New findings on the effects of stress on memory suggest that people tend to recall information better when the information is related to the stressful event.
However, the factor of delay—that is, the time between a stressful event and learning information—does not appear to have as strong an influence on the relationship between stress and memory as previously thought.
“The effects of acute stress on memory encoding are complex,” said Grant Shields, lead author of a study published in Learning & Memory. “Our work shows that relevance of information to a stressor appears to play an important role in the effects of stress on encoding.”
Shields is assistant professor of psychological sciences in the Fulbright College of Arts and Sciences at the U of A. As a cognitive neuroscientist, he studies the effects of stress on cognitive processes.
Shields and co-authors Colton Hunter, doctoral student in psychological sciences at the U of A, and Andrew Yonelinas, psychology professor at the University of California, Davis, tested the recall of 130 young adults by manipulating acute stress, the delay between stress and memory encoding, and the relevance of information to the stressful event. Encoding is the initial learning of information.
The researchers divided participants into two groups. Both groups were asked to remember a list of words related to personality traits and other words not related to personality traits. Members of one group were required to give a speech on their personality to a panel of evaluators. Members of a control group also spoke on their personality, but only among themselves within a non-stressful environment.
The researchers found that stress during encoding led to greater recall of stress-relevant materials—in this case, a list of personality-related words. This was true compared to material not related to the stressor, non-personality words such as “muddy.” This effect was slightly greater for materials encoded during the stressor, rather than those encoded after a short delay, although the stress-relevance effect was not significantly different across the delay conditions.
Attention to the effect of stress on cognition has increased over the past two years, as more people are dealing with a multitude of stressors. Research has shown that chronic or repeated exposure to stress has a negative effect on attention span, sleep and memory, and that it can even damage the brain.
In this survey study, we gathered beliefs from memory experts and laypeople related to the effects of stress on eyewitness memory. We were primarily interested in proportions of each group who agreed, disagreed, or selected don’t know for each statement (see Table 2). Additionally, we compared endorsements and selections between groups. In line with previous surveys, we found that most experts in this sample strongly endorsed the belief that high levels of stress impair the accuracy of eyewitness testimony (e.g., Kassin et al., 1989; Kassin et al., 2001; Yarmey & Jones, 1983). In addition, both groups strongly endorsed the statement that stress during retrieval impairs memory, which is in line with findings from fundamental research (e.g., Shields et al., 2017; Wolf, 2017). However, when examining more specific statements in regard to encoding (stress enhances encoding) and retrieval (stress impairs retrieval), we saw a divergence between eyewitness and fundamental memory experts. Fundamental memory experts generally agreed that experiencing stress at encoding enhances memory, whereas eyewitness memory experts did not.
Prior research examining the effects of stress during encoding on memory is mixed, with different results often emerging across research fields (e.g., S. D. Davis, Peterson, Wissman, & Slater, 2019; Deffenbacher et al., 2004, vs. Henckens et al., 2009; Hoscheidt, LaBar, Ryan, Jacobs, & Nadel, 2014; Vogel & Schwabe, 2016). These contrasting findings perhaps account for the contradictory understandings about the effects of encoding stress on memory that emerged in this survey, and are likely due to methodological differences between the research fields. Fundamental memory research tends to use robust experimental methodology including validated laboratory stressors to induce acute stress (e.g., Trier Social Stress Test; Kirschbaum, Pirke, & Hellhammer, 1993), physiological and subjective manipulation checks to confirm stress inductions, and sufficient retention intervals between sessions (i.e., at least 24 hours) to distinguish the stress effects of encoding and retrieval on memory performance. However, these fundamental studies often examine memory performance for more basic types of stimuli (e.g., word lists, static pictures; Schwabe, Bohringer, Chatterjee, & Schachinger, 2008; Smeets, Giesbrecht, Jelicic, & Merckelbach, 2007; Zoladz et al., 2011).
On the other hand, eyewitness memory laboratory research uses unvalidated stressors such as violent videos, electric shocks, or self-reports (e.g., Bailis & Mueller, 1981; Brigham, Maass, Martinez, & Wittenberger, 1983; Clifford & Hollin, 1981; Kramer, Buckhout, & Eugenio, 1990). Additionally, many eyewitness experiments rely only on self-reported stress as a manipulation check for the stress induction (e.g., Buckhout, Alper, Chern, Silverberg, & Slomovits, 1974; S. D. Davis et al., 2019). Indeed, as pointed out by Sauerland et al. (2016), only seven studies included in the Deffenbacher et al. (2004) meta-analysis report physiological stress measures. Subjective reports of stress, however, do not always correlate with physiological acute stress responses (Hellhammer & Schubert, 2012). Eyewitness field studies show similar limitations, failing to confirm HPA-axis activation (i.e., by examining cortisol) or lacking a sufficient retention interval to specifically examine effects of encoding stress on memory performance (e.g., Hope et al., 2016; Hulse & Memon, 2006; Morgan et al., 2004; Valentine & Mesout, 2008). The single session designs often used in eyewitness memory research make it impossible to isolate the effects of encoding stress on different memory phases (i.e., consolidation versus retrieval; Sauerland et al., 2016; Thomas & Karanian, 2019).
