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In press - Nature Reviews Neuroscience

The Neuroscience of : Implications for the Courtroom Joyce W. Lacy1* and Craig E. L. Stark2* Although memory can be hazy at times, it is often assumed that of violent or otherwise stressful events are so well-encoded that they are largely indelible and that confidently retrieved memories are likely to be accurate. However, findings from basic psychological research and neuroscience studies indicate that memory is a reconstructive process that is susceptible to distortion. In the courtroom, even minor memory distortions can have severe consequences that are in part driven by common misunderstandings about memory, e.g. expecting memory to be more veridical than it may actually be.

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1Department of Psychology Azusa Pacific University Azusa, CA 91702 2Center for the Neurobiology of Learning and Memory and Department of Neurobiology and Behavior University of California, Irvine Irvine, CA 92697-3800 Correspondence to C.E.L.S.: [email protected]

*Both authors contributed equally to this manuscript and author order was determined by coin toss.

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Introduction or loss is an unfortunate misunderstanding of Pioneers in neuroscience such as Ramón y Cajal, memory8 that has important consequences in Hebb, and Marr introduced the idea that memory court. The of eyewitnesses whose is encoded in the patterns of synaptic connectivity memories may have been distorted can lead to the between neurons. Increases in the strengths of conviction of innocent persons while true these synapses encode our experiences and perpetrators remain free. The in thereby shape our future behavior. Our New York City (www.innocenceproject.org, see understanding of the complex mechanisms that Box 2), which advocates the use of DNA testing underlie learning and memory has progressed to exonerate wrongfully convicted people, lists dramatically in recent decades, and studies have 310 exonerated individuals (as of July 8th, 2013). not provided evidence that memories are indelible. These individuals were typically convicted on the Quite the contrary, it is becoming clear that there basis of and spent an are several ways through which memories can average of 13.6 years in confinement before being change. released. They are thought to be only a small The ‘imperfection’ of memory has been sample of the total number of wrongfully known since the first empirical memory convicted people, as DNA evidence is only experiments by Ebbinghaus1, whose famous available in a limited number of cases (e.g., those ‘ curve’ revealed that people are unable involving sexual assault). to retrieve roughly 50% of information one hour Most individuals outside the field of memory after . In addition to simple forgetting, research (including jurors) are largely unaware of memories routinely become distorted2-7. The the substantial malleability of memory2,8,15-17 public perception of memory, however, is (however, also see ref. 18). Early studies on the typically that memory is akin to a video recorder8 public awareness of memory phenomena showed (Box 1). This distinction between the perception that when college students were asked how and reality of memory has important various factors influence memory (e.g., cross-race consequences in the context of the courtroom. In identification, , and the wording of the legal system, like among the general public, it questions), they were only 54% correct2. Although is generally assumed that memory is highly the students scored higher than chance, the score accurate and largely indelible, at least in the case was surprisingly low considering the implications of ‘strong’ memories. of these factors in court cases. Similar surveys Recently, some regional jurisdictions, such as have replicated these findings in nontraditional New Jersey10,11, Massachusetts12, Texas13, and (older, working) students and in citizens of North Carolina14 have implemented procedural Washington, D.C. In both of these studies, the changes designed to mitigate effects of memory respondents’ accuracy was below 50%, suggesting biases and to best preserve accurate memories of that college students may be slightly better eyewitnesses. However, the legal system writ informed about factors that influence memory large has been slow to adapt to research findings than the general public15. on memory, even though these findings have More recent studies revealed that judges and implications not only for eyewitness testimony, law enforcement personnel are not much more but also for how jurors remember and weigh aware of memory phenomena than college evidence. Interest in the research of memory students17. For example, on a 30-item processes and their relevance to the courtroom has questionnaire about memory-related topics, increased since the advent of DNA evidence, potential jurors (that is, citizens who have been which has exonerated hundreds of individuals summoned to jury duty), judges and law who were falsely convicted on the basis of enforcement personnel (including detectives, eyewitness testimony. police officers and special agents) responded differently from eyewitness testimony experts on 17 Common misunderstandings about memory 87%, 60%, and 60% of items respectively . Thus, In many countries, the justice system relies on although judges and law enforcement personnel judges and jurors weighing evidence from agreed with memory experts on more statements multiple sources and with varying levels of regarding memory myths than did jurors, their credibility. The belief that a confident memory is understanding of the majority of memory myths always highly accurate and resistant to distortion still differed from memory experts. There is

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Box 1 a b Video memory: : “Human memory works like a video camera, accurately “Hypnosis is useful in helping accurately recording the events we see and hear so that we can details of crimes”. review and inspect them later”.

Public Public

Experts Experts 0 25 50 75 100 0 25 50 75 100 c d Permanent memory: “Once you have experienced an event and formed should be enough to convict a defendant of a crime”. a memory of it, that memory does not change”.

