|Henry L. Roediger III and Elizabeth J. Marsh (2009), Scholarpedia, 4(8):3858.||doi:10.4249/scholarpedia.3858||revision #88994 [link to/cite this article]|
False memory refers to cases in which people remember events differently from the way they happened or, in the most dramatic case, remember events that never happened at all. False memories can be very vivid and held with high confidence, and it can be difficult to convince someone that the memory in question is wrong. Psychologists have studied false memories in laboratory situations in which events are well controlled and it can be known exactly what transpired. Such experiments have uncovered a number of factors that are responsible for creating false memories. In the next few paragraphs some of these factors will be reviewed.
Factors that cause false memories
Sometimes the problem begins while the original event is still occurring, that is, while the memory is being encoded. If the perception of an event is inaccurate, then it cannot be remembered accurately (The interested reader can link to interesting Scholarpedia pieces on categorical perception and event perception). Consider the eyewitness who is asked to accurately remember a crime; she may have seen the perpetrator only briefly, in the dark, from a distance, and while experiencing stress – all conditions that reduce her ability to see him in the first place, which will in turn dramatically reduce her later ability to identify him.
False memories may also arise from inferences made during an event. The witness to a crime is actively trying to figure out what is going on during the event, and uses prior knowledge to make sense of what is happening. Likewise, the reader interprets short stories while reading them, interpreting simple statements like “Nancy went to the doctor” differently if they know the character is worried about pregnancy (Owens et al. 1979). In both cases, applying knowledge changes what people remember; the witness may later remember the robbery as more typical than it was and the reader will misremember the passage to be consistent with the pregnancy theme. In another simple but highly reliable demonstration, people hear a list of words like bed, rest, awake, tired, dream, wake, snooze, blanket, doze, slumber, snore, nap, peace, yawn, drowsy. Later on, people claim “sleep” was on the list, even though it was not presented (Roediger et al. 1995). Humans are biased to extract meaning from events (e.g., that the list contains sleep-related words), and this may lead to confusions about what was inferred versus what actually happened. It may also lead to forgetting of non-semantic details, since people typically attend more to meaning than to perceptual and phonological details. For example, most people fail when asked to draw a penny, even though they have handled thousands of pennies; successfully using a penny does not require one to know the direction of Lincoln’s head or the exact wording on the coin (Nickerson et al. 1979).
Normally memories are retrieved after time has passed, meaning that many events occur after a memory was stored. Later events may interfere with retrieval of the original event; for example, Spanish learned in college may come to mind when trying to remember one’s high school French. The eyewitness may read newspaper accounts about a crime, answer investigator’s questions, talk to other witnesses, and imagine the event in her mind’s eye. All of these may yield representations that differ from what actually happened, and these new memories may block access to memories of those events. Consider a classic demonstration in which subjects watched a slide show of an automobile accident, which included a slide showing a red Datsun approaching a yield sign. Later, some participants were asked “Did another car pass the red Datsun while it was stopped at the stop sign?” This question contained an incorrect presupposition (that there was a stop sign), and affected later memory. The subjects’ ability to identify the original slide (depicting the yield sign) dropped after answering the misleading question (Loftus et al. 1978). The suggestion does not need to come from an external source; describing a face reduces a witness’ ability to pick it out of a line-up (Schooler et al. 1990), imagining an event can lead the subject to later think she completed the action (Goff et al. 1998), and telling a story about an event may bias the storyteller’s later memory for that event (Tversky et al. 2000).
Consider some of the problems that may arise when one tries to recognize whether or not an event occurred in the past. Recognition tests ask subjects to make decisions about whether or not they have seen each of a series of words, objects or people before, and some of the test items are old (studied) and some are new. The eyewitness lineup is an example of an everyday recognition test.
