Motivation and emotion/Book/2014/Eyewitness memory and emotion
What effect does emotion have on eyewitness memory?
The effect of emotion on eyewitness memory is a serious issue which demands public attention. As noted by Deffenbacher, Bornstein, Penrod, and McGorty (2004), when a person witnesses a crime their response is almost always emotional. This emotional response can take many forms such as stress, fear, anxiety, shock, and arousal, and has the potential to have crucial effects on memory (Bornstein & Robicheaux, 2009). As a result, the effect of emotion on eyewitness memory has serious implications for later identifying a perpetrator or perpetrators of a crime, and has the potential to result in miscarriages of justice; for example see the Innocence Project (Edelstein, Alexander, Goodman, & Newton, 2004). To understand the effect of emotion on eyewitness memory, this chapter will critically examine the role of emotion in the accuracy of eyewitness memory, and the influence of psychopathology on eyewitness memory.
What is Eyewitness Memory?
Eyewitness memory may be described as an individual's memory for a specific event that they have witnessed, that most often involves a crime of some sort (Psychology Dictionary, n.d.). For further information on eyewitness memory see the Wikipedia link on eyewitness memory.
Basic Memory Processes
Traditionally, human memory is believed to involve three basic processes:
Table 1. Basic Memory Processes
|Encoding||Is the initial processing of information arriving in memory|
|Storage||Is the maintaining of encoded information over time|
|Retrieval||Is the recovery of encoded information|
Note. Information contained in Table 1 is from Roediger, H., & Guynn, M. (1996). Retrieval processes. In E. Bjork., & R. Bjork. (Eds.), Memory (pp.197-263). California, America: Academic Press.
For further information on memory see the 2013 book chapter on memory and emotion.
Emotion and the accuracy of Eyewitness Memory
Central and Peripheral Information
Emotion has been shown to have both positive and negative effects on the accuracy of eyewitness memory. A main argument that has developed is that emotion may enhance eyewitness memory for information central to an event, while impairing memory for information peripheral to an event (Houston, Clifford, Phillips, & Memon, 2013). Information central to an event includes information which is spatially central to the eyewitness, and is most commonly the direct cause of stress in an eyewitness (Houston et al., 2013; Rush, Quas, & Yim, 2011). In contrast, information peripheral to an event includes information which is in the background, and is not usually the direct cause of stress in an eyewitness (Houston et al., 2013; Rush et al., 2011). This idea that emotion leads to an enhancement of eyewitness memory for information central to an event, and an impairment in memory for information peripheral to an event, was first proposed by Easterbrook in his cue-utilisation hypothesis (Easterbrook 1959, as cited in Griesel & Yuille, 2012). According to the cue-utilisation hypothesis, the more stressed an individual becomes, the more they restrict their focus on the cues in the environment, leading to improved recall for information central to an event, and impaired recall for information peripheral to an event (Griesel & Yuille, 2012).
A study by Christianson and Hubinette (1993) interviewed eyewitnesses who had witnessed a real bank robbery, and compared the accuracy of their statements with information provided from police. The study found that the eyewitnesses showed high memory accuracy for information central to the robbery, but impaired memory accuracy for information peripheral to the robbery (Christianson & Hubinette, 1993). These results are supported in a study by Rush et al. (2011), which examined the effect of stress on eyewitness memory. The study found that increased stress led to greater memory accuracy for information central to an event, and impaired memory accuracy for information peripheral to an event (Rush et al., 2011). Overall, these results suggest that when faced with a crime, emotion may enhance eyewitness memory for information central to the crime, at the cost of impairing memory for information peripheral to the crime.
Other research suggests that emotion also impairs eyewitness memory for information central to an event. According to the phenomenon of weapon focus, in the presence of a weapon an eyewitness's attention tends to be solely focused on the weapon, at the result of less attention being paid to other information in the environment (Kramer, Buckhout, & Eugenio, 1990). As such, in the presence of a weapon, heightened emotion may cause eyewitnesses to fixate their attention on the weapon, impairing their memory for other information which is central and crucial to the event, such as the perpetrator's face (Kramer et al., 1990). For example, a meta-analysis by Steblay (1992) examined the effect of weapon focus on eyewitness memory. The study found that in the presence of a weapon, eyewitnesses show a significant decrease in their memory accuracy for later identifying the perpetrator holding the weapon (Steblay, 1992). Furthermore, the study also found that the effect of weapon focus on eyewitness memory is most prominent when stress is high (Steblay, 1992).
