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Misattribution, False Recognition and the Sins of Memory

Misattribution, False Recognition and the Sins of Memory

doi 10.1098/rstb.2001.0938

Misattribution, false recognition and the sins of

Daniel L. Schacter* and Chad S. Dodson Department of Psychology, Harvard University, 33 Kirkland Street, Cambridge, MA, USA

Memory is sometimes a troublemaker. Schacter has classi¢ed memory's transgressions into seven fundamental `sins': transience, absent-mindedness, blocking, misattribution, , bias and persistence. This paper focuses on one memory sin, misattribution, that is implicated in false or illusory recognition of episodes that never occurred. We present data from cognitive, neuropsychological and studies that illuminate aspects of misattribution and false recognition. We ¢rst discuss cognitive examining possible mechanisms of misattribution associated with false recognition. We also consider ways in which false recognition can be reduced or avoided, focusing in particular on the role of distinctive information. We next turn to neuropsychological research concerning patients with and Alzheimer's disease that reveals conditions under which such patients are less susceptible to false recognition than are healthy controls, thus providing clues about the mechanisms that drive false recognition. We then consider neuroimaging studies concerned with the neural correlates of true and false recognition, examining when the two forms of recognition can and cannot be distinguished on the basis of brain activity. Finally, we argue that even though misattribution and other memory sins are annoying and even dangerous, they can also be viewed as by-products of adaptive features of memory. Keywords: misattribution; false recognition; neuroimaging; functional magnetic resonance imaging; amnesia;

Schacter (1999, 2001) recently classi¢ed the misdeeds 1. INTRODUCTION of memory into seven basic `sins': transience, absent- Memory plays an important role in numerous aspects of mindedness, blocking, misattribution, suggestibility, bias everyday life, allowing us to recollect past experiences and persistence. The ¢rst three sins involve types of and learn new facts, navigate our environments, and forgetting. Transience involves decreasing accessibility of remember what we need to do in the future. But memory information over time; absent-mindedness entails inatten- can also fail us and sometimes fool us: we may forget or tive or shallow processing that contributes to weak distort past experiences, and even claim to remember of ongoing events or forgetting to do things in events that never occurred. These imperfections can the future; and blocking refers to the temporary inaccessi- provide insights into how memory works, and are there- bility of information that is stored in memory. The next fore studied intensively by many researchers. But they can three sins all involve distortion or inaccuracy. Misattribu- also have serious consequences for many people in our tion involves attributing a recollection or idea to the society. Forgetfulness that turns into Alzheimer's disease wrong source; suggestibility refers to memories that are (AD), for instance, has profound e¡ects on patients and implanted at the time of retrieval; and bias involves retro- their families (Pierce 2000). During the 1990s, issues spective distortions and unconscious in£uences that are concerning the accuracy of memories of childhood related to current knowledge and beliefs. The seventh and trauma recovered during psychotherapy led to a bitter ¢nal sin, persistence, refers to intrusive memories that we controversy that divided professionals and destroyed cannot forget, even though we wish that we could. families (e.g. Conway 1997; Lindsay & Read 1994; Loftus resemble in some respects 1993; Pendergrast 1995; Schacter 1996). Similar concerns the ancient seven deadly sins (pride, anger, envy, greed, arose in cases of preschool children who, as a result of gluttony, lust and sloth). Both types of sins occur often in suggestive questioning,`remembered' abusive events at the our daily lives. Moreover, we can view the ancient sins as hands of teachers and othersödespite an absence of exaggerations of adaptive human traits that may be objective evidence that such events ever occurred (Bjork- necessary for survival. Similarly, memory's sins can be lund 2000; Ceci & Bruck 1995; Ceci & Friedman 2000). conceptualized as by-products of adaptive features of And cases in which DNA testing has documented memory, rather than as £aws in system design or errors wrongful imprisonment almost always involve some type made by Mother Nature during (Schacter 1999, of faulty (e.g. Wells et al. 1998). 2001; see also Anderson & Schooler 1991; Bjork & Bjork 1988). Given the focus of this issue on , it is *Author for correspondence ([email protected]). perhaps worth noting that all of the sins described by

