Enhanced accessibility of ignored neutral and negative items in nonclinical dissociative individuals

Consciousness and Cognition 57 (2018) 74–83

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Enhanced accessibility of ignored neutral and negative items in nonclinical dissociative individuals Chui-De Chiu

T



Clinical and Health Psychology Centre and Centre for Cognition and Brain Studies, Department of Psychology, The Chinese University of Hong Kong, Hong Kong Special Administrative Region

AR TI CLE I NF O

AB S T R A CT

Keywords: Dissociation Executive functions Intrusive memory Updating

While clinical studies showed paradoxical memory phenomena, including the intrusion and amnesia of stressful experiences that are features of dissociation, the results of laboratory studies on dissociative individuals’ forgetting of experimental stimuli through cognitive control varied. Some studies demonstrated ineffective inhibition, and others found that dissociative individuals could remember fewer trauma words in a divided-attention context. Dissociative individuals may utilize superior cognitive disengagement to forget the representations. This hypothesis was tested in nonclinical individuals with high, medium, and low dissociation proneness. In the study phase, the participants learned several lists of experimental words and kept updating working memory by remembering the last four items on a list (target) and ignoring those non-target items. A recognition test was then conducted. The high dissociation group performed better on updating working memory. However, the accessibility of the representations of neutral and negative nontarget items was elevated. Dissociative individuals disengaged attention effectively from items they intended to ignore, and the representations of the ignored items were more accessible when cues were available.

1. Introduction 1.1. Dissociation and dissociation proneness Dissociation, a disruption of ordinarily integrated functions in mental processing (DSM-5; American Psychiatric Association, 2013), is a feature of several stress-related psychiatric dysfunctions (Lyssenko et al., 2017; Putnam et al., 1996), including dissociative disorders (Carlson et al., 1993), post-traumatic stress disorder (PTSD, Stein et al., 2013; Wolf et al., 2012), borderline personality disorder (Vermetten & Spiegel, 2014; Zanarini, Ruser, Frankenburg, & Hennen, 2000), and recovered trauma memory (Geraerts, Merckelbach, Jelicic, Smeets, & Van Heerden, 2006; McNally, Clancy, Schacter, & Pitman, 2000). Two types of dissociation have been noted (Waller, Putnam, & Carlson, 1996). Pathological dissociation, such as depersonalization, gaps in awareness and intrusion, and amnesia, results in distress and disturbs socio-occupational function. Normative dissociation, such as absorption and mild gaps in awareness (Butler, 2006), prevails in the general population as well as in the clinical population and does not necessarily lead to distress or disability (Carlson, 1994; Ross, Joshi, & Currie, 1990). There exists a trait-like individual difference in normative dissociation, i.e., dissociation proneness. Dissociation proneness relates to biological heredity (Becker-Blease et al., 2004; Jang, Paris, Zweig-Frank, & Livesley, 1998; also see Waller & Ross, 1997) and the



Address: Department of Psychology, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong Special Administrative Region. E-mail address: [email protected]

https://doi.org/10.1016/j.concog.2017.11.009 Received 16 May 2016; Received in revised form 6 November 2017; Accepted 19 November 2017 1053-8100/ © 2017 Elsevier Inc. All rights reserved.

