8 The Brain Behind the Witness Stand: The Neuroscience of Eyewitness Testimony

About Eyewitness Testimony

It was a Friday night not much different than any other. Sarah was at the quaint corner store down the street from her house on a specific mission to find the perfect sweet treat to accompany her movie night in. She had been looking forward to this quiet evening all day. But, as her hand was hovering over the selection of chocolate bars, a blood-curdling scream pierced the air. Sarah whipped her head around to see an unfamiliar man holding a gun pointed directly at the cashier, aggressively demanding the contents of the register, and the cashier, visibly shaken, handing it all over without hesitation. In a matter of seconds, the man was gone, disappearing into the night, and Sarah and the cashier were left alone to process what they had just witnessed. It was a fleeting moment, but Sarah knew she would remember it forever. However, only minutes later when the police arrived on scene and started questioning her, Sarah began to question her own memory of the perpetrator’s appearance. Did he have black hair or brown? Was his hoodie blue or grey? Was he even wearing a hoodie at all? She struggled to recall even the most basic details.

Although we often think of our memory as a perfect recording of past events, the reality is that our memory can be better thought of as a Wikipedia page that can be edited by ourselves or others as the days go by – it is malleable. Even when we are certain that we will remember the details of something forever, as Sarah had been, our memory quickly proves to be fallible. While such errors may seem like a mere inconvenience for some, the consequences of false memories can be life-altering for others. Eyewitness testimony refers to “evidence given under oath in a court of law by an individual who claimed to have witnessed the facts under dispute” (American Psychology Association, n.d.). Eyewitness testimonies have long been thought of as a reliable source of information, being used as admissible evidence in a court of law since ancient times. The reliance on eyewitness testimony is heavily based on the belief that the human brain can accurately recall and report past events. However, in more recent years, it has become increasingly apparent among psychologists, legal scholars, and other experts, that eyewitness testimony is not as reliable as we once thought (Albright & Garrett, 2022).

Eyewitness testimony is the leading cause of wrongful conviction in Canada. In fact, eyewitness testimony has contributed to 70% of known wrongful convictions in Canada, as revealed by the more recent development of DNA testing (Innocence Canada, n.d.). DNA testing is a scientific technique that compares an individual’s DNA sample to evidence found at a crime scene to determine whether the individual could have been involved in the crime (Government of Canada, n.d.). Although there are several external factors that can account for the questionable conclusions derived from eyewitness testimony, ranging from witness biases and leading questions to post-event information, the inherent fallibility of human memory does not help.

Neurological Mechanisms of False Memories

Perhaps one of the most notable forms of memory error are false memories, referring to “the recollection of an event, or details of an episode, that did not actually occur” (Straube, 2012). Despite seeming unexplainable, researchers have uncovered potential neurological mechanisms underlying these errors in an effort to prevent detrimental mistakes such as wrongful convictions (Werner et al., 2013). By gaining a better understanding of the cognitive processes involved in memory formation and retrieval, we can develop strategies to reduce the risk of memory errors and improve the accuracy of eyewitness testimony. What researchers have found so far is that the process of creating memories involves a minimum of three distinct sub-stages: encoding, consolidation, and retrieval – each of which can be susceptible to particular errors and potentially cause the formation of inaccurate memories (Straube, 2012).

During the encoding stage, processes such as spreading activation, self-reference, and imagery can all contribute to the development of inaccurate memories. Spreading activation refers to the cognitive process in which the activation of one particular concept or node in a network of related concepts leads to the subsequent activation of related or associated concepts. This process often occurs when we think, retrieve information from memory, or process language (Foster et al., 2017). For instance, the activation of the concept of ‘man in a blue hoodie’ in Sarah’s memory may automatically lead to the activation of related concepts such as ‘robber’ and ‘criminal.’ Given that these concepts are now closely associated in her brain, she may be more inclined to mistakenly identify an individual as the perpetrator solely based on what he is wearing (i.e., a blue hoodie). Similarly, self-reference refers to the concept of one’s memory being enhanced when people categorize stimuli in relation to themselves and their lived experiences, opposed to others. For example, research has demonstrated that individuals are able to more accurately recall items which are judged in relation to the self, when asked to make judgements about either the self-relevance of positive and negative adjectives, or about the semantic meaning of the items (Sui & Humphreys, 2015). In the context of Sarah’s experience, if she had been closely following media coverage or discussions about the armed robbery following her witnessing the event, she may be more likely to remember details that she did not actually see, but were rather suggested by the media. In this case, her existing knowledge and expectations from her exposure to the media could inaccurately fill in those ‘gaps’ in her memory. In a similar vein, mental imagery refers to the mental representations and experiences of sensory information that occur in the absence of direct external stimuli. These representations are retrieved solely from one’s memory and can cause an individual to re-experience a version of the original sensory stimulus, or a new combination of stimuli, in their mind’s eye (Pearson et al., 2015). For example, if Sarah had visited that same corner store regularly, she may start to incorporate other customers’ faces from past experiences in the store, into her memory of the crime, potentially leading to inaccurate testimony.

Data from neuroimaging studies has indicated that brain structures involved in perception (e.g., occipital and parietal regions) as well as memory storage (e.g., hippocampus activation for true memories and deactivation for false contextual memories) play an instrumental role in whether a false memory is created or not. These memory encoding biases can be triggered by spreading activation, engaging in self-referential processes, or constructing a gist trace, in which only the main idea or essence of an event is remembered, rather than specific details. All of these processes often involve the frontal lobe, which typically influences processes related to true memory formation (Straube, 2012). Moreover, stress is thought to interfere in this process in several ways as it can significantly impair one’s attention and focus – both critical factors of the encoding process (Werner et al., 2013). This means that for an eyewitness like Sarah, whose heart was racing and palms sweating as an armed robber was only a few feet away from her, there is greater risk that the memory did not encode accurately.

