JOURNAL OF MEMORY AND LANGUAGE 35, 76±100 (1996) ARTICLE NO. 0005

Memory Illusions

HENRY L. ROEDIGER III Rice University

Memory illusions may be de®ned as cases in which a rememberer's report of a past event seriously deviates from the event's actual occurrence. This article introduces the special issue of the Journal of Memory and Language that is devoted to memory illusions by grounding their study in the context of perceptual illusions. Perceptual illusions have been investigated since the 1850s, whereas memory illusions have been systematically investigated only since the late 1960s or early 1970s (despite some pioneering research and writing before this time). I suggest possible reasons for this discrepancy in research activity, sketch a brief history of the study of memory illusions, and then consider the variety of memory illusions that are studied in contemporary psychology. The papers composing the special issue are introduced during this brief cataloging of memory illusions. Related areas of research are discussed in the concluding remarks. ᭧ 1996 Academic Press, Inc.

Illusions have fascinated philosophers, recall of a past experience.'' Even though both physicists, and psychologists throughout re- perceptual and memory illusions were men- corded history. Whenever our experience of tioned in this de®nition, by 1964 there had events is shown to be at odds with the actual been hundreds of studies of perceptual illu- nature of the events, our curiosity is piqued. sions but, even counting generously, there The word illusion is derived from the Latin probably existed fewer than 30 publications word illudere, meaning to mock. Illusions directed speci®cally at memory errors, with mock our belief that what we perceive, re- the term memory illusion rarely arising at all. member, and know is in perfect accord with One exception occurred in Titchener's (1928) the state of the external world. Textbook of Psychology, where he devoted a Despite long-standing interest in this topic, section to ``Illusions of Recognition and de®ning exactly what an illusion is can be a Memory.'' He wrote that ``Illusory memories dif®cult exercise. When psychologists see the and recognitions are of two kinds. We may word illusion, it is usually modi®ed by visual, remember or recognize something that is re- perceptual, or optical. The term memory illu- ally, objectively, unfamiliar to us, and we may sion is much less common. In a 1964 diction- fail to recognize or remember something ary of psychology, Drever included the fol- which once formed part of our common expe- lowing entry under Illusion. ``In the case of rience. Both types of illusion are quite com- sense perception, `a subjective perversion of mon'' (p. 424). Titchener discussed these mat- the objective content,' or actual sense data; in ters for only one and a half pages and alluded the case of memory a subjective falsi®cation to the existence of other memory illusions but by addition, omission, or substitution, in the did not describe them. The two illusions to which Titchener referred are usually called by their French names, deÂjaÁ vu and jamais vu, Preparation of this article was supported by Grant and have been little studied experimentally, F49620-92-J-0437 from the Air Force Of®ce of Scienti®c until lately when experimental analogs have Research. The article bene®ted from comments by Marcia 1 Johnson, Doug Nelson, Kathleen McDermott, Kerry Rob- been developed (as discussed below). inson, Dan Schacter, and Endel Tulving. I thank Kerry Robinson for help in preparing the manuscript. Corre- 1 It is clear from Titchener's examples that he did not spondence should be addressed to the author at Depart- mean that forgetting should be considered a memory illu- ment of Psychology, MS 25, Rice University, Houston, sion. Rather, the failure to recognize something quite fa- TX 77005-1892. E-mail: [email protected]. miliar (such as a well-known word) was intended.

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torical overview of their discovery and impor- tance to the study of perception. Due to the longer history of serious scienti®c inquiry, a consideration of the topic of perceptual illu- sions seems an appropriate way to ground the study of memory illusions. I then turn to the topic of memory illusions and survey some of the major milestones in their study, as well. I provide a brief catalog of some of the main types of memory illusions that have been stud- FIG. 1. A shape illusion. The shaded tops of the two ied, and in the process I introduce the set of ®gures appear quite different in shape, but are actually papers that constitute the special issue. congruent. Reprinted by permission of Roger Shepard and Lawrence Erlbaum, Inc. PERCEPTUAL ILLUSIONS Illusions occur in all sense modalities, al- We may ask why, historically, this imbal- though those occurring in vision have been ance has existed between interest in perceptual studied in greatest detail. The ancient Greeks illusions and in memory illusions. One answer were quite aware of visual illusions. The Par- probably lies in the immediacy of perceptual thenon was constructed to overcome two com- illusions relative to memory illusions. Shown mon visual illusions that would have caused it in Fig. 1 is the remarkable shape illusion that to look imperfect had steps not been taken in Shepard (1981) created. The darkened parts its design and construction to counteract their (the tops of the ®gures) appear quite different effects (see Coren & Girgus, 1978). Aristotle in shape, but they are actually congruent. described the moon illusionÐthe fact that it (Trace one on a sheet of paper and lay it over looks larger at the horizon than when over- the other, if you need to be convinced.) Such headÐand also described the illusion of touch a remarkable demonstration provides immedi- that still bears his name (Benedetti, 1985). ate and convincing evidence of a fascinating Closer to our own times, scienti®c interest process at work, one worthy of serious and in perceptual illusions began in the early thoughtful study. Most visual illusions have 1800s and had exploded by the turn of the just this quality. Even if memory illusions oc- century. In 1832 Louis Albert Necker, a crys- cur routinely in lifeÐand I think they doÐ tallographer, noted a curious effect he had dis- the evidence for their occurrence is quite dif- covered in gazing at crystals: Line drawings of ferent. Usually the events in question have crystals would spontaneously reverse in depth long since disappeared from life's stage and when an observer stared at them. This obser- we can believe that our memories are right, vation gave rise to the familiar Necker cube. despite claims to the contrary that may be pro- In 1854, J. J. Oppel reported the curious obser- vided by others. If we simply look at the two vation that a certain distance of linear extent shapes in Fig. 1, we are not aware of the illu- appeared longer if it were ®lled (say, with sion at allÐone shape is simply perceived as lines) than if it were un®lled. Coren and Gir- quite different from the other. It is only if gus (1978) estimated that over 200 scienti®c we are told to check that we can convince papers appeared on perceptual illusions in the ourselves of the difference. This critical 50 years after publication of Oppel's (1854) checking operation usually is not possible for paper. Many illusions identi®ed during this remembered events. period still bear the names of their discoverers: The purpose of this essay is to introduce ZoÈllner, MuÈller-Lyer, Ponzo, Ebbinghaus, and the special issue of the Journal on the topic so on. One important theoretical contribution of memory illusions. First I consider the topic from this era came from Hermann von Helm- of perceptual illusions, providing a brief his- holtz, who offered a general approach to per-

AID JML 2467 / a002$$$102 04-10-96 17:23:17 jmla AP: JML 78 HENRY L. ROEDIGER III ception still found in many theories today. As holtz's theme in this quote reverberates to the Coren and Girgus (1978, page 9) put it, ``He present day through the writings of scholars proposed that, in general, perception in the studying perception, but it is not a uniform adult observer is based on unconscious infer- view. Kolers (1964, p. 98) noted that ``Illu- ences that the mind makes about the pattern sions have not always had a good standing of stimulation in the nervous system. Since among the investigators of perception. When most stimulus arrays are ambiguous, the ob- perceptual illusions were introduced as a topic server must interpret the sensory stimulation of study in the nineteenth century, the prevail- arriving in the brain in light of his knowledge ing attitude about them was that they were of the environment. Thus perception is an in- mere parlor tricksÐminor imperfections or ductive process wherein the observer uses his errors'' in the workings of perception. (Kolers experience to interpret the patterns of excita- went on to discredit this view.) tion in his receptors.'' Helmholtz called this The study of illusions has occupied center constructive process unconscious inference stage in the study of perception since the turn because when people create their perceptual of the century and has even given rise to entire world, they are unconsciously weaving to- theories that developed largely to explain their gether data from the senses with prior knowl- occurrence (e.g., the transactional approach to edge about the world. A classic example of perception proposed in the late 1940s and unconscious inference occurs in depth percep- early 1950s by Ames, Ittelson, and Kilpatrick tion, wherein the two-dimensional display on and based on the remarkable demonstrations the retina gives rise to the experience of a they produced (e.g., Ittelson, 1952; Ittelson & three-dimensional world through the use of Kilpatrick, 1951). In 1978 Coren and Girgus many cues that are combined without our estimated that over 1000 articles had been awareness. The role of the active perceiver published on the topic of perceptual illusions. appears throughout the history of the study of Now, 18 years later, hundreds more have ap- perception (Neisser, 1968). Rather than the peared and whole books are devoted to special external world merely being projected onto illusions, such as the edited volume by Hers- the retina and faithfully transmitted to the henson (1989) on the moon illusion. brain, most perceptual theorists have empha- In the next section I turn to considering sized that top-down, constructive processes why illusions and errors have not, until lately, help determine what we perceive. In The played a central role in research and theory Principles of Psychology, William James about human memory. Before leaving the described his general law of perception, topic of perception, however, consider one which he believed was well substantiated: more quote noting the importance of studying ``...whilst part of what we perceive comes how systems fail in helping to understand how through our senses from the object before us, they normally operate. Gregory and Gombrich another (and it may be the larger part) always (1973) wrote that ``Illusions are also tools for comes . . . from our own head'' (1890, Vol. discovering processes in perception. In medi- II, p. 108). cine, in engineering, and very frequently in The topic of illusions plays a large role in biology, the abnormal and surprising lead to these constructive views of perception (e.g., key ideas and facts for understanding the nor- Gregory, 1970). Helmholtz (1881) wrote, mal. So here we may expect abnormal percep- ``The study of what are called illusions of the tions (deviations from truth) to give insights sense is, however, a very prominent part of and data for understanding normal (correct) the psychology of the senses; for it is just perception'' (p. 7). We may hope that studying those cases which are not in accordance with illusion and error can play the same role in reality which are particularly instructive for advancing our understanding of human mem- discovering the laws of those processes by ory. The study of perceptual illusions may which normal perception originates.'' Helm- need to become an integral part of the study