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quality of early relationships with caregivers (Dutra, Bureau, Holmes, Lyubchik, & Lyons-Ruth, 2009; Ogawa, Sroufe, Weinfield, Carlson, & Egeland, 1997). It moderates the presence of dissociative symptoms in the face of stress (Hallings-Pott, Waller, Watson, & Scragg, 2005; Leonard, Telch, & Harrington, 1999; Stiglmayr et al., 2008; Zoellner, Sacks, & Foa, 2007; also see Giesbrecht, Smeets, & Merckelbach, 2008). Dissociation proneness may interact with cumulative traumatization from childhood to adulthood, and then pathological dissociation emerges (Chiu et al., 2015, 2017). 1.2. Cognitive control and memory in dissociative individuals The cognitive mechanisms that underlie dissociation have gradually been unfolded. A series of laboratory studies of clinical and nonclinical dissociative individuals focused on cognitive control, which is responsible for the manipulation of mental representations (Miyake et al., 2000; for a review, Miyake & Friedman, 2012). The results were twofold. First, superior performance in nonclinical individuals with dissociation proneness was found in tasks pertaining to cognitive disengagement, such as dividing attention between dual tasks (De Ruiter, Phaf, Veltman, Kok, & Van Dyck, 2003; DePrince & Freyd, 1999; DePrince, Weinzierl, & Combs, 2008), updating working memory (Veltman et al., 2005), and switching attention from an attribute that had just been attended to (Chiu, Yeh, Huang, Wu, & Chiu, 2009). Second, inferior performance in nonclinical dissociative individuals was observed in tasks tapping into cognitive inhibition, including ignoring concurrent task-irrelevant representations (Freyd, Martorello, Alvarado, Hayes, & Christman, 1998), voluntarily suppressing distractors (Elzinga, De Beurs, Sergeant, Van Dyck, & Phaf, 2000), and involuntarily suppressing competing items (Chiu, Lin, Yeh, & Hwu, 2012; Chiu et al., 2010). Superior disengagement (Chiu et al., 2016a; Elzinga et al., 2007) and inferior inhibition (Dorahy, Irwin, & Middleton, 2004; Dorahy, Middleton, & Irwin, 2005; Elzinga, Phaf, Ardon, & Van Dyck, 2003) were also noticed in clinical patients with pathological dissociation. Atypical cognitive control may affect the regulation of memory representations and may contribute to the paradoxical memory symptoms of dissociation, namely, intrusion and amnesia (Van der Hart, Nijenhuis, Steele, & Brown, 2004; Van der Kolk & Fisler, 1995). Studies investigating the memory function of dissociative individuals have focused mostly on memory suppression, with paradigms primarily involving inhibition (Anderson, 2005). In general, the results did not find that patients with PTSD (McNally, Metzger, Lasko, Clancy, & Pitman, 1998) or individuals with recovered memory of child sexual abuse (Geraerts, Smeets, Jelicica, Merckelbach, & Van Heerden, 2006; McNally, Clancy, Barrett, & Parker, 2004; McNally, Clancy, & Schacter, 2001) are superior at forgetting materials. Instead, some studies showed that the ability of dissociative individuals to forget via inhibition may, in fact, be weakened (Chiu et al., 2010; Chiu, Lin, et al., 2012; Elzinga et al., 2000, 2003). Few studies have investigated how disengagement may impact the representations that dissociative individuals avoid. Two studies that are an exception examined nonclinical dissociative individuals’ forgetting in a task context requiring attention division (DePrince & Freyd, 2001, 2004). The participants were instructed either to forget or to remember words under a single- (a memory exercise) or a dual-task context (performing the memory exercise as well as detecting changes in the color of experimental stimuli). In comparison with non-dissociative individuals, dissociative individuals retained more neutral words but remembered fewer trauma words. However, some studies failed to reproduce this result (Devilly et al., 2007; Giesbrecht & Merckelbach, 2009; McNally, Ristuccia, & Perlman, 2005). The inconsistency may result from the experimental design, as either inhibition (suppressing an item) or disengagement (diverting attention away from an item) may be engaged in the dual-task context. It remains unclear whether unusual forgetting can be achieved via cognitive disengagement in dissociative individuals. 1.3. The current study This study aimed to examine the accessibility of mental representations that have been removed from the focus of attention in working memory via cognitive disengagement in individuals with dissociation proneness. Several studies from our laboratory (Chiu et al., 2009, 2010; Chiu, Lin, et al., 2012) have shown atypical cognitive control in nonclinical individuals with a cut-off score that informs a level of dissociation proneness with clinical significance (Carlson et al., 1993). Hence, the core comparison was between individuals with high dissociation proneness and those with a medium or low level of dissociation proneness (see the methods for details). A behavioral task that taps into updating verbal working memory, an operation separable from cognitive inhibition (Miyake & Friedman, 2012; Miyake et al., 2000), was applied to manipulate the experimental materials (Broadway & Engle, 2010; Collette et al., 2007; Conway et al., 2005). Words from a list were presented one by one. The participants, without knowledge of the number of words in the list (i.e., list length), were instructed to report the last four items at the end of the list presentation (Morris & Jones, 1990). Thus, the participants kept registering a new item and ignoring a previously held item. A recognition test was given to test the accessibility of the representations of the target (the last four items of each list) and non-target items (those that had been ignored). The valence of words was manipulated. Varying results were noted about the valence effect on dissociative individuals’ memory. While some studies showed that dissociative individuals forgot fewer trauma words (DePrince & Freyd, 2001, 2004), other studies did not find a reliable valence effect on dissociative individuals’ memory suppression (Chiu, Lin, et al., 2012; Devilly et al., 2007; Elzinga et al., 2000, 2003; Giesbrecht & Merckelbach, 2009; McNally et al., 2005). Dissociative individuals may, in fact, retain more negative materials (De Ruiter, Veltman, Phaf, & Van Dyck, 2007). Notably, the studies that found the valence effect compared memory for negative and neutral items (De Ruiter et al., 2007; DePrince & Freyd, 2001, 2004), and hence, arousal might confound these results. To tackle this issue, two experimental conditions were created, with non-emotional (neutral words) and emotional materials (negative and positive words). The valence effect can be examined by contrasting the memory of negative items with that of positive items. Finally, common covariates of dissociation proneness, including state anxiety and early relational trauma, were controlled for statistically to exclude their potential confounding effects. 75