Phil.Trans. R. Soc. Lond. B(2001)356, 1385^1393 1385 & 2001 The Royal Society 1386 D. L. Schacter and C. S. Dodson Misattribution and false recognition

Schacter (1999, 2001) involve episodic memory, although , night, blanket, doze, slumber, snore, pillow, they may involve other forms of memory as well. For peace, yawn and drowsy) that are related to a non- instance, a prominent example of the sin of blocking is presented lure (e.g. sleep). On a subsequent old^ the `tip-of-the ' state, where people cannot produce new recognition test containing studied (e.g. tired, a word or name even though they feel that they are on dream), new words that are unrelated to the study list the verge of recovering it (for reviews, see Brown 1991; items (e.g. butter) and new words that are related to the Schwartz 1999). Although tip-of-the-tongue states study list items (e.g. sleep), participants frequently claim primarily involve , blocking can also that they previously studied the related lure words. In occur in episodic memory (Roediger & Neely 1982; many instances, false recognition of the related lure words Schacter 1999, 2001). is indistinguishable from the true recognition rate of In this paper we consider evidence and ideas studied words (e.g. Dodson & Schacter 2000; Mather et al. pertaining to one of the major sins of episodic memory: 1997; Norman & Schacter 1997; Payne et al. 1996; the sin of misattribution. Misattribution of memories to Roediger & McDermott 1995; Schacter et al. 1996a; cf. the wrong source is a common form of memory distor- Miller & Wolford 1999; Roediger & McDermott 1999). tion, both in the laboratory (Dodson & Schacter 2001a; Although the mechanisms underlying this robust false Jacoby et al. 1989; Johnson et al. 1993; Schacter et al. recognition e¡ect are not yet fully understood, two main 1998a), and in everyday life. For instance, after the tragic sources of the e¡ect have been considered. First, false 1995 bombing of an o¤ce building in Oklahoma City, recognition could be the result of `implicit associative law enforcement o¤cers quickly apprehended a suspect responses' (Underwood 1965) that occur when partici- called `John Doe 1', Timothy McVeigh, who was even- pants are exposed to lists of semantic associates during tually convicted of the crime. But the o¤cers also the study phase of the experiment: studying associated conducted a failed search for a second suspect called words (e.g. bed, tired, doze, and so forth) might lead `John Doe 2' who, they believed, had accompanied participants to generate on their own the non-presented McVeigh when he rented a van two days before the lure word (i.e. sleep). On a later memory test, participants bombing. An artist's sketch of John Doe 2 depicted a may experience source confusion (Johnson et al. 1993): young square-faced man with dark hair and a stocky they may mistakenly recollect that they heard or saw the build wearing a blue-and-white cap. A who had related lure word on the study list when in fact they had seen McVeigh rent his van also recalled seeing John Doe 2 generated it on their own (Roediger & McDermott 1995; with him. But it was later discovered that the witness had Roediger et al. 2001). A second possibility is that studying actually seen a man who ¢t the description of John Doe 2 numerous related words results in high levels of semantic at the body shop the day after he saw McVeigh there. The