AID JML 2467 / a002$$$102 04-10-96 17:23:17 jmla AP: JML MEMORY ILLUSIONS 79 of memory illusions, as they both reveal con- this sort of procedure is that the investigator structive errors in the overall cognitive sys- typically has no reliable way to check the ac- tem. Later I consider some illusions that could curacy of a reported recollection'' (p. 5). We be classi®ed as either perceptual or memory may add that this dif®cultyÐlack of control illusions, illustrating that no ®rm boundaries over the original eventsÐplagues many mod- exist between these phenomena. ern treatments of the question of accuracy and inaccuracy in memory. The experimentalist's MEMORY ILLUSIONS credo is that unless one can be sure as to the Perceptual illusions reveal the constructive course of original events, one cannot make nature of perception: We can misperceive a strong claims and statements about the accu- stimulus while it appears before us under lei- racy or inaccuracy of later recollections. surely and optimal viewing conditions, as in There is a sense in which the study of mem- Fig. 1. If perceiving is conceived as an active ory errors is quite old. After all, every time process, one full of inference and hence at subjects provide intrusions in recall tasks or least occasional error, then it is hardly surpris- make false alarms in recognition tests, these ing that remembering would be so considered, errors could be interpreted as memory illu- as well (Neisser, 1967, 1968). After all, if the sions. However, in the history of experimental cognitive system can err in misrepresenting studies of memory, errors were rarely of inter- objects when they are present before the eyes, est in their own right. The emphasis has tradi- the opportunities for error when a person later tionally been on correct responding and errors tries to recreate happenings of the past must were typically considered a methodological be even greater. nuisance, re¯ecting guessing or criterion The origins of formal memory research in shifts. Errors were most commonly used to Ebbinghaus's (1885/1964) great experiments correct accurate recall or recognition for probably helped keep early researchers from guessing and other biases, as in signal detec- examining errors and illusions. Ebbinghaus tion theory. Exceptions to this general meth- learned and relearned his series of nonsense odological attitude concerning errors are de- syllables and measured the savings during re- scribed below, but it should be borne in mind learning. The relearning and savings method that (at least until the 1970s), mainstream ex- was ingenious and set the ®eld off on a scien- perimental psychologists were not usually in- ti®c and sure path, but like any method, it was terested in illusions of remembering that better adapted to asking some questions than might be re¯ected in errors. others. The method was generally unsuitable The ®rst experiments showing the inaccu- for investigating memory errors and illusions, racy of memory were conducted with children despite the fact that Ebbinghaus had a keen by Binet (1900) in France and by Stern (1910) interest in the topic of perceptual illusions. in Germany (see Ceci & Bruck, 1993). Both Nonetheless, one of Ebbinghaus's method- investigators exposed children to objects or ological contributions is critically important events and later tested their memories with a even for the study of memory illusions. As series of misleading questions. The results of Schacter (1995) noted in this context, both studies revealed memory distortions in ``. . .Ebbinghaus introduced a methodologi- the children. At about this same time, Mun- cal innovation that has proved to be essential sterberg (1908) reviewed evidence of the un- to evaluating whether a memory is true or reliability of eyewitness testimony in his book, false: he gained control over the input to the On the Witness Stand. memory system. In earlier philosophical and In a totally different tradition, Freud (1895) clinical treatises on memory, discussion cen- began exploring memory distortions in the tered on introspective recollections of past ex- 1890s and continued to revise his statements periences by the writers themselves or by pa- on the subject throughout his life. His most tients whom they observed. The problem with famous idea was that of repressionÐthe no-

AID JML 2467 / a002$$$102 04-10-96 17:23:17 jmla AP: JML 80 HENRY L. ROEDIGER III tion that painful early memories are banished ences of a variety of psychical forces. Thus to an unconscious state where they may be the `childhood memories' of individuals come revealed only indirectly, through dreams, in general to acquire the signi®cance of slips, and symptoms of psychopathology. Er- `screen memories' and in so doing offer a re- delyi (1985, Chapter 5) describes the many markable analogy with the childhood memo- changes in Freud's concept of repression, ries that a nation preserves in its store of leg- from people simply not wanting to think about ends and myths.'' However, without the meth- bad events of their lives at one extreme (Erde- odological stricture of the experimental lyi & Goldberg, 1979) to a deep and mysteri- schoolÐknowledge of the original events and ous process of psychological banishment of how they occurredÐFreud's various discus- memories to an unconscious state at the other. sions of whether childhood memories are ac- One corollary of the idea that memories of curate or inaccurate is based more on conjec- threatening experiences could be removed or ture than on empirical evidence. banished to an unconscious state is that they These two streams of study of memory illu- could somehow reside in this state relatively sions I have brie¯y describedÐone based on intact and then be recalled (through therapy) experimental methods and the other rooted in at some later time in life. However, in his later the psychoanalytic traditionÐhave guided writings Freud abandoned his earlier belief discussion of memory errors to the present that childhood memories obtained during ther- day. However, as previously noted, within ac- apy should be treated as genuine and empha- ademic psychology the main issues in memory sized instead the processes of distortion that research lay elsewhere. Researchers from could occur during therapy. In 1910 he wrote early in the century worried about the course that childhood memories are ``. . .only elic- of forgetting and its causes (retroactive inter- ited at a later age when childhood is already ference and retroactive inhibition), but rarely past; in the process they are altered and falsi- worried about error and illusion. There are two ®ed, and are put in the service of later trends, prominent exceptions to this generalization, so that generally speaking they cannot be dis- however. The ®rst is represented in the Gestalt tinguished from phantasies'' (p. 83). tradition of memory research in which it was Two other types of distortions that Freud believed that memories changed over time in (1903) analyzed were paramnesias (or false the directions that were in line with the Gestalt recollections of forgotten events that took on laws of organization. Brie¯y, people would subjective certainty), and screen memories (or remember events in a more organized fashion cases when one memory substituted for an- (the events would represent good patterns) other and screened it out of consciousness). when they were remembered at increasing in- Freud interpreted both in terms of defense tervals from the original event. For example, mechanisms to protect against psychic threat Wulf (1922) reported that visual forms were and analyzed several cases that seemed to ®t remembered as being more regular and sym- this mold. The dif®culty with interpretation of metrical over time, and many other research- screen memories, in particular, is that there is ers conducted similar studies. The topic re- no rule to decide which may be the real mem- mained of sporadic interest in experimental ory and which the screen memory, except for psychology, but Riley's (1964) piercing re- ad hoc supposition (Schacter, 1995). Nonethe- view of the methodological dif®culties and the less, Freud (1903, p. 68) likened memories of inconsistencies in results in this area quelled early childhood to screen memories: ``One is continued interest. Most commentators have thus forced by various considerations to sus- concluded more recently that nothing much pect that in the so-called earliest childhood was gained from this study (Baddeley, 1976; memories we possess not the genuine mem- Schacter, 1995). However, as Loftus (1979b) ory-trace but a later revision of it, a revision pointed out, Riley's (1964) analysis of re- which may have been subjected to the in¯u- search from the Gestalt tradition did empha-