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A significant difference was predicted between the individuals with high dissociation proneness and those with either medium or low dissociation proneness, with superior updating expected in the individuals with high dissociation proneness (Chiu et al., 2016a; Elzinga et al., 2007; Veltman et al., 2005). This effect may appear even for the test materials that are affect-laden (Chiu et al., 2009; Oathes & Ray, 2008). The a priori hypothesis for memory recognition was that ignored, non-target representations may be less accessible because their encoding may be interrupted, as demonstrated by DePrince & Freyd, 2001, 2004. Alternatively, inhibition may not be recruited to suppress non-target representations because the competition between these distractors and the representations of target items has been resolved by the dissociative individuals’ superior cognitive disengagement (Chiu et al., 2009). The accessibility of non-target representations would increase, instead, as shown by Chiu et al. (2010), Chiu, Lin, et al. (2012) and Elzinga et al. (2000, 2003). 2. Material and methods 2.1. Participants Participant recruitment was performed through two waves of group surveys (N = 237), where the Mandarin version of the Dissociative Experiences Scale (DES, Bernstein & Putnam, 1986; Carlson & Putnam, 1993), a popular measure of dissociation proneness (Van IJzendoorn & Schuengel, 1996), was administered together with other scales for projects pertinent to industrial and organizational psychology, personality and social psychology, and clinical psychology. Case identification was based on the average score of the DES items. Scores below 10, between 10 and 30, or above 30 were the cut-offs for the low-, medium-, and high-DES groups, respectively (Carlson et al., 1993; Chiu et al., 2009). Candidate participants were randomly selected and invited to take part in the memory experiment. Thirty-one, thirty, and twenty-eight participants with high-, medium-, and low-DES scores joined the experiment, respectively. In this selected sample, 43 percent were male, and the average age was 21 years. There were no significant differences among the three groups in terms of gender [χ2 (2, N = 89) = 0.93, p > .6] or age [F(2, 85) = 0.02, p > .9]. The participants received a bonus credit for a psychology course. One-way ANOVAs were conducted to examine the between-group differences in the DES scores. As expected, the three groups differed in both the total and the three subscale scores of the DES [for the total score and the subscale scores of absorption, depersonalization, and amnesia, F(2, 86)s = 260.5, 220.44, 84.15, and 31.55; ps < .001, ηp2s = 0.86, 0.84, 0.66, and 0.42]. With the Ryan-Einot-Gabriel-Welsch (REGW) multiple range test (Kirk, 1995) at a significance level of 0.05, post hoc comparison showed that all four scores of the three groups were mutually different, with the highest scores in the high-DES group and the lowest in the lowDES group. To characterize our participants and to facilitate comparisons across different studies, additional self-report scales were administered to assess state anxiety (Beck Anxiety Inventory, BAI, Beck & Steer, 1990) and early interpersonal adversity (the short form of the Childhood Trauma Questionnaire, CTQ-SF, Bernstein & Fink, 1998; Bernstein et al., 2003). Table 1 summarizes the results of the self-report measures. The three groups varied in state anxiety [F(2, 86) = 6.79, p < .01, ηp2 = 0.14]. Post hoc comparisons showed that the high- and medium-DES groups exhibited higher state anxiety than the low-DES group. The three groups reported different degrees of early interpersonal adversity, particularly in regard to physical neglect and emotional abuse [for the total CTQ-SF score, the physical neglect subscale, and the emotional abuse subscale, F(2, 86)s = 4.58, 4.33, and 3.85, ps = .01, .02, and 0.03, ηp2s = 0.10, 0.09, and 0.08]. Post hoc comparisons showed that the high-DES group had higher scores on the total and two subscale scores than the low-DES group. The scores of the medium group were not different from those of the other two groups, except for a Table 1 The means and standard deviations of dissociation proneness, state anxiety, and childhood interpersonal adversity in the three dissociation groups. Dissociation proneness Measures

