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Are nonconscious processes sufficient to produce false memories?
Consciousness and Cognition Consciousness and Cognition 13 (2004) 158–168 www.elsevier.com/locate/concog
Are nonconscious processes sufficient to produce false memories?q Abstract Seamon, Luo, and Gallo (1998) reported evidence that nonconscious processes could produce false recognition in a converging-associates task, whereby subjects falsely remember a nonstudied lure (e.g., sleep) after studying a list of related words (bed, rest, awake. . .). Zeelenberg, Plomp, and Raaijmakers (2003) failed to observe this false recognition effect when list word recognition was at chance. We critically evaluate the evidence for nonsconscious processing and report the results of a new experiment designed to overcome previous methodological limitations. Consistent with Seamon et al., we found that conscious activation of a related lure during study was not necessary for its subsequent recognition; consistent with Zeelenberg et al., we found no evidence for recognition of related lures under conditions where there was no memory for studied words. It is currently unknown whether conscious recollection of the studied items is necessary for false recognition or if nonconscious activation of the lure is sufficient. Ó 2003 Elsevier Inc. All rights reserved.
1. Introduction Seamon, Luo, and Gallo (1998) presented evidence that suggested that nonconscious processes were sufficient to cause false memories. Zeelenberg, Plomp, and Raaijmakers (2003) questioned this conclusion. In this commentary, we review the original findings and conclusions of Seamon et al. (1998), and we argue that the apparent shortcomings of those experiments, noted by Zeelenberg et al. (2003), are irrelevant to the debate. We then discuss an ambiguity in Zeelenberg et al.Õs findings, and also discuss a limitation of Seamon et al.Õs original methodology. Finally, we present new data from a modified task that avoided this limitation, and we summarize the present status of this research.
q Commentary on Zeelenberg, R., et al. (2003). Can false memories be created through nonconscious processes? Consciousness and Cognition, 12, 403–412.
1053-8100/$ - see front matter Ó 2003 Elsevier Inc. All rights reserved. doi:10.1016/j.concog.2003.09.001
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1.1. Seamon et al.’s (1998) experiments In the Deese, Roediger, and McDermott (DRM) false memory paradigm (Roediger & McDermott, 1995), subjects study lists of words (bed, rest, awake. . .) that are associated to nonstudied critical words (sleep). It has been shown repeatedly that subjects will often falsely recall and recognize the nonstudied critical words (hereafter the ‘‘related lures’’) on subsequent memory tests (see Roediger & Gallo, in press, for a recent review). Because these false memories are difficult to avoid strategically (e.g. Gallo, Roberts, & Seamon, 1997), Seamon et al. (1998) proposed that, in addition to conscious processes, part of the illusion can be caused by relatively automatic or nonconscious processes occurring during the study phase. To investigate this issue, Seamon et al. (1998) introduced conditions that should have minimized conscious processing at study. In particular, we compared standard rates of study presentation (i.e., approximately 2 s per list item) to rapid rates of study presentation (i.e., approximately 20 ms per list item). We reasoned that rapid list presentation (less than half a second for each 15 word list) should make conscious processing during the study phase extremely difficult. As an additional tax of conscious resources, we also had some subjects rehearse a sevendigit number while the study words were presented. Consider the most relevant conditions of Experiment 1, in which subjects were presented with list items under the rapid presentation conditions (20 ms) and with the concurrent memory load. Under these conditions, memory discrimination for list items was poor—hits were only 13% above the baserate false alarms to control lures (as a measure of discrimination, we used hits minus false alarms, which tends to be a more sensitive measure than dÕ or AÕ, see Snodgrass & Corwin, 1988).1 Nevertheless, discrimination for related lures (.23) was actually greater than discrimination for list items (.13), t [31] ¼ 3.43, p < :01, and this finding was replicated under similar conditions in Experiment 2. These basic results—significant false memory using rapid rates of presentation—have been replicated several times by different researchers (e.g. Buchanan, Brown, & Westbury, 1999; McDermott & Watson, 2001; Roediger, Balota, & Robinson, 2001a; Seamon et al., 2002b). For an additional analysis we divided subjects into two groups: good memory and poor memory (defined by a median-split on discrimination for list items). Subjects in the poor memory group were of particular interest because, on average, they did not significantly discriminate list words from control lures. When adjusted for baserate false alarms, false recognition in Experiment 1 was significantly greater than true recognition for this group (.20 vs .03), and a similar pattern was obtained in Experiment 2 (.14 vs .02). Thus, associatively based false recognition was present in these subjects, even when they showed no evidence of memory for list items. We took these findings as evidence for nonconscious processing during list presentation. In our conditions, the study lists were presented extremely rapidly, and available resources were reduced further with a concurrent memory load. Thus, there was not much opportunity to use deep or elaborate processing to encode the list words, let alone to use these words to generate the related lure through some sort of conscious associative process. The fact that recognition memory for list 1
For related lures, discrimination was defined as false alarms to related lures minus false alarms to the corresponding control lures (i.e., the critical lures from nonstudied lists). The difference between these two false alarm rates is the relatedness effect on false alarms, or the associatively based false recognition effect.