AID JML 2467 / a002$$$103 04-10-96 17:23:17 jmla AP: JML MEMORY ILLUSIONS 81 size the effect of verbalization on memory. while violating most other strictures that care- The words that people used to label visual ful experimentalists might prefer (Kintsch, ®gures, for example, determined how they 1995). His data were in the form of sample were later remembered (e.g., Carmichael, Ho- protocols produced by some of his subjects gan & Walters, 1932). The importance of ver- and showed numerous omissions, with the sto- balization on memory continues to be studied ries becoming shorter over time. More inter- to the present day, as represented in the current estingly, the subjects made errors of commis- issue in Melcher and Schooler's experiments sion in which they added material to make the on verbal overshadowing. story more rational and consistent. Supernatu- The second, and more important, contribu- ral elements dropped out and in general the tion during the 1930s to the study of memory students seemed to convert the story more to distortions was publication of Bartlett's the form of an English fairytale, sometimes (1932) great book, Remembering: A Study in even tacking on a moral. Bartlett noted that Experimental and Social Psychology. Bartlett this property of rationalization in the protocols took it as axiomatic that remembering was brought the story in line with schemas with imperfect and even argued that it would be which the students were more familiar. unnatural for people to remember events ver- A few years before his death, Donald batim. Before turning to remembering, he de- Broadbent (Bartlett's student) related to me an voted a chapter to discussing constructive pro- interesting story about rationalization in ``The cesses in perceiving. In one demonstration, he War of the Ghosts.'' Brie¯y, it did not start showed people a painting for a brief period of with Bartlett's subjects, but with Bartlett him- time and noted that their reports of what it self, when he created the materials. One of contained were quite different and seemed to the most memorable parts of ``The War of the depend more on the background and proclivit- Ghosts'' occurs at the end, when an Indian ies of the observers than on the content of falls down, something black comes from his the painting. Further, when he exposed the mouth, and he dies. Bartlett's version put it painting repeatedly, but with quite brief expo- this way: ``Something black came out of his sures, his subjects would often cling to their mouth.'' Broadbent told me that Bartlett had earlier interpretations and fail to perceive the revised this part of the story, omitting an of- actual scenes portrayed, a ®nding presaging fensive phrase. Sure enough, in checking that of Bruner and Potter (1964) years later. Franz Boas' (1901) original version, the sen- Bartlett argued that both perceiving and re- tence read ``Something black came out of his membering were constructive processes mouth and blood came out of his anus.'' guided by schemas, or cognitive frameworks Broadbent opined that this version was too that people brought to the events and through vivid for Bartlett to present to his re®ned Cam- which they interpreted them. bridge students! In fairness, Bartlett seems to Bartlett's most famous experiments were have rewritten the entire story to make it ¯ow those in which college students read and later better than Boas' original literal translation, recollected an Indian folktale, ``The War of but this is the only case where an important the Ghosts.'' In one type of experiment, which change of content occurred. he called repeated reproduction, subjects re- Bartlett's (1932) book, so important today called the story from memory on at least two in hindsight, actually seems to have had little occasions, without intervening study. Typi- impact on the questions experimental psychol- cally, Bartlett required a ®rst recall 15 min ogists asked at the time, as re¯ected in the after his subjects (Cambridge University stu- mainstream literature of the 1930s, 1940s, and dents) had read the story twice. Then he tested 1950s. However, as noted below, the book them at various later points in time. His exper- received renewed attention in the late 1960s imental methods were casual, to say the least, and early 1970s when Bartlett's approach to but he did at least control the input material remembering gained renewed interest and fa-

AID JML 2467 / a002$$$103 04-10-96 17:23:17 jmla AP: JML 82 HENRY L. ROEDIGER III vor. The legend of Bartlett's repeated repro- ``There are probably many ways to do this duction experiments lives on today in most recoding, but probably the simplest is to group textbooks of psychology (introductory, cogni- the input events, apply a new name to the tive, and memory texts alike). However, to group, and then to remember the new name my knowledge no one has successfully repli- rather than the input event'' (1956b, page 93). cated his repeated reproduction experiments Recoding is an active process of transforma- on materials like ``The War of the Ghosts'' tion and therefore the possibility of errors in when they used instructional sets requesting recoding and later decoding may arise. Miller that people remember the story. Gauld and (1956a) wrote: Stephenson (1967) found errors like Bartlett's when they told people to make up a story like A . . . more general technique for organizing our the one they had heard, but not when they experience into convenient units is provided by asked them to remember the story. Wheeler language. . . When you witness a scene or hear a story that you want to remember, you try to trans- and Roediger (1992) gave subjects repeated late it 'into your own words,' into the linguistic tests on both ``The War of the Ghosts'' and units that will ®t into your own cognitive hierar- on another prose passage and found that they chy. This highly schematic, verbalized abbrevia- actually recalled more on the second test than tion is remembered. Then when you try to recall on the ®rst, at least with short delays between you must decode. Since the ®t of words to experi- ence is seldom as tight as the ®t of laws to data, tests. It seems odd that experimental observa- the decoding process often goes astray. You supply tions could live on for so long in textbooks details by secondary elaboration that are consistent when the original methods were so casual and with your coded memory. Often these details are when no one has successfully replicated the wrong. (p. 132) work.2 The probable reason lies in the fact that most observers thought Bartlett's (1932) Miller (1956a, 1956b) paved the way to the basic story about memory rang true, regardless information processing approach to remem- of his methods and results, and if so, that as- bering, which has largely guided research for sessment still seems accurate today. the past 40 years. As Koriat and Goldsmith (in press) have noted, research conducted in THE MODERN ERA this tradition has largely been devoted to is- The information processing approach to sues of how much (how many units) could be cognition began in the 1950s as researchers remembered, and errors have been given carried concepts and methods from communi- rather short shrift. However, nothing within cations theory and electrical engineering into the information processing approach itself or- psychology. In the 1950s Donald Broadbent dained this emphasis, as the quotes from (1958) produced the ®rst information ¯ow dia- Miller indicate; and some researchers did at- grams and George Miller (1956a, 1956b) pro- tend to error analyses. For example, Conrad duced two papers that began a revolution in (1964) studied errors of short-term memory the study of human memory. One of Miller's and concluded that they had a phonological key ideas was the concept of recoding, basis, whereas other researchers found seman- wherein information is received from the out- tic confusion errors in studies of long-term side world in one form but is transformed and memory (e.g., Underwood, 1965). However, represented in a different way internally. most researchers in¯uenced by Miller (1956a, 1956b) studied how material was organized so as to be remembered better. For example, 2 Bartlett's (1932) serial reproduction experiments, in Tulving (1962, 1964) studied how subjects or- which one person reads and recalls a passage, the second ganized random word lists into subjective person reads the ®rst person's recollections and then re- calls the information, etc., also induce systematic distor- units in multitrial free recall so as better to tions. These experiments have been successfully repli- remember the words. Glanzer and Clark cated (e.g., Paul, 1959). (1963) developed the verbal loop hypothesis,

AID JML 2467 / a002$$$103 04-10-96 17:23:17 jmla AP: JML MEMORY ILLUSIONS 83 seeking to show that when people are faced hypothesis of remembering (pages 284±286). with visual information, they recode it into Perceiving and remembering were seen to be a verbal description and that this description amenable to similar interpretation: ``The anal- guides later recall. ogy being offered asserts only that the role Many different trends in the modern era which stored information plays in recall is like launched psychologists on the road to study- the role which stimulus information plays in ing errors and distortions of memory. I review perception'' (page 285). In neither case can some of the main trends in the ®eld and, while the information to be used directly enter con- doing so, show how articles in the current sciousness or be reproduced in behavior in issue ®t in. a literal manner; rather, constructive activity (top-down processing) operates on the infor- Neisser's Cognitive Psychology mation and the perceiver and rememberer be- In 1967 Ulric Neisser published his great come conscious only of the product of this book, which gave an entire ®eld its name and constructive activity. Therefore, ``. . .stored set many of the topics that were to be the information is not revived, but simply used, center of attention in the new ®eld: iconic in the constructive activity of recall'' (page memory, echoic memory, reading, imagining, 289). Just as constructive activity can give rise and so on. Traditional memory research in the to illusions in perceiving, the same is true in Ebbinghaus tradition was not much in evi- remembering. dence, but more importantly for present pur- Although it is not possible to pinpoint a poses, Neisser capped his book with a chapter cause and effect relationship with certainty, it on remembering and thinking that harked back seems likely that Neisser's famous book, and to Bartlett's (1932) idea of remembering as a especially its ®nal chapter, may have helped constructive process. Neisser emphasized the launch the renaissance of experiments in the unity of cognitive processes and noted that 1970s that examined errors in prose retention perceiving, remembering, and thinking were in the Bartlett (1932) tradition. all active and interdependent processes. It seems obvious that remembering depends on Memory for Prose: The In¯uence perceiving, but less so that higher cognitive of Schemas processes usually studied as issues of problem solving and thinking are also involved in re- In the early 1970s several groups of re- membering, at least to the extent that remem- searchers began studying errors in prose reten- bering is conceived as a constructive activity. tion that implicated the active role of the re- Neisser's (1967) assumptions were stated memberer in bringing his or her knowledge clearly: to bear in recoding information. Bransford and Franks (1971) presented subjects sentences of It is assumed that remembering and thinking are varying complexity that created a coherent analogous to adaptive movement and to motor idea. Later they tested subjects' memories for skill; they also resemble the synthetic processes sentences that had been presented, ones that of visual memory and speech perception. Stored information consists of traces of earlier construc- had not been presented but were consistent tive acts, organized in ways that correspond to the with the complex idea, and ones that were structure of those acts. However, the 'traces' are unrelated to the idea. Subjects could easily not dormant copies of earlier experiences, some- reject the unrelated sentences, but they failed how aroused into consciousness from time to time. to distinguish between presented and not pre- Stored information is never aroused, it is only used, just as stimulus information is used in the sented sentences so long as they were consis- act of perception. (page 279) tent with the overall idea. Subjects' con®dence in recognition was directly related to the num- Neisser (1967) developed the idea in the ber of propositions in the test sentence that last sentence just quoted into the utilization were consistent with the overall idea, regard-