Dimensions

High (n = 31) M

Medium (n = 30) SD

M a

Low (n = 28) SD

M

SD

b

DES-II

Total score Absorption Depersonalization Amnesia

37.89 47.94 33.39 15.59

7.29 8.94a 12.68a 11.09a

20.42 28.84 12.72 5.67

5.04 7.53b 8.66b 4.48b

5.93 8.75 3.03 1.31

2.52c 3.69c 3.48c 1.78c

BAI

Total score

8.17

4.96a

7.07

6.47a

3.00

2.69b

CTQ-SF

Total score Emotional abuse Physical abuse Sexual abuse Emotional neglect Physical neglect

41.64 9.63 6.51 5.87 11.72 7.90

9.70a 3.41a 2.10 1.84 4.12 2.47a

38.14 8.43 6.09 5.43 10.78 7.40

8.36ab 3.15ab 1.63 1.30 3.35 2.46a

34.79 7.46 5.73 5.21 10.20 6.18

7.77b 2.31b 1.40 0.50 3.73 1.89b

Notes: For the abbreviations of the self-report instruments, DES-II = Dissociative Experiences Scale-II, BAI = Back Anxiety Inventory, CTQ-SF = Childhood Trauma Questionnaire, Short Form; for post hoc comparisons with the REGW test, significant between-group differences are indicated by different letters (a, b, or c) for each two groups.

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higher score on the physical neglect subscale in the medium-DES group than that of the low-DES group. No between-group differences were found on the sexual abuse, physical abuse, and emotional neglect items (ps > .16). 2.2. Materials and designs 2.2.1. Experimental word The neutral and emotional words used in this study were selected from a Mandarin Chinese emotional word norm (Cho, Chen, & Cheng, 2013). All selected words were two-character traditional Chinese words. Word frequency among the neutral, negative, and positive words (p > .4) and the arousal between the positive and negative words (p > .2) were comparable.1 2.2.2. Running span task The whole task consisted of two within-subjects conditions (non-emotional versus emotional). Each of the conditions was composed of six lists, with 5, 6, 8, 9, 11, and 12 words, respectively. In the non-emotional condition, all the lists were composed of neutral words. In the emotional condition, all the lists were composed of positive and negative words. The number of positive and negative words was comparable on each list (equal when the number of words was even; one more when it was odd). To avoid a cueing effect, the proportion of negative and positive words in the last four words varied, with two lists having 3 negative and 1 positive words, two having 2 negative and 2 positive words, and two having 1 negative and 3 positive words. The neutral and emotional lists were presented in two blocks. To avoid a potential contamination effect of emotion, the nonemotional block was done before the emotional block. The six lists in each condition were randomly presented. The words on a list were presented one by one randomly. A word remained on the screen for 3000 ms, and a blank screen followed for 500 ms before the next word appeared. There was an auditory sound to signal the arrival of a new word. 2.2.3. Recognition task Two recognition tests were prepared, one for the non-emotional condition and the other for the emotional condition. Each recognition test consisted of 24 words, with 12 studied words and 12 new words. One target and one non-target word in each list were randomly selected. For the test of emotional words, half of the test items were positive, and the others were negative. The 24 words were randomly presented. The participants were instructed to indicate whether the items appeared in the study phase. There were no time limits on their responses. 2.3. Procedure The participants visited our laboratory individually for the experiment. The study was explained, and each participant signed the informed consent form. The participants were told that this was a working memory experiment targeting the efficiency of updating and that several lists of words would be presented on a computer screen. The goal of the task was to keep remembering the last four target items, and at the end of each list, they would be asked to report these target items. Hence, they should continuously register a new item and remember it together with the other three target items while removing non-target items away from the focus of attention. The participants were informed explicitly that the list length varied. Hence, they should remember each item at the beginning of a list, and then keep the last four items and ignore the non-target items. Participants had some practice on a filler list to ensure that they understood the updating instruction. The non-emotional condition of the running span task and the memory recognition task commenced, and the emotional condition followed. Finally, the self-report instruments were administered, and the participants were debriefed about the study. 3. Results Table 2 summarizes the descriptive statistics for the accuracy rates of remembering the last four items on each list (updating working memory) and those of recognizing the target and non-target items in the follow-up test (memory recognition). To specifically examine the difference between the high-DES group and the medium- and low-DES groups (Chiu et al., 2009, 2010), contrast analysis was utilized. This analysis with focused contrast can provide a statistically more powerful approach to hypothesis testing than omnibus ANOVA (Rosenthal & Rosnow, 1985). Weights of 2, −1, and −1 were respectively assigned to the high-, medium-, and lowDES groups to test the difference between the high-DES group and the other two (medium- and low-DES) groups (i.e., the H-ML contrast). Updating working memory was analyzed by a mixed two-way ANOVA (dissociation proneness: the H-ML contrasts; Emotionality: the non-emotional and emotional conditions).2 The two-way interaction was not significant (p > .6), and there was a significant effect of emotionality [F(1, 86) = 23.61, p < .01, ηp2 = 0.22]. The participants remembered more target items at the end of each list in the emotional condition (M = 0.84, SD = 0.11) than in the neutral condition (M = 0.78, SD = 0.11).3 More importantly, the main 1 The means and standard deviations of word frequency (16.2 ± 8.5, 18.4 ± 9.7, and 17.8 ± 8.2), degree of positivity (1.1 ± 1.2, 3.5 ± 1.8, and −2.8 ± 1.5), and level of arousal (0.9 ± 0.5, 3.0 ± 1.1, and 2.8 ± 1.2) for neutral, positive, and negative emotions, respectively. 2 A preliminary analysis showed that list length did not interact with dissociation proneness on the key variables of interest, including updating and memory recognition (ps > .1). Therefore, the data were pooled in the analysis. 3 The most common errors were omission (57%) and within-list intrusion (34%).

