Stress and False Memories

Abstract

Previous research has suggested that both chronic and acute stress can impair memory (Sandi, 2013); however, there is little research on which type of stress creates more false memories. Thus, the present study aims to determine whether chronic or acute stress has a greater impact on the formation of false memories. It is hypothesized that there will be an interaction between chronic and induced stress, such that chronically stressed people who are exposed to stress will create the most false memories and that non-chronically stressed people who are not exposed to stress will create the least false memories. Participants for this study will be obtained from an introductory psychology class at the University of California, Santa Barbara. 100 participants will be chronically stressed and 100 will be non-chronically stressed (determined based on their responses on the Perceived Stress Scale (Cohen, Kamarck, & Mermelstein, 1983)). Then, both groups will be randomly assigned to either the stress or no-stress conditions. Stress will be induced using the Trier Social Stress Test (Birkett, 2011). At the first session, participants will listen to a list of words that are part of the Deese, Roediger and McDermott (DRM) task (Pardilla-Delgado & Payne, 2017). On the next day, participants will be exposed to either the stress or no-stress condition and then will have ten minutes to write down the words they remember from the previous day. Individual differences between participants’ responses to the Trier Social Stress Test may be a threat to this study’s internal validity.

Introduction

According the American Psychological Association, stress is defined as “any uncomfortable emotional experience accompanied by predictable biochemical, physiological and behavioral changes” (Alvord, Davidson, Kelly, McGuiness, & Tovian, n.d.). A survey done by the APA in 2014 showed that 75% of adults reported experiencing moderate to high levels of stress in the past month and nearly half reported that their stress has increased in the past year (Stress Facts, n.d.). Stress can have many negative effects on mental and physical health (Alvord, Davidson, Kelly, McGuiness, & Tovian, n.d.), as well as on cognitive abilities, such as memory (Kuhlmann, Piel, & Wolf, 2005). In fact, research has shown that stressed participants create more false memories than non-stressed participants (Payne, Nadel, Allen, Thomas, & Jacobs, 2002). False memory refers to circumstances in which we have definite memories of events that did not actually happen to us (Brainerd & Reyna, 2005). In a study done by Shaw and Porter (2015), participants were induced to generate both criminal and noncriminal emotional false memories. After three highly suggestive interviews, 70% of participants were classified as having false memories of committing a crime that led to police contact in early adolescence and gave a detailed false account of the crime. (Shaw & Porter, 2015). This demonstrates that false memories can and do form, and they can have devastating consequences; they can lead to wrongful convictions and false confessions in court, placing innocent people in prison. By understanding and measuring how stress affects the formation of false memories, juries can better know to what extent they can rely on witness testimonies and confessions in court (Brainerd & Bookbinder, 2019).

There are many theories that attempt to explain how false memories form. The constructive view of memory emphasizes the malleability of memory, suggesting that the merging of knowledge, understanding, and development with experience makes memory vulnerable to systematic distortion. In this view, false memories cannot be confidently distinguished from true memories. Another theory about false memories is the Source Monitoring Theory. This theory states that most instances of false memories are due to source misattributions or confusions. For example, if a participant is presented with visual information and then presented with verbal information that misleads subjects about the details of the original information, then on a later memory test, the misled subjects are more likely than the non-misled subjects to claim that they saw the misinformation. Thus, the theory states that participants erroneously attribute information from the verbal source to the visual one. Finally, fuzzy-trace theory can explain the formation of false memories. Fuzzy-trace theory suggests that verbatim and gist memories are encoded and stored separately, and that false memories occur in two ways: as a result of the retrieval of gist memories when verbatim are called for, and the retrieval of the wrong verbatim memories (Reyna and Lloyd, 1997). These theories help to explain how false memories form. Another theory, Wicken’s Working Memory Theory, attempts to explain the effects of stress on cognition. This theory suggests that under stress, working memory appears to be less available for storing and rehearsing information and less useful when performing computations or other attention-demanding tasks (Wickens, Gordon, and Liu, 1998).

