

Over the past 15 years, a great deal ofresearch in cog­ typically have poorer performance than younger adults nitive psychology and neuropsychology has focused on on explicit tests but not on implicit tests (see Light, 1991, the distinction between explicit and implicit memory (e.g., for a review). Experimental manipulations, such as the Graf & Masson, 1993; Roediger & McDermott, 1993; levels-of-processing and the read/generate manipulation, Schacter, 1987). Explicit memory refers to intentional or also produce dissociations on explicit and implicit mem­ conscious recollection of prior experiences and is mea­ ory tests (see Roediger & McDermott, 1993, for a recent sured by directing subjects to think back about some prior review). event and report on it, as is done with free-recall, cued­ One potentially important difference between implicit recall, and recognition-memory tests. Implicit memory, and explicit tests centers on the controlled/automatic pro­ in contrast, refers to changes in behavior that are produced cessing distinction. Controlled (or attention-demanding) by prior experience and that affect performance on mem­ encoding processes appear to be necessary for later ex­ ory tests that do not require any intentional or conscious plicit memory (e.g., Fisk & Schneider, 1984), but auto­ recollection, such as the identification of perceptually matic (or non-attention-demanding) encoding processes degraded stimuli or the completion of word fragments. may suffice for later implicit memory (e.g., Eich, 1984). Memory for prior events is inferred from increased ease Several studies indicate that very poorly attended stim­ in identifying, generating, or otherwise processing pre­ uli, which may show no retention on explicit memory viously experienced information. The enhanced perfor­ tests, may nevertheless lead to significant levels ofprim­ mance on implicit memory tests is called priming (Roe­ ing on implicit memory tests (Bornstein, Leone, & Gai­ diger & McDermott, 1993). ley, 1987; Eich, 1984; Hawley & Johnston, 1991; Jelicic, The principles that govern performance on explicit Bonke, Wolters, & Phaf, 1992; Kunst-Wilson & Zajonc, and implicit memory tests differ in many ways. Particu­ 1980; MacKay, 1973; Mandler, Nakamura, & Van Zandt, larly striking examples come from neuropsychology and 1987; Merikle & Reingold, 1991; Seamon, Marsh, & cognitive gerontology. Compared with healthy control sub­ Brody, 1984; cf. Woods, Stadler & Cowan, 1995). Other jects, amnesics are profoundly impaired on explicit mem­ studies have demonstrated that division ofattention dur­ ory tests but often not on implicit memory tests (see Shi­ ing encoding impairs explicit test performance but may mamura, 1986, 1993, for reviews). Likewise, older adults leave the amount of priming completely unaffected (Gabrieli et aI., 1995; Isingrini, Vazou, & Leroy, 1995; Jacoby, Woloshyn, & Kelley, 1989; Mulligan & Hartman, This research was supported, in part, by a university research grant 1996; Parkin, Reid, & Russo, 1990; Parkin & Russo, 1990; from Illinois State University, These results were presented at the an­ nual meeting of the Psychonomic Society, Los Angeles, in November Russo & Parkin, 1993; Smith & Oscar-Berman, 1990). 1995. I would like to thank Philip Merikle, Michael Masson, Kathleen Such findings have prompted some researchers to suggest McDermott, Tim Curran, Marilyn Hartman, Elliot Hirshman, and Gor­ that performance on implicit memory tests largely re­ don Redding for very useful comments and suggestions. The assistance flects automatic encoding processes, whereas performance of Mark Stilling and Kristin Van Schelven is gratefully acknowledged. Address correspondence to N. Mulligan, Department of Psychology, on explicit tests is crucially dependent on encoding pro­ Illinois State University, Campus Box 4620, Normal IL 61790-4620 cesses that require attentional resources (Besson, Fisch­ (e-mail: [email protected]). ler, Boaz, & Raney, 1992; Graf & Mandler, 1984; Isin-

11 Copyright 1997 Psychonomic Society, Inc. 12 MULLIGAN