AID JML 2467 / a002$$$103 04-10-96 17:23:17 jmla AP: JML 84 HENRY L. ROEDIGER III less of whether they had actually been pre- nition tests composed in part of lures that bear sented in the study phase. various semantic relations to the studied In a later study, Bransford, Barclay, and words. Underwood (1965) gave subjects a Franks (1972) showed that people would continuous recognition test in which they de- falsely remember events as having occurred cided if each presented word had been studied when the events had only been implied by previously in the list. When subjects encoun- prose passages but not actually stated (see too tered a word that bore an associative relation Johnson, Bransford, & Solomon, 1973). For to a previously studied word (e.g., to decide example, subjects studied sentences such as if chair had been previously presented, when ``Three turtles rested on a ¯oating log, and a in fact table had been), they were more likely ®sh swam beneath them.'' Later subjects were to provide false alarms to the words (to chair asked if the sentence ``Three turtles rested on in this example) than if there were no associa- a ¯oating log and a ®sh swam beneath it'' had tive connection between the test word and appeared in the passage and a large percentage prior words. Others replicated this effect (e.g., said yes. Other research also shows that infor- Anisfeld & Knapp, 1968; Paul, 1979), but it mation implied, but not actually stated, is of- is sometimes rather small or even nonexistent ten remembered as if it had actually occurred (Gillund & Shiffrin, 1984). However, others (Brewer, 1977; Harris, 1974). have shown that the false recognition effect Much work in this tradition showed how increases with the number of previously pre- what a person already knew, or the context in sented words that are semantically related to which information was presented, determined the test word or lure (Hall & Kozloff, 1973; whether and how it would be remembered. Hintzman, 1988; Shiffrin, Huber, & Marinelli, Sulin and Dooling (1974) showed that sub- 1995). Underwood (1965) interpreted the false jects would falsely recognize a statement recognition phenomenon in this paradigm as about a person if an appropriate schema had being caused by implicit associative responses been invoked. For example, a week after read- during encoding; when studying table, chair ing a story about a troubled girl, subjects were might be aroused and therefore later recog- more likely to recognize the sentence ``She nized. With increasing numbers of related was deaf, dumb, and blind'' if they had been words, the chances of subjects producing the told the story was about Helen Keller than if critical associates might be increased, thereby they had been told it was about Carol Harris. accounting for the more powerful effect ob- Many other experiments of similar form have served in later studies. demonstrated the power of schema (and The great bulk of the evidence about mem- scripts) in organizing incoming information, ory distortion relies on recognition paradigms, in line with Bartlett's (1932) and Miller's the primary measure in the studies described (1956b) ideas, cited above (see Bower, in this section and the previous one being false Black, & Turner, 1979; Owens, Bower, & alarms. Studies examining false recall, either Black, 1979; and Spiro, 1980, for some further in the schema/prose tradition or the more stan- examples and Alba & Hasher, 1983, and dard word list tradition are much rarer, espe- Brewer & Nakamura, 1984, for reviews). cially with the failures to replicate Bartlett's (1932) ®ndings (but see Brewer, 1977; Relatedness Effects Hasher & Grif®n, 1978; and Spiro, 1980, for The experiments described in the previous exceptions in the prose tradition). Deese section show that people will recognize sen- (1959) reported results of a paradigm that tences or passages as having occurred if they showed robust levels of false recall following are similar in meaning to previously studied presentation of word lists, at least for certain prose materials. Similar phenomena have been lists. Deese (1959) constructed his lists from uncovered in other paradigms in which sub- word association norms by selecting words jects study word lists and then are given recog- associated to one target word. For example,

AID JML 2467 / a002$$$103 04-10-96 17:23:17 jmla AP: JML MEMORY ILLUSIONS 85 hill, valley, climb, summit, and top are all re- presented by two different speakers during lated to mountain. Deese (1959) presented lists study and subjects were asked on a later recog- of 12 related words and then measured the intru- nition test to make judgments about which sion of the critical nonpresented word from speaker had said words that were recognized which the lists were derived, such as mountain. as old or studied. Payne et al. found that sub- For some lists (ones in which there was a high jects were quite willing to indicate which of probability of generating the critical nonpre- the two people had spoken words that had sented target from list members, as measured actually never been presented in either voice. by free association norms), the level of intru- The conclusion that they reached is similar to sions, or false recalls, was quite high. Cramer that derived from the remember/know judg- (1965) reported similar observations, but neither ments: subjects apparently experience the rec- study received widespread attention. ollection of these events that never happened Roediger and McDermott (1995) revived as quite real, as real as the recall of the word Deese's (1959) paradigm, replicated the phe- events that actually had occurred. ``False nomenon of high levels of false recall follow- memories'' may be a misnomer, at least from ing presentation of related word lists, and ex- the subjects' viewpoint, because the experi- tended the ®ndings in several directions. For ence of recollecting the critical nonpresented example, they showed that false recognition words appears as real to the subjects as their of the target words (the false alarm rate) recollections of the presented words. equaled the hit rate in some conditions and Schacter, Verfaille, and Pradere used the that the act of recall later enhanced both accu- same paradigm to study development of false rate and false recognition. Further, using Tul- memories in amnesic patients. Interestingly, ving's (1985) paradigm in which subjects they found that patients were less susceptible were asked to judge whether they actually re- to this memory illusion than were control sub- membered the occurrence of words (rather jects. They argued that this outcome indicates than knowing that they occurred, but not spe- that development of false memories in this ci®cally remembering the moment of presen- paradigm can be interpreted with the Reyna tation), subjects frequently remembered the and Brainerd (1995) fuzzy trace theory (as did words that were never presented. Payne et al., too). In particular, Schacter et al. Three papers in this issue use Roediger and interpreted the ®nding of less false recall and McDermott's (1995) paradigm. McDermott recognition in amnesic patients as indicating replicates the basic phenomenon and adds sig- that the gist representations that normally sup- ni®cant new information. For example, she port recollective processes are impaired in the shows that multiple study and test opportuni- patients, relative to normal controls. ties cause the levels of false recall to decline, The paradigms introduced by Deese (1959) but that they are still substantial after ®ve and Underwood (1965) and their variations study/test trials. In addition, blocked presenta- serve as tractable experimental manipulations tion of words leads to higher levels of false for studying the development of false memo- recall than does random presentation and, over ries. As noted by Roediger and McDermott time, accurate recall declines, whereas false (1995), the robust levels of false recall and recall actually becomes somewhat greater. false recognition are remarkable, because they Payne, Elie, Blackwell, and Neuschatz also occur under conditions that often promote replicate the basic phenomena reported by good verbatim (or reproductive) recall: simple Roediger and McDermott (1995) while adding word list materials, free recall tests that dis- important new insights. For example, the false courage guessing, short retention intervals, memory effect grew over repeated testing (un- and the use of metamemory judgments (re- der conditions, unlike those of McDermott, in member/know judgments, modality judg- which there were no additional study opportu- ments) that direct subjects' attention to the nities). In another experiment, words were bases of veridical judgment.