overlap among the corresponding memory representa- witness misattributed his memory of John Doe 2 to the tions (Schacter et al. 1998a). This failure to keep represen- wrong episode, leading to needless confusion and wasted tations of each item separate will produce robust memory e¡ort (for more details, see Schacter 2001). for semantic similarities among the items, together with We will discuss cognitive, neuropsychological and poor memory for the unique or distinctive aspects of each neuroimaging evidence that has bearing on a form of item. Because subjects have di¤culty recollecting the misattribution known as false recognition, where indivi- distinctive characteristics of the speci¢c studied items, duals mistakenly claim that a novel item or episode is they tend to make recognition responses on the basis of familiar (e.g. Underwood 1965). During the past several overall similarity of the lure item to the studied itemsö years, false recognition has been studied extensively, and that is, participants will respond on the basis of semantic we are beginning to understand some of its cognitive and gist (Brainerd & Reyna 1998; Payne et al. 1996; Schacter neural underpinnings. After summarizing relevant et al. 1996a) rather than on the basis of speci¢c recollect- evidence from some of our own and others' research, we ions. will argue that misattribution can be viewed as a by- It seems likely that both implicit associative responses product of otherwise adaptive memory processes. and memory for semantic gist play some role in the robust false recognition that occurs in the DRM para- digm (e.g. Roediger et al. 2001). Evidence that false recog- 2. FALSE RECOGNITION: COGNITIVE PERSPECTIVES nition can be driven mainly by gist-based processes, Cognitive have studied false recognition rather than implicit associative responses, comes from a for decades, using a variety of experimental procedures categorized pictures paradigm developed by Koutstaal & and paradigms (for reviews, see Alba & Hasher 1983; Schacter (1997). In their paradigm, younger and older Johnson et al. 1993; Roediger 1996; Schacter 1995). During adults studied large numbers of pictures from a variety of the past few years, however, interest in the phenomenon di¡erent categories (e.g. cars, shoes, and so forth). On a has intensi¢ed, in large part because of demonstrations of subsequent recognition test, participants were shown conditions under which extremely high levels of false previously studied pictures, related new pictures from recognition can be obtained (Hintzman 1988; Roediger previously studied categories, and unrelated new pictures. & McDermott 1995; Shi¡rin et al. 1995). In particular, Koutstaal & Schacter reasoned that it is highly unlikely Roediger & McDermott (1995) demonstrated exception- that participants would generate the related new pictures ally high levels of false recognition in experiments using a during the study phase of the experiment, in the same modi¢ed version of a paradigm initially developed by way that they might generate the word `sleep' as an Deese (1959). In what has come to be known as the implicit associative response when studying related words Deese^Roediger^McDermott (DRM) paradigm, parti- in the DRM procedure. Koutstaal & Schacter found that cipants study lists of words (e.g. tired, bed, awake, rest, participants often falsely recognized related new pictures