grini et aI., 1995; Jacoby,Toth, & Yonelinas, 1993; Jacoby fected (see Gabrieli et aI., 1995, and Mulligan & Hart­ et aI., 1989; Jelicic et aI., 1992; Parkin et aI., 1990; Par­ man, 1996, for reviews). This implies that attentional re­ kin & Russo, 1990).1 sources (beyond those necessary for identification) play A somewhat more differentiated view on the relation­ little or no role in perceptual implicit memory. ship between attention and implicit tests of memory is With regard to conceptual implicit tests, the picture is offered by the transfer-appropriate processing (TAP) not as clear. Some studies indicate that conceptual prim­ framework, a prominent account ofimplicit and explicit ing requires little or no attention during encoding (lsingrini memory (e.g., Blaxton, 1989, 1992; Roediger & McDer­ et aI., 1995; Koriat & Feuerstein, 1976), whereas other mott, 1993; Roediger, Weldon, & Challis, 1989).The TAP studies indicate that the conceptual priming is crucially view proposes that performance on a memory test bene­ dependent on attention (Gabrieli et aI., 1995; Mulligan & fits to the extent that the cognitive processes carried out Hartman, 1996). during encoding are reengaged at test (Morris, Bransford, To begin resolving this inconsistency, I compare two & Franks, 1977). Furthermore, the TAP framework dis­ very similar studies that produced conflicting results. tinguishes between two broad classes of cognitive pro­ Both Isingrini et al. (1995) and Mulligan and Hartman cessing: conceptual processing-the analysis ofmeaning (1996) used the category-exemplar production task to or semantic features-and perceptual processing-the measure conceptual priming. In this task, subjects are analysis ofperceptual or surface-level features (Blaxton, first presented with a series ofexemplars from different 1989; Roediger & McDermott, 1993; Roediger et aI., taxonomic categories. Later, subjects are presented with 1989). The most commonly used explicit tests rely on con­ the names of categories and asked to rapidly produce ex­ ceptual processing (e.g., free and cued recall, recognition), amples. Although the subjects are not informed ofthis, whereas many commonly used implicit tests rely heavily some ofthe categories correspond to studied exemplars on perceptual processing (e.g., perceptual identification, and some do not. Conceptual priming is computed as the word-fragment completion). Consequently, many im­ difference between the proportion of the studied exem­ plicit and explicit tests benefit from different types ofen­ plars produced and an appropriate baseline measure. In coding procedures (Craik, Moscovitch, & McDowd, 1994; addition to the category-exemplar production test, both Roediger et aI., 1989; Weldon, Roediger, Beitel, & John­ Isingrini et al. and Mulligan and Hartman used category­ ston, 1995). cued recall, an explicit memory test that uses the same re­ According to the TAP framework, it is critical to note trieval cues. that not all implicit tests are perceptual. Some, such as In both experiments, the study words were presented free association and category-exemplar production, en­ visually and attention was divided with a concurrent au­ courage the reengagement ofconceptual processes (Blax­ ditory detection task. Isingrini et al. (1995) found that ton, 1992; Roediger & McDermott, 1993; Roediger et aI., dividing attention significantly reduced performance on 1989). Performance on conceptual implicit memory tests the category-cued recall task, but not on the category­ bears interesting similarities with and differences from exemplar production task.? In contrast, Mulligan and performance on perceptual implicit memory tests. For Hartman (1996) found robust effects ofdivided attention instance, both amnesics and older adults have shown nor­ on both tasks. Furthermore, dividing attention elimi­ mal levels of priming on both types ofimplicit tests (Blax­ nated conceptual priming but not recall. Isingrini et al.'s ton, 1992; Graf, Shimamura, & Squire, 1985; Light & results support the idea that conceptual priming does not Albertson, 1989). In contrast, several other variables (e.g., require attentional encoding and, more generally, that levels of processing, read/generate, organizational vari­ conceptual implicit memory tests are less dependent on ables, and modality match between study and test) affect attention than are comparable explicit tests. The Mulli­ perceptual and conceptual priming differently (Roediger gan and Hartman results indicate just the opposite: con­ & McDermott, 