Public Public

Experts Experts

0 25 50 75 100 0 25 50 75 100

Strongly agree Mostly agree Mostly disagree Strongly disagree Don’t know

Box 1. Is memory common sense? Public opinion versus memory experts. When asked about statements about memory-related phenomena in a national survey across the United States, members of the general public (n = 1500) accepted many phenomena that were not endorsed by experts in the field (i.e., professors with more than 10 years of experience in memory research), who showed strong consensus among themselves (see the figure) 8. Such misunderstandings of memory can have significant consequences in court, where judges and jurors often assume memory to be more accurate and veridical than is indicated by the neurobiologically reconstructive nature of memory. Note that one limitation of these surveys is that expert opinion about memory-related phenomena may change over time as more research findings become available. For example, a 1989 study16 showed that expert opinion regarding the phenomenon of “” had changed compared to a survey published in 198215 and further changes in expert opinion regarding “weapon focus” as well as other phenomena were shown in 200119. Although expert opinion about memory-related phenomena may sometimes be wrong, it is presumably the best indication of the true nature of such phenomena. The authors of one recent study18 suggested that public and expert opinion are beginning to converge. However, other studies suggest that in some aspects lay beliefs are still quite different from those of experts. There is, therefore, a need for periodic updating of both expert and public opinion. Data from Ref. 8.

evidence that some populations, such as a This phenomenon is due to the fact that we use surveyed sample of Canadian citizens, hold our entire existing body of knowledge and beliefs that are more in line with those of experiences to filter for what we perceive, attend experts18. However, the most recent studies show to and use in memory reconstruction (this is that there remains a large discrepancy between known as memory’s ‘bias’21). In the case of facial public knowledge of memory and expert identification, we are typically most familiar and consensus8 (Box 1). knowledgable about the facial features of our One memory phenomenon of which the own race and less so of other races or ethnic general public (and therefore also a jury) is often backgrounds. Bartlett first drew to unaware is cross-race bias17,19 — a reduction in memory’s ‘bias’ in his famous study on the “War accuracy when identifying faces of a race or of the Ghosts”22, in which participants had ethnic background different from one’s own2,20. difficulty recalling short stories word for word when the stories did not fit into their conceptual

NATURE REVIEWS | NEUROSCIENCE PREPRINT 3 In press - Nature Reviews Neuroscience framework. Barlett’s work was later developed by given instruction on how to detect behavioral cues Neisser23, who famously likened memory of deception. This ‘lie detection’ training tends to retrieval to paleontology by saying “out of a few increase confidence in evaluating wether a stored bone chips, we remember a dinosaur”. Put ’ testimony is truthful or deceitful without simply, if we think an event should have happened necessarily improving the actual accuracy of in a certain way on the basis of our previous deception detection29-31. The relationship between experiences, we are likely to think that the event confidence and accuracy is far more complicated did indeed happen this way. For example, a study than is often acknowledged. Accuracy often showed that people who read a brief passage produces confidence, but confidence does not about a wild and unruly girl and are told that it is necessarily indicate accuracy. about Helen Keller are more likely to mistakenly Misunderstandings about memory can have remember, a week later, the text saying “she was effects on criminal cases even before they make it deaf, dumb, and blind” than if they were told that to court. The belief that confident, detailed the passage is about a fictitious Carol Harris24. memories are always accurate and reliable is Thus, if people expect certain things to occur contrary to research that suggests the opposite is during a crime or expect a particular group of possible — confidently recalled recollections can people to be more or less involved in crimes, it sometimes be inaccurate and real memories are should perhaps not come as a surprise that their not always highly confident and detailed. memories reflect these biases. Especially in cases involving violence and high Another commonly held belief among the levels of stress, real — which general public is that an eyewitness’ confidence in can be disjointed — may sound unreliable to law the accuracy of his or her memory is a strong enforcement personnel and to the general public indicator of the actual accuracy of the memory17. and may therefore never make it to court. One Jurors often place great weight on how confident striking example of this is that an estimated 86% an eyewitness is regarding their memory of the of sexual assaults are never prosecuted on the event — enough to convict an individual even if grounds that the victim’s testimony does not seem eyewitness testimony is the only condemning to be reliable32. evidence (Box 1). Meta-analyses have reported that mistaken eyewitness identification occurred in 75% or more of cases in which a convicted How memory distortions occur individual was later exonerated on the basis of Memory distortions can occur in different ways. DNA evidence25. Importantly, memory experts Most distortions involve some form of explicit or generally do not endorse the idea that the covert misleading information. One form of this confidence and accuracy of a memory are always phenomenon, the ‘’, has tightly linked8,19. Although studies in cognitive been thoroughly studied for the last 30 years4. psychology have shown a positive correlation This effect refers to a distortion in an original between memory confidence and accuracy26,27, memory after being exposed to misleading these studies were typically laboratory based, information related to that memory, e.g. an used neutral stimuli, and observed general impairment in the memory of the face of a memory phenomena rather than the attributes of perpetrator after being exposed to a photo of a memory most relevant to court. Research that police suspect who was not the true perpetrator. specifically examines eyewitness testimony or the This ‘misinformation’ is considered misleading in memory of traumatic events has shown weak28 or that in distracts from the original memory, not even negative6 correlations between a person’s because it is purposefully deceitful. Laboratory confidence in the accuracy of a memory and the studies have shown that it is possible to induce actual accuracy of that memory. One reason for memories in a participant that are entirely false, such as a special hospital visit at age 4 when no these weak correlations is that confidence can be 4 influenced independent of accuracy, for example, such visit happened . Misleading information is by post-identification feedback, which has no often given unintentionally and can be as subtle as influence on accuracy (see below). A decoupling slight variations in the wording of a question. For between memory confidence and accuracy in example, when participants viewed footage of a jurors and law enforcement can be seen when car accident, the question “How fast were the cars college students or law enforcement personnel are going when they smashed into each other?” (italics added) elicited reports of 20%