Phil.Trans. R. Soc. Lond. B(2001) Misattribution and false recognition D. L. Schacter and C. S. Dodson 1387 from the same categories as the studied pictures. Rates of hypothesized `rule of thumb' in the picture- false recognition for young adults were considerably lower condition as a distinctiveness heuristic. than in the DRM procedure, whereas older adults showed Related evidence indicates that the distinctiveness heur- high levels of false recognition that, in some conditions, istic has some generality across subject populations and approached the levels observed in the DRM procedure. experimental paradigms. For instance, Schacter et al. Overall, these data indicate that similarity or gist-based (1999) examined false recognition in the DRM paradigm false recognition can occur even when implicit associative after word and picture encoding in a group of elderly responses are an unlikely source of misattribution. adults. Replicating previous studies (Norman & Schacter Whether driven by implicit associative responses or 1997; Tun et al. 1998), in the word-encoding condition gist-based similarity, false recognition of related lures older adults showed relatively higher levels of false recog- re£ects some form of memory for semantic or associative nition than younger adults. But in the picture-encoding information acquired during list presentation that is condition, older adults reduced their levels of false recog- misattributed to a speci¢c past sensory encounter with nition just as much as the younger adults did, indicating the item. an intact ability to use the distinctiveness heuristic. One implication of this line of reasoning is that false We have also found that participants can use the recognition can be reduced by encouraging subjects to distinctiveness heuristic to reduce false recognition in focus on distinctive characteristics of individual items, paradigms other than the DRM procedure. Dodson & rather than on semantic or associative properties that are Schacter (2001b,c) used a repetition lag procedure common to all items. Israel & Schacter (1997) and adapted from Jennings & Jacoby (1997). In this paradigm, Schacter et al. (1999) tested this idea by examining subjects study a list of unrelated words, and later make whether false recognition of semantic associates is old^new recognition judgements about previously studied reduced when subjects encode DRM lists along with words and new words. The critical manipulation is that detailed pictures corresponding to each item. They some new words on the recognition tests are repeated reasoned that presenting study-list items as pictures after varying lags. Even though participants are speci¢- should increase encoding of distinctive, speci¢c details of cally instructed to say `old' only to words from the study each item (Hunt & McDaniel 1993), which in turn list, and not to new words that are repeated, after su¤- should make them easier to discriminate from non- ciently long lags participants make false alarms to some studied semantic associates. The experiments involved repeated new words. Participants misattribute their famil- two key study conditions. In the word-encoding condi- iarity with the repeated new words to a prior appearance tion, participants both heard and saw lists of DRM in the study list. Jennings & Jacoby (1997) demonstrated semantic associates, whereas in the picture-encoding that the e¡ect is especially pronounced in older adults. In condition, participants heard the same lists of semantic recent experiments by Dodson & Schacter (2001b), associates and also saw line-drawings corresponding to younger and older adults studied words, pictures, or a each word. After the word- or picture-encoding condi- mixture of both, and then completed a recognition test in tions, previously studied words, related lures and un- which studied items appeared once and new items related lures were tested on an old^new recognition task appeared twice. Several experiments demonstrated that, (test items presented as pictures or as words). Consistent compared with the word-encoding condition, studying with the reasoning outlined earlier, false recognition of pictures produced a signi¢cant reduction in false recogni- related lures was signi¢cantly reduced after pictorial tion rates to repeated new words for both older and encoding compared with word encoding. Dodson & younger adults. The reduction in false recognition was Schacter (2000) reported a similar pattern of results particularly dramatic for older adults, who showed high using a di¡erent manipulation of distinctive encoding false recognition rates in the word-encoding condition, (saying words aloud compared with hearing them). replicating the earlier results of Jennings & Jacoby (1997). We (Dodson & Schacter 2000; Israel & Schacter 1997; Dodson & Schacter (2001b) attributed the reductions in Schacter et al. 1999, experiment 1) have argued that false recognition to the use of a distinctiveness heuristic. reduced false recognition after encoding distinctive information depends on a shift in responding based on participants' metamemorial assessments of the kinds of 3. NEUROPSYCHOLOGY OF FALSE RECOGNITION: information they believe they should remember. For EVIDENCE FROM AMNESIA AND ALZHEIMER'S instance, having encountered pictures with each of the DISEASE presented words, participants in the picture-encoding Cognitive studies have provided important information condition may have used a rule of thumb where they about the properties of misattribution and false recogni- demanded access to detailed pictorial information in tion, but they are mute about relevant underlying brain order to support a positive recognition decision systems. Studies of brain-damaged patients have begun to (cf. Rotello 1999; Strack & Bless 1994). Thus, reduced provide some insights into the brain regions that are false recognition appears to result from a general expecta- implicated in false recognition. For example, a number of tion that a test item would elicit a vivid perceptual recol- studies have revealed that patients with damage to lection if it had in fact been presented previously. various sectors of the frontal lobes show increased levels Participants in standard word-encoding conditions, by of false recognition compared with age-matched control contrast, did not expect to retrieve distinctive representa- subjects (Curran et al. 1997; Delbecq-Derouesne¨ et al. tions of previously studied items. By our account, they 1990; Parkin et al. 1996, 1999; Ward et al. 1999; Rapcsak were much less likely to demand access to detailed et al. 1999; Schacter et al. 1996b). Explanations for this recollections. Schacter et al. (1999) referred to the increased false recognition have varied across patients,