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items was severely impoverished, even nonsignificant in the poor memory group, was consistent with the idea that conscious processing of the list words was minimal. Even if subjects had consciously processed a few list items, and had used this knowledge to generate a related lure at study, it was unclear why false memory for this internally generated word would be greater than accurate memory for those list words that were actually perceived. For a more likely explanation, we discussed nonconscious activation of the related lure during the study phase, an idea owing to UnderwoodÕs (1965) implicit associative response and elaborated by Roediger and McDermott (1995). Presenting the studied associates briefly may have resulted in automatic activation of the related lure, a process akin to that found in the semantic priming literature (e.g., Balota, 1983; Marcel, 1983). If this activation summated, then activation of the related lure (which is the most highly associated word to the list words) might have been sufficient to cause false recognition, even when each individual list item was not processed enough to support later true recognition. Based on these and other results, we concluded that both conscious and nonconscious processes likely contribute to the DRM false recognition effect. 1.2. Zeelenberg et al.’s (2003) criticisms The motivation for Zeelenberg et al.Õs (2003) study was to revisit the method of stimulus presentation in Seamon et al. (1998). They argued that, although our computer was programmed to present stimuli for 20 ms, the actual presentation was potentially longer on some trials. We agree. Due to the monitorÕs refresh rate, and other imperfections that are inherent to any stimulus presentation device, there was certainly variance in the presentation rate of our stimuli. Thus, although the stimuli were presented very quickly, and our subjects (and we) mostly had the subjective experience of perceiving rapidly presented visual noise, it is unlikely that these subjects never perceived a list item for more than 20 ms. In fact, none of our theoretical conclusions were based on our use of a 20 ms presentation per se. Rather, the important point was that the stimulus presentation was very rapid. To be clear, we made no claims with regard to subliminal perception; such claims almost always elicit controversy (e.g., see Bernstein & WelchÕs (1991) criticism Jacoby & WhitehouseÕs (1989) claim of unconscious perception in a different false recognition paradigm). When we discussed the issue of ‘‘nonconscious processing,’’ we were referring to the conscious processing of the list items, and not the threshold for perception of those items. In fact, we felt that there could still be some minimal conscious processing of the list items even in the rapid presentation condition, which is why we used the concurrent memory load. The goal was not to eliminate the perception of list words, but to minimize the conscious processing of those list words, and thus to minimize the conscious generation of related lures at study. Even without the median-split analysis, it is obvious from the poor recognition performance that we achieved this goal. A second criticism of Seamon et al. (1998) was that we used a median-split analysis to provide evidence for nonconscious processing. Zeelenberg et al. (2003) suggested that this could have led to spurious results. This is a valid point, but it is unclear to us what kind of spurious effect would have lead to the observed pattern of results (memory for related lures but not for list items) across the two experiments that we reported, each with slightly different procedures. Further, even if such a factor could be identified, our findings before the median-split analysis—greater false recognition than true recognition under extremely impoverished study conditions—still needs to be explained.
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1.3. Zeelenberg et al.’s (2003) experiments To address these perceived concerns, Zeelenberg et al. (2003) conducted two experiments. They replicated some conditions of Seamon et al. (1998) using a more advanced computer monitor that presented stimuli with more exacting parameters. In their first experiment, they presented DRMtype lists for 2 s or 20 ms, using parameters similar to those of Seamon et al. Their second experiment was also similar, except that they added a 40 ms study condition and the subjects were told to make recognition decisions by following their intuition. In the 2 s condition, these researchers observed true and false recognition, comparable to prior research. However, in the rapid presentation conditions, they failed to find significant levels of true or false recognition, and they concluded that Seamon et al.Õs claim for nonconscious processes was premature. That conclusion might yet be warranted, but not on the basis of Zeelenberg et al.Õs data. Although their subjects did not show any memory for related lures in the rapid presentation conditions, they also did not show any memory for list items. This pattern is ambiguous. In the absence of any effect of rapid list presentation on subsequent memory (for list items or related lures), there is no evidence that their subjects even saw the lists during study. By using presentation rates that potentially were more consistent than in Seamon et al. (1998), these researchers may have presented the lists so fast that subjects in their study were, effectively, not presented with the lists. Given this possibility, it is impossible to know why Zeelenberg et al. failed to find a false recognition effect at rapid rates. One interpretation is that minimal processing of list words does not elicit nonconscious activation of the related lure. But an equally valid alternative is that minimal processing can lead to nonconscious activation (and subsequent false recognition), but that Zeelenberg et al.Õs presentation rates were so rapid that even the necessary minimal amount of processing did not occur, so that both conscious and nonconscious process were precluded. Their results cannot differentiate these alternatives. Despite the ambiguity of their results, we agree with these researchers that the Seamon et al. (1998) results are worthy of reconsideration. Understanding the role of nonconscious processes in creating false memories is important, and the claim that nonconscious processes are sufficient to create false memories needs to be carefully evaluated. 1.4. A new experiment We believe that there are two critical questions to answer. First, is conscious activation of the related lure during study necessary to cause subsequent false recognition (via a source monitoring error)? This is the question that was addressed in Seamon et al.Õs (1998) general discussion, and based on the results of two studies, we concluded that conscious activation of the related lure during list presentation was not necessary for false memory. Later in this paper we will report newer evidence that bolsters this conclusion. Second, and more debatable, is conscious recollection of the list words at test necessary to cause subsequent false recognition? Seamon et al.Õs results (1998) suggest that the answer is ‘‘no,’’ but Zeelenberg et al.Õs findings indicate that this question requires more consideration. In the Seamon et al. (1998) study, we only tested list items from Serial Positions 1, 8, and 10. This procedure was adopted from Roediger and McDermott (1995), and has been widely used in
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many studies involving the DRM task (including the Zeelenberg et al. experiments). A limitation of this procedure is that not all of the list items are tested. We addressed this limitation in our original article by reanalyzing our data from Experiment 1 using only the list items in the first position (which were thought to be the most memorable), and we again found no evidence for memory of list items. Nevertheless, the possibility remains that subjects may have seen and remembered a list item that was not in one of the three tested serial positions, and this may have resulted in false recognition of the related lure through conscious processes. For instance, a subject may have consciously recollected this studied item when given the related lure on the recognition test. This retrieved associate may have made the related lure more familiar, or it may have caused the subject to guess that the related lure also was studied, leading to false recognition. In either case, conscious processes at test would be necessary for false recognition. Another important consideration is that the lists were presented under intentional study conditions, and subjects knew that there would be a subsequent memory test. It is therefore possible that subjects spontaneously rehearsed the few list items that they perceived during the study phase. If they had detected the associative nature of the study lists, they may have thought of the related lure during this rehearsal process. Thus, conscious generation of the related lure before the test phase might have also contributed to subsequent false recognition. We devised a new task to investigate these issues more directly. Subjects were rapidly presented with DRM lists, one at a time, on the computer screen. After each list, the subjects wrote down any words that they recalled seeing from that list. In this way, we were able to measure whether they had consciously generated the related lure during study, and whether they consciously perceived any of the words in the list (and hence whether they could have recalled these list words on the final recognition test). Following the last list, the subjects were given a surprise forcedchoice recognition test. Because the subjects did not know that they would be given a final test until this time, there was little reason for them to rehearse the list items (and potentially generate the related lure) after the immediate recall of each list. This test contained a related lure and an unrelated control lure for each of the presented lists. The subjects were told to indicate which item had been studied, guessing if necessary (in fact, neither word in a test pair had been studied).2 The important question was whether they would be more likely to choose the related lure, and whether this would depend on the generation of the lure and/or conscious processing of the list words during study.