NATURE REVIEWS | NEUROSCIENCE PREPRINT 4 In press - Nature Reviews Neuroscience greater traveling speeds than the question “How often use these factors as indications of the fast were the cars going when they hit each accuracy and reliability of a witness’s testimony. other?”, despite the fact that participants in both Memory distortions can even occur in highly conditions viewed the same footage2. The former trained individuals. One series of studies question was also more likely to elicit a false examined highly selected military personnel in memory of broken glass at the site of the crash2. survival school who received a week of classroom Witnesses are often called to testify on specific instruction on how to handle stressful details such as these and their reports may interrogations before they were exposed to a influence the likelihood of conviction and the mock prisoner of war camp (POWC, see Box degree of punishment, i.e. a harsher crime 3)39,40. The mock POWC provides a controlled sentence for traveling at higher speeds. setting of realistic and personally relevant stress. Distortions in memory can also occur from In one study of over 500 active-duty military feedback provided to the witness after their personnel, participants were asked to identify testimony. Positive post-identification feedback, their interrogator after being released from the such as informing a witness that their choice in a mock POWC. These individuals had had a clear suspect line-up matched the police suspect or was view of their assailant during the 30-40 minute the same as that of other witnesses, increases the interrogation. However, only approximately a eyewitness’ level of confidence in their Box 2. The Innocence Project choice33,34. Positive In 1981, Linda Mae Craig, a young sales associate, was abducted from her car on post-identification her way home from work. The next day, her body was found in a church parking lot feedback also beaten and sexually assaulted. Days later, 20 year old Nicholas Yarris was stopped increases a witness’ for a routine traffic violation, which escalated into a physical altercation and later estimate of the resulted in Yarris being taken into custody. In a bid to speed his release from amount of attention he custody, Yarris told police he believed an acquaintance was involved in the murder. or she paid to the However, when the acquaintance's alibi was cleared, Yarris became the chief crime and of how well suspect. After a short trial, which involved eyewitness testimony of the victim’s they could see the coworkers, Yarris was sentenced to death row and solitary confinement for the scene and/or kidnapping, rape, and murder of Craig. Yarris spent over 21 years behind bars perpetrator34,35. before he was exonerated via DNA testing. He was the 13th individual in the United Conversely, negative States to be exonerated from death row. feedback can deflate Yarris’ story is one of hundreds recorded by the Innocence Project confidence in a (www.innocenceproject.org), a nonprofit ligation organization in the United States. memory and other According to their data, exonerees spend an average of 13.6 years in prison before measures33,36. In being released. After , there is little support or assistance. The average addition, nonverbal compensation, which is not guaranteed, amounts to $24,000 a year for each year feedback via body spent behind bars, often capping at a maximum of 10 years. This does not take into language and facial consideration money exonerees have spent on legal fees. Not only have they lost expressions can occur precious and prime years of their life, many exonerees are never acknowledged as if the officers victims of legal injustice. They find it difficult to regain a normal life after release conducting the line-up from prison. Many have lost friends and family over the years in confinement and are aware of which bear the social stigma of a criminal, which leads to difficulties finding employment, individual is the police even after their record is cleared. suspect37. Even in the Eyewitness testimony plays a role in roughly 75% of all cases in which absence of feedback, individuals are wrongfully convicted25. The Innocence Project aims to reform the mere repeated criminal justice system by raising awareness on these issues and advocating for questioning of an changes in public policy. event can increase a witness’ confidence in the accuracy of their third of the identifications were correct. memory38. Such changes in a witness’ reported Strikingly, the subjects identified someone in the estimations of confidence and attention are highly line-up as the interrogator in almost two thirds of relevant in the courtroom, as judges and jurors cases in which the actual interrogator was not

