Consciousness and Cognition 22 (2013) 1189–1194

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Consciousness and Cognition

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Experimentally-induced dissociation impairs visual memory

1053-8100/$ - see front matter � 2013 Elsevier Inc. All rights reserved.http://dx.doi.org/10.1016/j.concog.2013.07.007

⇑ Corresponding author.E-mail address: c.brewin@ucl.ac.uk (C.R. Brewin).

Chris R. Brewin ⇑, Niloufar MersaditabariUniversity College London, United Kingdom

a r t i c l e i n f o

Article history:Received 28 March 2013Available online 8 September 2013

Keywords:DissociationTraumaVisual memoryAttention

a b s t r a c t

Dissociation is a phenomenon common in a number of psychological disorders and hasbeen frequently suggested to impair memory for traumatic events. In this study weexplored the effects of dissociation on visual memory. A dissociative state was inducedexperimentally using a mirror-gazing task and its short-term effects on memory perfor-mance were investigated. Sixty healthy individuals took part in the experiment. Induceddissociation impaired visual memory performance relative to a control condition; however,the degree of dissociation was not associated with lower memory scores in the experimen-tal group. The results have theoretical and practical implications for individuals who expe-rience frequent dissociative states such as patients with posttraumatic stress disorder(PTSD).

� 2013 Elsevier Inc. All rights reserved.

1. Introduction

Dissociation is established empirically as a common feature of posttraumatic stress disorder (PTSD) (Brewin & Patel,2010; Carlson, Dalenberg, & McDade-Montez, 2012). Based on the evidence for dissociation-related symptom and responsevariations (e.g., Lanius et al., 2010), a dissociative subtype of PTSD has been introduced into the latest version of theAmerican Psychiatric Association’s Diagnostic and Statistical Manual (DSM-5: APA, 2013). Dissociation also commonlyoccurs during stressful or traumatic events, i.e. peri-traumatically, and these responses predict the development of PTSD(Lensvelt-Mulders et al., 2008). The increased risk is thought to derive from dissociation-induced disturbance in the encodingof the traumatic memory but little direct evidence exists for this conjecture. Previous research using experimentally-induceddissociation in healthy volunteers has found disturbances in digit span and delayed verbal recall but no evidence for deficitsin perceptual attention or spatial span (Brewin, Ma, & Colson, 2013). Given that PTSD is associated with larger deficits inverbal than non-verbal memory (Brewin, Kleiner, Vasterling, & Field, 2007), the present experiment sought to replicatethe finding of preserved perceptual attention and further investigate the presence of possible dissociation-induced deficitsin non-verbal memory.

Dissociation is a complex construct and a recent definition is as follows: ‘‘An experienced loss of information or controlover mental processes that, under normal circumstances, are available to conscious awareness, self-attribution, or control, inrelation to the individual’s age and cognitive development. Symptoms are characterized by (a) a loss of continuity in sub-jective experience with accompanying involuntary and unwanted intrusions into awareness and behavior (so-called positivedissociation); and/or (b) an inability to access information or control mental functions or behaviors, manifested as symptomssuch as gaps in awareness, memory, or self-identification, that are normally amenable to such access/control (so-called neg-ative dissociation); and/or (c) a sense of experiential disconnectedness that may include perceptual distortions about the selfor the environment’’ (Cardeña & Carlson, 2011, pp. 251–252). Peritraumatic dissociation (i.e. feelings that the experience isunreal coupled with the breakdown of identity, memory, and consciousness during or immediately following a traumatic

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event) has been linked to the disruption in information encoding and subsequent intrusive trauma-related memories (e.g.,Allen, Console, & Lewis, 1999; Bremner & Brett, 1997). Consistent with this view, numerous studies have reported incoher-ent, fragmented autobiographical memories of the traumatic event in PTSD patients and found that the degree of fragmen-tation was associated with reports of greater dissociation during the traumatic event (see Brewin, 2013, for review).