Phil.Trans. R. Soc. Lond. B(2001) 1388 D. L. Schacter and C. S. Dodson Misattribution and false recognition depending on particular features of their performance. (2001) have found that AD patients show reduced false Some investigators have focused on inadequate encoding recognition of pictures of abstract objects from large cate- of item-speci¢c details (e.g. Parkin et al. 1999), whereas gories in the paradigm developed by Koutstaal et al. (1999). others have emphasized defective retrieval monitoring Interestingly, studies of both amnesic patients and AD processes (e.g. Delbecq-Derouesne¨ et al. 1990; Rapcsak patients have identi¢ed conditions within the DRM para- et al. 1999; Schacter et al. 1996b,1998a; for more detailed digm in which patients can show as much or more false discussion, see Dodson & Schacter 2001a). recognition of related lures compared with controls. Studies of false recognition in amnesic patients with Schacter et al. (1998b) presented amnesiacs and controls memory disorders resulting from damage to the medial with DRM lists of semantic associates, and then gave a temporal lobes (MTLs) and related structures in the standard old^new recognition test. This study^test proce- diencephalon have provided important additional dure was repeated ¢ve times. On the ¢rst trial, amnesiacs insights. Such patients have great di¤culty remembering showed reduced true and false recognition of semantic recent experiences and acquiring new information, associates compared with controls, replicating the despite relatively intact perception, and general previous results discussed (Schacter et al. 1996a,1997a). intellectual function (e.g. Parkin 2001; Squire 1992). Across the ¢ve study^test trials, control subjects showed Schacter et al. (1996a) used the DRM paradigm to inves- increased true recognition of studied words together with tigate false recognition in amnesic patients. Amnesiacs and reduced false recognition of semantic associates. As they matched control subjects studied lists of semantic associates, remembered more detailed information about speci¢c and then made old^new recognition judgements about words that actually appeared on the study list, control studied words, new related words (e.g. sleep after studying subjects were able to use this information to reduce or tired, bed, awake, rest, and so forth), and new unrelated suppress their tendency to make false recognition words (e.g. point).They found that, as expected, amnesiacs responses based on or gist informa- recognized fewer studied items than did the matched tion. Amnesic patients, in contrast, showed no reduction controls, and also made more false alarms to unrelated new in false recognition across study^test trials. In fact, they words. More importantly, amnesiacs showed reduced false showed an opposite tendency for increased false recogni- recognition of the related lure words (for replication and tion across study trials. This latter result was mainly attri- extension, see Melo et al. 1999). Schacter et al. (1997a) butable to patients with amnesia that resulted from demonstrated that amnesiacs' reduced false recognition of Korsako¡ 's disease, who are characterized by damage to related lure items extends to perceptual materials. After diencephalic structures and often show signs of frontal studying perceptually related words (e.g. fade, fame, face, lobe damage. Patients with amnesia that resulted from fake, mate, hate, late, date and rate), amnesiacs were less MTL damage tended to show a £at or £uctuating pattern likely than controls both to correctly recognize studied of false recognition across trials. Budson et al. (2000) used words and to falsely recognize perceptually related lure the same paradigm, and found that AD patients who words (e.g. fate). The results thus indicate that in amnesic exhibited reduced false recognition of semantic associates patients, the same processes that support accurate recogni- on the ¢rst trial, showed steadily increasing levels of false tion of studied words also contribute to the false recognition recognition across trials. By the ¢fth and ¢nal trial, AD of semantically or perceptually related lures. patients showed higher levels of false recognition than did The same general pattern of results has been observed controls. in experiments involving pictorial materials. Using Both Schacter et al. (1998b) and Budson et al. (2000) Koutstaal & Schacter's (1997) categorized pictures para- argued that with repeated study and testing of semantic digm described earlier, Koutstaal et al. (2001) found that associates, patients strengthened their initially degraded amnesic patients were less likely than controls to falsely representation of the semantic features or gist of the recognize new pictures after studying numerous similar studied items, leading them to false alarm more items from the same category. Koutstaal et al. (1999) frequently to related lure words. Unlike control subjects, reported a similar pattern in an experiment that exam- however, amnesic and AD patients do not develop ined true and false recognition of pictures of abstract increasingly detailed representations of the speci¢c words objects. Each picture belonged to a particular perceptual they studied. Whereas controls can use such speci¢c category and was similar to a prototype that de¢ned the representations to counter or oppose the increasing in£u- category. The categories included either one, three, six or ence of semantic gist, amnesic and AD patients do not. In nine pictures. All participants then completed a recogni- this paradigm, then, misattribution occurs when partici- tion test containing studied pictures and new pictures that pants rely on representations of semantic gist that are were either related or unrelated to studied items. They unchecked by speci¢c episodic memories of the actual list (Koutstaal et al. 1999) found that, for control subjects, words. For control subjects, this pattern of in£uences is both true and false recognition of the abstract pictures maximal on the ¢rst trial and reduced by the ¢nal trial. increased with category size, whereas category size had For amnesic and AD patients, it takes several trials to only a slight e¡ect on true and false recognition in amnesic build up the semantic gist information that is responsible patients. With larger categories, amnesic patients showed for the misattribution error. less true and false recognition than did control subjects. Recent work by Budson et al. (2000) has revealed the same general pattern of results in studies of patients with 4. NEUROIMAGING OF TRUE AND disorders resulting from AD. AD patients showed RECOGNITION reduced false recognition of semantic associates in the Several neuroimaging studies using positron emission DRM word recognition paradigm. Further, Budson et al. tomography (PET), functional magnetic resonance imaging