2. Method 2.1. Subjects Twenty-eight Harvard University undergraduates participated for course credit or payment of $10.
2
We used a forced-choice test because it avoids issues of response criterion, and chance is readily defined as 50%. Thus, this test is ideally suited to detect a recognition memory effect for related lures, although we would not necessarily consider this a ‘‘false’’ recognition effect (because subjects were forced to respond).
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2.2. Materials and design Thirty-six DRM lists were used, each containing 15 associates to a nonstudied critical word. Thirty-three of these lists were drawn from the Stadler, Roediger, and McDermott (1999) norms because they had elicited the highest levels of false recognition of the related lure (ranging from .45 to .84 in that study). Three additional lists were drawn from the Gallo and Roediger (2002) norms because they had elicited false recognition above .53 in that study. Words (or their derivatives) that were repeated within a list or across lists were replaced with the next available associate from the Nelson, McEvoy, and Schreiber (1999) word norms. The lists were randomly divided into two counterbalancing sets (A and B). Half of the subjects studied lists from Set A, and half studied Set B. The presentation order of the lists was held constant for each counterbalancing condition, but the order of the recognition test pairs was freshly randomized for each subject. There were 18 recognition test trials, one for each of the 18 study lists. Each recognition trial contained two items: a critical lure from a studied list, and a critical lure from a nonstudied list (one from list Set A and the other from a yoked list in Set B). Thus, across counterbalanced conditions, each item in a pair was the related lure equally often. Test pairs were presented side-by-side on the computer screen, and for each subject the related lure was tested in each position (left or right) equally often. List items were not presented on the recognition test because the immediate recall procedure was deemed to be a more sensitive measure of the conscious processing of those items than a final test. This procedure also avoided the possibility that the presentation of list items on the recognition test would activate the related lure (e.g. Marsh, McDermott, & Roediger, in press).3 2.3. Procedure Subjects were tested individually, after the completion of an unrelated memory experiment. They were told that they would be presented with word lists, very rapidly, in the center of the computer screen. All stimuli were presented on the same PowerMac computer using PsyScope software. Before each list, a ‘‘get ready’’ prompt appeared in the center of the computer screen, and the subjects pressed the space bar when they were ready to see the list. List items were presented in descending order of associative strength, using 55 point font, in black lowercase letters on a white background. Each list item was programmed for 20 ms presentation, although random fluctuations in this timing were inevitable (and not of concern). Each list item was preceded and followed by a pattern mask (&#&#&#&#&#&) for 80 ms that was sufficiently large (65 point font) to cover all of the letters of every stimulus. After each list was presented, the computer prompted the subjects to write down the words from that list on the corresponding line of their response sheet. They were told that ‘‘It is very 3 In Seamon et al. (1998), because we did test list items, activation of the related lure from these tested list items was a possibility. However, we also included the appropriate control lures on the recognition test (i.e. list items and critical lures from nonstudied lists), so that this type of test-based activation should have affected critical lures from studied and nonstudied lists to the same extent. By taking these baserate false alarms into account (via the subtraction technique), we had controlled for this factor (and all other factors that could have influenced false alarms, other than list presentation).
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difficult to read the words, but please try your best to write down any words that you saw. If you did not read any of the words, write ÔnoneÕ on the line.’’ The subjects were given as much time as possible to write down the words for each list, and when they were done they pressed the spacebar to advance the screen to the next ‘‘get ready’’ prompt (and they then initiated the next list with another spacebar press). Following the recall of the final list, the experimenter read the instructions for the surprise recognition test. The subjects were told that each test pair contained a studied word and a nonstudied word, and that they were to indicate whether the first or second word was the studied word (by pressing ‘‘1’’ or ‘‘2’’), guessing if necessary. After each response, the next test pair appeared on the screen. This entire procedure took approximately 10 min.
3. Results and discussion The immediate perception/recall data were liberally scored to ensure that any semantically similar variant of a list item (e.g., ‘‘measure’’ for ‘‘measuring’’) would be counted as a consciously perceived item. Even with this liberal criterion, subjects correctly reported list items at a very low rate of .07, for an average of about one word per list of 15 words. Confirming our earlier assumption that the first item of the list would be the easiest to perceive and remember (Seamon et al., 1998), recall of the first item was the highest, at .29 (i.e., on average, this item was recalled for 5 of the 18 lists). Recall of the remaining items, in order of position, was .14, .10, .04, .03, .08, .06, .05, .08, .04, .04, .05, .06, .05, and .03. False recall of the critical nonstudied associate occurred at a rate of .03, which was the same rate as studied items presented in some of the serial positions. Finally, the frequency of other noncritical intrusions was about 3 or 4 per subject, across all 18 lists, for an average rate of .21 per list. These intrusions were often misperceptions (e.g., ‘‘Einstein’’ for ‘‘stein’’). More important, for the surprise recognition test, the mean recognition of related lures was .58, a level greater than chance (.50), one sample t (27) ¼ 3.12, SEM ¼ .03, p < :01. This result replicates previous findings of memory for related lures following very rapid list presentation (e.g. McDermott & Watson, 2001; Seamon et al., 1998). We turn now to the two primary questions that were outlined in the introduction to this experiment. First, is conscious activation of the related lure during study necessary to cause subsequent recognition of that lure? We assume that subjects would have produced the related lure on the recall/perception test if they had consciously generated this word during study. We therefore reanalyzed the recognition data, after excluding those trials where the subject reported the related lure on the immediate perception/recall test (this occurred on 14 out of 504 trials). Even when these trials were excluded, the recognition of the related lure (.57) was still significantly greater than chance, t (27) ¼ 2.66, SEM ¼ .03, p < :01. Conscious activation of the related lure during study was not necessary to elicit subsequent recognition of this item. Second, is conscious recollection of the list words at test necessary to produce subsequent recognition of the related lure? To address this question, we analyzed the recognition data as a function of the number of corresponding list items that were perceived/recalled on the immediate test. We reasoned that the recollection of list words at test would depend on whether these items were actually seen (as reported on the immediate test). These data, shown in Fig. 1, indicate that
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Fig. 1. Mean recognition of the related lure (chance ¼ 50%) as function of the number of items recalled from the corresponding list on the immediate perception/recall test. Out of the total number of trials, the percentage of observations corresponding to each level of recall (0, 1, 2, and 3 or more items) is .44, .24, .17, and .16, respectively.
when no list items were perceived/recalled, the recognition of related lures was at chance (.49). But, as more list items were recalled, recognition steadily increased. On average, the recognition of related lures (.66) was greater than chance when at least one list item was perceived/recalled, t (26) ¼ 4.23, SEM ¼ .04, p < :01. (One subject was excluded from this analysis because this person did not report seeing any items from any of the study lists.) This finding suggests that the recognition of a related lure is dependent on the perception/recall of at least one studied item.