1993). ceptual implicit-memory tests require attentional encod­ Consideration ofconceptual priming raises an interest­ ing and, in addition, are more dependent on attention ing contrast between the predictions ofthe TAP view and than are comparable explicit tests. expectations based on prior research on attention and im­ Although there are several differences between these plicit memory. The studies cited earlier imply that atten­ two studies which might account for these divergent re­ tion plays little or no role during initial learning, when sults (e.g., use ofdifferent category norms; different num­ learning is to be measured with implicit tests. Alterna­ bers of exemplars per category), the most promising is tively, the TAP view proposes that, if attention is required the strength ofthe divided-attention manipulation. Both for conceptual processing (as is typically assumed: e.g., the type of concurrent task and subjects' accuracy on this Craik, 1983; Craik & Byrd, 1982), then attention during task differed across the two studies. Subjects in the Isin­ encoding is crucial to subsequent memory as measured grini et al. (1995) study monitored a tape recording ofa by conceptual implicit tests (Mulligan & Hartman, 1996). series ofconsonants and signaled if they detected a B or As cited earlier, the role ofattention in implicit mem­ a G; they correctly identified 67% of the target conso­ ory tests has been examined in several divided-attention nants. Subjects in the Mulligan and Hartman (1996) study studies. For perceptual implicit tests, the results are con­ monitored a tape recording of a series ofnumbers and sig­ sistent: if the division ofattention does not disrupt iden­ naled if they detected a sequence ofthree odd numbers tification of study stimuli, then later priming is unaf- in a row; they correctly identified 85% of the target digit ATTENTIONAL LOAD AND CONCEPTUAL PRIMING 13 strings. Although we do not know for certain which of ment, a part of the human body, a vegetable, a dance, an insect, a these two tasks requires more attention, it can be argued substance for flavoring food, a fish, a part ofa building) in the Bat­ that Isingrini et al.'s was a weaker manipulation of atten­ tig and Montague (1969) norms. The items chosen did not rank in the tion, because subjects had to evaluate only one stimulus 10 most frequent instances, but were produced by at least 10 of the 400 subjects used in the Battig and Montague norms. The average at a time; they did not have to maintain any preceding con­ rank of the selected category members was 17.4. sonants in memory. In contrast, subjects in the Mulligan Two sets ofcritical items were created by randomly splitting the and Hartman study had to evaluate each stimulus plus 16 categories into two groups of 8, thus creating two master lists of maintain information about immediately preceding stim­ 48 items each. From each master list, four study lists were created uli. In addition, Mulligan and Hartman kept their sub­ by randomly dividing the 8 categories into four groups of 2 and ro­ jects focused on the detection task by prompting the sub­ tating the exemplars from these categories through each of the four attentionalload conditions. In each of the resulting eight study lists, jects if they missed a target sequence, which may also all ofthe exemplars from a given category were in the same atten­ have contributed to the difference in accuracy between tion condition. Finally, the critical items in each list were randomly the two studies. ordered, subject to the constraint that no two consecutive items If Isingrini et al.'s (1995) was a weaker manipulation were from the same category. Twelve additional items were chosen ofattention, and if attention is necessary for later concep­ from nonselected Battig and Montague categories; four were pre­ tual priming, we might expect some small (though pos­ sented before the list, as practice items, and four were placed at the beginning and end of each list as primacy and recency buffers. Each sibly nonsignificant) effect ofthis manipulation. In fact, ofthe additional items came from a different category, and the av­ subjects in the divided-attention condition had lower av­ erage rank of these items was similar to that of the critical items. erage performance than