Previous research has shown that inducing acute stress leads to a significant reduction in the recall of words (Kuhlmann, Piel, & Wolf, 2005) and that false memories are significantly more frequent under conditions of high arousal than under conditions of low arousal (Corson, Verrier, 2007). In Kuhlmann, Piel, and Wolf’s study (2005), participants studied a word list containing 30 words, and the next day, participants were either exposed to the Trier Social Stress Test or a control condition for 15 minutes. Then, ten minutes after the stressor, participants’ free-recall of the words was tested. The results reveal that stress caused a significant reduction in free-recall of the words, suggesting that psychosocial stress impairs memory retrieval in humans. In Corson and Verrier’s study (2007), results showed that high-arousal groups recalled more critical words than weak-arousal groups, suggesting that false memories are significantly more frequent under conditions of high arousal than under conditions of low arousal (Corson & Verrier, 2007). In another study, participants were exposed to the Trier Social Stress Test, and then told to listen to a list of 15 words from the Deese, Roediger and McDermott (DRM) task. Immediately after hearing the words, participants were shown words on a computer screen and asked to indicate by pressing a key how confident they were that is was a word they heard or a new word. The results revealed that participants who were exposed to stress incorrectly recognized a significantly higher proportion of critical lures than subjects who were not exposed to stress, indicating that the stressed participants created more false memories than the non-stressed participants (Payne, Nadel, Allen, Thomas, & Jacobs, 2002).

Due to the ethical concerns of exposing humans to repeated stress in experimental studies, there is scarce evidence for the impact of chronic stress on explicit memory in healthy humans. There is some indirect evidence, however, that seems to support the idea that chronic stress impairs memory. For example, “elevations in plasma cortisol levels occurring over years in older adults were found to negatively correlate with hippocampal volume and performance in explicit memory tasks” (Sandi, 2013). Research using rats has also suggested that chronic stress impairs memory. In one study using rats, it was found that chronically stressed rats had a greater working memory impairment than non-stressed rats (Mizoguchi, Yuzurihara, Ishige, Sasaki, Chui, & Tabira, 2000). In another study, rats were housed under stress or no stress conditions for 3 months, and the results showed that stressed rats exhibited significant memory deficits when compared to the non-stressed rats (Jeong, Park, Yoo, Shin, Ahn, Kim, Lee, Emson, & Suh, 2006). This research suggests that chronic stress is also likely to negatively impact memory.

Although previous research has suggested that both chronic and acute stress can impair memory, there is little research on which type of stress creates more false memories. Thus, the present study aims to determine whether chronic or acute stress has a greater impact on the formation of false memories. In addition, many studies induce stress before the participants are exposed to the list of words to remember, but not many studies expose participants to the list of words, then induce stress, and then ask them to remember the words. The present study will examine how stress affects memory when it is induced after being exposed to the list of words to remember, but before the memory test. Finally, although many of the theories in this area of study do suggest explanations for the formation of false memories, they do not account for how stress can have an impact on this process. Therefore, this study will attempt to provide more information for the existing theories.

Hypothesis

Based on the previous research, it is hypothesized that there will be an interaction between chronic and induced stress such that chronically stressed people who are exposed to the Trier Social Stress Test will create the most false memories and that non-chronically stressed people who are not exposed to the Trier Social Stress Test will create the least false memories. It is also hypothesized that there will be a main effect of inducing stress; those exposed to the Trier Social Stress Test will form more false memories than those who are not, regardless of whether they are chronically stressed or not. Finally, it is hypothesized that there will be a main effect of chronic versus no stress; chronically stressed people will create more false memories than non-chronically stressed people, regardless of whether acute stress was induced or not.