AID JML 2467 / a002$$$104 04-10-96 17:23:17 jmla AP: JML 86 HENRY L. ROEDIGER III

Effects of Interference and Misleading present in the scene, so these responses consti- Information tuted errors. Loftus and Palmer (1974) argued that the question involving the powerful verb Perhaps the most studied way of systemati- smashed caused subjects to recode the acci- cally distorting memory is presenting other dent differently and consequently to be more events or information to interfere with reten- likely later to remember broken glass where tion of a critical target event of interest. MuÈller none existed. and Pilzecker (1900) ®rst identi®ed the role The Loftus and Palmer (1974) paradigm of interference in forgetting and it has been eventually developed into what has come to studied, in various traditions, ever since. The be called the misinformation effect paradigm. critical roles of both retroactive interference In the standard case (e.g., Loftus, Miller, & (McGeoch, 1932) and proactive interference Burns, 1978) subjects view a scene (for exam- (Underwood, 1957) in producing forgetting ple, a traf®c accident in which an automobile have long been recognized. Although error pulls into an intersection where there is a stop analyses played a role in the classic study of sign) and then later they are asked questions interferenceÐfor example, the curious pat- (or read a passage) that contain information tern of intrusions as a function of trials of about the original scene. Some subjects are interpolated learning convinced Melton and told that the sign was a yield sign (the misin- Irwin (1940) that a Factor X (unlearning) formation condition), whereas it is referred to needed to be added to response competition in a neutral manner (a traf®c sign) or not men- to explain forgettingÐthe primary interest of tioned at all for subjects in the control condition. the times was not in how interfering informa- Typically, memory for the information in the tion created memory distortions and illusions. original scene is worse when misinformation has Rather, the interest was in the forgetting of been given relative to performance in the control studied information. condition, although the magnitude of the effect At about the historic point when interfer- depends on many factors. ence theory had peaked and a decline in re- This paradigm has produced a huge amount search interest was occurring (usually dated of research (see Loftus, 1979a, 1993b, for re- from the Postman and Underwood (1973) pa- views) showing how information coming after per), Loftus and Palmer (1974) introduced a an event can shape and mold remembrance of paradigm that bore formal similarity to a retro- the event. Interest centers both on forgetting active interference paradigm, but that was of the original event and, more importantly for used to ask different questions with different present purposes, on the case where subjects materials. They showed subjects a videotape come to remember the suggested event as ac- of an automobile accident and later gave them tually having occurred (Lindsay & Johnson, a questionnaire in which a critical question 1989; Weingardt, Toland, & Loftus, 1994). was embedded: ``About how fast were the two Two papers in the special issue are devoted cars going when they ___ each other?'' The to this problem. Mitchell and Zaragoza exam- verb was varied for different groups of sub- ine the effects of repeating the misinformation jects. For example, when hit was used, sub- on memory for the target event and for the jects estimated the speed at 34 miles per hour misinformation itself. Repeating the mis- but when smashed into was used, the estimate leading statements makes subjects less likely grew to 41 miles per hour. More interestingly to recall the original events accurately. Roe- for present purposes, when subjects were later diger, Jacoby, and McDermott examine the asked the question ``Did you see broken effects of repeated testing on recall of events glass?'' 14% of those who had received the in this paradigm. In particular, they provided question with the verb hit answered yes, conditions in which subjects were encouraged whereas 32% of those who had received to produce the misleading information on a smashed answered yes. No broken glass was ®rst test, but then examined subjects 2 days

AID JML 2467 / a002$$$104 04-10-96 17:23:17 jmla AP: JML MEMORY ILLUSIONS 87 later under strict instructions to recall only negative effects of verbalization on remem- events that they had actually witnessed during bering. In line with Glanzer and Clark's the ®rst phase of the experiment, in the slides. (1963) verbal loop hypothesis, people remem- Subjects who had provided the misinformation ber the events as they described them to them- on the ®rst test were still quite likely to do selves, not as they actually happened. so again on the second test (relative to control groups). Further, subjects in this condition Illusions of Reality Monitoring and Source claimed to remember the actual occurrence of Monitoring the suggested event, even though it had never In the 1970s Marcia Johnson and her col- happened. The misinformation paradigm intro- leagues began a program of research that has duced by Loftus continues to play a prominent identi®ed a variety of interesting and im- role in studies of memory errors (see the edited portant facts about accuracy and inaccuracy volume by Ross, Read, and Toglia (1994) for of remembering. In the original work (e.g., recent reviews of these issues). Johnson, Taylor, & Raye, 1977; Johnson & Raye, 1981), interest was in how subjects dis- Verbal Overshadowing tinguish between information derived from A situation related to that of Loftus' para- external sources (events that really happened) digm was developed by Schooler and En- and those that were generated by sources in- gstler-Schooler (1990), which they called ver- ternal to the person (such as events that were bal overshadowing. Carmichael, Hogan, and only generated or imagined), or, to use the Walter (1932) showed long ago that ambigu- question that formed the title of a related paper ous visual stimuli were remembered in differ- by Anderson (1984): ``Did I do it or did I only ent ways depending on the verbal description imagine doing it?'' Early experiments were given to the stimuli. Of course, in many situa- concerned with estimating the frequency with tions verbalization can aid memory, and many which events were presented externally or studies have revealed positive effects of re- were internally generated. For example, sub- hearsal and verbal elaboration. However, jects show better relative frequency judgments Schooler and Engstler-Schooler (1990) argued for internally than externally produced events. that verbalization may harm memory when More interestingly for present purposes, the the events to be remembered are dif®cult to more subjects imagined an event, the greater capture in words. They have demonstrated this the impact on judgments of frequency that the in a number of studies using stimuli from vari- event actually occurred (Johnson et al., 1977; ous domains. For example, when subjects Johnson & Raye, 1981). Subjects confused the viewed faces and had to describe them, mem- imagined events with those that actually oc- ory for the faces was worse than when subjects curred in estimating their frequency, a failure did not describe the faces. to monitor real events accurately, or a failure In their article in this issue, Melcher and of reality monitoring, as Johnson and Raye Schooler extend their verbal overshadowing (1981) called it. paradigm to recognition of the taste of wine. Johnson and Raye (1981) proposed that Untrained wine drinkers were impaired in people distinguish between internal and exter- their recognition of wines when they engaged nal events in memory both by the types of in verbalization during their initial tasting, rel- information encoded and by decision rules ative to the case in which they participated in used when tested. Encoded representations of an unrelated verbal activity. Consistent with external events are especially rich in percep- their predictions, this verbal overshadowing tual information (sensory features or attri- effect did not occur in trained wine drinkers butes) and contextual information (such as who had considerable expertise in translating time and place of occurrence). On the other their tastes into words. We can expect to see hand, encodings of internally generated events many more experiments on the positive and are assumed to include considerable informa-

AID JML 2467 / a002$$$104 04-10-96 17:23:17 jmla AP: JML 88 HENRY L. ROEDIGER III tion about cognitive operations that were used reading about the accident, as actually having to encode the event. People are assumed to occurred at the original scene (Lindsay & use these differences in information when de- Johnson, 1989; Zaragoza & Lane, 1994). ciding on whether something ``really hap- In the present issue, Johnson, Nolde, and pened'' to them. However, confusions can DeLeonardis add important new information arise in some cases, such as when an imagined about the impact of subjects' emotional focus event may have been vividly imaged in a par- (either on themselves or on another person) ticular time, at a particular location, and with on their abilities to accurately monitor the considerable sensory detail. source of information. Johnson et al. asked Another critical aspect of Johnson' theory, people to focus either on how they personally as developed in later writings (e.g., Johnson, felt about statements that were read to them 1983, 1995) is the distinction between two gen- or about how they thought the speakers of the eral types of judgment processes (similar to statement felt when reading them. Although those proposed by others; Atkinson & Juola, focusing on their own reactions to statements 1973; Jacoby & Dallas, 1981; Mandler, 1980). made people recognize the statements better Brie¯y, subjects can use either a relatively on an old/new recognition test, this self-focus quick, nondeliberative heuristic process in mak- actually reduced their ability to monitor the ing judgments or they can use more systematic source (to tell which of two people had spoken processes that are slower and more deliberate. the statement). The difference in self versus The heuristic process is quick and dirty, used other focus was eliminated, however, in an to make snap judgments and resulting in errors experiment when subjects were instructed to when the snap judgment leads to the conclusion focus on how they felt about the speakers (for example) that something actually happened rather than (as in the studies described above) when it only seems familiar because the person when subjects focused on how they thought thought about it (or generated it internally). Sys- the speakers felt about what they were saying, tematic judgment processes bring other features a ®nding in line with predictions made from to bear on the decision as to whether something the source monitoring framework. actually happened and are therefore less likely The contribution by Hyman and Pentland to be error prone. in this issue also can be interpreted within A large variety of evidence has been col- Johnson's source monitoring framework. lected that supports Johnson's general ap- They use the technique of having people proach, which has been broadened to a general imagine events that may or may not have oc- source monitoring framework (Johnson, curred during their childhoods and show that Hashtroudi, & Lindsay, 1993). Information imagining the events sometimes induces peo- can arise from many sources that vary in mo- ple to believe that the events did happen. The dality (auditory, visual, verbal, pictorial), time events are, on the face of it, fairly improbable of occurrence, place of occurrence, and so on, ones. This outcome agrees with others in rather than simply being external or internal. showing the powerful role of imagination in A primary type of data used to support the creating false memories (Johnson, Foley, theory is confusion that subjects show among Suengas, & Raye, 1989; see too Garry, Man- sources, leading to interesting illusions of ning, Loftus, & Sherman, in press). Imagining memory. The source monitoring framework seems to involve brain mechanisms similar to has assumed increased importance in the ®eld, those used in perceiving (e.g., Farah, 1989), as researchers have interpreted other phenom- so it is not surprising that imagining events ena under its umbrella. For example, the im- can make people later remember that they had pact of misleading postevent information can happened (even when they did not). However, be conceived as a failure of source monitoring; the positive effects of imagery have usually subjects may remember the stop sign, which been emphasized by psychologists interested was only suggested by a question or from in memoryÐhow imagining studied events