Phil.Trans. R. Soc. Lond. B(2001) Misattribution and false recognition D. L. Schacter and C. S. Dodson 1389

(fMRI) and event-related potentials (ERPs) have begun anterior MTL region within the showed to explore misattributions associated with false recogni- signi¢cantly increased activity for both studied words and tion. Two studies from our laboratory made use of the related lures compared with unrelated lures. The DRM false recognition paradigm. posterior MTL region may have been sensitive to percep- Schacter et al. (1996c) investigated true and false recog- tual di¡erences between studied words and non-studied nition with PET, and Schacter et al. (1997b) carried out a semantic associates. Consistent with this suggestion, an similar study with fMRI. In both studies, participants earlier study by Schacter et al. (1997c) revealed that this heard lists of semantic associates prior to entering the same posterior MTL region responded more strongly to scanner; scanning was performed later as participants previously studied visual objects that were tested in the made old^new judgements about previously studied same perceptual format than in a di¡erent perceptual words, critical lures that were semantically related to the format (i.e. when the size or orientation of the object was studied items, and unrelated lure words. The main altered between study and test). In contrast, the anterior ¢nding from the two studies is that patterns of brain MTL region appeared to be responding on the basis of activity were highly similar during true and false recogni- semantic information common to both studied words and tion. Di¡erences in brain activity during true and false related lures. Cabeza et al. (2001) thus suggested that recognition were relatively small and depended on anterior MTL is involved primarily in the recovery of speci¢c characteristics of recognition testing procedures semantic information, whereas posterior MTL is involved (for discussion, see Schacter et al. 1997b; also see Johnson primarily in the recovery of sensory information (for et al. 1997). further evidence of di¡erent brain responses during true activation was quite prominent in each of and false recognition, see Fabiani et al. 2000). the PETand fMRI studies of false recognition. Consistent Studies concerned with the neural correlates of misat- with other imaging evidence concerning episodic tribution have also examined false recognition errors memory (e.g. Henson et al. 1999), both studies reported within the context of source confusions (e.g. Johnson et al. evidence that regions within the frontal lobes may be 1993, 1996; Nolde et al. 1998). As discussed earlier (½ 2), involved in strategic monitoring processes that are one explanation for the robust false recognition e¡ect in invoked as participants struggle to determine whether a the DRM paradigm involves source confusion: when related lure word was actually presented earlier in a study individuals fail to distinguish between what they generate list (for further relevant evidence, see Johnson et al. 1997). as an implicit associative response (e.g. sleep) and what These ¢ndings ¢t well with the neuropsychological data was actually presented during the study phase (e.g. bed, discussed earlier (½ 3) that damage to areas within the tired, dream, etc., cf. Mather et al. 1997; Roediger et al. frontal lobe can be associated with heightened false recog- 2001). This source confusion error, also known as an error nition. in reality monitoring, can also refer to instances in which Consistent with the studies discussed earlier (½ 3), an individual confuses test items that were earlier showing reduced false recognition of semantic associates in imagined with items that were earlier perceived (Johnson amnesic patients, both the PETand fMRI studies revealed & Raye 1981). Recently, Gonsalves & Paller (2000) used some evidence of MTL activity during false and true ERPs to investigate brain potentials at encoding and at recognition. However, there were no detectable di¡er- retrieval that are associated with reality monitoring ences in MTL activity during true and false recognition. errors (see also Johnson et al. 1996; Nolde et al. 1998). In a more recent fMRI experiment, Cabeza et al. During the study phase of their experiment, participants (2001) attempted to create conditions that would increase saw words and imagined the corresponding object, such the likelihood of ¢nding di¡erences in brain activity as seeing the word `cat' and then imagining a picture of a during true and false recognition. the behavioural cat. However, half of the words were followed by a corre- evidence discussed earlier (½ 2) that di¡erences between sponding picture (the `word plus picture' trials), whereas true and false recognition can be increased when study no picture was presented for the remaining study words lists are presented in a perceptually distinct manner (e.g. (the `word only' trials). On a later memory test, partici- presenting pictures with words in the DRM paradigm; pants indicated whether or not each test item had been Israel & Schacter (1997) and Schacter et al. (1999)). In seen earlier as a picture. the previous neuroimaging studies that used the DRM As expected on the basis of previous work (e.g. Durso procedure, words were presented auditorily to partici- & Johnson 1980), participants made reality monitoring pants. In an attempt to increase the perceptual encoding errors and claimed that some items in the `word only' of study list words, Cabeza et al. (2001) had a male and study condition had been presented with a picture. female speaker present lists of semantically related words. Because ERPs were recorded during the study phase, it Participants were speci¢cally instructed to try to re- was possible to examine whether there were di¡erent member which speaker said each word. Thus, studied patterns of brain activity at encoding that were later asso- words should be associated with a speci¢c source or ciated with true and false recognition, as has been done perceptual input in a way that related lure words would previously in ERP and fMRI studies of true recognition not. (for review, see Wagner et al. 1999). In other words, are The most relevant imaging ¢ndings from the Cabeza there di¡erences in brain potentials when participants et al. (2001) experiment concern the MTL. They found initially see the study words that predict whether or not that a region of posterior MTL, in the parahippocampal that word will be falsely recognized on the test as having gyrus, showed increased activity (relative to an unrelated been seen as a picture? Interestingly, Gonsalves & Paller lure baseline) for previously studied words but not for (2000) found that ERPs recorded during the study phase semantically related lure words. By contrast, a more in posterior cortical regions (i.e. occipital and parietal