Other research on memory and dissociation has utilized groups high on dissociative tendencies. Guralnik, Schmeidler, andSimeon (2000) found that a sample of patients with depersonalization disorder performed significantly worse, comparedwith healthy controls, on a number of visual memory measures. Guralnik et al. (2000) argued that given their impaired func-tioning on a computerized test of attention, short-term memory deficits might be the result of lowered perceptual sensitivityand depleted attentional resources disrupting information encoding. In contrast, Wright and Osborne (2005) failed to findimpairments on short-term visual memory in healthy participants characterized by high trait dissociation.

Pre-existing memory-related deficits in clinical populations and predisposing factors in high dissociators (e.g. a distinctcognitive style; De Ruiter, Phaf, Elzinga, & Dyck, 2004) hinder the use of these samples to investigate the role of dissociationin memory anomalies. Furthermore, the correlation between the time of test administration and the experience of dissoci-ation episodes is weak, and thus the immediate effects of these episodes on memory are not captured in the tests. Individualswith strong dissociative tendencies may also have adopted compensatory mechanisms that make it difficult to detect mem-ory impairments related to dissociation. For all these reasons, experimental studies that induce dissociation directly andmeasure its immediate or delayed effects on cognitive functions offer significant advantages.

One common method of inducing dissociative experiences is to simulate stressful situations, analogous to real worldstressor events, to which individuals may exhibit dissociative responses and measure these responses under controlledconditions. For instance, in a study with special operations soldiers (Morgan, Doran, Steffian, Hazlett, & Southwick, 2006),participants underwent different levels of stress induction procedure. Participants who completed the Rey-OsterriethComplex Figure (ROCF) test of visual memory during the stress induction (i.e., the high stress group) reported moredissociative symptoms and performed significantly worse in both copy and recall parts of the ROCF test compared with thosewho finished the tests before or after the stress induction. Interestingly, in the copy phase there was evidence of the highstress group switching from a more configurational to a more piecemeal strategy, which the authors attributed to theirincreased arousal. Furthermore, dissociative symptoms were negatively correlated with ROCF recall in the stress group.Morgan et al. (2006) argued that symptoms of dissociation, as well as visual memory impairments, might be the conse-quences of the high state of arousal induced in their study. Therefore, in order to better explore the effects of dissociationper se, symptoms should be induced in the absence of intense stress and arousal.

Another recently developed method which induces dissociative symptoms involves gazing at one’s own face in a mirrorunder low illumination for at least 10 min (Caputo, 2010a,b). Recent evidence shows that similar effects may be obtained bygazing at another person’s face instead of one’s own (Caputo, 2013). Using the mirror-gazing version Brewin et al. (2013)provided the first experimental evidence of the effects of dissociative states on short-term memory for emotionally neutralstimuli. The results showed that higher dissociation scores were associated with less accurate time estimation, smaller digitspan, and worse delayed story recall, but not with deficits on perceptual attention or spatial span.

Given the inconsistent findings between, on the one hand, dissociative patient samples and samples under severe stressand, on the other hand, healthy volunteers exposed to induced dissociation, the current study sought to further investigatevisual memory performance in the face-gazing paradigm. We employed the ROCF test used by Morgan et al. (2006) to enablemore direct comparison between the studies. The ROCF test is particularly well-suited because participants must first copy acomplex figure, thereby separately assessing their level of perceptual attention. As Guralnik et al. (2000) pointed out, theeffects of such attentional deficits need to be ruled out when assessing the influence of complex mental states such as dis-sociation on memory. Based on previous findings, we hypothesized that induced dissociation would impair performance onthe ROCF test of visual memory while leaving perceptual attention intact.

2. Method

2.1. Participants

Sixty students from University College London took part in this experiment (12 males, 48 females). Their age range was18–29 and the mean age was 25.41 years (SD = 1.96). Participants had no history of psychiatric treatment and were unfamil-iar with the mirror-gazing technique (Caputo, 2010a). Fifty-eight percent of them were familiar with the Rey-Osterriethfigure. Participants had normal vision or were shortsighted, in which case they had to remove their glasses to avoidinterference with their face perception in the mirror.

2.2. Design

A between-group design was used with control and dissociation conditions, the dependent variables being the ROCF copyand recall scores. First, equal numbers of participants were recruited to the two conditions to enable fully randomized com-parisons testing the effects of the manipulation. Afterwards, additional non-randomized participants were recruited to theexperimental group in order to increase the power for exploring the association between dissociation and memoryperformance.