NATURE REVIEWS | NEUROSCIENCE PREPRINT 5 In press - Nature Reviews Neuroscience present in the line-up39. A related study involving objects43. By contrast, endorsement rates for a population of over 800 military personnel repeated items and for novel items unrelated to revealed that interrogator identifications were also the listed items are largely unaffected by age. easily influenced by misinformation. For Aging seems to be associated with an over- example, exposure to a misleading photograph of generalization of memories such that an event that someone who was not the interrogator before is similar to a prior event is more often identification increased the likelihood of a false remembered as being identical to the prior event. identification40. The misidentifications that Aged individuals are also more susceptible to the occurred with and without exposure to misinformation effect than young adults4,5. Thus, misinformation were robust, despite the fact that as people age, memory for the gist of an event these studies involved a select group of may remain intact, but memory for specific individuals thought to be superior in their ability details of the event degrades and individuals are to handle stressful situations. Although a more likely to falsely incorporate similar limitation of these studies is that subject selection information into our memories. may be biased because they involved participants The fallibility of memory has implications for who chose to enroll in survival school, their the question of how much weight should be given findings converge with data from laboratory- to eyewitness testimony in court cases. In based studies of eyewitness testimony under addition, jurors are subject to memory biases. For highly stressful situations41,42 and the example, when mock jurors listened to audio misinformation effect4. recordings of a mock trial, they ‘recalled’ 15% of Memory distortions can also occur simply details of that were not mentioned in the trial but with the passage of time and with repeated that fit a typical crime description (e.g., “pulled recounting of events. Although it might not be out a gun” was never stated, but fits the surprising that mundane memories become description of a robbery)9. This reflects people’s weaker and more susceptible to distortion over natural bias to “fill in the gaps” of a memory, but time, emotional and traumatic ‘flashbulb such fill-ins are inaccurate accounts of the actual memories’ are also susceptible to these automatic events. The occurrence of ‘false memories’ can be distortions. For example, after the September 11th increased by leading questions, such as those that terrorist attacks on New York City, U.S. citizens might be asked by prosecutors. Mock jurors were asked to remember when they first heard ‘recalled’ 25.8% of details that were implied in about the attacks. They were asked to recall this leading questions from the prosecuting attorney in episode approximately one to two weeks after a mock trial but that were not stated by the 9/11, one year later, and three years later6. eyewitness of the trial, suggesting that jurors have Memories of the details had changed in 37% of difficulty in sorting statements from eyewitnesses the people after one year and in 43% after three and attorneys. Moreover, even when mock jurors years. Interestingly, despite the drop in memory were given explicit instructions to focus on the accuracy, confidence in the accuracy of the testimony of witnesses and not on information memory remained high — an example of a implied from attorneys, they still ‘recalled’ 20.4% negative relationship between memory confidence of details that were not mentioned in the and accuracy — and was driven primarily by eyewitness testimony9. Thus, such instructions to attention paid to media reports and by talking jurors only marginally reduced the effect of about the attack in the intervening time6. leading questions and did not completely prevent These types of memory distortion increase as it. we age. For example, for words that were not in a list of words presented to the Insights from the neuroscience of memory participant but that were semantically related to Our understanding of the neurobiological the words on the list (a test known as the Deese- mechanisms of memory formation, consolidation Roediger-McDermott (DRM) paradigm) increases and retrieval can explain, at least to some extent, with age3. Similarly, when shown lists of objects, why some types of memory distortions occur and some of which are similar but not identical to why ‘imperfect’ memory is the norm. At the previously seen objects, older participants are cellular and molecular level, these mechanisms more likely than younger participants to are thought to involve processes linked to long- incorrectly identify these as being repeated term potentiation (LTP) and long-term depression

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Figure 1 a (LTD). Training Test Figure 1. Long-term potentiation (LTP) and long-term Context B Memory depression (LTD) Hebb44 proposed a conceptual framework that Context A linked associative memory formation to activity- dependent changes in the strength of connections in a network, and Bliss and Lømo provided the Context A first direct evidence for such a link45. They found that by strongly stimulating the perforant pathway from the entorhinal cortex to the dentate gyrus they had increased the ease with which neurons in the entorhinal cortex could excite neurons in the b 60 dentate gyrus . This strengthening of the * * 50 connections remained quite stable and was dubbed LTP. LTP is activity dependent and 40 requires coincident firing of pairs of neurons. 30 Thus, the learning rule underlying LTP 20 Context A corresponds quite well to the associative learning Freezing (%) Freezing Context B rule posited by Hebb. There is now substantial 10 evidence that LTP, or at least a similar process that 0 shares many mechanisms with LTP, underlies 1 14 28 36 46 Day numerous forms of learning and memory . c A great deal has been learned about LTP, its 0.7 mechanisms, and its various forms. For example, depolarization without activation of NMDA

0.6 receptors and protein synthåesis results in an ‘early’ Hebbian form of LTP that only lasts several hours. By contrast, NMDA receptor-dependent 0.5 LTP leads to structural changes that show little sign of degradation with time47. This could Discrimination ratio suggest that once a memory undergoes such 0.4 ‘synaptic consolidation’ and is associated with the 1 14 28 36 Day structural changes of late-phase LTP, it is generalization over time in rodents. Rats were exposed to a immutable. Unfortunately, this is not the case as training context (context A) and given a small shock in that these changes are not permanent nor are the context, which induces a “freezing” behaviour (a common memories that have been thus encoded indelible. fear response in rodents). After a delay, they were placed in Although coincident firing of neurons can lead to either the training context (context A) or a novel context LTP and the strengthening of a memory, if the (context B). Memory for the shock and the specific neurons fire in an uncorrelated way (as may be environment it was given in can be assessed by measuring the case if the neurons individually activate in the amount of time the rats spend “freezing” in each context. One day after training, rats froze less in the novel context different experiences and therefore different than they did when re-exposed to the training context. This memories of those experiences) this leads to the behavior displays memory of the specific context in which opposite, namely a reduction in the strength of they were shocked, and this ability to discriminate between these same synapses that LTP strengthens. Thus, the two context decreases with time. Rats that were tested 4 there is a mechanism, known as LTD, for weeks after training froze an equal amount of time in the weakening synaptic connections, and therefore training context and the novel context. This suggests that presumably memories, as well. Importantly, LTP both the training and test contexts (both of which involve the and LTD occur at the level of individual synapses rat being removed from the home cage, taken to another and the same individual neurons and synapses are room, placed in a box, etc.) match the contents of the 48 59 likely involved in several or many memories , memory. Figure adapted from ref . leading to the potential for interference of one memory with another49 and suggesting that the