AID JML 2467 / a002$$$105 04-10-96 17:23:17 jmla AP: JML MEMORY ILLUSIONS 89 makes them more memorableÐso the role of (if the subjects' attention is focused on per- imagery in undermining memory may at ®rst forming some other task) this ¯uency may be glance seem surprising. However, Johnson's misattributed to some other source besides the framework permits us to understand how im- past events. For example, Jacoby, Allan, Col- agery can both make studied events more lins, and Larwill (1988) tested subjects' judg- likely to be correctly recalled, and imagined ments of the loudness of background noise in ``nonevents'' more likely to be falsely re- which words were embedded when some of called. In the former case, imagining adds ad- the words had been previously heard and oth- ditional cognitive operations to the encoded ers had not. When subjects had previously event that serve to enhance later memory for heard the words, they judged the noise to be the event's occurrence; in the latter case, the less loud than when nonstudied words were cognitive operations help make the ``non- judged, despite the fact that the objective noise event'' appear real by specifying perceptual level was the same in the two cases. The facili- detail, which usually signi®es an event that tating effects of prior experience on hearing actually occurred (Johnson et al., 1989). Other the words through noise were misattributed illusions on the border between perceiving and to differences in the noise levels rather than remembering are considered below, in the accurately attributed to memory for prior ex- next two sections. perience of the words. Jacoby and Whitehouse (1989) manipulated Fluency Illusions: Misattributions the ease with which words were perceived on of Memory a recognition test by preceding them with a Jacoby, Kelley, and their colleagues have brie¯y presented prime. Subjects judged the developed an attributional view of memory words that were primed as more familiar on that is similar in some ways to Johnson's a recognition test, presumably mistaking the (1983) source monitoring approach (Jacoby, ¯uency of processing for familiarity. Jacoby Kelley, & Dywan, 1989; Kelley & Jacoby, and Whitehouse proposed that such ¯uency 1990). They borrow from attribution theory in may be the cause of deÂjaÁ vu experiences (such social psychology, where (for example) emo- as described by Titchener in the opening para- tional states are thought to arise from a partic- graphs). The enhanced ¯uency of an experi- ular combination of physiological arousal and ence from a prior event that is not remembered appropriate cognitions induced by the situa- may create a strange sense of familiarity, with tion (e.g., Schachter & Singer, 1962). Simi- no obvious source to which it should be attrib- larly, Jacoby, Kelley, and their colleagues uted. Whittlesea, Jacoby, and Girard (1990) conceive of remembering as a combination of and Whittlesea (1993) reported illusions of ¯uent processing of an event with the mental immediate memory that were similarly caused set that attributes the ¯uency to past experi- by manipulations of perceptual ¯uency. ence, or to remembering. As in Johnson's Two papers in the current issue draw on framework, Jacoby and Kelley distinguish dif- Jacoby and Kelley's attributional framework. ferent bases of judgment: a more intuitive, Lindsay and Kelley show that enhanced ¯u- rapid, and nonanalytic basis on the one hand, ency can drive know judgments in Tulving's and a more deliberate, re¯ective, and analytic (1985) remember/know paradigm. In their ex- basis on the other. For the experience of re- periments, either easily solved word fragment membering there needs to be ¯uent processing cues, or ones that were dif®cult to solve, were of information (of it readily coming to mind) presented as test cues following study of a and an attribution of the ¯uency as arising word list. Subjects were told that the cues from past experience. should remind them of list words and that they Several interesting illusions support Jacoby were to report the word and to judge whether and Kelley's attributional framework. First, they remembered details of its list presenta- past events may lead to ¯uent processing and tion, or rather simply knew that it had been

AID JML 2467 / a002$$$105 04-10-96 17:23:17 jmla AP: JML 90 HENRY L. ROEDIGER III on the list. Most studied words were repre- we can look at our writing more as someone sented by fragments appearing on the test, just coming to it, without being quite so ego- leading subjects to believe that the fragments centric. Kelley and Jacoby studied these fasci- were reliable retrieval cues for the list items. nating processes of judgment with an anagram Lindsay and Kelley's primary interest was in solution task. When subjects had studied ana- judgments for a small group of words that had grams, they solved them faster on a later test not been presented in the study phase. In this (a priming effect), but they misattributed this case, making the solution easy led subjects to ease to properties of the anagram rather than report the word as having been presented, but to their previous experience. Subjects' order- to judge that they knew it had been on the ing of the general dif®culty of the anagrams list (but did not remember the details of its was different when the anagrams had been occurrence). This interesting illusion of know- studied than when they had not; presumably, ing depends a bit on assumptions used to ana- when subjects had studied solutions to the lyze know responses. In addition, recall that anagrams, they partly used ¯uency to deter- Roediger and McDermott (1995) reported that mine the ease of arriving at the anagram's subjects would often provide remember re- solution, or they relied more on nonanalytic sponses for nonpresented items recognized in bases of judgment. When anagrams had not their paradigm. The differences between their been studied, subjects probably used more de- results and those of Lindsay and Kelley may liberate, rule-based judgments. Thus, some- lie in the tests and the types of processing they what paradoxically, experience within a do- engender. The Lindsay and Kelley paradigm main may reduce one's ability to assess how capitalizes on perceptual (data-driven) factors others assess and comprehend the same infor- in producing ¯uent output, with powerful cues; mation, a form of adult egocentrism (as Kelley this sense of false familiarity arising from per- and Jacoby call it) that doubtless af¯icts us ceptual factors may lead to know judgments. all. All college professors have had the experi- The Roediger and McDermott (1995) subjects ence of explaining an interesting point, with produced an erroneous memory conceptually re- what they imagine to be great clarity, only to lated to other memories and judged them as be confronted with the befuddled looks of being remembered (rather than known) most of most of the students in the class. the time. One hypothesis is that facile processing driven by perceptual ¯uency may lead to the Illusions of Perception and Memory illusion of knowing, whereas when material The illusions arising from perceptual ¯u- pops to mind that is conceptually related to other ency discussed in the previous section docu- memories, it may give rise to the illusion of ment the intimate link between perceiving and remembering. This speculation awaits further re- remembering, which can be easily demon- search (see Rajaram & Roediger, in press, for strated either during the encoding or retrieval related observations). phase of memory experiments (as in the work In another set of studies, Kelley and Jacoby of Jacoby and Kelley). Many illusions seem studied how memory of past events may inter- to lie on the border of perceiving and remem- fere with making good subjective judgments. bering. Consider the thought experiment of Writers are frequently unable to judge whether testing subjects' retention of the shapes in Fig. what they have written is comprehensible, and 1. If they were simply shown the ®gures with a frequently suggested strategy, once a paper instructions to attend to the shaded space and is written, is to put it away for a few weeks then asked, a few moments later, which was before revising it. Presumably this advice cap- wider and shorter, the one on the right or the italizes on the intuition that our judgment of one on the left, they would doubtless respond the goodness of our writing will be better once that it was the one on the right. They would we have forgotten what we wanted to say and of course be wrong, as the shaded portions are why we wrote what we did; if we wait a while, identical. Is this an illusion of perception? an