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2.3. Materials

The setting was a quiet cubicle. A desk lamp with a 25 W incandescent bulb with a spotlight pointing to a wall was placedabout 1 m away from the participants’ chair to illuminate the room in the experimental condition. A 0.5 m � 0.5 m mirrorstanding on a supporting foot (height = 15 cm) was placed on a table for the mirror-gazing task.

2.3.1. Measures2.3.1.1. State dissociation. The 19 subjective items from Clinician Administered Dissociative States Scale (CADSS) (Bremneret al., 1998) were employed to assess dissociation following the mirror-gazing task. Each item is rated on a 5-point scaleanchored with 0 (‘not at all’) and 4 (‘extremely’); total scores for subject-rated items range from 0 to 76. Depersonalization(e.g., ‘Do you feel disconnected from your own body?’) and derealization (e.g., ‘Do things seem to be unreal to you, as if youare in a dream?’) are among the areas assessed through this self-report measure. The CADSS has shown to be a reliable andvalid measure of present-state dissociative symptoms (Bremner et al., 1998).

2.3.1.2. Rey-Osterrieth Complex Figure (ROCF) test. This neuropsychological test of visual memory (Osterrieth, 1944;Rey, 1941) consists of a figure that contains 18 scorable elements. The test includes three phases: copy, immediate recall,and delayed recall, but the immediate recall phase was not employed. Performance on the copy and delayed recall phaseswas scored using a standardized approach developed by Meyers and Meyers (1995). Unlike Morgan et al. (2006) we didnot use pens of different colors during the copy phase.

2.4. Procedure

The first 40 participants were randomly allocated to the control (n = 20) or the dissociation group (n = 20), and an addi-tional 20 participants then recruited to the dissociation group. In the dissociation condition, the room lighting was reducedfrom the ceiling fluorescent lamp to a desk lamp with a 25 W incandescent bulb facing the wall behind the participants. Thelamp was not visible to the participants throughout the experiment. This allowed for a uniform illumination of faces andaccurate perception of face details.

Participants in the dissociation condition sat in front of the mirror placed about 0.4 m in front of them; they had to leantowards the mirror up to 30�, depending on their height, in order to be able to perceive their whole face in the mirror.After turning the lights down, the experimenter informed the participants that she would monitor them through the smallopening on the room’s door, not directly visible to them, and then left the room in order to minimize the distractions.Participants were instructed to gaze continuously at their face, in particular the eyes, under the low illumination, for10 min after which the experimenter entered the room and turned on the light. In the control condition, participantssat in a similar room, but under normal illumination. In order to rule out any effects of mind-wandering they proceededimmediately to the ROCF task.

After the briefing in the control condition and the gazing task in the dissociation condition, the experimenter showed theROCF to the participants and enquired whether they had seen the figure before. Participants were then given a blank A4 re-sponse sheet in a horizontal orientation and a black ink pen and were asked to copy the ROCF as accurately as possible andwith no time limit. They were further informed that their drawing skills would not be scored. The time required to completethe copy phase did not exceed five minutes in any of the sessions. Following the ROCF-copy task, participants completed theCADSS items. Afterwards, participants were given a blank A4 paper and asked to redraw the ROCF from memory with theblack ink pen without any time limit. At the end of the experiment, participants were fully debriefed and the experimenterconfirmed that participants were no longer in a dissociative state.

3. Results

Randomized and non-randomized members of the experimental group did not differ in their scores on the CADSS,F(1,38) = .00, p > 0.10, or ROCF recall, F(1,38) = 1.08, p > 0.10, and so were combined in the subsequent analyses. Therewas no significant difference in age between the control and the experimental groups, t(58) = .60, p > .10, and both groupscontained the same proportion of females (75%). Gender did not significantly affect scores on either the CADSS, F(1,58) = .06,p > 0.10, or ROCF recall, F(1,58) = .02, p > 0.10. The proportion of participants who were familiar with the Rey-Osterrieth fig-ure did not differ significantly between the conditions, X2 (1, N = 60) = 3.42, p > 0.05.