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Table 2 The accuracy rates of updating working memory (proportion) and the accuracy rates of memory recognition (proportion) for the representations of target and nontarget items in the three dissociation groups. Dissociation proneness High (n = 31)

Medium (n = 30)

Low (n = 28)

M

SD

M

SD

M

SD

Updating working memory Neutral lists Emotional lists

0.81 0.86

0.09 0.10

0.76 0.82

0.11 0.11

0.77 0.82

0.12 0.10

Memory recognition Neutral items New Target Non-target

0.94 0.66 0.76

0.07 0.23 0.21

0.92 0.77 0.73

0.07 0.16 0.18

0.96 0.72 0.72

0.06 0.16 0.18

Positive items New Target Non-target

0.80 0.82 0.92

0.16 0.21 0.14

0.74 0.83 0.83

0.17 0.21 0.23

0.84 0.83 0.76

0.19 0.23 0.24

Negative items New Target Non-target

0.90 0.83 0.80

0.13 0.21 0.22

0.86 0.84 0.89

0.15 0.23 0.20

0.89 0.83 0.87

0.14 0.21 0.21

effect of the H-ML contrast reached significance [F(1, 86) = 4.33, p = .04, rcontrast = 0.22], with rcontrast = F/( F+ dfwithin) (Rosnow, Rosentha, & Rubin, 2000). Individuals with high dissociation proneness performed better than those with medium or low dissociation proneness on updating working memory, regardless of the valence of the materials. Then, the memory recognition for the target and non-target representations was analyzed. Following the signal detection theory (Snodgrass & Corwin, 1988), indices for memory discrimination (i.e., d′) and response bias (i.e., β) were calculated (Stanislaw & Todorov, 1999). Three-way mixed ANOVAs were performed to test the effects of updating status (target versus non-target), valence (neutral, positive, and negative), and dissociation proneness (the H-ML contrast). For response bias, there was no effect that involved the H-ML contrast reaching significance. The three-way interaction was not significant [F(2, 172) = 2.29, p = .11] nor was the twoway interactions with updating status [F(2, 86) = 2.36, p = .13] or with valence [F(2, 172) = 0.65 p = .49]. There was also no main effect of the H-ML contrast [F(2, 86) = 0.22, p = .64]. Individuals with high dissociation proneness were not different from those with medium and low dissociation proneness on response bias. For memory discrimination, the three-way interaction reached significance [F(2, 172) = 3.72, p = .02, rcontrast = 0.15]. Three mixed two-way ANOVAs were subsequently performed to test the effects of dissociation proneness and updating one’s status on items with varying valences. A significant two-way interaction was found on neutral items [F(1, 86)s = 4.78, ps < .03, rcontrast = 0.23]. As demonstrated in Fig. 1a, the high-DES group showed a distinct pattern with a higher rate of neutral non-target items than that of neutral target items [t = 2.41, df = 30, p = .02] in comparison with a comparable rate in the medium- and low-DES groups [t = 0.54, df = 57, p = .59]. This pattern was also found for negative items [F(1, 86) = 4.57, ps < .03, rcontrast = 0.22] (see Fig. 1b), with a higher rate of negative non-target items than that of negative target items in the high-DES group [t = 2.22, df = 30, p = .03] but a comparable rate in the medium- and low-DES groups [t = −0.85, df = 57, p = .40]. This pattern was not observed for positive items, and neither the two-way interaction nor the main effect of the H-ML contrast was significant (ps > .2, see Fig. 1c). The elevated scores on the early interpersonal adversity and the state anxiety items in the high-DES group gave rise to a concern about whether the characteristic updating and memory discrimination in the high-DES group could be confounded with by these variables. Covariate analysis was conducted