4. Conclusions The present results lead to two conclusions. First, consistent with Seamon et al. (1998), conscious activation of a related lure during study is not necessary for the its subsequent recognition. Significant recognition effects were obtained even on those trials where the subject did not (falsely) report seeing the related lure at study. The present experiment also takes this finding one step further. Because subjects were not told that they would be given a final memory test, it is unlikely that they would have rehearsed the study list (and potentially generated the related lure) at any point prior to the test. Thus, recognition of the related lure in the DRM paradigm does not have to be due to a source confusion, whereby prior thoughts of the lure are mistaken for its actual presentation. This result is consistent with recent work by Seamon et al. (2002a), who used more standard presentation rates and had subjects overtly rehearse the list items as they were presented during study. In that study, significant levels of false recognition of the related lure were found even when it had not been previously generated during study. Thus, using a very different methodology than that used here, Seamon et al.Õs (2002a) results also indicate that the related lure does not need to be consciously generated at study in order to obtain false recognition. This is not to conclude that conscious generation at study plays no role in the false memory effect—surely it does (for some relevant findings see Bredart, 2000; Gallo et al., 1997; Goodwin, Meissner, & Ericsson, 2001; and Multhaup & Conner, 2002)—but only that such conscious thoughts are not necessary for false recognition.
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The second conclusion from the present results is that, unlike the results observed with the poor memory subjects in Seamon et al.Õs (1998) experiments, there was no evidence for recognition of related lures under conditions where there was no demonstrated memory for studied items. On its own, this null result would be prone to the same ambiguity that we discussed in relation to the Zeelenberg et al. (2003) findings. However, our additional finding that recognition of related lures increased as a function of the number of list items reported on the immediate perception/recall test is informative. This finding indicates that there was some minimal processing of the list items under our conditions. Some lists were apparently processed more thoroughly than others, and this additional processing supported the subsequent recognition of the related lure. There are two possible interpretations of this last finding. One interpretation is that recognition of the related lure is dependent on the subsequent recollection of at least some of the presented list items. For instance, at test, subjects may have recalled that a related item was studied and this may have made the related lure more familiar. A second interpretation is that the additional processing of the list boosted nonconscious activation of the related lure, much like the automatic activation that results from briefly presented semantic primes (see Roediger, Balota, & Watson, 2001b, for a discussion), and this resulted in familiarity-based recognition, regardless of whether the list items were consciously recollected at test. These alternatives cannot be tested with the present dataset, and either of these processes may have been responsible for the significant false recognition effects reported by Seamon et al. (1998). Thus, we agree with Zeelenberg et al. that there is currently no unquestionable evidence that nonconscious processes alone are sufficient to cause these types of false memories. In contrast, there is sufficient evidence that the false recognition effect can be caused by ‘‘relatively’’ automatic processes. Converging evidence shows that false memory in the DRM task is affected less than true memory by a variety of variables, including forewarning instructions (Gallo et al., 1997; Gallo, Roediger, & McDermott, 2001), directed forgetting instructions (Kimball & Bjork, 2002; Seamon, Luo, Shulman, Toner, & Caglar, 2002c), the presence or absence of rehearsal during study (Seamon et al., 2002a), divided attention during study (Dodd & MacLeod, in press; Perez-Mata, Read, & Diges, 2002; Seamon et al., 2003), and speeded responding at test (Benjamin, 2001). As Seamon et al. (2003) recently noted, false memory in the DRM task has been reliably demonstrated under conditions where subjects have little opportunity for conscious processing (rapid presentation rates at study or rapid responding at test), little success at conscious control (forewarnings), or no success at conscious control (directed forgetting). Strictly speaking, it may be the case that conscious processes are always needed to elicit false recognition, but the required level is certainly minimal, and regardless, the false memory effect is driven by processes (conscious or not) that are quite resistant to conscious control. Given this interpretation, future research might best be aimed at understanding ‘‘how’’ conscious processes can affect false memories, as opposed to ‘‘whether’’ conscious processes are involved. In sum, the evidence is clear that conscious activation of the related lure is not necessary for false recognition, but the evidence is mixed as to whether conscious recollection of the list items is necessary. The current data provide additional insights into this last issue by showing that increased perception/recall of the list items increases false recognition. But exactly how this increased processing of the list items leads to increased false recognition is still unclear. Additional processing of the list items could drive false recognition through nonconscious processes (e.g.,
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automatic activation), conscious processes (e.g., guessing that the lure was presented because an associate was seen), or both.
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Seamon, J. G., Goodkind, M. S., Dumey, A. D., Dick, E., Aufseeser, M. A., Strickland, S. E., Woulfin, J. R., & Fung, N. S. (2003). If I didnÕt write it, why would I remember it? Effects of encoding, attention, and practice on accurate and false memory. Memory and Cognition, 31, 445–457. Seamon, J. G., Lee, I. A., Toner, S. K., Wheeler, R. H., Goodkind, M. S., & Birch, A. D. (2002a). Thinking of critical words during study is unnecessary for false memory in the Deese, Roediger, and McDermott procedure. Psychological Science, 13, 526–531. Seamon, J. G., Luo, C. R., & Gallo, D. A. (1998). Creating false memories of words with or without recognition of list items: Evidence for nonconscious processes. Psychological Science, 9, 20–26. Seamon, J. G., Luo, C. R., Schwartz, M. A., Jones, K. J., Lee, D. M., & Jones, S. J. (2002b). Repetition can have similar or different effects on accurate and false recognition. Journal of Memory and Language, 46, 323–340. Seamon, J. G., Luo, C. R., Shulman, E. P., Toner, S. K., & Caglar, S. (2002c). False memories are hard to inhibit: Differential effects of directed forgetting on accurate and false recall in the DRM procedure. Memory, 10, 225–237. Snodgrass, J. G., & Corwin, J. (1988). Pragmatics of measuring recognition memory: Applications to dementia and amnesia. Journal of Experimental Psychology: General, 117, 34–50. Stadler, M. A., Roediger, H. L., III, & McDermott, K. B. (1999). Norms for word lists that create false memories. Memory and Cognition, 27, 494–500. Underwood, B. J. (1965). False recognition produced by implicit verbal responses. Journal of Experimental Psychology, 70, 122–129. Zeelenberg, R., Plomp, G., & Raaijmakers, J. G. W. (2003). Can false memories be created through nonconscious processes? Consciousness and Cognition, 12, 403–412.