Level of Arousal and Eyewitness Memory
The level of arousal experienced by eyewitnesses has also been proposed as a significant factor affecting eyewitness memory. As noted by Mathews and Deary (as cited in Tiwari, 2011), arousal and emotion are interlinked states, that is increases in heart rate often lead to increases in anxiety, and increases in anxiety often lead to increases in heart rate. The effects of arousal on eyewitness memory may be interpreted according to the Yerkes-Dodson curve (Yerkes & Dodson, 1908, as cited in Valentine & Mesout, 2009). According to this theory, increased levels of arousal associated with the ascending curve lead to improved memory performance until an optimal point is reached (Deffenbacher, 1994). Increased levels of arousal past this point lead to impaired memory performance associated with the descending curve (Valentine & Mesout, 2009).
However, a more recent theory which has been applied to the effect of arousal on eyewitness memory is the theory of activation and arousal mode of attention (Deffenbacher et al., 2004). According to this theory, when the activation mode of attention is dominant the individual experiences sudden increases in arousal, such as increased heart rate and blood pressure, increases in anxiety or stress, and difficulties processing information (Deffenbacher et al., 2004). Experiences associated with the activation mode of attention include anxiety or stress, such as during experiences which are threatening (Deffenbacher et al., 2004). Conversely, when the arousal mode of attention is dominant, the individual experiences a decrease in arousal, such as lowered heart rate and blood pressure (Deffenbacher et al., 2004). Experiences associated with initiating the arousal mode of attention include any experience which elicits little or no anxiety or stress, such as experiences which are not threatening (Deffenbacher et al., 2004). Therefore, the activation mode of attention is most likely to be dominant when eyewitnesses are witnessing a crime (Valentine & Mesout, 2009).
A study by Valentine and Mesout (2009) examined the effect of increased arousal and anxiety on eyewitness memory. Participants in the study were to identify and describe a target individual who would be encountered in a horror theme park (Valentine & Mesout, 2009). To measure increases in arousal the participants wore heart rate monitors, and to measure increases in anxiety the participants completed anxiety questionnaires before and after they entered the horror theme park (Valentine & Mesout, 2009). The study found that an increase in anxiety was significantly associated with an increase in arousal (Valentine & Mesout, 2009). The study also found that high anxiety and arousal was significantly associated with less accurate description and identification of the target individual (Valentine & Mesout, 2009). These findings are supported in a study by Morgan et al. (2004) which found that, compared to participants exposed to a low-stress condition, participants exposed to a high-stress condition showed significant memory impairments in later identifying a target individual who had physically confronted them.
In contrast, the effects of emotion on eyewitness memory found in an experiment may not be the same as in a real crime. As noted by Bornstein and Robicheaux (2009), participants in experiments may lack the same sense of threat that real eyewitnesses may experience when witnessing a crime. Actual eyewitnesses do not have the same sense of reassurance for their safety as do participants in an experiment, and this might lead to heightened emotion and trauma (Bornstein & Robicheaux, 2009). As added by Christianson and Hubinette (1993), real eyewitnesses who have been threatened and have experienced intense fear tend to have quite accurate memories for these events. These memories are often very different from memories created in an experimental setting (Yuille & Cutshall, 1989, as cited in Christianson & Hubinette, 1993).
A study by Yuille and Cutshall (1986) examined the memory accuracy of a group of eyewitnesses who witnessed a real shooting incident in which one person was killed. The study found that the eyewitnesses were very accurate in their memories for the crime, and this accuracy was consistent even after five-months (Yuille & Cutshall, 1986). The study also found that the eyewitnesses' stress levels at the time of the crime appeared to have no detrimental effects on their later memory performance (Yuille & Cutshall, 1986). These results are supported in a study by Nachson and Slavutskay-Tsukerman (2010) which found that victims of a bombing incident who were injured, and bystanders who were not injured, had very accurate memories of the crime. Taken together, these results suggest that the effect of emotion on eyewitness memory in a real crime may be different to that in an experimental setting, with actual eyewitnesses experiencing real threat and intense emotion, that may create vivid memories for these events.