by re-examining the effect of the H-ML contrast on updating and memory discrimination when the effects of early interpersonal adversity and anxiety were removed. The residuals of the accurate rates of updating and the d′ rates of memory discrimination were calculated with regression models (see Chiu et al., 2009 for details). The residuals were then standardized and analyzed. The main effect of dissociation proneness on updating remained significant [F(1, 85) = 4.38, p = .04, rcontrast = 0.22]. For memory discrimination, there was still a trend of the three-way interaction between dissociation proneness, updating status, and valence [F(2, 170) = 2.70, p = .07, rcontrast = 0.12]. The characteristic updating and memory discrimination in the high-DES group could not be sufficiently explained by early interpersonal adversity or state anxiety. 4. Discussion The current study aimed to examine the accessibility of representations that have been removed from the focus of attention by cognitive disengagement in individuals with high dissociation proneness. Through the running span paradigm, the status of representations in working memory was manipulated, and recognition tests were conducted to examine their accessibility. The result showed that the high-DES group remembered more target items for both the neutral and affect-laden materials in the running span 78

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Fig. 1. A distinct pattern of memory discrimination (d′) in dissociative individuals in comparison with non-dissociative individuals. While comparable d′ rates between the target and the non-target items were found in the medium- and low-DES groups, the d′ rates of the non-target items were higher than those of the target items for (A) neutral and (B) negative items in the high-DES group.

tests. More importantly, in the recognition tests, the high-DES group differed from the medium- and low-DES groups. In comparison with the accessibility of the target representations, a higher accessibility of the non-target representations of neutral and negative words was observed in the high-DES group. The characteristic updating and memory recognition could not be accounted for by early interpersonal adversity and state anxiety. This superior updating is consistent with other studies of nonclinical (Veltman et al., 2005) and clinical dissociative individuals (Chiu et al., 2016a; Elzinga et al., 2007). The paradigms used to assess the updating function varied in the four studies (the n-back task, the random number generation test, and the running span test). As a core component of executive control (Miyake & Friedman, 2012), updating is considered to be a domain-free operation (Miyake et al., 2000). The consistency across the various paradigms increases the validity of the findings. One novel finding from the current experiment is that the dissociative individuals’ superior updating still appeared for affect-laden materials, as previous studies merely adopted non-emotional materials such as English letters and Arabic numbers. Affect-laden information does not hamper dissociative individuals’ superior updating. Some people may find superior cognitive disengagement surprising (Giesbrecht, Lynn, Lilienfeld, & Merckelbach, 2008), especially when it is found in the clinical populations (Chiu et al., 2016a; Elzinga et al., 2007). In fact, superior cognitive propensity that manifests in a standardized cognitive test can be either adaptive or maladaptive in daily situations, depending upon the goal it served (Horowitz, 1987). Brain imaging studies in victimized individuals with a dissociative type of post-traumatic stress disorder showed an 79