AID JML 2467 / a002$$$105 04-10-96 17:23:17 jmla AP: JML MEMORY ILLUSIONS 91 illusion of memory? or is it both? If the origi- what do you remember?). Obviously, the experi- nal event is wrongly perceived, then usually mental situations blend into one another and it the resulting memory will be wrong too, un- is impossible to say when perceiving is com- less some other factor corrects the false per- pleted and remembering takes over in subjects' ception later (making memory for the event reports. better, in a sense). One memory illusion at the border between Another issue: Are sensory memories perceiving and remembering is the phenome- (iconic and echoic) veridical, or illusory, or non of boundary extension, studied by Intraub both, in different aspects? Sensory memories and her collaborators. Observers view a pic- are thought to be quite faithful replicas of the ture and then later remember seeing more of original experience, at least for their brief life- the scene than was actually shown; it is as times. On the other hand, the perceiver/re- though the scene's boundaries have become memberer still experiences events as being extended when it is remembered. The effect perceived that have disappeared. So perhaps occurs both in recall and recognition tests (In- sensory memories have both veridical and il- traub & Richardson, 1989; Intraub, Bender & lusory aspects. Like the questions above, this Mangels, 1992). In this issue, Intraub, Gottes- one about sensory memories is dif®cult to an- man, Willey, and Zuk examine the effects of swer conclusively. Similarly, the illusory phe- brevity of exposure on the phenomenon, as nomenon known as the McCollough effect well as testing after very short delays. They (McCollough, 1965) can last for days. (The found that the effect occurs even when expo- McCollough effect is an illusion of color that sure durations for the studied pictures are is contingent on the particular orientation of quite brief (250 or 333 ms) and when the re- adaptation and test lines.) Is it a phenomenon tention interval is only 1 s. In conjunction with of erroneous perception, of memory, or both? other evidence, they interpret the illusion as These questions also illustrate again the dif®- arising just after a picture is perceived. In par- culty of rigorously de®ning what an illusion ticular, subjects interpret a picture in terms of is; such a de®nition has thus far eluded psy- a perceptual schema that contains information chologists studying perceiving and it will likely to exist just outside the actual picture. probably be even more dif®cult to achieve for When the scene is comprehended, subjects re- remembering. member information that did not actually exist Several other types of illusion are also dif®- in the picture, but only in their schema used cult to classify as perceptual or as memorial and to comprehend the picture. The error is clearly both labels likely apply. Part of the problem memorial, in one sense, because boundary ex- is that the operational procedures for studying tension does not occur while subjects are look- perception and memory are often formally quite ing at the scene, so it is not a perceptual illu- similar. In many experiments on perception of sion in the usual sense. However, the Intraub words or pictures, the stimuli are presented very et al. results show that the illusion develops brie¯y and subjects are asked to report what very rapidly upon offset of the picture, pre- they saw (or heard) as soon as possible, or they sumably as it is still being interpreted. There- are asked to make a rapid decision or judgment fore, the phenomenon falls at the boundary about the event. In many memory experiments between perceiving and remembering. words and pictures are shown and the subjects Another illusion falling at this boundary is are asked, after some retention interval, to recall representational momentum (Freyd & Finke, what occurred or to make a judgment about the 1984). In the original experiments, subjects presented events. Often the primary differences received three computer animated rectangles in the situations are (a) the duration of the origi- (called inducing stimuli) and then later had to nal display, (b) the amount of time before a judge whether a fourth stimulus, the probe or report or judgment is required, and (c) the nature test stimulus, occurred in the same position as of the query (what did you perceive? versus the last inducing stimulus. On some occasions

AID JML 2467 / a002$$$105 04-10-96 17:23:17 jmla AP: JML 92 HENRY L. ROEDIGER III the three inducing stimuli implied rotation in rather small but Reinitz, Lammers, and Coch- either a clockwise or a counterclockwise di- ran (1992) and Reinitz, Morrisey, and Demb rection. The interesting ®nding was that sub- (1994) replicated it and showed similar results jects were more likely to respond same to the in encoding of faces (see too Solso & McCar- probe stimulus if it was slightly forward of thy, 1981). The interpretation of such illusory the ®nal inducing stimulus in the direction of conjunctions in memory, as in perception, is implied motion, as if the representation of the that features may not be tightly bound together motion of the inducing stimuli had momentum into unitized wholes. Rather, features are free- and was carried forward (hence the name). ¯oating to some degree and, when two fea- The effect increased with the velocity of the tures are combined from different units, they implied motion and is not due to eye move- may be falsely recognized. ments (see Hubbard, 1995, for a review). Two papers in the current issue use the illu- Again, it is dif®cult to classify this illusion as sory conjunction paradigm to explore the roles perceptual, mnemonic, or both. of attention and consolidation in encoding. In- A third and ®nal case to be considered is terestingly, both sets of researchers also used that of illusory conjunctions in perceiving, a a neuropsychological approach in which pa- topic of study introduced by Treisman and tients with memory disorders arising from Schmidt (1982). Subjects are presented quite brain damage were tested. Reinitz, Verfaellie, brie¯y with stimuli that contain several fea- and Milberg compared amnesic patients to tures, such as letters that differ in color (e.g., control subjects in the basic recognition para- a blue R, a red M, a green C, and so on). The digm in which subjects are tested with pre- interesting observation, now replicated many viously studied words, conjunction words (the times, is that subjects will often report seeing two syllables have been presented, but in dif- objects that represent illusory conjunctions of ferent words), feature words (one syllable has features, such as a red R or a blue C in the been studied and the other is new), or com- above example. Because the displays are so pletely new words. Control subjects showed rapid in this research, these errors have a per- the pattern expected from prior experiments: ceptual feel, yet they occur at a short interval The hit rate for studied words was much after the perceptual display has disappeared. higher than the false alarm rate for conjunc- However, as we see in the next section, illu- tion words, and in turn this false alarm rate sory conjunctions also arise in remembering. was higher than that for either feature words or new words. Amnesic patients showed a dif- Illusory Conjunctions in Memory ferent pattern in that they were unable to dis- Underwood and Zimmerman (1973) and criminate between studied words and conjunc- Underwood, Kapelak, and Malmi (1976) in- tion words. The patients seemed not to have troduced a way of studying illusory conjunc- formed a global representation of the words, tions in memory by presenting compound because parts of the words could ``¯oat'' and words for subjects to study (e.g., handstand, be erroneously joined together, leading to shotgun). Later subjects were tested for recog- false alarm rates as high as the hit rates. nition of previously studied words, words that Kroll, Knight, Metcalfe, Wolf, and Tulving had one syllable in common with the studied use a variant of the illusory conjunction para- words (handmaid) or, in the most interesting digm on patients having left, right, or bilateral case, words in which both syllables had been hippocampal damage. In a running recogni- previously studied (handgun, in this example). tion task in which subjects judged every pre- Subjects produced more false alarms to the sented word as old or new, items could repre- conjunction test items like handgun than to sent either previously studied items, conjunc- either words with one syllable of overlap with tion items, single feature items, or completely the studied word or control words that were new items. They found that patients with left unrelated to the studied words. The effect was hippocampal damage classi®ed more conjunc-

AID JML 2467 / a002$$$105 04-10-96 17:23:17 jmla AP: JML MEMORY ILLUSIONS 93 tion items as old (i.e., they produced more ing evidence that hypnosis leads to illusory false alarms on these items) relative to normal memories (e.g., Lynn & Nash, 1994; White- subjects or those with right hippocampal dam- house, Orne, Orne, & Dinges, 1991). Subjects age. Kroll et al. interpreted these results, and under hypnosis are often encouraged to generate those from a similar experiment involving pic- everything they can think of to free associate tures, as evidence for a binding process during about the event they are trying to remember. consolidation of information occurring via the Much of the information obtained under this hippocampus. state is erroneous, although some is correct The illusory conjunction paradigm using (but no more than that retrieved by nonhypno- words, pictures, or faces may prove to be im- tized control subjects given extra time). The portant in the study of false memories. It is dif®culty comes later when subjects (back in also worth noting that both papers discussed their normal waking state) try to distinguish here (and the one by Schacter et al. described what actually happened in the target event previously) used memory-disordered patients from what they recalled during hypnosis. The to study memory illusions. Certain patients, available evidence shows that subjects who especially those with damage to the frontal score high on hypnotic susceptibility scales lobes and to the areas surrounding the hippo- often confuse events they retrieved under hyp- campus, display profound memory disorders. nosis with those that actually occurred and Although amnesic patientsÐthose with dam- that they cannot even distinguish the memo- age in and around the hippocampus who are ries they retrieved under hypnosis from those rendered incapable of consciously recollecting that they retrieved prior to the hypnotic ses- newly presented informationÐrepresent an sion (Sheehan, 1988; Lynn and Nash, 1994; interesting type of disorder, those patients Whitehouse et al., 1991). with frontal damage who confabulate and These ®ndings of false memories induced claim to remember events that never happened by hypnosis bear many points of similarity may turn out to be just as interesting in the with phenomena discussed previously. In a study of memory illusions (Johnson, 1991; sense, hypnotized subjects are encouraged to Moscovitch, in press; Schacter, Curran, Gal- provide their own misinformation about lucio, Milberg, & Bates, in press). events during the hypnotic session and it may even be that such internally generated misin- Hypnosis and Guessing Effects formation (in the form of guesses of what The use of hypnosis in attempts to aid mem- might have happened) could be even more ory retrieval has a long and checkered history. powerful than externally presented misinfor- The topic has been examined intensively for mation in creating interference, although this the past 20 to 30 years and there now seems hypothesis awaits experimental test. At the general agreement that hypnosis does not very least, subjects who are queried later seem serve as the key to unlock forgotten memories, to display reality monitoring and source moni- as some had hoped (see Smith, 1983, and toring confusions, not being able to tell what Lynn & Nash, 1994, for reviews and discus- actually happened from descriptions that they sion). Relative to appropriate control groups, produced while hypnotized. In addition, the hypnotized subjects generally recall no more Jacoby et al. (1989) attributional approach veridical information than do control subjects may help here, because as Schacter (1995) has and, on the few occasions when they have noted, ``The evidence suggests that hypnosis been shown to do so (e.g., Dywan & Bowers, creates a retrieval environment in which peo- 1983), the increased recall comes only at the ple are more willing than usual to call a mental expense of an increase in errors, suggesting a experience a `memory,' and in which they ex- general criterion shift. press a great deal of con®dence in both true Although hypnosis does not lead to en- and false memories'' (p. 17). hanced accuracy of retrieval, there is mount- Although most researchers attribute the illu-