David A. Gallo Psychology Department Harvard University Cambridge, MA 02138 USA E-mail address: [email protected] John G. Seamon Psychology Department Wesleyan University Middletown, CT 06459 USA
Are nonconscious processes sufficient to produce false memories?q Abstract Seamon, Luo, and Gallo (1998) reported evidence that nonconscious processes could produce false recognition in a converging-associates task, whereby subjects falsely remember a nonstudied lure (e.g., sleep) after studying a list of related words (bed, rest, awake. . .). Zeelenberg, Plomp, and Raaijmakers (2003) failed to observe this false recognition effect when list word recognition was at chance. We critically evaluate the evidence for nonsconscious processing and report the results of a new experiment designed to overcome previous methodological limitations. Consistent with Seamon et al., we found that conscious activation of a related lure during study was not necessary for its subsequent recognition; consistent with Zeelenberg et al., we found no evidence for recognition of related lures under conditions where there was no memory for studied words. It is currently unknown whether conscious recollection of the studied items is necessary for false recognition or if nonconscious activation of the lure is sufficient. Ó 2003 Elsevier Inc. All rights reserved.
1. Introduction Seamon, Luo, and Gallo (1998) presented evidence that suggested that nonconscious processes were sufficient to cause false memories. Zeelenberg, Plomp, and Raaijmakers (2003) questioned this conclusion. In this commentary, we review the original findings and conclusions of Seamon et al. (1998), and we argue that the apparent shortcomings of those experiments, noted by Zeelenberg et al. (2003), are irrelevant to the debate. We then discuss an ambiguity in Zeelenberg et al.Õs findings, and also discuss a limitation of Seamon et al.Õs original methodology. Finally, we present new data from a modified task that avoided this limitation, and we summarize the present status of this research.
q Commentary on Zeelenberg, R., et al. (2003). Can false memories be created through nonconscious processes? Consciousness and Cognition, 12, 403–412.
1053-8100/$ - see front matter Ó 2003 Elsevier Inc. All rights reserved. doi:10.1016/j.concog.2003.09.001
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1.1. Seamon et al.’s (1998) experiments In the Deese, Roediger, and McDermott (DRM) false memory paradigm (Roediger & McDermott, 1995), subjects study lists of words (bed, rest, awake. . .) that are associated to nonstudied critical words (sleep). It has been shown repeatedly that subjects will often falsely recall and recognize the nonstudied critical words (hereafter the ‘‘related lures’’) on subsequent memory tests (see Roediger & Gallo, in press, for a recent review). Because these false memories are difficult to avoid strategically (e.g. Gallo, Roberts, & Seamon, 1997), Seamon et al. (1998) proposed that, in addition to conscious processes, part of the illusion can be caused by relatively automatic or nonconscious processes occurring during the study phase. To investigate this issue, Seamon et al. (1998) introduced conditions that should have minimized conscious processing at study. In particular, we compared standard rates of study presentation (i.e., approximately 2 s per list item) to rapid rates of study presentation (i.e., approximately 20 ms per list item). We reasoned that rapid list presentation (less than half a second for each 15 word list) should make conscious processing during the study phase extremely difficult. As an additional tax of conscious resources, we also had some subjects rehearse a sevendigit number while the study words were presented. Consider the most relevant conditions of Experiment 1, in which subjects were presented with list items under the rapid presentation conditions (20 ms) and with the concurrent memory load. Under these conditions, memory discrimination for list items was poor—hits were only 13% above the baserate false alarms to control lures (as a measure of discrimination, we used hits minus false alarms, which tends to be a more sensitive measure than dÕ or AÕ, see Snodgrass & Corwin, 1988).1 Nevertheless, discrimination for related lures (.23) was actually greater than discrimination for list items (.13), t [31] ¼ 3.43, p < :01, and this finding was replicated under similar conditions in Experiment 2. These basic results—significant false memory using rapid rates of presentation—have been replicated several times by different researchers (e.g. Buchanan, Brown, & Westbury, 1999; McDermott & Watson, 2001; Roediger, Balota, & Robinson, 2001a; Seamon et al., 2002b). For an additional analysis we divided subjects into two groups: good memory and poor memory (defined by a median-split on discrimination for list items). Subjects in the poor memory group were of particular interest because, on average, they did not significantly discriminate list words from control lures. When adjusted for baserate false alarms, false recognition in Experiment 1 was significantly greater than true recognition for this group (.20 vs .03), and a similar pattern was obtained in Experiment 2 (.14 vs .02). Thus, associatively based false recognition was present in these subjects, even when they showed no evidence of memory for list items. We took these findings as evidence for nonconscious processing during list presentation. In our conditions, the study lists were presented extremely rapidly, and available resources were reduced further with a concurrent memory load. Thus, there was not much opportunity to use deep or elaborate processing to encode the list words, let alone to use these words to generate the related lure through some sort of conscious associative process. The fact that recognition memory for list 1
For related lures, discrimination was defined as false alarms to related lures minus false alarms to the corresponding control lures (i.e., the critical lures from nonstudied lists). The difference between these two false alarm rates is the relatedness effect on false alarms, or the associatively based false recognition effect.