False memories can arise when subjects (incorrectly) endorse new items on a recognition test due to their similarity to original events. Imagine that witnesses to a crime see a male perpetrator in clear daylight, and give a description of the man to police. Later the police apprehend a man fitting the description and put him into a line-up with other people fitting the same general description (e.g., 6 foot white male, receding hairline, no facial hair). Witnesses pick the suspect out of the line-up (the recognition test) and he is later convicted of the crime. However, several years later, after being captured in an unrelated incident, another man who looks like the convicted man confesses to the original crime and he also possesses information about the crime that only the perpetrator could know. In this case, the man originally convicted of the crime was falsely recognized because of his visual similarity to the actual culprit. While this is a hypothetical example, much laboratory research shows that exposure to similar events can create illusory memories, with a person confusing the original event with one that looks (or sounds) like it. In addition, such similarities have led to erroneous convictions, such as the real case of Ronald Cotton; Cotton was arrested for rape in 1984 and wrongfully imprisoned for more than ten years.
Misattributions of familiarity
False memories can also arise when subjects misinterpret why new items on a recognition test feel familiar. An elegant demonstration of this is known as the false fame effect. Subjects study a list of non-famous names (e.g., Sebastian Weisdorf), and a day later decide whether each of a series of names is famous or not (the recognition test). Critically, the final test includes somewhat famous names (e.g., Minnie Pearl), studied non-famous names (e.g., Sebastian Weisdorf), and new non-famous names that were not studied in the first session (e.g., Adrian Marr). Subjects judged the studied non-famous names as more famous than the new non-famous names, presumably because they seemed familiar from their recent exposure (Jacoby et al. 1989). That is, the studied non-famous names were familiar because they were seen in the first session of the experiment and subjects misattributed this familiarity to fame.
False autobiographical memories
Of course many of the most striking examples of false memories may be caused by a combination of the factors just described. Consider how false autobiographical memories are implanted in the laboratory. The original demonstration involved implanting a false memory for having been lost in a mall as a child (Loftus et al. 1995). The experiment required cooperation from close family members, who told the experimenters several true events that each subject had actually experienced. When the subject came into the lab, she was interviewed about three true memories and the critical false one (one the relatives assured researchers that the subject had not experienced as a child). Subjects were interviewed several times over the course of a month, and by the end of the experiment more than a quarter of subjects retrieved some information about the false event.
Since the original demonstration, experimenters have successfully implanted false memories for a wide range of events, including a religious ceremony (Pezdek et al. 1997), a hot air balloon ride (Wade et al. 2002), and a hospitalization (Hyman et al. 1995). Generally speaking, it is harder to implant false memories of implausible events. For example, it is hard to convince people that they experienced (but then forgot) receiving an enema in childhood (Pezdek et al., 1997). Implantation is more likely if the subject elaborates on the suggestion or imagines it, yielding a richer representation (Hyman et al., 1995). The final step involves misattributing the event to memory, as opposed to another source. In other words, implanting false autobiographical memories depends upon many of the factors discussed earlier: the subject brings prior knowledge (e.g., about getting lost and about malls) to bear and elaborates on the suggestion, the subject continues to think about the event after the original suggestion was encoded, and the memory is misattributed to childhood rather than to recent experiences in the lab.
Individual differences in suggestibility
Not all people are equally likely to form false memories. Generally speaking, children and older adults are more suggestible than college students in most false memory paradigms, although there are a few exceptions to this rule. Suggestibility also tends to increase with higher scores on the Dissociative Experiences Scale (DES), a measure of distraction as well as less normal experiences such as hearing voices (Clancy et al. 2002; Eisen et al. 2001; Hyman et al. 1998). Understanding individual differences in suggestibility is an important direction for future research.
Many false memories are byproducts of processes that normally support veridical memory. It is efficient for the perceptual and memory systems to take shortcuts and focus on meaning extraction, since that will suffice in many cases. Similarly, oftentimes relying on familiarity or other external sources is a good strategy, because these can be accurate indicators of the past. However, the cost to these shortcuts is that neither a detailed memory nor a confidently held one is necessarily true. False memories can trick third party observers like juries and lawyers in addition to tricking the rememberer, and they can be very difficult to correct once a person becomes confident about an erroneous memory (often from repeatedly remembering the event a certain way).
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