3.1. Manipulation check

The mean CADSS scores are shown in Table 1. Due to the marked skewness, a square root transformation was carried outto normalize the sample distribution. A one-way ANOVA on the transformed CADSS scores indicated that participants in thedissociation group had significantly higher scores than in the control group, F(1,58) = 90.71, p < 0.001. CADSS items mostcommonly endorsed in the experimental group are shown in Table 2.

Table 1Mean dissociation and visual memory test scores (standard deviations in parentheses).

Variable Dissociation group (n = 40) Control group (n = 20)

CADSS 16.37 (7.63) 2.7 (3.04)ROCF copy 35.32 (1.09) 35.75 (.71)ROCF recall 23.66 (4.48) 28.92 (3.02)

Note: ROCF = Rey-Osterrieth Complex Figure.

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3.2. ROCF test

A one-way ANOVA indicated that familiarity with the Rey-Osterrieth figure did not significantly affect ROCF recall scores,F(1,58) = .16, p > 0.10. There was no significant difference in ROCF copy scores between the control and dissociation condi-tions, F(1,58) = 2.47, p > .10. Despite this the group difference in ROCF recall was highly significant, F(1,58) = 22.31, p < 0.001,and as shown in Table 1 recall was greater in the control than in the dissociation group. However, transformed CADSS scoreswere not significantly correlated with ROCF recall after controlling for gender and experimental group, r(38) = 0.01, p > 0.10.Partial correlations of transformed individual CADSS items with ROCF recall, controlling for gender and experimental group,are shown in Table 2 – endorsement of items 15 (spacing out) and 14 (happening that cannot be accounted for) was posi-tively correlated with recall whereas endorsement of item 4 (out-of-body experiences) was negatively correlated with recall.

4. Discussion

In accordance with the findings by Morgan et al. (2006), participants in the dissociation group had worse ROCF visualmemory recall compared with the controls. The pattern of results is also in line with previous findings by Guralnik et al.(2000) with respect to impaired visual memory performance in subjects with depersonalization disorder. Our data add tothese studies in two ways. First, they show for the first time that dissociation can adversely affect visual memory even inhealthy samples who are not being exposed to high levels of stress. Second, and consistent with by the findings of Brewinet al. (2013), they suggest it is unlikely that this result is due to a deficit in perceptual attention, but rather implicate a prob-lem with memory encoding and storage.

However, higher levels of dissociation symptoms were not significantly correlated with lower ROCF recall scores in theexperimental group. Similarly, there was no significant correlation between short-term visual memory and dissociative ten-dencies in the study by Wright and Osborne (2005). In previous studies using mirror-gazing a wide range of dissociativereactions, both within and between individuals, were reported (Caputo, 2010a; Brewin et al., 2013). Individual differencesin reporting style and in sensitivity to the perceptual and physical symptoms induced by the task may have introduced error

Table 2Mean endorsement of CADSS items in the experimental group and partial correlations of transformed CADSS items with ROCF recall in the entire samplecontrolling for experimental condition and gender.

Items Mean SD Partialr

16. Do sounds almost disappear or become much stronger than you would have expected? 1.50 1.10 �.0015. Do you space out, or in some other way lose track of what is going on? 1.45 1.03 .32*

6. Do you feel disconnected from your own body? 1.30 1.01 �.222. Do things seem to be unreal to you, as if you are in a dream? 1.25 .92 �.0912. Does this experience seem to take much longer than you would have expected? 1.22 1.02 .2018. Does it seem as if you are looking at the world through a fog, so that people or objects seem far away or unclear? 1.20 1.26 .2210. Do colors seem to be diminished in intensity? 1.15 1.00 .001. Do things seem to be moving in slow motion? 1.12 0.79 .017. Does your sense of your own body feel changed: for instance, does your own body feel unusually large or unusually small? 1.07 1.18 �.033. Do you have some experience that separates you from what is happening; for instance, do you feel as if you are in a movie

or a play, or as if you are a robot?.72 .96 �.22

17. Do things seem to be very real, as if there is a special sense of clarity? .70 .85 .234. Do you feel as if you are looking at things from outside of your body? .67 .97 �.33*

5. Do you feel as if you are watching the situation as an observer or spectator? .65 .73 �.108. Would people seem motionless, dead, or mechanical? .55 .81 �.129. Do objects look different than you would expect? .55 .63 �.0511. Do you see things as if you were in a tunnel, or looking through a wide angle photographic lens? .52 .71 �.2119. Do colors seem much brighter than you would have expected? .40 .67 .1014. Do things happen that you later cannot account for? .30 .51 .27*

13. Do things seem to be happening very quickly, as if there is a lifetime in a moment? .25 .49 .03

Note: CADSS = Clinician Administered Dissociative States Scale; ROCF = Rey-Osterreith Complex Figure.* p < .05.