Many of these methodological differences between fields stem from the distinct goals of each particular research field. While the fundamental memory field often aims to examine the basic neurobiological activities underlying the stress–memory relationship, the eyewitness memory field is more interested in the impact that acute stress can have on memory for a crime in applied witness contexts. Thus, the eyewitness memory field notably attempts to mimic witness experiences. However, in such applied experiments, isolating stress effects can be difficult, sometimes leading to a mischaracterization and overgeneralization of the term acute stress (i.e., a physiological response involving HPA axis activation, as defined in the fundamental memory field). Stemming from these unique research aims, the varied methodology between fields likely contributes to the contrasting results, and perhaps explains why experts from the two fields often express opposing views about how encoding stress affects memory performance. This divergence in perspectives suggests an absence of interactions between research fields. Critically, understanding results from fundamental memory studies that use more precise methodology might be useful for eyewitness experts. Eyewitness researchers examining the effects of stress on memory performance should strive to gain knowledge about the fundamental stress literature and the methodological gold standards (see Shields, 2020), and should also aim to collaborate with fundamental stress experts. In addition, fundamental memory researchers could conduct research alongside or in consultation with eyewitness memory researchers to produce work that better reflects conditions in the real world—for example, by using more ecologically valid scenarios (e.g., mock crimes).
Expert beliefs about moderators between encoding stress and memory
To better parse responses to the more general statements about encoding stress effects on memory performance, we also probed for experts’ beliefs about potential moderating factors that may affect the relationship between encoding stress and memory. Many of the statements that showed low levels of expert endorsement (i.e., below 50%; abstractness, faces affected differently, violent events, children less affected, older adults less affected) have not been thoroughly empirically tested. For example, although some findings indicate that children (Deffenbacher et al., 2004) or older adults (Hidalgo, Pulopulos, & Salvador, 2019; Smith, Dijkstra, Gordon, Romero, & Thomas, 2019) may be less affected by stress than younger adults, the vast majority of studies have focused solely on younger adults.
Therefore, the lack of consensus and higher levels of don’t know responses are in line with available research findings. These data may help guide future research by emphasizing some of the moderators that need to be further examined with empirical work. However, some statements received high levels of endorsement despite ambiguity in research findings. There are conflicting findings regarding differences in stress effects on victims versus bystander eyewitnesses (e.g., Hope et al., 2016; Hosch & Bothwell, 1990; Kassin, 1984), yet most of the eyewitness memory experts and fundamental memory experts endorsed the idea that a victim’s memory will be more affected by encoding stress (victims more affected). Similarly, the vast majority of both expert groups disagreed that stress experienced during a short crime will not affect memories (short crime), although we have not been able to identify any empirical research conducted on this specific topic.
Furthermore, both groups generally agreed that eyewitnesses who experience moderate levels of stress during a crime display better levels of memory than those who experience low levels of stress (moderate stress). Most experts from both groups also endorsed the idea that severe but not moderate levels of stress generally harm eyewitness memory (severe stress). Neuroscientific research supports this inverted-U-shape idea, which suggests poorer cognitive performance at low and high levels of stress and better performance at medium levels of stress (e.g., Abercrombie, Kalin, Thurow, Rosenkranz, & Davidson, 2003; de Kloet, Oitzl, & Joëls, 1999; Lupien, Maheu, Tu, Ficco, & Schramek, 2007).
This inverted U might also explain the different findings between the eyewitness and fundamental memory fields. For example, some fundamental memory research suggests that stress induced in the laboratory during encoding enhances stressor-related memory (e.g., Vogel & Schwabe, 2016), while field studies have found impairments in stressor-related memory (e.g., Metcalfe et al., 2019). Although research directly supporting the statements discussed in this section is not substantial, experts might have drawn from relevant theories to support their choices on these topics (e.g., dual mode model, temporal dynamics model, Yerkes-Dodson law; Diamond et al., 2007; Joëls et al., 2006; Yerkes & Dodson, 1908). Empirical work on these generally endorsed but underresearched topics would also be beneficial for understanding the intricacies of the stress–memory relationship.