Retrograde and Anterograde amnesia and Eyewitness Memory
The effect of emotion on eyewitness memory may not only influence memory for information during an event, but also for information before and after an event. As noted by Loftus and Burns (1982), the term retrograde amnesia refers to an impairment in memory for information prior to some event. In contrast, the term anterograde amnesia refers to an impairment in memory for information following some event (Bornstein, Liebel, & Scarberry, 1998). Although retrograde and anterograde amnesia are most commonly found in cases where a person has had a head injury, studies have shown retrograde and anterograde amnesia to occur also in eyewitnesses in response to events which initiate shock and stress (Christianson & Nilsson, 1984; Loftus & Burns, 1982). For example, in relation to retrograde amnesia, a study by Loftus and Burns (1982) found that after watching a shocking film in which a boy was shot, participants showed significant memory impairments for neutral information in the film prior to the shooting. Likewise, a study by Sakaki, Fryer, and Mather (2014) found that exposing participants to an emotionally arousing image impaired memory for a preceding neutral image.
Similarly, a number of studies have also found increased stress to lead to anterograde amnesia in eyewitness memory. For example, a study by Christianson and Nilsson (1984) exposed participants to a series of disturbing images, followed by a series of neutral images. Participants' stress levels were measured throughout the experiment (Christianson & Nilsson, 1984). The study found that increased stress in response to the disturbing images led to significant memory impairments in participants' memory for neutral images which followed the disturbing images (Christianson & Nilsson, 1984). This finding is upheld in a study by Kramer, Buckhout, Fox, Widman, and Tusche (1991) which found that, compared to participants in a low-stress condition, participants in a high-stress condition had a significant decrease in memory for information following exposure to a series of distressing images. Overall, these studies of retrograde and anterograde amnesia imply that due to heightened emotion, eyewitnesses may suffer serious impairments in memory for information before and after some distressing event. Consequently, this may impede eyewitnesses in providing information which may be vital to solving a crime.
Emotion and the Misinformation Effect in Eyewitness Memory
Emotion may also make eyewitnesses vulnerable to incorporate misinformation into their memory for events. As noted by Porter, Spencer, and Birt (2003), a common finding in the eyewitness literature is that information to which an eyewitness is exposed to after an event can have a significant influence on their later memory accuracy. The incorporation of incorrect information into an eyewitness's memory is called the misinformation effect (Loftus, Miller, & Burns, 1978, as cited in Porter et al., 2003). To explain this phenomenon, Loftus, Donders, Hoffman, and Schooler (as cited in Tiwari, 2011) proposed the memory impairment hypothesis. According to this hypothesis, erroneous information to which an eyewitness is exposed to after an event erases or overrides the eyewitness's original memory for the event (Loftus et al., 1989, as cited in Tiwari, 2011). As added by Porter et al. (2003), heightened emotion may make eyewitnesses particularly vulnerable to accept post-event misinformation.
A study by Porter et al. (2003) examined whether eyewitnesses are more susceptible to accept misinformation when the witnessed event is highly emotional. The study found that compared to participants who were exposed to a series of neutral photographs, participants who were exposed to a series of highly negative emotional photographs were more likely to incorporate post-event suggested misinformation into their final memory reports (Porter et al., 2003). This result is supported in a study by Tiwari (2011), which found that participants who were tensely aroused after watching a video of a murder were more likely to accept misinformation than participants who were less aroused. Overall, these studies suggest that heightened emotion may make eyewitnesses vulnerable to incorporate misinformation into their memory for events.