AID JML 2467 / a002$$$106 04-10-96 17:23:17 jmla AP: JML 94 HENRY L. ROEDIGER III sions created when subjects are hypnotized to source of information. Are some types of peo- the state of hypnosis per se, it may be that they ple more susceptible to memory illusions than are caused in part by the instructions during others? Considerable work has already been hypnosis that lead people to produce errone- conducted with children in an attempt to deter- ous information. That is, it may well be that mine how accurately they remember, espe- nonhypnotized subjects who are instructed to cially for the practical purpose of whether guess during retrieval will show the same dif- children's testimony should be admitted in ®culties in later monitoring their recollections court (see Ceci & Bruck, 1995, for a compre- that hypnotized subjects show. Studies brie¯y hensive review). The research activity with reported in Jacoby et al. (1989, p. 413) and older people has also begun, but is less volu- Roediger, Wheeler, and Rajaram (1993, pp. minous. For example, Johnson and her collab- 114±122) provide evidence for this hypothe- orators have asked if reality and source moni- sis (although neither study used groups tested toring is less accurate for children and for under hypnosis for comparison). For example, older adults than for young adults (e.g., Foley, Roediger et al. used a forced recall procedure Johnson, & Raye, 1983; Hashtroudi, John- in which subjects were made to guess during son, & Chrosniak, 1989). Similarly, other recall. They later asked subjects to rate all studies have shown that people high in imag- items they had produced as to whether the ery ability are more likely to be confused in response actually occurred during the study a reality monitoring paradigm after imagining phase of the experiment. They found that sub- events than are poor imagers (Johnson, Raye, jects who had guessed often judged that their Wang & Taylor, 1979). As already noted erroneous responses, presumably produced as above, another rich source of information is guesses, had actually occurred. Therefore, it that supplied by various patient populations, may be that the act of guessing while retriev- as in the Kroll et al., Reinitz et al., and ing information about an event produces false Schacter et al. papers appearing in this issue. memories even when subjects are not hypno- Finally, people who score high on scales of tized. However, study of this possibility is just hypnotic suggestibility are more easily led to beginning. memory illusions than are those who score low. • Illusions of judging and deciding. Many CONCLUSIONS cognitive illusions discovered by psycholo- Perceptual illusions have been thoroughly gists studying judgment and decision making studied for nearly 150 years, whereas memory have a memorial basis. For example, the avail- illusions have been intensively studied for ability heuristic (Tversky & Kahneman, 1974) (perhaps) 30 years. Like perceptual illusions, refers to the tendency of decision makers to there are doubtless many types of memory assess the frequency of events by the ease illusions that are caused by different factors. with which instances come to mind. So, for We are as unlikely to ®nd unitary explanations example, subjects judge that more people die of memory illusions as we are of perceptual from shark attacks than from being hit by fall- illusions. ing parts from airplanes, but actually the This essay has touched on only some illu- chances of dying from falling airplane parts sions that can be considered memory illusions. are 30 times higher (Plous, 1993). Hindsight My survey in the second half of this paper bias and the knew-it-all-along effect may sim- was motivated more by setting the stage for ilarly be caused by problems in assessing our articles in the special issue than by an exhaus- own metamemories (Fischoff, 1975; Wood, tive review of the relevant phenomena. I con- 1978). After something has happened, we can clude by noting brie¯y a number of phenom- no longer access our mental state prior to the ena and issues that deserve attention and that happening, to see how unlikely we might then have not been emphasized here. have judged the event to be. (The processes • Individual differences represent a rich may be similar to those studied by Kelley and

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Jacoby, this issue.) In a different arena, people related example, Glenberg, Wilkinson, and notice and remember streaks of events and Epstein (1982) reported an illusion of know- may then judge them as representative of a ing in which subjects' ratings of how well general rule, even though careful analyses they comprehended a passage failed to corre- show that these streaks are probably occurring late with how well they could later answer no more than would be expected by chance. questions about it (but see Weaver, 1991, for For example, basketball players' belief in the some limitations on this ®nding). These exam- phenomenon of the hot handÐthat players ples could be extended (see Nelson, 1992). suddenly get hot and make streaks of shotsÐ Two of the most famous illusions of mem- is probably due to this illusion of perceiving oryÐdeÂjaÁ vu and jamais vuÐare illusions of and remembering clusters in a random se- metacognition. In the former case, which we quence (Gilovich, Vallone, & Tversky, 1985). have considered, people suffer the strange These and other examples of phenomena of feeling that a new situation is very familiar; bias and illusion in judgment, often studied as noted, Jacoby and Whitehouse (1989) ana- more by social psychologists than by cogni- lyzed this feeling as possibly arising from mis- tive psychologists, seem to have their basis in attributed perceptual ¯uency in the apparently memory illusions (see Gilovich, 1991; Pia- new situation. Jamais vu is the failure to ®nd telli-Palmarini, 1994; and Plous, 1993, for sur- familiar something that was recently experi- veys of these phenomena). Just as there is no enced and should feel familiar. An experimen- ®rm dividing line between illusions of per- tal example may be the phenomenon of the ceiving and remembering, there is no ®rm line recognition failure of recallable words, re- between illusions of remembering and those ported by Tulving and Thomson (1973). Sub- of judging and deciding. Future work may jects fail to recognize in one context that a seek commonalities that underlie illusions in word has recently been presented, yet they different domains. can recall that word as a recently experienced • Other illusions of metacognition. The episode with a different cue. In pathological study of metacognitionÐthe assessment of cases, amnesic patients fail to recognize as our own knowledge of how we learn and what familiar events that have been recently experi- we knowÐhas greatly informed the study of enced and that can be produced in implicit memory illusions. Studies of source monitor- or indirect tests of memory (Warrington & ing, of remember/know judgments, and of Weiskrantz, 1968; Graf, Squire, & Mandler, over- and undercon®dence in decisions all rely 1985). However, the concept of jamais vu has on metamemory judgments. However, the been given very little attention and the two study of metacognition is rife with other possi- phenomena mentioned here are not usually bilities (see Nelson, 1992, for an introduction). raised in this context (although they seem to Whenever our metacognitive monitoring fails ®t the de®nition). to track our performance accurately (and espe- • The topic of memory illusions has not cially when our judgments about our perfor- been con®ned to the psychologists' labora- mance are totally at odds with our behavior), tory, but is now a topic of concern in several our judgments re¯ect an illusion of knowing. areas of society. The accuracy of eyewitness For example, Nelson and Leonesio (1988) testimony (Munsterberg, 1908; Loftus, 1979) showed that subjects would continue to study is of long-standing interest. The problem of material (under self-paced study conditions) false identi®cation of suspects and false re- in attempting to master it, even though the ports of details in criminal investigations is of additional study time produced little or no gain prime concern. Recently, the issue of memo- in performance. Subjects could not accurately ries that appear to be recovered in therapy monitor when to call it quits in studying the (often an adult recalling being abused as a information, which Nelson and Leonesio (1988) child) has been a topic of much debate (see referred to as the labor-in-vain effect. In a Lindsay & Read, 1994; Loftus, 1993a). Do

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