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over-modulation of mental regulation that involves top-down controls (Lanius et al., 2010). Superior cognitive disengagement may be utilized to divert attention away from the hotspot of a stressful experience (Grey & Holmes, 2008; Holmes, Grey, & Young, 2005), helping dissociative individuals survive intolerable stress. However, it may become a disadvantage if this over-modulation arrests the natural process to accommodate stressful experiences (Horowitz, 1974), such as habituation for the high arousal of traumatic experience (Lanius et al., 2010). Intriguingly, dissociative individuals did not forget the ignored items, as the accessibility of the representations that had been removed from the focus of attention did not decrease in the subsequent recognition tests. Their accessibility was enhanced. This finding does not support the hypothesis that cognitive disengagement may lead to a lowered accessibility of the non-target representations in dissociative individuals (DePrince & Freyd, 2001, 2004). Instead, superior cognitive disengagement may facilitate the diversion of attention away from the non-target items, rendering these representations less distracting (Chiu et al., 2009). Hence, inhibitory function may not be recruited at the study phase, leaving these representations disinhibited and highly accessible afterward (Chiu et al., 2010; Chiu, Lin, et al., 2012; Elzinga et al., 2000, 2003). This increase in the accessibility of the ignored representations may be pertinent to another phenomenon commonly reported by dissociative individuals, such as intrusive memory (Van der Hart et al., 2004; Van der Kolk & Fisler, 1995). The accessibility of the hotspot of a stressful experience may increase when dissociative individuals attempt to ignore it, and these representations unexpectedly intrude into consciousness when cues are available (Van der Kolk & Van der Hart, 1991). Some limitations should be noted. First, the participants in this study were selected on the basis of their proneness to normative dissociation. Researchers should be cautious to generalize these findings to pathological dissociation, as some qualitative differences between normative and pathological dissociation have been documented (Chiu et al., 2015; Waller et al., 1996), and there exists a conceptual debate about their relationship as well (Nijenhuis & van der Hart, 2011; also see Butler, 2011). In particular, it is unclear whether the amnesia of stressful experiences can be completely explained by temporary mental escape via deliberate cognitive disengagement (Epstein & Bottoms, 2002; Melchert, 1999). A clinical study of individuals with pathological dissociation may help clarify this issue. Second, to minimize the putative confounding effect of emotional contamination, the order of the neutral and emotional conditions was fixed, and the neutral condition preceded the emotional condition. Hence, the participants knew that they would complete a recognition test for the emotional condition. The possibility of using another strategy for the running span task cannot be excluded in the emotional condition, although similar updating performance was found between the neutral and emotion conditions. Third, this study addressed verbal working memory. One should be cautious to generalize the results to the regulation of perceptual representations. Abundant perceptual detail is an essential feature of pathological trauma memory (Brewin, Gregory, Lipton, & Burgess, 2010). Laboratory experiments suggest that visuo-spatial working memory may play a role in the development of intrusive memory (e.g., Holmes, Brewin, & Hennessy, 2004; Tsai & McNally, 2014). Although cognitive control is proposed as a modalityindependent operation, modality-dependent components may exist in the storage and rehearsal of the two types of representations (Kane et al., 2004). Whether atypical cognitive control over verbal information can be found as well over perceptual representations remains unclear. Finally, given the lack of support for the link between superior cognitive disengagement and forgetting, some researchers may doubt the validity of atypical memory experience in individuals with dissociation proneness (e.g., Chiu, 2018; Chiu, Yeh, et al., 2012) and its relation to the symptom of over-reporting (Merckelbach et al., 2015). However, amnesia may result from other cognitive mechanisms (e.g., Chiu et al., 2016b). More studies should be conducted to clarify this issue.

5. Conclusion Inconsistent results have been observed in laboratory studies investigating dissociative individuals’ forgetting. While several studies reported that dissociative individuals remembered to-be-forgotten materials too well in the single-task context tapping into cognitive inhibition (Chiu et al., 2010; Chiu, Lin, et al., 2012; Elzinga et al., 2000, 2003), other studies demonstrated an enhanced forgetting of negative materials in the dual-task context tapping into cognitive disengagement (DePrince & Freyd, 2001, 2004). The enhanced forgetting of negative materials in the dual-task context posed the question of whether the representations that are ignored via cognitive disengagement can be less accessible. The result of this study showed that the accessibility of the ignored items was enhanced rather than lowered even though the memory status of the representations was manipulated with the paradigm tapping into the cognitive disengagement. The finding does not support the notion that dissociative individuals can forget memory through cognitive disengagement.

Declaration of conflicting interests The author declares no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding The author discloses receipt of the following financial support for the research, authorship, and/or publication of this article: the study was supported in part by the Research Grants Council, University Grant Committee (Early Career Scheme, no. 2191102) and The Chinese University of Hong Kong (no. 4052067) to C.-D. Chiu. 80

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