NATURE REVIEWS | NEUROSCIENCE PREPRINT 7 In press - Nature Reviews Neuroscience learning of new information can overwrite previously extinguished memory) (reference) and previously learned information by changing the disinhibition (re-emergence of a conditioned strengths of the synapses that had been used to response after experiencing a novel stimulus) encode that information. Conversely, as noted (reference) also support this notion. above, previously learned information (experiences, biases, etc.) can influence the Generalization over time and with retrieval learning of new information. Memory distortions in humans may occur simply Moreover, there is evidence on the molecular with the passage of time. This is partly because level that memories can be lost or altered. First, over time memories typically become less the maintenance of LTP appears to be an active episodic (highly detailed and specific) and more process, as administering zeta-inhibitory peptide semantic (more broad and generalized) as the (ZIP) can de-potentiate synapses and erase information is repeatedly retrieved and re- memories50,51. Second, the act of retrieving a encoded in varying contexts. This generalization memory (that is, reactivating a memory) is of a memory over time has also been observed in thought to put that memory and the potentiated animals. For example, if a rodent receives an synapses in the memory into a labile state, from electric footshock in a particular context, which it must re-stabilize in order to persist. subsequent exposures to that context induce a Without this process, known as ‘freezing’ behavior56. The specificity of the ‘reconsolidation’ (which, like long-lasting LTP, memory can be probed by exposing the animal to requires protein synthesis), the information is a different context. Comparing the levels of lost52. This reconsolidation process is thought to freezing in the two contexts reveals how well the be functionally beneficial as it provides an animal animal discriminates between them (Figure 1). A with an opportunity to strengthen or weaken a typical finding is that freezing in the training memory or to update its contents53. If the content environment may not degrade much with delay of a memory is updated at the time of retrieval, (i.e. the animal shows little forgetting of the memory distortion could occur of which the memory) and that the level of freezing in the individual would presumably be entirely alternate context is initially very low. However, unaware53. freezing in the alternate context typically Note that thus far, we have discussed how the increases with delay, indicating a reduction in the contents of an existing memory may be changed. ability to discriminate between the contexts in There is reason to believe that more recent memory or an increased reliance on the ‘gist’ of a memories can compete with older memories at context than on specific contextual details57,58. time of retrieval, leading to memory errors when Thus, even highly salient, strong memories, such trying to retrieve the original information 54. That as the memory of receiving a shock, that are is, if two different memories exist of an event initially detailed and specific but become more (e.g., the original memory and a memory formed generalized with the passage of time. Such while retelling the event) or if there are two generalization is stronger for similar contexts than overlapping memories (e.g., the original memory for highly dissimilar ones, and the is of the event in question and memories of a required to differentiate between contexts as it subsequent event that shares several of the same maintains the representations of the details that components), attempting to retrieve the original distinguish them59. event may very well inadvertently and During the formation of a new episodic unknowingly draw upon information from the memory, information about a related memory can second event. There are neurobiological findings be automatically retrieved. New learning taking that support this mechanism for altering memory place to encode this new episode can spill over performance. For example, the extinction of a and alter the contents of this automatically conditioned response engages many (though retrieved information. For example, in one study60 perhaps not all) of the same mechanisms that rats were exposed to two distinct contexts (A and were engaged during the initial learning of the B) on the same day over the course of several response55, supporting the notion that extinction is days, so that some association would probably be not simply the loss of an existing association but formed between the two contexts (A–B). The rats involves new learning. The phenomena of were then exposed to one of the contexts (B). spontaneous recovery (reappearance of a Given the prior training, rats quite likely retrieved

NATURE REVIEWS | NEUROSCIENCE PREPRINT 8 In press - Nature Reviews Neuroscience a memory of the other context (A). At this point, confident in the accuracy of their false memory63. rats were given a shock. Subsequently, the level of Thus, the formation of ‘true’ and ‘false’ memories freezing the animals showed in context A was appears to involve the same processes. At time of higher than that in a novel context (C)60. This retrieval, differences in activity in early sensory finding is consistent with the idea that being regions for true and false memories can be placed in the B context reactivated the memory of observed64,65, consistent with findings that true context A, so that the association between context memories contain greater sensory detail than false B and shock ‘spilled over’ to form a false memories3,66. Some regions in the prefrontal association between context A and shock. Just like cortex may be more active during the formation the learning of accurate associations, the learning and/or retrieval of false than true memories67. of this inaccurate retrieval-mediated association However, these differences in activation cannot relies upon NMDA receptors in the discriminate true from false on a trial by trial hippocampus61. basis (reference - it’s that same Ref 67). . This is Thus, experiencing an event can lead to the important in the context of eyewitness testimony, automatic retrieval of information that is not as the time elapsed between witnessing an event present but has been previously associated with and testifying about it in court may render these similar events. Given that a goal of our memory signals useless for distinguishing true and false system should be the use of prior information to memories via brain activity. Lastly, most guide current behavior in an adaptive manner, differences in brain activity are observed in early such automatic retrieval of memories from related sensory regions of the cortex, which are not events would be expected. However, a problem typically associated with conscious awareness, arises with the notion that learning is occurring at suggesting that we may not be able to consciously this point and that it does not clearly discriminate know the truth even if some regions of our brains between the current event and retrieved could differentiate true from false. information from specific prior events or from The closest that experimenters have come in generalized expectations of what should happen being able to distinguish ‘true’ from ‘false’ in such an event. As a result, whatever happens in memories on a trial by trial basis is with the use of this event becomes associated not just to elements multi-voxel pattern analysis (MVPA), a relatively that are actually present, but also to what we novel method of analyzing fMRI data using expect to be present based on our prior pattern classifiers that learn to use stimulus- experiences and biases. This phenomenon was related activity across voxels to categorize shown in an elegant neuroimaging study in stimuli. MVPA can distinguish subjectively humans62. Here, participants initially encoded a remembered from forgotten images with ~70-75% series of image pairs (A–B). After a test on the accuracy68. However, MVPA classifiers performed memory for these pairs, they again encoded a either at chance or only marginally above chance series of image pairs. Some of these pairs when trying to distinguish objectively true from repeated an element from the initial encoding list false memories — far below their accuracy for (A–C). During this second encoding phase, there subjective memory68. Thus, even the most cutting was evidence for the reactivation of previous, edge neuroimaging techniques are currently related events (A–B) in activity of the unable to distinguish objectively true and false hippocampus. The amount of activity for the memories from analyzing brain activity. original A–B event during this related A– C retrieval predicted how much of the original A–B Stress and memory information was lost and how much of the novel It is well-established that arousal and the stress A-C information was retained62. hormones epinephrine and cortisol that are It is important to note that even without released during arousal can modulate synaptic considering the notion of deception, it is difficult consolidation and memory strength69. Decades of to distinguish true memories from false memories research have supported the view that emotional by examining brain activity. The relative amount arousal leads to activation of the basolateral of hippocampal activity during the encoding of an (BLA), which modulates memory event and during subsequent encoding of , leading to more strongly encoded misinformation predicts which version will be memories. This does not imply, however, that remembered, even when participants are memories encoded during a state of heightened