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variance that reduced the size of the correlations. The delay in administering the CADSS (approximately five minutes afterthe end of the mirror gazing task) may have introduced additional error variance.

The dual representation theory of PTSD (Brewin, Gregory, Lipton, & Burgess, 2010) suggests that peritraumatic dissocia-tion conveys a vulnerability to posttraumatic stress reactions because it leads to greater impairment in contextualized thanimage-based memory representations of events. According to the theory there is an image-based memory system, which re-cords sensation-near perceptual and spatial data from the person’s own viewpoint and supports action on the environment;there is also a contextualized memory system that recodes perceptual data into a more abstract format and which supportsconfigural knowledge, the generation of alternative viewpoints, and verbal descriptions. Consistent with this, Brewin et al.(2013) found dissociation to produce reductions in verbal memory (digit span, story recall) but not in perceptual attention orspatial span. The current results replicated the preservation of perceptual attention. The deficits we found in visual memory,according to the theory, are likely to arise from a loss of the ability to perceive or record a more abstract configurationalstructure. This could be tested by repeating the experiment using the differently colored pens employed by Morgan et al.(2006). To the extent that dual representations exist in other sensory modalities (Brewin et al., 2010), similar deficits areto be expected there also, for example in auditory memory.

One limitation of this study is that the degree of induced dissociation symptoms was relatively mild compared with thoseexperienced in clinical populations. Thus, it is not clear how well these results are generalizable to diagnosed samples ofindividuals with PTSD or depersonalization disorder. Furthermore, dissociative experiences after the mirror-gazing taskare not homogeneous in type and intensity across the participants. For instance, in the study by Brewin and colleagues(2013), only about half of the participants reported experiencing a loss of identity during the gazing. Thus, the mirror-gazingmethod can be criticized with respect to ecological validity (i.e., the ability to effectively induce states that are analogous toperitraumatic and naturally-occurring dissociation). It is also not entirely clear whether the mirror-gazing itself is essentialor whether the effects are due to reduced sensory stimulation from the low light conditions (c.f., Marcusson-Clavertz,Terhune, & Cardeña, 2012). Future studies might therefore profitably include a third, low-light condition in whichmirror-gazing was omitted.

The findings of this study have a number of practical and theoretical implications for interpreting the visual memory per-formance of individuals currently suffering from high levels of dissociation. For instance, refugees applying for asylum maybe required to give detailed accounts of places or traumatic events that include visual descriptions, with any lack of consis-tency being interpreted as evidence for unreliability or mendacity and impacting on official decisions (Herlihy, Jobson, &Turner, 2012). During asylum interviews both dissociative responses and difficulties in answering questions are reported(e.g., Bögner, Herlihy, & Brewin, 2007). In addition, the poorer visual memory of those who tend to dissociate in stressfulsituations may result in poorer military performance in numerous situations requiring recall of visual and spatial layouts,including pre-operation planning, battlefield tactics, and subsequent reconstruction of battle situations (e.g., Morganet al., 2006).

In summary, a recently developed method, mirror-gazing, was used in this study to explore the effects of experimentallyinduced dissociative states on visual memory. Although there was no linear relationship between degree of dissociativesymptoms and memory impairments, dissociation negatively affected memory performance in the experimental conditioncompared with the control participants who did not experience those symptoms. These findings add to existing evidencethat dissociation is associated with less accurate time estimation, smaller digit span, and worse delayed story recall (Brewinet al., 2013), extending the deficit to short-term visual recall. The results have implications for understanding and assistingboth individuals who have temporarily dissociated, for example in response to stress, and for those who experience frequentdissociative episodes.

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