Conversely, other research demonstrates that it may not be the role of emotion that makes eyewitnesses vulnerable to accept misinformation, but that of compliance. For example, a study by Paz-Alonso, Goodman, and Ibabe (2013) investigated the effects of compliance on eyewitness memory to accept misinformation following exposure to a negative emotional event. The results of the study showed that participants who were complaintin agreeing with specific misleading misinformation were also more suggestible in terms of incorporating misinformation into their final memory reports (Paz-Alonso et al., 2013). The results of the study also showed that participants who demonstrated a high resistance to agreeing with specific misleading misinformation also demonstrated a high resistance to incorporating suggested misinformation into their final memory reports (Paz-Alonso et al., 2013). As such, it may not be the effect of emotion that makes eyewitnesses susceptible to incorporate misinformation into their memory for events, but other factors such as compliance.
Psychopathology and Eyewitness Memory
Post-Traumatic Stress Disorder (PTSD) and Eyewitness Memory
As eyewitnesses often experience events which are traumatising, we must consider what effect this trauma may have on the well-being of eyewitnesses, and therefore their memory. As noted by Edelstein et al. (2004), a number of studies have shown an association between experiencing traumatic events and the development of emotion-related disorders such as PTSD. PTSD is a type of trauma and stressor-related disorder in which an individual develops in response to a traumatic event or a series of traumatic events (American Psychiatric Association (APA), 2013). It is characterised by a reaction of intense distress to a traumatic event which is constantly brought into memory through nightmares and flashbacks (APA, 2013). As noted by Elbert and Schauer (2002), these flashbacks and nightmares can be so intense that individuals sometimes believe they are back in the traumatic event. Given that eyewitnesses often witness events which may be traumatising, it may be assumed that some eyewitnesses may develop PTSD.
As PTSD is characterised by the constant re-living of traumatic events through flashbacks and nightmares (APA, 2013), it may be suggested that PTSD may enhance eyewitness memory for traumatic events. According to the networks model of memory, information which the individual experienced as traumatic is more easily brought into memory than non-traumatic information (Bower, 1992, as cited in Edelstein et al., 2004). As such, PTSD may enhance eyewitness memory for traumatic events, by increasing access to traumatic information through flashbacks and nightmares, which may facilitate opportunities for increased rehearsal for details of traumatic events (Edelstein et al., 2004). For example, a study by Griesel and Yuille (2012) interviewed prostitutes about violent sexual events which they had experienced. The study found that events which were well remembered were more detailed than events which were poorly remembered (Griesel & Yuille, 2012). The study also found that symptoms of PTSD were more significantly associated with events which were well remembered than events which were poorly remembered (Griesel & Yuille, 2012). However, a limitation of this study was that the accuracy of the events described by the prostitutes' were not verified, and as such limits the ability to generalise the effects of PTSD on eyewitness memory.
In contrast, other evidence suggests that PTSD may also be related to inconsistencies in eyewitness memory. For example, a study by Engelhard, Van Den Hout, and McNally (2008) examined the consistency in memories for which Dutch soldiers had for traumatic events in their deployment to Iraq. The soldiers completed measures for memories of traumatic events at two time points; once at five-months after deployment and another at 15-months after deployment (Engelhard et al., 2008). The study found that compared to soldiers with less symptoms of PTSD, those with more symptoms of PTSD had less consistent memory reports for traumatic events over the two time points (Engelhard et al., 2008). The study also found that the more a soldier reported symptoms of PTSD, the more he or she increased the number of traumatic events remembered (Engelhard et al., 2008). However, a flaw of the study was the actual occurrences of the traumatic events were not verified, and therefore leaves no way to determine which time point represented a more accurate description of the traumatic events (Engelhard et al., 2008).
Overall, the evidence in the current literature indicates that emotion has both positive and negative effects on eyewitness memory. Although emotion may potentially enhance eyewitness memory for certain aspects of an event, emotion may also significantly impair eyewitness memory for other aspects of an event. To obtain a better understanding of the effect of emotion on eyewitness memory further research is needed. First, it is recommended that further research examine the effect of emotion on eyewitness memory for real life crimes. Second, further research should examine the influence of trauma on eyewitness memory, particularly PTSD. Last, further research should also investigate the effect of emotion on increasing eyewitnesses' vulnerability to incorporate misinformation into their memory for events. Examining these factors may be the only way to inform the public of the true relationship between emotion and eyewitness memory.
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