NATURE REVIEWS | NEUROSCIENCE PREPRINT 9 In press - Nature Reviews Neuroscience arousal cannot be lost or distorted. In fact, high retrieval is a probabilistic process. This was first levels of stress during an event are not necessarily shown by Ebbinghaus for retrieval of simple, associated with an increase in memory strength neutral lists of syllables1. As stress is added into for that event and can even result in a reduced the process, the picture is clouded even more. memory for the event. Indeed, in both animals The animal data discussed above suggest that the and humans there is an inverted-U shaped dose– stress of witnessing a crime or the stress of the response relationship between plasma stress first interview can either enhance or impair the hormone levels and memory performance69,70. encoding and retrieval of the crime event. Stress Very high levels of stress during an event are not will also therefore affect the likelihood of necessarily associated with an increase in memory establishing false memories during a second strength for that event and can even result in a interview. Laboratory studies have shown that reduced memory for the event. For example, high over time false memories are more likely to be levels of either endogenous or exogenous cortisol endorsed as real memories and these false in humans can impair declarative memory memories tend to include more peripheral details formation71. Thus, in high states of arousal, such with time75-77. Thus, there is no set rule that as witnessing a crime or being a victim of crime, information retrieved across multiple interviews is memory encoding may be enhanced or impaired inherently true or false. A broader understanding depending on the person’s individual stress of memory processes (the effects of and response. time), situational factors (how stressful was the Emotional arousal has effects during retrieval experience to the witness), and testimony as well. The retrieval of arousing information consistency (what information was consistent or leads to a reactivation of the BLA, which can lead incongruent across interviews) must be taken into to further strengthening of memory72. However, account when considering information provided distortions can occur if any aspect of the retrieval by eyewitnesses. or reconstruction of the memory is erroneous. As the retrieved information is re-encoded, these distortions (be they self-generated or externally Application to courts suggested) can potentially become part of the The data reviewed above show that memory is memory. In addition, in humans, high levels of the imperfect, and that we cannot assume that this is stress hormone cortisol during retrieval (induced well-understood by the general public and by the either exogenously73 or endogenously74) have courts. Relatively simple changes in procedures been shown to impair the retrieval of personal can help to reduce the occurrence of memory retrieval. Importantly, distortions.. Even in situations where the arousal may enhance memory for some aspects of possibility of memory distortions cannot be an event and impair memory for other aspects. avoided, judges and jurors can be better educated For example, violence and trauma tend to on the limitations of memory. The fact that improve memory for the central gist of an event memory is imperfect cannot be changed, Perhaps (e.g. witnessing a homicide), but impair memory we can change how much weight is placed on of the peripheral details of the event (e.g. the evidence drawn from memory and on the clothing of the perpetrator)41,42. confidence ascribed to memory. Clearly, the relationship between stress and Most of the time, peripheral details of events memory is complicated. Veridical memories may are of low importance and are therefore often not not always be accompanied by a high level of well recalled. However, in the courtroom, confidence and details. In particular, victims of witnesses are often called to testify on precisely violent or otherwise upsetting crimes may have such very specific details. Some witnesses may vague and disjointed memories of the event, give accounts that are missing details, hazy in especially during a first interview soon after the places, and may even have some amount of crime, when stress levels are still high. It should demonstrable distortion. They may report to be not be surprising if a second interview, conducted unconfident in much of the memory as well. when the stress hormones have returned closer to Other witnesses with the same actual amount of baseline levels, contains a more coherent story, information available for retrieval may present far with additional details that were not recalled on clearer, more detailed accounts with strong the first interview. Even without stress, memory confidence given to their memory. As described above, the extra information presented and the