Phil.Trans. R. Soc. Lond. B(2001) 1390 D. L. Schacter and C. S. Dodson Misattribution and false recognition locations) were more positive for items in the `word only' lines and noted that generalization often results from gist- condition that were later falsely remembered as pictures like, accumulated e¡ects of prior experiences. While than for those items that were correctly rejected as not depicting such generalization as central to intelligent accompanied with a picture. These positive ERPs may be behaviour and cognitive development, McClelland also providing an index of brain activity related to words that noted that `such generalization gives rise to distortions as elicit strong visual imagery at encoding, which in turn an inherent by-product'. enhances their likelihood of being falsely remembered as We have already considered evidence that ¢ts well with pictures on a later test. such a position, namely the consistent ¢nding that amnesic patients show reduced false recognition of semantically and perceptually related words (Schacter et al. 5. MISATTRIBUTION AND FALSE RECOGNITION: 1996a,1997a,1998b). Further, amnesiacs also show VICES OR VIRTUES? reduced false recognition of categorized pictures and Misattribution and false recognition are sins of memory novel objects that depend on retaining gist information in the sense that they are associated with inaccurate (Koutstaal et al. 1999). These observations suggest that reports about the past: people make claims about previous false recognition and misattribution based on gist re£ect experiences that are, at least in some respects, incorrect. the workings of a normally functioning, healthy memory Similar sentiments apply to the other memory sins, which system. A damaged system such as that in amnesic involve errors of omission or commission. These observa- patients does not either encode, retain or retrieve the tions could easily lead one to conclude that evolution information that leads healthy people to show high levels burdened us with an extremely ine¤cient, even defective, of gist-based false recognition. memory systemöa system so prone to error that it may Beversdorf et al. (2000) have recently provided striking even jeopardize our well-being. evidence that supports this point. They studied adults In contrast to this rather dark view of memory, with a condition known as autistic spectrum disorder. Schacter (1999, 2001) argued that each of the sins is a by- Such individuals are in many respects similar to autistic product of adaptive features of memory, and in that sense children, except that they tend to function at a higher they do not represent £aws or defects in the system level. Autistic children rely on a relatively literal style of (cf. Anderson & Schooler 1991; Bjork & Bjork 1988). processing information, and do not take advantage of Instead, the memory sins can be of as costs asso- semantic context to the same extent as normal children. ciated with bene¢ts that make memory work as well as it Beversdorf et al. (2000) used the DRM semantic associ- does most of the time. Here we consider the case for the ates paradigm to assess whether adults with autistic spec- adaptive value of misattribution. trum disorder also show impaired sensitivity to semantic Consider that many instances of misattribution re£ect context. After studying lists of semantic associates, the poor memory for the source of an experience, such as the autistic spectrum disorder group showed signi¢cantly less precise details of who said a particular fact, when and false recognition of semantically related lure words than where a familiar face was encountered, or whether an did the healthy controls. However, the autistic spectrum object was perceived or only imagined. When source disorder group showed normal hit rates for previously details are not initially well encoded, or become inacces- studied words, resulting in greater discrimination sible with the passing of time, conditions