those in the full-attention con­ Each study list was presented to equal numbers of subjects. dition. If we consider all four ofthe age groups in Isin­ Study items were preceded by an attentionalload. Nonzero loads grini et aI., we see that each age group exhibited a small were constructed by randomly selecting items from a set ofdigits (but nonsignificant) effect ofdivided attention. By a sign (1-9) and a set ofletters (B, C, D, F,G, H, J, K, L) according to the test, the null hypothesis of no effect of attention yields following rules: (I) digits and letters occupied alternating positions, with a digit in the first position (attentionalloads of I consisted of p = .0625 (one-tailed). This suggests that differences in a single digit); and (2) no repetition of digits or letters within a load. the strength of the attention manipulation may account It was thought that the use of these materials and rules would help for the conflicting results. to minimize chunking. In the present experiment, attention at encoding was var­ In the category-exemplar production test, all 16 category names ied by manipulating short-term memory loads. Prior to the were used as cues, 8 ofwhich corresponded to studied words (2 cat­ presentation ofeach study word, the subject was presented egories per load condition) and 8 to new words. Production rates of the nonstudied critical items served as the baseline response rate. with an attentionalload of0 (a full-attention condition), I, Across subjects, each category appeared equally often as studied 3, or 5 digits and letters. The digits and letters were to be and new. In the category-cued recall task, the cue set consisted of maintained in memory until a RECALL signal was presented the 8 category names corresponding to the studied items (2 cate­ a few seconds later. This technique allowed a controlled di­ gories per load condition). vision of attention over severalleve1s within a single exper­ iment (see, e.g., Engle, Conway,Tuholski, & Shisler, 1995; Procedure Logan, 1979). Subsequently, memory for the study words The subjects were tested individually. The experiment consisted of a study task and a memory test. At the beginning of the experi­ was measured with either the category-exemplar produc­ ment, the subjects were informed that they would perform several tion test or its explicit counterpart, category-cued recall. different tasks, some having to do with memory and some having This design allows a more extensive exploration of the to do with language abilities and problem-solving. relationship between attention and implicit and explicit Each study trial consisted of the following. First, a ready prompt tests of memory, and speaks to a central aspect ofthe im­ was displayed for 500 msec. Then, the digit-letter string compris­ plicit/explicit distinction. Specifically, are implicit mem­ ing the attentionalload (or a dash in the O-Ioadcondition) was pre­ sented for 2.5 sec. For the non-O-Ioad trials, subjects were in­ ory tests dependent on attention? If so, are explicit or im­ structed to read the digit-letter string aloud and retain it in memory plicit memory tests more sensitive to (or dependent on) until the RECALL signal was given. For the O-Ioad trials, subjects manipulations ofattention? were simply instructed to say "blank" in response to the dash. Next, the study word was presented for 3 sec. Subjects were instructed to METHOD read the word aloud and try to remember it for a later (unspecified) memory test. Finally, either the word RECALL (in the non-O-Ioad Subjects conditions) or the word BLANK (in the O-Ioad condition) appeared Forty-eight undergraduates at Illinois State University partici­ for 2.5 sec. The subjects were instructed either to recall the digits pated in exchange for extra credit in psychology courses. and letters (in the non-O-Ioad conditions) or to again say "blank" (in the O-Ioadcondition). Design and Materials After the study list, the subjects were given one of the two mem­ The experiment used a 2 X 4 design in which memory test ory tests. In the category-exemplar production task, the 16category (category-exemplar production or category-cued recall) was ma­ names were presented, I at a time, with instructions to produce as nipulated between subjects and attentional load (0, I, 3, or 5) was