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Box 3 Experiential phase [1 week] [4 days] phase Evasion stress Interrogation Isolation stress Release and [4 days]

Box 3. Mock Prisoner Of War Camp (POWC) studies on eyewitness identification Although eyewitness testimony has been empirically studies for decades, the majority of Natureresearch Reviews involved | Neuroscience videotaped scenes or live simulations of crimes. A critique of such laboratory experiments is that they lack personally relevant and realistic stress. A few studies did involve actual crimes87,88,28, but these studies suffered from a lack of control over the amount and duration of stress as well as objective data on the true perpetrator. The mock Prisoner Of War Camp (POWC) portion of military survival school, which enlists only the most highly trained military personnel, provides an ideal venue to study eyewitness identification in a highly realistic and yet controlled setting. High levels of personally relevant stress can be applied in a uniform and consistent manner to all participants. The levels of stress induced in mock-POWC participants have noticeable physiological and psychological effects89 on par with real-world threats such as combat. Survival school begins with a week of training to prepare students for the mock POWC, including training to withstand intense interrogation and to resist counter-cultural propaganda. During the mock POWC, each participant is placed in isolation, deprived of food and uniform for approximately 48 hours and is interrogated in a manner that threatens physical violence (e.g. slapping, punching, submission positions40). Interrogations last 30-40 minutes and participants have a clear view of their interrogator the entire time. The participants were asked to identify their interrogator approximately 24 hours after being released from the mock POWC and after being given access to food and sleep (see the figure). In some cases, they were given misinformation before making identifications. One mock POWC study with over 500 survival camp attendees implemented three different types of line-ups39: live, in-person line-ups; simultaneous photo line-ups, in which photos of possible interrogators are shown at the same time and witnesses must select the interrogator (if present) in the photo spread; and sequential photo line-ups, in which photos of possible interrogators are shown one at a time and witnesses must decide for each of them whether they were the perpetrator. Participants correctly identified their interrogator in ~33% of cases in which the interrogator was present in the line-up. When the interrogator was not present in the line-up, participants made false-positive identifications (that is, they identified an ‘innocent’ person as the interrogator) in almost 66% of cases. These mock POWC results support previous findings that sequential line-ups elicit fewer misidentifications than simultaneous line-ups83.Another POWC study involving a separate population of over 800 military personnel40 has replicated findings of the misinformation effect4: exposure to misleading photographs or leading questions increased the likelihood of false identifications or inaccurate memories. The participants of survival school are successful military personnel who are often selected for their perceived ability to handle high-stress situations. Strikingly, these mock-POWC studies show that even such highly trained individuals are susceptible to memory distortions, to making false identifications, and are

confidence in the recall would be driven in these “perfect” memories that are accompanied by a witnesses by the reconstructive nature of memory high level of confidence and detail should be retrieval. Thus, although in general, accurate taken with a grain of salt and “imperfect” memories are more confidently recalled and memories that are vague and missing details detailed than inaccurate memories, jurors should should not be immediately discredited. However be aware that sometimes vague, somewhat ‘good’ a witness’ memory of an event may be, the distorted memories may be more veridical than witness’ memory may not actually be accurate, very detailed and confident accounts. Given what and currently there is no clear way to tell. This we know about the neurobiology of memory and does not mean that memory-based evidence the cognitive psychological research on memory, should be thrown out, but rather that police,

NATURE REVIEWS | NEUROSCIENCE PREPRINT 11 In press - Nature Reviews Neuroscience judges and jurors should be educated on these mind that the wording of a question can lead to nuances so that they may give memory-based memory distortions (as discussed above). evidence its proper weight. Indefinite articles should be used over definite articles. For example, asking whether the witness Interviewing eyewitnesses saw ‘the gun’ as opposed to ‘a gun’ implies that a Although the relationship between confidence in gun was present2. Lastly, it should be kept in mind the accuracy of a memory and the actual accuracy that congruency among multiple eyewitness of a memory is complex, confidence statements accounts does not necessarily entail greater should be recorded immediately after an interview accuracy as witnesses may communicate with or suspect identification25 before the witness’ each other and all are susceptible to the same subjective feeling of confidence can be influenced memory errors. by post-identification feedback33-36 or other factors37,38. If confidence is to be used as an Identification of suspects indication of memory accuracy, this would be the There are many guidelines for constructing and best estimate of confidence to use. conducting suspect line-ups. These guidelines There is a large literature on different suggest that each line-up should only contain one approaches to interviewing eyewitnesses. The suspect and the suspect should not stand out from (CI), sometimes referred to as the rest of the line-up. Fillers (other non-suspects the ‘enhanced’ cognitive interview, was developed in the line-up) should be selected on the basis of by psychologists in response to a request from the eyewitness’ description of the perpetrator. If law enforcement for better interviewing an innocent suspect fits the description of the methods25,78. Here we will review the general perpetrator more than the other people in the line- outline of the CI as it lays a solid foundation of up, there is a higher likelihood that the suspect best practices. will be misidentified as the perpetrator. In a truly Interviewing should begin with a transfer of unbiased line-up, naive ‘mock witnesses’ who did control to the witness, i.e. witnesses should be put not witness the crime should not select any one at ease and made to feel comfortable. This is individual more frequently than the others2,25. important in avoiding unintentional bias as Although no line-up method can completely witnesses may be easily manipulated by eliminate false identifications and increase the individuals of perceived power and authority, such likelihood of a correct identification, some as law enforcement. It is recommended that recommendations will reduce the number of officers request the witness to mentally recreate misidentifications without substantially reducing the scene of the crime. This is based on research the likelihood of a correct identification. The first on context-dependent memory, which has shown is to warn witnesses that the true perpetrator may that recall is better when it occurs in the same not be present in the line-up. Research has found context as learning79. that experimental witnesses have a tendency to Testimony ought to begin with an open-ended select a suspect even if the actual target is not in narrative; that is, witnesses should be encouraged the line-up39,40. The instruction that the suspect to recall as much detail as possible, even if they may not be present in the line-up has substantially recall events out of order or the details seem reduced the number of misidentifications, trivial. The interviewer should allow time for long especially in line-ups in which the target was pauses while the eyewitness thinks, relaxes, and absent. Although the number of correct gathers his or her thoughts. This approach identifications were also reduced in these studies, contrasts with standard police interviews, in this was only to a small degree25,80. Secondly, which a witness may often be interrupted and sequential line-ups (in which the potential asked to report events in a specific order. suspects are shown one after the other) tend to Allowing witnesses to report events in their own produce fewer false identifications than order and at their own pace results in a more simultaneous line-ups (in which all potential detailed and more accurate report25. Witnesses suspects are shown together) (see Box 3). This should be asked to indicate when they are unsure approach also reduces the number of correct and should be informed that they should not identifications, but typically to only to a small guess. degree81,82. The adoption of these procedures has After the free narrative, the interviewer can met resistance, which generally is based on the follow up with open-ended questions, keeping in fear that it may lead to fewer convictions of guilty