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items was severely impoverished, even nonsignificant in the poor memory group, was consistent with the idea that conscious processing of the list words was minimal. Even if subjects had consciously processed a few list items, and had used this knowledge to generate a related lure at study, it was unclear why false memory for this internally generated word would be greater than accurate memory for those list words that were actually perceived. For a more likely explanation, we discussed nonconscious activation of the related lure during the study phase, an idea owing to UnderwoodÕs (1965) implicit associative response and elaborated by Roediger and McDermott (1995). Presenting the studied associates briefly may have resulted in automatic activation of the related lure, a process akin to that found in the semantic priming literature (e.g., Balota, 1983; Marcel, 1983). If this activation summated, then activation of the related lure (which is the most highly associated word to the list words) might have been sufficient to cause false recognition, even when each individual list item was not processed enough to support later true recognition. Based on these and other results, we concluded that both conscious and nonconscious processes likely contribute to the DRM false recognition effect. 1.2. Zeelenberg et al.’s (2003) criticisms The motivation for Zeelenberg et al.Õs (2003) study was to revisit the method of stimulus presentation in Seamon et al. (1998). They argued that, although our computer was programmed to present stimuli for 20 ms, the actual presentation was potentially longer on some trials. We agree. Due to the monitorÕs refresh rate, and other imperfections that are inherent to any stimulus presentation device, there was certainly variance in the presentation rate of our stimuli. Thus, although the stimuli were presented very quickly, and our subjects (and we) mostly had the subjective experience of perceiving rapidly presented visual noise, it is unlikely that these subjects never perceived a list item for more than 20 ms. In fact, none of our theoretical conclusions were based on our use of a 20 ms presentation per se. Rather, the important point was that the stimulus presentation was very rapid. To be clear, we made no claims with regard to subliminal perception; such claims almost always elicit controversy (e.g., see Bernstein & WelchÕs (1991) criticism Jacoby & WhitehouseÕs (1989) claim of unconscious perception in a different false recognition paradigm). When we discussed the issue of ‘‘nonconscious processing,’’ we were referring to the conscious processing of the list items, and not the threshold for perception of those items. In fact, we felt that there could still be some minimal conscious processing of the list items even in the rapid presentation condition, which is why we used the concurrent memory load. The goal was not to eliminate the perception of list words, but to minimize the conscious processing of those list words, and thus to minimize the conscious generation of related lures at study. Even without the median-split analysis, it is obvious from the poor recognition performance that we achieved this goal. A second criticism of Seamon et al. (1998) was that we used a median-split analysis to provide evidence for nonconscious processing. Zeelenberg et al. (2003) suggested that this could have led to spurious results. This is a valid point, but it is unclear to us what kind of spurious effect would have lead to the observed pattern of results (memory for related lures but not for list items) across the two experiments that we reported, each with slightly different procedures. Further, even if such a factor could be identified, our findings before the median-split analysis—greater false recognition than true recognition under extremely impoverished study conditions—still needs to be explained.
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1.3. Zeelenberg et al.’s (2003) experiments To address these perceived concerns, Zeelenberg et al. (2003) conducted two experiments. They replicated some conditions of Seamon et al. (1998) using a more advanced computer monitor that presented stimuli with more exacting parameters. In their first experiment, they presented DRMtype lists for 2 s or 20 ms, using parameters similar to those of Seamon et al. Their second experiment was also similar, except that they added a 40 ms study condition and the subjects were told to make recognition decisions by following their intuition. In the 2 s condition, these researchers observed true and false recognition, comparable to prior research. However, in the rapid presentation conditions, they failed to find significant levels of true or false recognition, and they concluded that Seamon et al.Õs claim for nonconscious processes was premature. That conclusion might yet be warranted, but not on the basis of Zeelenberg et al.Õs data. Although their subjects did not show any memory for related lures in the rapid presentation conditions, they also did not show any memory for list items. This pattern is ambiguous. In the absence of any effect of rapid list presentation on subsequent memory (for list items or related lures), there is no evidence that their subjects even saw the lists during study. By using presentation rates that potentially were more consistent than in Seamon et al. (1998), these researchers may have presented the lists so fast that subjects in their study were, effectively, not presented with the lists. Given this possibility, it is impossible to know why Zeelenberg et al. failed to find a false recognition effect at rapid rates. One interpretation is that minimal processing of list words does not elicit nonconscious activation of the related lure. But an equally valid alternative is that minimal processing can lead to nonconscious activation (and subsequent false recognition), but that Zeelenberg et al.Õs presentation rates were so rapid that even the necessary minimal amount of processing did not occur, so that both conscious and nonconscious process were precluded. Their results cannot differentiate these alternatives. Despite the ambiguity of their results, we agree with these researchers that the Seamon et al. (1998) results are worthy of reconsideration. Understanding the role of nonconscious processes in creating false memories is important, and the claim that nonconscious processes are sufficient to create false memories needs to be carefully evaluated. 1.4. A new experiment We believe that there are two critical questions to answer. First, is conscious activation of the related lure during study necessary to cause subsequent false recognition (via a source monitoring error)? This is the question that was addressed in Seamon et al.Õs (1998) general discussion, and based on the results of two studies, we concluded that conscious activation of the related lure during list presentation was not necessary for false memory. Later in this paper we will report newer evidence that bolsters this conclusion. Second, and more debatable, is conscious recollection of the list words at test necessary to cause subsequent false recognition? Seamon et al.Õs results (1998) suggest that the answer is ‘‘no,’’ but Zeelenberg et al.Õs findings indicate that this question requires more consideration. In the Seamon et al. (1998) study, we only tested list items from Serial Positions 1, 8, and 10. This procedure was adopted from Roediger and McDermott (1995), and has been widely used in
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many studies involving the DRM task (including the Zeelenberg et al. experiments). A limitation of this procedure is that not all of the list items are tested. We addressed this limitation in our original article by reanalyzing our data from Experiment 1 using only the list items in the first position (which were thought to be the most memorable), and we again found no evidence for memory of list items. Nevertheless, the possibility remains that subjects may have seen and remembered a list item that was not in one of the three tested serial positions, and this may have resulted in false recognition of the related lure through conscious processes. For instance, a subject may have consciously recollected this studied item when given the related lure on the recognition test. This retrieved associate may have made the related lure more familiar, or it may have caused the subject to guess that the related lure also was studied, leading to false recognition. In either case, conscious processes at test would be necessary for false recognition. Another important consideration is that the lists were presented under intentional study conditions, and subjects knew that there would be a subsequent memory test. It is therefore possible that subjects spontaneously rehearsed the few list items that they perceived during the study phase. If they had detected the associative nature of the study lists, they may have thought of the related lure during this rehearsal process. Thus, conscious generation of the related lure before the test phase might have also contributed to subsequent false recognition. We devised a new task to investigate these issues more directly. Subjects were rapidly presented with DRM lists, one at a time, on the computer screen. After each list, the subjects wrote down any words that they recalled seeing from that list. In this way, we were able to measure whether they had consciously generated the related lure during study, and whether they consciously perceived any of the words in the list (and hence whether they could have recalled these list words on the final recognition test). Following the last list, the subjects were given a surprise forcedchoice recognition test. Because the subjects did not know that they would be given a final test until this time, there was little reason for them to rehearse the list items (and potentially generate the related lure) after the immediate recall of each list. This test contained a related lure and an unrelated control lure for each of the presented lists. The subjects were told to indicate which item had been studied, guessing if necessary (in fact, neither word in a test pair had been studied).2 The important question was whether they would be more likely to choose the related lure, and whether this would depend on the generation of the lure and/or conscious processing of the list words during study.