rapidly as possible the first 8 category exemplars that came to mind. manipulated within subjects. Eight exemplars were required to be sure that exemplars other than The materials were the same as those used in Mulligan and Hart­ the most common were produced (Graf et aI., 1985; Rappold & man (1996) and consisted of six common instances from each of 16 Hashtroudi, 1991). The experimenter recorded the subjects' re­ categories (a sport, a fruit, a piece of furniture, a bird, a color, a sponses, and no time limit was imposed. When 8 exemplars were four-footed animal, an article of clothing, a tree, a musical instru- produced, the experimenter signaled the subject to proceed to the 14 MULLIGAN

next category by pressing the space bar on the computer's keyboard. Category-Exemplar Production No mention was made ofthe relationship between this task and the 0.3 studied words. In the category-cued recall test, the subjects were presented with the 8 category names that corresponded to the study to list. They were instructed to use the category cues to recall mem­ c: bers ofthe category that had been previously studied. No time limit :~ was imposed, and the number of responses required was not fixed. ! 0.2 ... 'ij.. RESULTS :> ii e 0 During the study task, the mean proportion of atten­ Z 0.1 tionalload items recalled was .97, .98, and .91 for the 1-, ... 3-, and 5-load conditions, respectively [F(2,94) = 17.34, :;:;.. MS = 0.0039, p < .0005]. Post hoc comparisons using :> e Ui the Fisher-Hayter test ' indicate that performance was significantly worse in the 5-loadcondition than in either 0.0 the 1- or 3-load conditions. No other differences were o 3 5 significant. In addition, the mean proportion of study Attenllonal Load words correctly identified was .993 and did not vary as a function of attentional load (p > .20). Thus, subjects Category-Cued Recall were able to identify virtually all study words while simul­ 0.3.,------, taneously maintaining the attentionalloads. The results ofthe memory tests are presented in Fig­ ure 1. For the category-exemplar production task, the de­ ... pendent measure is the amount of priming (the differ­ ~ 0.2 ii ence between the proportion of studied and nonstudied u exemplars produced). For category-cued recall, the de­ a:.. pendent measure is the proportion of studied items re­ called. As can be seen in the figure, attentionalload had a significant impact on performance in both tasks, but the details differ. In the category-exemplar production task, a substantial division ofattention is required before performance drops, at which point performance drops to approximately zero. In contrast, performance in the 0.0 category-cued recall task decreases with the most mild o 3 5 division of attention, but is still substantially above zero Attenllonal Load even when attention has been strongly divided. Figure 1. Summary of results: Mean priming (+SE) in the cat­ Statistical analyses confirm these impressions. The egory-exemplar production task and mean proportion of words priming scores from category-exemplar production and recalled (+SE) in the category-cued recall test as a function of at­ proportions correct from category-cued recall were sub­ tentional load at encoding. Note that baseline responding (pro­ mitted to separate analyses ofvariance, using attentional portion of nonstudied exemplars produced) for the category-ex­ emplar production task was .13. load as a within-subjects factor. Both analyses revealed an effect ofattentionalload [category-exemplar produc­ tion, F(3,69) = 4.40, MSe = 0.015, P < .007; category­ cued recall, F(3,69) = 11.49, MSe = O.0071,p < .001], did not significantly differ in the 1-and 3-load conditions. indicating that increased attentionalload at encoding de­ Additionally, t tests indicated that performance in each creased test performance on both memory tests. load conditionwas significantly abovezero (allps < .00I).4 For the category-exemplar production test, the Fisher­ The present results may be viewed as a resolution of Hayter test indicated that priming was significantly lower the conflicting results ofIsingrini et al. (1995) and Mulli­ in the 5-load condition than in any ofthe other conditions gan and Hartman (1996). Ifwe consider the O-Ioad condi­ and that no other pair ofconditions