Methods

Design

This study will be a between-subjects quasi-experimental design. The study will be a 2 (stress type: chronic or none) x 2 (induced stress: stress or no-stress) factorial design. The quasi-independent variable will be whether participants are chronically stressed or not based on their responses on the Perceived Stress Scale (Cohen, Kamarck, & Mermelstein, 1983). The true independent variable will be whether the participant is in the stress or no-stress condition. This will be manipulated by exposing the stress group to the Trier Social Stress Test. The no-stress group will not be exposed to the Trier Social Stress Test (Birkett, 2011). The dependent variable will the number of false memories formed, measured using the DRM task (Pardilla-Delgado, Payne, 2017).

Participants

The participants for this study will come from a large introductory psychology class (approximately 400 students) at the University of California, Santa Barbara. Every student in the class will take the Perceived Stress Scale, and those who score between 0 and 13 will be considered not chronically stressed and those who score between 27 and 40 will be considered chronically stressed (Cohen, Kamarck, & Mermelstein, 1983). Then, a simple random sampling method will be used to select 100 non-stressed students from those who scored between 0 and 13 and 100 stressed students from those who scored between 27 and 40. The selected participants will be 17-23 years of age and will be of varying gender and ethnicity. Random assignment will be used to assign each group to either the stress condition or the no-stress condition.

Measures

The first measure, the Perceived Stress Scale, is used to determine which students are chronically stressed and which are not. This scale consists of ten questions, and participants are asked to indicate on a scale from 0 to 4 how often they felt or thought a certain way during the last month (0=never, 1=almost never, 2=sometimes, 3=fairly often, 4=very often). Some examples of questions on the scale are “In the last month, how often have you been upset because of something that happened unexpectedly?” and “In the last month, how often have you felt that you were unable to control the important things in your life?”. The full scale can be found in the appendix. Questions 4,5,7, and 8 are reverse scored so that 0 = 4, 1 = 3, 2 = 2, 3 = 1, 4 = 0. Then, the scores for each question are added up to get a total score. A total score ranging from 0-13 indicates low stress, a total score ranging from 14-26 indicates moderate stress, and a total score ranging from 27-40 indicates high stress. The Perceived Stress Scale is a valid measure; higher Perceived Stress Scale scores have been associated with “failure to quit smoking, failure among diabetics to control blood sugar levels, greater vulnerability to stressful life-event-elicited depressive symptoms, and more colds” (Cohen, Kamarck, & Mermelstein, 1983). The next measure, the State Trait Anxiety Inventory (STAI), is a commonly used measure of trait and state anxiety. Form Y of the STAI is used as a manipulation check to assess whether the Trier Social Stress Test effectively induces stress or not, and to make sure that the no-stress condition is less stressed than the stress condition. Form Y of the STAI has two subscales: 20 items for assessing trait anxiety (feelings in general) and 20 for state anxiety (current feelings). State anxiety items include: “I am tense; I am worried” and “I feel calm; I feel secure.” Trait anxiety items include: “I worry too much over something that really doesn’t matter” and “I am content; I am a steady person.” All items are rated on a 4-point scale from “Almost Never” to “Almost Always”. The range of scores for each subscale is 20–80 and higher scores indicate greater anxiety (Spielberger, 2010). The last measure, the Deese, Roediger and McDermott (DRM) task, is used to measure the false memory effect. The task first involves having participants listen to list of words that are semantically related (ex: nurse, hospital, etc.). Then, at the next testing session, participants are given ten minutes to write down all the words they can remember. Participants are then shown words on a computer screen and are asked to indicate by pressing a key whether it is a word they heard before or if it is a new word. The DRM task has been widely used, and typically, the critical word (a related but never presented word, such as “doctor”) is recognized with high probability and confidence (Pardilla-Delgado, Payne, 2017).