During the consolidation stage, false memories can be created due to post-event information. For instance, when police officers were asking Sarah, “what did the man with the gun look like?” her ability to accurately recall that information could have been inhibited by the cashier mentioning that she thought he was a brunette. In fact, those in the legal sphere, especially police officers who have arrived on the scene of a crime, must be very careful not to use misleading post-event information (MPI), which refers to new information or suggestions that may alter a witness’s memory of the original event (Wikibooks, n.d.). For instance, posing a leading question such as, “was the man wearing a hoodie?” or suggesting “he would have to be young to flee the scene that quickly” can plant seeds of doubt in Sarah’s mind of what she had actually witnessed and hinder her ability to provide an accurate eyewitness testimony.

Memory updating processes, which involve perceptual recombination of recall cues with new information mediated by memory and attention processes, are likely responsible for this malleability of memory (Straube, 2012). Research to date suggests that binding processes of the hippocampus and later the prefrontal cortex may be involved in binding together single ‘pieces’ of an episode stored across different parts of the brain. For example, Sarah would have been engaging various parts of her brain as she was remembering what the perpetrator was wearing, the sound of the gunshot, and the emotions she experienced, but both the hippocampus and prefrontal cortex play a role in ensuring this can all later be retrieved as one coherent memory. Research has also illustrated how memories can be affected or distorted during consolidation due to novel incoming information and sleep or sleep deprivation, with different mechanisms at play. Retroactive interference due to new incoming information is likely dependent on encoding and memory updating processes, while sleep may affect the formation of false memories through semantic generalization by active reorganization of the memory trace in the post-learning sleep period (Straube, 2012).

It has also been made evident that false memories can be developed during the retrieval stage, however the neural mechanisms underlying this process are not as well understood. What we do know so far is that retrieval is an active process that involves reconsolidation of the engram, which is comparable to replaying the circuit’s activity. During this process, certain elements of the memory may be accentuated while others may be lost (Lim, 2021) Some studies have indicated that the hippocampus and other regions are equally activated during the retrieval of both true and false information (Straube, 2012). Conversely, other studies suggest that these regions are more engaged during the retrieval of true memories or even more active during the creation of imaginary events compared to true memories, as observed in research on future event simulation. Moreover, earlier evidence proposes that frontal areas are more active when cognitive demands are higher, such as during source vs. old/new recognition tests, which require greater monitoring and retrieval of contextual information from memory. The hippocampus has been found to play a role in constructive memory by binding elements together flexibly in memory, which can sometimes lead to false memory recognition due to incorrect recombination (Straube, 2012).

When it comes to eyewitness testimony, being able to distinguish familiar from unfamiliar faces is crucial. Misidentifying an innocent person as the perpetrator can lead to wrongful convictions, while failing to identify a guilty person can allow them to escape justice altogether. To put this into perspective, if Sarah were to incorrectly identify another man as the robber, it could result in that man being punished for a crime he did not commit, potentially causing irreparable harm to his life and reputation. On the other hand, if Sarah were unable to identify that true perpetrator, he may go free and continue posing a threat to society.

Although activation in the fusiform face regions appear to be consistent during face processing, the encoding and recall of learned faces seems to require the involvement of more extensive networks (Werner et al., 2013). For example, the participation of the anterior temporal cortex, including the anterior tip of the collateral sulcus, would be necessary. Research using fMRI has indicated that familiarity with a face leads to higher activation in the precuneus while observing new faces typically causes higher activation in the fusiform gyrus and the amygdala. These findings, among others in an article by Werner et al. (2013), demonstrate that facial recognition involves a set of different brain areas, depending on the precise face processing demands. Although a complete understanding of facial recognition on a neural level is still rather ambiguous, some neural correlates allow for increased predictability in a specialized setting (Werner et al., 2013).

A prime example of the potential value of laboratory studies is a study by Jeye et al. (2017), which used fMRI to investigate the neural mechanisms underlying false memories. The study found a negative correlation between activity in the hippocampus and the anterior prefrontal cortex during the formation of false memories. These findings not only suggest that these regions are interacting during false memories, but also that it is possible that the left anterior/dorsolateral prefrontal cortex may be activated due to incorrect context memory or high confidence, as activation in this area has been shown to be associated with high confidence ratings of a memory’s accuracy. As a result, this may be inhibiting the hippocampus to reduce the amount of potentially conflicting information – like whether the perpetrator was wearing a hoodie or jacket (Jeye et al., 2017). Alternatively, the hippocampus may be activated due to incorrect binding of memories, and it may inhibit the anterior/dorsolateral prefrontal cortex to reduce the amount of potentially conflicting information. While the direction of the interaction is rather uncertain, the anterior/dorsolateral prefrontal cortex is seemingly associated with inhibition, so it is likely that this region plays a role in inhibiting the hippocampus during the formation of false memories (Jeye et al., 2017).

In conclusion, while obtaining original neuroimaging data of real-life events like the one Sarah was faced with may be near impossible, it is important to consider the potential value of laboratory studies in attempting to understand the nature of eyewitness memory. In more recent years, as technological advancements have progressed, standardized methods used in experimental settings have provided a framework for comparing different eyewitnesses and identifying potential pitfalls in how we examine memory. While these impressive advancements have their merits and can undoubtedly contribute to our understanding of the human memory, it is important to conclude by mentioning that the use of brain imaging as a dependable tool in legal proceedings still has a considerable distance to cover (Werner et al., 2013).