differed significantly. tion as a full-attention condition and the 3-load condition In addition, t tests revealed that priming was signifi­ as a moderately divided attention condition, the results cantly greater than zero in the 0-, 1-, and 3-load condi­ replicate Isingrini et al. Over this range, dividing atten­ tions (allps < .005) but not in the 5-load condition (p > tion produced a small and nonsignificant decrease on the .39). For the category-cued recall test, the Fisher-Hayter category-exemplar production task and a larger, signifi­ test indicated that performance was significantly greater cant, decrease on category-cued recall. If we again con­ in the O-Ioadcondition than in any other condition, that sider the O-Ioad condition as a full-attention condition performance was significantly lower in the 5-load con­ and the 5-load condition as a strongly divided-attention dition than in any other condition, and that performance condition, the results replicate Mulligan and Hartman: Di- ATTENTIONAL LOAD AND CONCEPTUAL PRIMING 15

Table 1 attention depends on the strength of the manipulation. Comparison of Mulligan and Hartman (Experiment 1, 1996) With a weak manipulation, the explicit test appears more Results With the 0- and S-Load Conditions dependent on attention, in the sense that the manipula­ Memory Test tion reduces explicit but not implicit test performance. Category-Exemplar Category-Cued With a stronger manipulation, the implicit test appears Production Recall more dependent on attentional resources, in the sense Mulligan and Hartman that implicit test performance (as measured by priming), Full attention .11 .23 Divided attention .02 .11 but not explicit test performance, is eliminated. Present study One appealingly simple account ofthe present results, oLoad .13 .26 based on the TAP framework, is that conceptual explicit 5 Load .02 .12 tests are simply more sensitive to variations in the amount ofprior conceptual processing than their implicit coun­ terparts. This account posits that dividing attention de­ viding attention produced large, significant decreases in creases the amount ofconceptual processing and that ex­ performance on both memory tests. Furthermore, divid­ picit tests are more sensitive to the small decreases that ing attention not only decreased priming, it eliminated accompany weaker divisions of attention. According to it. As can be seen in Table 1, the current within-subjects this account, conceptual implicit tests are not completely manipulation ofattention provides a very good quantita­ insensitive to variation in the amount ofprior conceptual tive replication ofthe between-subjects manipulation in processing, but rather require greater variation before an Mulligan and Hartman. effect is observed. Finally, strong divisions of attention The results from the O-Ioadcondition are also quanti­ (e.g., the 5-load condition) presumably lead to small tatively quite similar to those reported by Rappold and amounts of conceptual processing which go undetected Hashtroudi (1991) in a study using full-attention encoding. by the relatively insensitive implicit tests. At a general In Rappold and Hashtroudi's Experiment 1 (random con­ level, this account is consistent with the findings ofHintz­ dition), mean priming in category-exemplar production man and Hartry (1990), which suggest that old-new study was .10 and mean proportion recalled in category-cued status has substantially less impact (i.e., accounts for recall was .27. Because this experiment was so similar to much less ofthe variance) on the overall performance of the O-Ioad condition in terms of subjects and materials, implicit tests than of explicit tests (though it should be the similarity in results lends further credence to the noted that the Hintzman and Hartry study focused on a claim that the current within-subjects manipulation ofat­ perceptual implicit test, word-fragment completion). tention produces results consistent with between-subjects Although the sensitivity account provides a parsimo­ manipulations. nious explanation of the present data, it may be incom­ Finally, it should be noted that the present results sat­ plete when considered in the context ofthe amnesic lit­ isfy the retrieval-intentionality criterion (Schacter, Bow­ erature, cited earlier. The