2. Method 2.1. Subjects Twenty-eight Harvard University undergraduates participated for course credit or payment of $10.
2
We used a forced-choice test because it avoids issues of response criterion, and chance is readily defined as 50%. Thus, this test is ideally suited to detect a recognition memory effect for related lures, although we would not necessarily consider this a ‘‘false’’ recognition effect (because subjects were forced to respond).
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2.2. Materials and design Thirty-six DRM lists were used, each containing 15 associates to a nonstudied critical word. Thirty-three of these lists were drawn from the Stadler, Roediger, and McDermott (1999) norms because they had elicited the highest levels of false recognition of the related lure (ranging from .45 to .84 in that study). Three additional lists were drawn from the Gallo and Roediger (2002) norms because they had elicited false recognition above .53 in that study. Words (or their derivatives) that were repeated within a list or across lists were replaced with the next available associate from the Nelson, McEvoy, and Schreiber (1999) word norms. The lists were randomly divided into two counterbalancing sets (A and B). Half of the subjects studied lists from Set A, and half studied Set B. The presentation order of the lists was held constant for each counterbalancing condition, but the order of the recognition test pairs was freshly randomized for each subject. There were 18 recognition test trials, one for each of the 18 study lists. Each recognition trial contained two items: a critical lure from a studied list, and a critical lure from a nonstudied list (one from list Set A and the other from a yoked list in Set B). Thus, across counterbalanced conditions, each item in a pair was the related lure equally often. Test pairs were presented side-by-side on the computer screen, and for each subject the related lure was tested in each position (left or right) equally often. List items were not presented on the recognition test because the immediate recall procedure was deemed to be a more sensitive measure of the conscious processing of those items than a final test. This procedure also avoided the possibility that the presentation of list items on the recognition test would activate the related lure (e.g. Marsh, McDermott, & Roediger, in press).3 2.3. Procedure Subjects were tested individually, after the completion of an unrelated memory experiment. They were told that they would be presented with word lists, very rapidly, in the center of the computer screen. All stimuli were presented on the same PowerMac computer using PsyScope software. Before each list, a ‘‘get ready’’ prompt appeared in the center of the computer screen, and the subjects pressed the space bar when they were ready to see the list. List items were presented in descending order of associative strength, using 55 point font, in black lowercase letters on a white background. Each list item was programmed for 20 ms presentation, although random fluctuations in this timing were inevitable (and not of concern). Each list item was preceded and followed by a pattern mask (&#&#&#&#&#&) for 80 ms that was sufficiently large (65 point font) to cover all of the letters of every stimulus. After each list was presented, the computer prompted the subjects to write down the words from that list on the corresponding line of their response sheet. They were told that ‘‘It is very 3 In Seamon et al. (1998), because we did test list items, activation of the related lure from these tested list items was a possibility. However, we also included the appropriate control lures on the recognition test (i.e. list items and critical lures from nonstudied lists), so that this type of test-based activation should have affected critical lures from studied and nonstudied lists to the same extent. By taking these baserate false alarms into account (via the subtraction technique), we had controlled for this factor (and all other factors that could have influenced false alarms, other than list presentation).
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difficult to read the words, but please try your best to write down any words that you saw. If you did not read any of the words, write ÔnoneÕ on the line.’’ The subjects were given as much time as possible to write down the words for each list, and when they were done they pressed the spacebar to advance the screen to the next ‘‘get ready’’ prompt (and they then initiated the next list with another spacebar press). Following the recall of the final list, the experimenter read the instructions for the surprise recognition test. The subjects were told that each test pair contained a studied word and a nonstudied word, and that they were to indicate whether the first or second word was the studied word (by pressing ‘‘1’’ or ‘‘2’’), guessing if necessary. After each response, the next test pair appeared on the screen. This entire procedure took approximately 10 min.
3. Results and discussion The immediate perception/recall data were liberally scored to ensure that any semantically similar variant of a list item (e.g., ‘‘measure’’ for ‘‘measuring’’) would be counted as a consciously perceived item. Even with this liberal criterion, subjects correctly reported list items at a very low rate of .07, for an average of about one word per list of 15 words. Confirming our earlier assumption that the first item of the list would be the easiest to perceive and remember (Seamon et al., 1998), recall of the first item was the highest, at .29 (i.e., on average, this item was recalled for 5 of the 18 lists). Recall of the remaining items, in order of position, was .14, .10, .04, .03, .08, .06, .05, .08, .04, .04, .05, .06, .05, and .03. False recall of the critical nonstudied associate occurred at a rate of .03, which was the same rate as studied items presented in some of the serial positions. Finally, the frequency of other noncritical intrusions was about 3 or 4 per subject, across all 18 lists, for an average rate of .21 per list. These intrusions were often misperceptions (e.g., ‘‘Einstein’’ for ‘‘stein’’). More important, for the surprise recognition test, the mean recognition of related lures was .58, a level greater than chance (.50), one sample t (27) ¼ 3.12, SEM ¼ .03, p < :01. This result replicates previous findings of memory for related lures following very rapid list presentation (e.g. McDermott & Watson, 2001; Seamon et al., 1998). We turn now to the two primary questions that were outlined in the introduction to this experiment. First, is conscious activation of the related lure during study necessary to cause subsequent recognition of that lure? We assume that subjects would have produced the related lure on the recall/perception test if they had consciously generated this word during study. We therefore reanalyzed the recognition data, after excluding those trials where the subject reported the related lure on the immediate perception/recall test (this occurred on 14 out of 504 trials). Even when these trials were excluded, the recognition of the related lure (.57) was still significantly greater than chance, t (27) ¼ 2.66, SEM ¼ .03, p < :01. Conscious activation of the related lure during study was not necessary to elicit subsequent recognition of this item. Second, is conscious recollection of the list words at test necessary to produce subsequent recognition of the related lure? To address this question, we analyzed the recognition data as a function of the number of corresponding list items that were perceived/recalled on the immediate test. We reasoned that the recollection of list words at test would depend on whether these items were actually seen (as reported on the immediate test). These data, shown in Fig. 1, indicate that
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Fig. 1. Mean recognition of the related lure (chance ¼ 50%) as function of the number of items recalled from the corresponding list on the immediate perception/recall test. Out of the total number of trials, the percentage of observations corresponding to each level of recall (0, 1, 2, and 3 or more items) is .44, .24, .17, and .16, respectively.