are ripe for the between true and false memories than in the control kinds of misattributions associated with false recognition. group. The autistic spectrum disorder group appeared to But consider the consequences and costs of retaining each be relying on a highly literal form of memory, missing out and every contextual detail that de¢nes our numerous on the semantic gist that supports false recognition daily experiences. Anderson & Schooler (1991) (see also responses. Once again, misattributions resulting in false Schooler & Anderson 1997) have argued persuasively that recognition appear to re£ect the operation of a healthy memory is adapted to retain information that is most memory system. likely to be needed in the environment in which it oper- These ¢ndings support the idea that misattribution can ates. Because we do not frequently need to remember all re£ect adaptive aspects of memory function. Buss et al. the precise, source-specifying details of our experiences, (1998) (see Schacter 1999, 2001) have distinguished an adapted system should not routinely record all such between two senses of the term `adaptive' in evolutionary details as a default option. Instead, the system would discussions. One is based in evolutionary theory: it rests record such details only when circumstances warn that on a technical de¢nition of an as a feature of a they will be neededöand this is what human memory species that came into existence through the operation of tends to do. because it in some way increased repro- A second and related factor that contributes to misat- ductive ¢tness. The other is a non-technical, everyday tributions involving false recognition concerns the distinc- sense of the term that refers to features of that tion between memory for gist and speci¢c information have positive functional consequences, regardless of discussed earlier (½ 2) (Brainerd & Reyna 1998; Reyna & whether they arose directly from natural selection. Some Brainerd 1995). False recognition often occurs when generally useful or `adaptive' features of organisms are not people remember the semantic or perceptual gist of an in the strict sense. Sometimes termed `exapta- experience but do not recollect speci¢c details. However, tions' (Gould & Vrba 1982), these useful functions arise memory for gist may also be fundamental to such abilities as a consequence of other related features that are adapta- as categorization and comprehension, and may facilitate tions in the technical sense. Such adaptations are some- the development of transfer and generalization across times coopted to perform functions other than the one for tasks. McClelland (1995, p. 84) has argued along these which they were originally selected.

Phil.Trans. R. Soc. Lond. B(2001) Misattribution and false recognition D. L. Schacter and C. S. Dodson 1391

With respect to the memory sins, it is di¤cult to deter- REFERENCES mine de¢nitively which (if any) are genuine adaptations and which are exaptations (for detailed discussion, see Schacter 2001). One strong candidate for an adaptation is Alba, J. W. & Hasher, L. 1983 Is memory schematic? Psychol. the sin of persistenceöintrusive, unwanted recollection of Bull. 93, 203^231. Anderson, J. R. & Schooler, L. J. 1991 Re£ections of the envir- disturbing experiences which usually results from the ö onment in memory. Psychol.Sci. 2, 396^408. encoding and retrieval of enduring memories for highly Beversdorf, D. Q. (and 10 others) 2000 Increased discrimination emotional or arousing events. If persistence arose in of `false memories' in autistic spectrum disorder. Proc.Natl response to life-threatening situations that endangered an Acad.Sci.USA 97,8734^8737. 's survival, animals and people who could Bjork, R. A. & Bjork, E. 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Phil.Trans. R. Soc. Lond. B(2001) 1392 D. L. Schacter and C. S. Dodson Misattribution and false recognition

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