sensitivity account proposes ers, & Booker, 1989) in a way that might not have been that conceptual implicit and explicit tests differ along a established ifattention had been manipulated as a binary single dimension, sensitivity to prior conceptual process­ variable. If we consider only the first three load condi­ ing. This view would predict that if explicit memory is tions (0, I, and 3), we see a dissociation between implicit eliminated, then conceptual implicit memory would be and explicit versions ofa memory test. Ifthe implicit sub­ eliminated as well. The amnesic literature contains sug­ jects had surreptitiously used intentional retrieval strate­ gestive, though not definitive, data to the contrary. In a gies, we would expect decreases in the 1- and 3-load con­ study by Grafet al. (1985), amnesics demonstrated nor­ ditions relative to the O-Ioad condition, as was seen with mal priming on category-exemplar production coupled the explicit subjects. There is no such decrease across with near-zero explicit memory, as measured by free these load conditions. In fact, mean priming in the l-load recall. However, in this study, the overt memory cues condition is (nonsignificantly) higher than in the O-Ioad were not equated across the conceptual implicit and ex­ condition, a very unlikely outcome if the implicit sub­ plicit tests. Blaxton (1992) examined the performance of jects had engaged in intentional retrieval. memory-impaired patients in a study which did equate test cues across implicit (category-exemplar production) DISCUSSION and explicit (category-cued recall) tests. Blaxton found that, in some conditions, the memory-impaired subjects The current results resolve the discrepancies between exhibited normal conceptual priming coupled with im­ the Isingrini et al. (1995) and Mulligan and Hartman paired recall. In contrast to Grafet aI., Blaxton's memory­ (1996) studies, and have two primary implications. First, impaired subjects still exhibited a level of recall sub­ these results provide strong evidence that attention plays stantially above zero. However, it should be noted that a role in performance on implicit memory tests. Consis­ Blaxton's subjects were not nearly as impaired as Graf tent with the TAP view, implicit tests that have a strong et al.s subjects (as measured by the Wechsler Memory conceptual component are adversely affected by divided Scale). In sum, Grafet al.'s results appear to be at odds with attention at encoding. Second, the relative sensitivity of the sensitivity account, whereas Blaxton's results are very conceptual implicit and explicit tests to manipulations of consistent with this account, although neither of these 16 MULLIGAN

studies provides the optimal test ofthe sensitivity account. S. L., LADD, S. L., VAIDYA, C. J., & CHARI, A. (1995). Attelllion and A more rigorous test would examine the effects ofmod­ implicit memory for words. Manuscript submitted for publication. erate to profound amnesia on conceptual implicit and ex­ GRAF, P.,& MANDLER, G. (1984). Activation makes words more acces­ sible, but not necessarily more retrievable. Journal ofVerbal Learn­ plicit memory tests with equivalent overt memory cues. ing & VerbalBehavior, 23, 553-568. An alternative to the sensitivity account is based on GRAF, P, & MASSON, M. (1993). Implicit memory. Hillside, NJ: Ertbaum. the common assumption that spatiotemporal context plays GRAF, P., SHIMAMURA, A., & SQUIRE, L. (1985). Priming across modal­ a more important role in explicit than in implicit mem­ ities and priming across category levels: Extending the domain of preserved functions in amnesia. Journal ofExperimental Psychol­ ory tests (e.g., Humphreys, Bain, & Pike, 1989; Jacoby ogy: Learning, Memory, & Cognition, 11, 386-396. & Dallas, 1981; Jacoby & Hollingshead, 1990; Light & HAWLEY, K. J., & JOHNSTON, W. A. (1991). Long-term perceptual mem­ LaVoie, 1993; Schwartz, Rosse, & Deutsch, 1993; see, ory for briefly exposed words as a function ofawareness and atten­ also, Weldon et al., 1995). Under this view, conceptual ex­ tion. Journal ofExperimental Psychology: Human Perception & Per­ plicit tests are sensitive to both prior conceptual process­ formance, 17, 807-815. HINTZMAN, D. L., & HARTRY, A. L. (1990). Item effects in recognition ing and contextual