when no list items were perceived/recalled, the recognition of related lures was at chance (.49). But, as more list items were recalled, recognition steadily increased. On average, the recognition of related lures (.66) was greater than chance when at least one list item was perceived/recalled, t (26) ¼ 4.23, SEM ¼ .04, p < :01. (One subject was excluded from this analysis because this person did not report seeing any items from any of the study lists.) This finding suggests that the recognition of a related lure is dependent on the perception/recall of at least one studied item.
4. Conclusions The present results lead to two conclusions. First, consistent with Seamon et al. (1998), conscious activation of a related lure during study is not necessary for the its subsequent recognition. Significant recognition effects were obtained even on those trials where the subject did not (falsely) report seeing the related lure at study. The present experiment also takes this finding one step further. Because subjects were not told that they would be given a final memory test, it is unlikely that they would have rehearsed the study list (and potentially generated the related lure) at any point prior to the test. Thus, recognition of the related lure in the DRM paradigm does not have to be due to a source confusion, whereby prior thoughts of the lure are mistaken for its actual presentation. This result is consistent with recent work by Seamon et al. (2002a), who used more standard presentation rates and had subjects overtly rehearse the list items as they were presented during study. In that study, significant levels of false recognition of the related lure were found even when it had not been previously generated during study. Thus, using a very different methodology than that used here, Seamon et al.Õs (2002a) results also indicate that the related lure does not need to be consciously generated at study in order to obtain false recognition. This is not to conclude that conscious generation at study plays no role in the false memory effect—surely it does (for some relevant findings see Bredart, 2000; Gallo et al., 1997; Goodwin, Meissner, & Ericsson, 2001; and Multhaup & Conner, 2002)—but only that such conscious thoughts are not necessary for false recognition.
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The second conclusion from the present results is that, unlike the results observed with the poor memory subjects in Seamon et al.Õs (1998) experiments, there was no evidence for recognition of related lures under conditions where there was no demonstrated memory for studied items. On its own, this null result would be prone to the same ambiguity that we discussed in relation to the Zeelenberg et al. (2003) findings. However, our additional finding that recognition of related lures increased as a function of the number of list items reported on the immediate perception/recall test is informative. This finding indicates that there was some minimal processing of the list items under our conditions. Some lists were apparently processed more thoroughly than others, and this additional processing supported the subsequent recognition of the related lure. There are two possible interpretations of this last finding. One interpretation is that recognition of the related lure is dependent on the subsequent recollection of at least some of the presented list items. For instance, at test, subjects may have recalled that a related item was studied and this may have made the related lure more familiar. A second interpretation is that the additional processing of the list boosted nonconscious activation of the related lure, much like the automatic activation that results from briefly presented semantic primes (see Roediger, Balota, & Watson, 2001b, for a discussion), and this resulted in familiarity-based recognition, regardless of whether the list items were consciously recollected at test. These alternatives cannot be tested with the present dataset, and either of these processes may have been responsible for the significant false recognition effects reported by Seamon et al. (1998). Thus, we agree with Zeelenberg et al. that there is currently no unquestionable evidence that nonconscious processes alone are sufficient to cause these types of false memories. In contrast, there is sufficient evidence that the false recognition effect can be caused by ‘‘relatively’’ automatic processes. Converging evidence shows that false memory in the DRM task is affected less than true memory by a variety of variables, including forewarning instructions (Gallo et al., 1997; Gallo, Roediger, & McDermott, 2001), directed forgetting instructions (Kimball & Bjork, 2002; Seamon, Luo, Shulman, Toner, & Caglar, 2002c), the presence or absence of rehearsal during study (Seamon et al., 2002a), divided attention during study (Dodd & MacLeod, in press; Perez-Mata, Read, & Diges, 2002; Seamon et al., 2003), and speeded responding at test (Benjamin, 2001). As Seamon et al. (2003) recently noted, false memory in the DRM task has been reliably demonstrated under conditions where subjects have little opportunity for conscious processing (rapid presentation rates at study or rapid responding at test), little success at conscious control (forewarnings), or no success at conscious control (directed forgetting). Strictly speaking, it may be the case that conscious processes are always needed to elicit false recognition, but the required level is certainly minimal, and regardless, the false memory effect is driven by processes (conscious or not) that are quite resistant to conscious control. Given this interpretation, future research might best be aimed at understanding ‘‘how’’ conscious processes can affect false memories, as opposed to ‘‘whether’’ conscious processes are involved. In sum, the evidence is clear that conscious activation of the related lure is not necessary for false recognition, but the evidence is mixed as to whether conscious recollection of the list items is necessary. The current data provide additional insights into this last issue by showing that increased perception/recall of the list items increases false recognition. But exactly how this increased processing of the list items leads to increased false recognition is still unclear. Additional processing of the list items could drive false recognition through nonconscious processes (e.g.,
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automatic activation), conscious processes (e.g., guessing that the lure was presented because an associate was seen), or both.
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David A. Gallo Psychology Department Harvard University Cambridge, MA 02138 USA E-mail address: [email protected] John G. Seamon Psychology Department Wesleyan University Middletown, CT 06459 USA