Other relevant factors endorsed by experts have a more solid research evidence base. For example, both expert groups agreed that emotional stressful experiences are remembered better than nonemotional ones (emotional better remembered), an account supported by research (Cahill, Gorski, & Le, 2003; Kuhlmann, Piel, & Wolf, 2005; Shields et al., 2017; but see Schwabe et al., 2008; Shermohammed, Davidow, Somerville, & Murty, 2019). Additionally, both agreed that encoding stress enhances memory for central details and undermines memory for peripheral details (detail type).
These opinions are generally supported by research that suggests simultaneous helping and harming effects of stress on different types of details (Christianson, 1992; Christianson & Loftus, 1987; Heuer & Reisberg, 1990; but see Lanciano & Curci, 2011; Wessel, van der Kooy, & Merckelbach, 2000). Eyewitness memory experts likely related this statement to the weapon focus effect (e.g., Kramer et al., 1990; Loftus, Loftus, & Messo, 1987), a phenomenon demonstrating that eyewitness memory for faces and other details is poorer if a weapon was present during a crime (Fawcett, Fawcett, Peace, & Christie, 2013). Finally, the majority of both groups disagreed that those who experience stress are more likely to have repressed memories than those who do not (repression), which is in fact not supported by empirical data (e.g., Otgaar et al., 2019).
Expert beliefs about moderators between retrieval stress and memory
We also examined factors relevant to stress effects at memory retrieval. The majority of experts who agreed that retrieval stress impairs memory also endorsed a more applied version of this statement, though to a lesser extent. This more applied statement (police interview) stems logically from the broader statement (stress impairs retrieval), though specific research has not yet been conducted on this topic. Other retrieval-related statements were based on limited prior research.
For example, some research suggests that free recall is impaired more than recognition ability by stress before retrieval (test type; de Quervain et al., 2003; de Quervain, Roozendaal, Nitsch, McGaugh, & Hock, 2000; Gagnon & Wagner, 2016), a statement generally endorsed by both groups. Some experimental results also suggest that if memory is tested immediately after a stressor, memory is not harmed, but rather is sometimes even enhanced (immediate retrieval enhances; Schönfeld, Ackermann, & Schwabe, 2014; Schwabe & Wolf; 2014). However, less than a third of both expert groups agreed. Finally, around two thirds of eyewitness memory experts and one third of fundamental memory experts believed that memory tested 2 hours after a stressor will be worse than memory tested 30 minutes after a stressor (retrieval timing), a statement based on some limited results (e.g., Schwabe & Wolf, 2014). These statements have some basis in research but lack a substantial literature, which may explain the absence of expert consensus in this sample.
Expert beliefs on neuroscientific statements
Experts answered eight additional statements about neuroscientific explanations of stress effects on memory. These statements were mostly based on theoretical research (e.g., Diamond et al., 2007; Joëls et al., 2011; Joëls et al., 2006; Quaedflieg & Schwabe, 2018; Roozendaal, 2002; Schwabe et al., 2012) that delineate the specific timing and roles the autonomic nervous system and glucocorticoid activity play in the relationship between stress and memory. Overall, eyewitness memory experts selected don’t know more often than fundamental memory experts for each statement.
This disparity between expert groups suggests that eyewitness memory experts understand less about the neuroscience behind the stress–memory relationship. That being said, perhaps most striking in regard to the eight neuroscientific statements was the proportion of don’t know selections across both groups of experts. Over a third of fundamental experts also selected don’t know for most of the neuroscientific statements.
Some statements had a more limited research basis, including statements about how noradrenergic stimulation and glucocorticoid activation act specifically alone or together to affect brain networks related to memory (noradrenergic alone, glucocorticoid alone, HPA & ANS activated). Other statements were more established (see Joëls et al., 2006; Quaedflieg & Schwabe, 2018), but did not receive a majority endorsement from fundamental memory experts (slow cortisol is detrimental, HPA & ANS retrieval). The proportion of don’t know selections indicate a lack of knowledge in this research area, suggesting that certain topics are not yet established and accepted by an expert majority—at least in these two research domains.
A majority of fundamental memory experts generally showed consensus on three statements, which point towards research findings that are more accepted. Fundamental memory experts mostly disagreed that effects of stress on memory are primarily driven by autonomic nervous system activity, though nearly all agreed that encoding is facilitated when the autonomic nervous system is activated while experiencing an emotional event such as a crime. Additionally, most fundamental memory experts agreed that rapid nongenomic glucocorticoids have a beneficial effect on memory formation. Considering that 78% of fundamental memory experts agreed that experiencing encoding stress enhances memory, these endorsements of neuroscientific explanations of encoding enhancements are perhaps unsurprising.