Procedure

On the first day, all participants will arrive and be taken into a room, where they will first sign a consent form. Next, participants will listen to a list of 15 words that are part of the DRM task (Pardilla-Delgado, Payne, 2017). Participants will then be free to go. The next day, participants will return at the same time and those in the induced-stress condition will take a pre-stress State Trait Anxiety Inventory while the no-stress condition fills out a simple questionnaire to pass the time. Then, the participants in the induced-stress condition will take part in the Trier Social Stress Test. These participants will be told they have ten minutes to prepare a speech about why they are the ideal candidate for their dream job. The participant will then give a five-minute speech that they are told will be videotaped and shown to a panel of judges. At the end of the five-minute speech, the participant will be instructed to sequentially subtract the number 13 from 1,022 for five minutes. If they make a mistake, they will be asked to start over from 1,022. After the test is complete, a post-stress State Trait Anxiety Inventory will be administered (Birkett, 2011). While these participants are partaking in the Trier Social Stress Test, the participants in the no-stress condition will be asked to continue filling out the questionnaire. After 20 minutes (at which point the stress group will be done with the Trier Social Stress Test), the no-stress group will also take the State Trait Anxiety Inventory to ensure that they are less stressed than the induced-stress group (Spielberger, 2010). Then, after a ten-minute resting period, all participants will be placed at separate desks and will be given ten minutes to write down all the words they remember hearing at the first testing session. Then, each participant will be placed in front of their own computer and will be instructed to press the left arrow key if they heard the word before, or the right arrow key if it is a new word (Pardilla-Delgado, Payne, 2017).

Threats to Validity

One threat to validity to consider is the threat to external validity. Because this study is conducted with university students (a WEIRD sample – Western, Educated, Industrialized, Rich, Democratic), the results may not generalize to other populations (i.e. less educated individuals). In addition, although random assignment will be used to assign the participants to either the stress or no-stress conditions, it is possible that not all confounds will be eliminated. There may be differences in geography, age, gender, ethnicity, and socioeconomic standing (the GAGES) between the participants in the two conditions that could influence the dependent variable’s value and vary systematically with the independent variable. In addition, because this is a quasi-experimental design, it is not as internally valid as a true experiment would be; it will be harder to make causal claims. However, it was necessary to conduct a quasi-experimental design in order to examine the differences in false memory between chronically stressed and acutely stressed people; there is no way to induce chronic stress in a laboratory, so the participants had to come from pre-existing groups.

Participant reaction bias may also be a threat to validity. For example, participant expectancies may cause participants in the no-stress group to consciously or unconsciously respond differently on the State Trait Anxiety Inventory; they may respond in a way that downplays their stress because they know they are in the no-stress group and want to be consistent with the researchers’ expectations. Participants in the stress condition may also respond differently; they may be more likely to exaggerate their stress after being exposed to the Trier Social Stress Test because they know they are expected to be stressed. In addition, participant reactance may also cause participants to respond differently. Participants in the no-stress group may change their responses on the State Trait Anxiety Inventory by exaggerating the amount of stress they feel because they know the researchers are expecting them to be non-stressed. Similarly, participants in the stress condition may downplay their stress on the State Trait Anxiety Inventory because they know the researchers are expecting them to be stressed.

Another threat to validity could be the individual differences between participants’ emotional and physical responses to the Trier Social Stress Test. One study revealed that women reported more fear, irritability, confusion and less happiness immediately following Trier Social Stress Test compared to men (Kelly, Tyrkaa, Anderson, Pricea, & Carpentera, 2007). Another study showed that salivary cortisol increases after the Trier Social Stress Test in men were up to twice as high as in women. The same study also showed that in men, but not women, the mere anticipation of the stress task led to a cortisol response (Kudielka, Hellhammer, & Kirschbaum, 2007). These studies suggest that men and women respond differently to the Trier Social Stress Test and have varying amounts of stress before and after they have completed it. This is a potential confound that could contribute to the internal validity of the present study.

References

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Appendix

Cohen, S., Kamarck, T., & Mermelstein, R. (1983). A global measure of perceived stress. Journal of Health and Social Behavior, 24(4), 385-396. doi:169.231.113.134

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