encoding, whereas conceptual im­ and fragment completion: Contingency relations vary for different plicit tests are primarily sensitive to prior conceptual subsets of words. Journal ofExperimental Psychology: Learning, processing. This may explain why performance on ex­ Memory, & Cognition, 16,955-969. plicit tests is preserved even after performance on im­ HUMPHREYS, M. S., BAIN, J. D., & PIKE, R. (1989). Different ways to cue a coherent memory system: A theory for episodic, semantic, and plicit tests is reduced to zero; explicit memory tests are procedural tasks. Psychological Review, 96, 208-233. supported by more types of encodings. Although evi­ ISINGRINI, M., VAZOU, E, & LEROY, P. (1995). Dissociation between dence exists that both conceptual processing and con­ implicit and explicit memory tests: Effects of age and divided atten­ textual processing have attentional requirements (see tion on category exemplar generation and cued recall. Memory & Cowan, 1995), the relationship between the memorial ef­ Cognition, 23, 462-467. JACOBY, L. L. (199\). 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I. M. Craik (Eds.), Vari­ et aI., 1989). In the present study, we focus on the role ofautomatic en­ eties ofmemory and consciousness: Essays in honour ofEndel Tulving coding processes. (pp. 3-14). Hillsdale, NJ: Erlbaum. 2. Isingrini et al. (1995) also examined the effects ofage. The results Russo, R, & PARKIN, A. J. (1993). Age differences in implicit memory: discussed here specifically refer to the youngest ofIsingrini et al.'s four More apparent than real. Memory & Cognition, 21, 73-80. age groups (age range 20 to 35 years), although the pattern ofresults did SCHACTER, D. L. (1987). Implicit memory: History and current status. not differ across age groups. The youngest group bears the closest sim­ Journal ofExperimental Psychology: Learning, Memory, & Cogni­ ilarity to the subjects who participated in the Mulligan and Hartman tion, 13,501-518. (1996) study. SCHACTER, D. L., BOWERS, J., & BOOKER, 1. (1989). Intention, aware­ 3. The Fisher-Hayter test is used for post hoc mean comparisons be­ ness, and implicit memory: The retrieval intentionality criterion. In cause (I) unlike the Newman-Keuls test, it controls the familywise S. Lewandowsky, 1.C. Dunn, & K. Kirsner (Eds.), Implicit memory: Type I error rate at the nominal a level (.05 for this and subsequent Theoretical issues (pp. 47-65). Hillsdale, NJ: Erlbaum. tests); and (2) it is more powerful than the Tukey HSD test (see Kirk, SCHWARTZ, B. L., ROSSE, R. B., & DEUTSCH, S. I. (1993). Limits ofthe 1995, pp. 148-150). processing view in accounting for dissociations among memory mea­ 4. Base-rate guessing in the category-cued recall test may be mea­ sures in a clinical population. Memory & Cognition, 21, 63-72. sured with the number of intrusions in each load condition. Note that SEAMON, J., MARSH, R., & BRODY, N. (1984). Critical importance ofex­ this contrasts with the measurement ofpriming in the category-exemplar posure duration for attentive discrimination of stimuli that are not production task and with the measurement ofcategory-cued recall (Fig­ recognized. Journal ofExperimental Psychology: Learning, Mem­ ure I), both ofwhich are based on proportions. The mean number ofin­ ory, & Cognition, 10,465-469. trusions in the category-cued recall test (.54, .54, .42, and .67 for the 0-, SHIMAMURA, A. P. (1986). Priming effects in amnesia: Evidence for a 1-, 3-, and 5-load conditions, respectively) did not significantly vary dissociable memory function. Quarterly Journal ofExperimental over attentionalloads (F < I). An alternative measure ofaccuracy in re­ Psychology, 38A, 619-644. call tasks is the difference between the number ofold words recalled and SHIMAMURA, A. P. (1993). Neuropsychological analysis of implicit the number ofintrusions. Analyses ofthe alternative measure produced memory: History, methodology and theoretical interpretations. In the same results as those reported above. P. Graf & M. E. 1. Masson (Eds.), Implicit memory: New directions in cognition, development, and neuropsychology (pp. 265-285). Hills­ dale, NJ: Erlbaum. (Manuscript received December 21, 1995; SMITH, M. E., & OSCAR-BERMAN, M. (1990). Repetition priming of revision accepted for publication February 29, 1996.)