NATURE REVIEWS | NEUROSCIENCE PREPRINT 12 In press - Nature Reviews Neuroscience suspects83. Although these procedures may indeed can alter the memory; that a witness’ confidence increase the number of type I errors (no that their memory is accurate is no guarantee that identification of guilty suspects, and therefore the memory is indeed accurate6,28,31,34-36; and that fewer convictions), they reduce the number of even what is encoded in the first place is filtered type II errors (wrongful identification of innocent by a person’s preconceived notions and suspects, and therefore wrongful convictions) schemas84, and people have a tendency to ‘fill in without a cost to overall accuracy; i.e., they lead the gaps’ in a memory9. An understanding of these to a shift towards more conservative issues may help jurors to realize that eyewitness identification, which favours protecting innocent testimony is not equivalent to DNA evidence in suspects. probative value. Some regional jurisdictions, such As previously discussed, distortions in as New Jersey10,11, Massachusetts12, Texas13, and memory can occur as a result of post- North Carolina14 have begun to provide identification feedback, whether intentional or instructions to jurors on how to approach not33-36. Double-blind line-ups, in which the eyewitness testimony10,12-14. official who administers the line-up does not Additionally, it is recommended that jurors be know who the police suspect is, would reduce allowed to take notes as the sheer amount of such unintentional bias25. One critique against information presented to jurors often exceeds using double-blind line-ups has been the cost of reasonable demands on memory capacity. As and need for extra manpower to administer these jurors are eyewitnesses to the events in the line-ups. However, computer programs can be courtroom, their memories of these events may used to administer the line-ups in a blind fashion also be vague and may be reconstructed based on by showing photos of suspects on a computer biases, prior beliefs and expectations, and screen without any police officers being present, misinformation. Courtroom transcripts may be thereby alleviating this concern. available, but they are often not useful because jurors have difficulty finding the pertinent Recommendations for judges and jurors information in the lengthy transcripts. Taking It is important to remember that the courtroom notes not only provides a source of reference, but also places large demands on the memory of improves the memory itself (reference). Although judges and jurors. Jurors are often faced with some might argue that a juror who takes notes complex legal instructions and procedures. might dominate deliberations, encouraging all Simple, clear written instructions from judges jurors to take notes could overcome this problem. help to clarify the deliberation process. In Like eyewitnesses, a juror espousing great particular, given the data described above confidence in his or her recollection is more likely concerning misinformation2,4, jurors should be to be trusted. It would be beneficial to at least warned of the effects of misleading questions by have this trust based on notes rather than on attorneys. Jurors are subjected to prosecutors and memory alone. defence attorneys who may deliberately try to confuse them, redirect their attention, and play to their . There are opportunities for Conclusions retroactive and proactive interference as lawyers Memory is imperfect and is susceptible to interject arguments during the court proceedings. distortion and loss. There are adaptive reasons for In particular, misleading questions may imply that generalization and forgetting7. Indeed, Luria’s facts were presented in evidence by a witness famous report of the mnemonist S.85 readily which were not actually presented. Although such shows how an inability to forget can severely education does not eliminate the tendency to impair normal functioning. In addition, the incorporate information based on biases, it does neurobiological mechanisms that underlie the reduce its effects9. occurrence of distortions in memory also allow Jurors should likewise be instructed that the memories to be updated and strengthened. memory of an eyewitness should not be Unfortunately, in the courtroom ‘memory’ is often considered to be indelible, even if the event was misunderstood and undue assumptions are made traumatic39-42; that a person’s biases and about its veridicality. expectations will change with time and new Thus, there needs to be greater education and information (or misinformation4,40), and that this awareness of memory processes in judicial

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