Layperson beliefs about stress effects on memory
As juror opinions about stress effects on memory can also enter the courtroom and may affect decision-making (Bornstein et al., 2008), we examined laypeople’s responses and compared them with experts’ responses. In line with experts, most laypeople agreed that high levels of stress impair eyewitness testimony (high stress impairs).
Other differences between laypeople’s and experts’ responses point towards diverging opinions of the public, including the controversial belief that stress causes repressed memories (repression, 85%), which research suggests is not the case (e.g., Otgaar et al., 2019). Additionally, the majority of laypeople believed that police officers’ memories are resistant to stress effects, while eyewitness and fundamental memory experts did not (professionals less affected), a view more in line with the limited research on this topic (e.g., Stanny & Johnson, 2000). Finally, laypeople also believed that stress affects faces differently than other types of stimuli (faces affected differently), contrasting lower endorsement levels from eyewitness memory experts and fundamental memory researchers on this underresearched and inconclusive topic.
Whereas expert beliefs are generally formed from research on these topics in academic settings, laypersons’ beliefs likely stem from intuitive feelings or perceptions about each statement. Given that stress is generally viewed as a negative experience (e.g., Adams, 2016; Becker, 2013), it is unsurprising that laypeople seem to view any degree of stress as harmful, in contrast with expert opinion. Laypeople’s agreement that police officers’ memories can withstand stress is also an evident erroneous, but understandable commonsense belief (e.g., Hope, 2016; Stanny & Johnson, 2000). A related statement used in past surveys showed that low percentages of laypeople (28% and 39%) endorsed the idea that Police officers and other trained observers are no more accurate as eyewitnesses than is the average person (e.g., N = 111, Benton et al., 2006; N = 79, Kassin & Barndollar, 1992, respectively). Taken together, these responses suggest that many laypeople believe that professionals are generally better eyewitnesses who are less influenced by external factors such as stress. Two recent surveys also show that large proportions of participants (59% and 67%, respectively) endorsed the idea that traumatic experiences can be unconsciously repressed for many years and then recovered (N = 230 and N = 79; Otgaar et al., 2019), a statement similar to repression in our survey.
Factors such as television and media may influence such beliefs. For example, 75% of students (N = 613) who reported hearing about someone recovering a repressed memory said they heard about such a circumstance though television (Golding, Sanchez, & Sego, 1996). Additionally, amount of media exposure to information about repressed memories was positively correlated with beliefs in repressed memories. Thus, perhaps the endorsement of the idea that stress causes repressed memories from laypeople in this sample originally stemmed from media or television exposure. To sum up, as demonstrated in this survey and previous surveys, commonsense beliefs do not always align with expert assessments concerning what the contemporary science suggests (e.g., Benton et al., 2006; Simons & Chabris, 2011).
Implications for applied legal settings
These data serve as an initial empirical attempt of expert and layperson beliefs about the effects of acute stress on memory performance. Although agreement between expert groups was observed on several statements, the most striking difference between groups pertained to the statement that stress enhances encoding (φ = .462), where fundamental memory experts mostly agreed and eyewitness memory experts mostly disagreed. From an exploratory analysis, we also saw a descriptive split among experts who had testified in court. That is, not all testifying experts fell on one side of the belief (i.e., agreeing vs. disagreeing with the statement that stress enhances encoding). These results further support the idea that different expert witnesses bring different views into the courtroom. In this way, jurors and judges could hear contrasting statements from opposing expert witnesses, or hear from only one expert witness, who could fall on either side of the belief. If an expert witness strongly endorses the idea that encoding stress enhances memory, jurors could assume that testimony provided by an eyewitness who experienced stress is highly reliable. If an expert witness reports the opposite, jurors may unreasonably disregard the testimony of an eyewitness who experienced stress. Thus, for seemingly irresolute statements such as stress enhances encoding, exercising caution in the courtroom is important.
On the other hand, these data also suggest that jurors already likely bring their own conceptions about the effects of stress on memory performance into the courtroom. Understanding these preexisting commonsense beliefs is crucial for knowing where expert witness knowledge is needed. For example, if laypeople assume that any amount of stress will automatically impair memory, they may view the testimony from a stressed eyewitness as lacking in probative value. This could later affect their legal decisions. Similarly, if laypeople are unaware of how stress can affect the memories of professionals such as police officers, they may give too much credence to their testimonies over others. For topics like these that show greater consensus from experts in general, reports from an expert witness could be particularly valuable in the courtroom.
reference link :https://link.springer.com/article/10.3758/s13421-020-01115-4
More information: Grant S. Shields et al, Stress and memory encoding: What are the roles of the stress-encoding delay and stress relevance?, Learning & Memory (2022). DOI: 10.1101/lm.053469.121
