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A hypnotic paradigm for studying intrusive memories
J. Behav. Ther. & Exp. Psychiat. 41 (2010) 433e437
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A hypnotic paradigm for studying intrusive memories Zoe Hill, Lynette Hung, Richard A. Bryant* School of Psychology, University of New South Wales, Sydney, NSW 2052, Australia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 April 2009 Received in revised form 24 April 2010 Accepted 4 May 2010
Despite the importance of intrusive memories in clinical disorders, research has been limited by a dearth of paradigms that permit experimental study of intrusions. This study describes a hypnotic paradigm for eliciting intrusive memories. Forty-nine highly hypnotisable participants nominated a distressing memory prior to being hypnotised. During hypnosis, they received the suggestion that they would remember the memory in response to a designated cue after the hypnosis session. Half of the participants also received a posthypnotic amnesia suggestion for the source of the memory. Following hypnosis, all participants completed a cognitive task and during the task received the cue to recall the memory. Results demonstrated that memories experienced after posthypnotic amnesia were experienced as more involuntary and more distressing than those that were knowingly retrieved. Participants in the posthypnotic amnesia condition also demonstrated greater interference on the cognitive task after the retrieval cue was given than those who intentionally retrieved the memory. These findings suggest that posthypnotic suggestion provides a useful paradigm to elicit intrusive memories under experimental conditions. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Intrusions Hypnosis Unwanted thoughts
Intrusive thoughts and memories are common in many clinical disorders, including posttraumatic stress disorder (Brewin, 1998), obsessive compulsive disorder (Salkovskis, 1985), depression (Brewin, 1998), social phobia (Hackmann, Clark, & McManus, 2000), and agoraphobia (Day, Holmes, & Hackmann, 2004). Across all these disorders, intrusions share the common properties of occurring involuntarily and causing significant distress (Clark & Rhyno, 2005). In general, intrusive memories are experienced as more vivid and distressing than non-intrusive memories (Berntsen, Willert, & Rubin, 2003). They are also experienced as spontaneous, repetitive, and difficult to control, regardless of the content (Clark & Rhyno, 2005; Dougall, Craig, & Baum, 1999). Since the early proposals of Janet (1904), theorists have asserted that intrusive memories of trauma are different from ordinary autobiographical memories (e.g., Brewin, Dagleish, & Joseph, 1996; Ehlers & Clark, 2000). Such memories have been described as being more vivid and more emotionally intense than voluntary memories of traumatic or non-traumatic events (Bryant & Harvey, 1998). Intrusive memories have also been shown to be difficult to control (Wegner, 1994), and to interfere with ongoing task performance (Hellawell & Brewin, 2002). Most research has relied on retrospective reports of intrusive memories (e.g., Brewin, 1998; Bywaters, Andrade, & Turpin, 2004; Hackmann, Ehlers, Speckens, & Clark, 2004;
* Corresponding author. Tel.: þ61 2 93853640; fax: þ61 2 93853641. E-mail address: [email protected] (R.A. Bryant). 0005-7916/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jbtep.2010.05.001
Reynolds & Brewin, 1998) or diary methods (e.g., Berntsen, 2001). Other studies have studied intrusions by presenting participantsS200 with evocative stimuli (Lynch, Schneider, Rosenthal, & Cheavens, 2007) or reminders of traumatic events (Bryant & Harvey, 1998). All of these approaches are potentially confounded by retrospective bias or by extraneous environmental factors (Clark & Purdon, 1995). There is a need to develop new paradigms to examine intrusions under experimental conditions. There are several reasons to suggest that hypnosis may provide a useful model for studying intrusions. Hypnotisability is associated with susceptibility to intrusive thoughts (Bryant & Idey, 2001) and a tendency to attribute involuntariness to internal experiences (Kirsch & Lynn, 1999). Numerous clinical disorders that are characterised by intrusive memories are associated with elevated levels of hypnotisability, including PTSD (Spiegel, Hunt, & Dondershine, 1988), acute stress disorder (Bryant, Guthrie, Moulds, Nixon, & Felmingham, 2003), and phobias (Frankel & Orne, 1976). One of the classic responses during hypnosis is posthypnotic amnesia. Posthypnotic amnesia involves suggesting to hypnotised persons that following hypnosis they will be unable to recall particular aspects of the hypnotic experience until they receive a cancellation instruction. A number of studies have demonstrated that a suggestion for posthypnotic amnesia can alter an individual’s access to autobiographical memories to create profound but reversible forgetting in highly hypnotisable individuals (Barnier, 2002; Bryant, Barnier, Mallard, & Tibbits, 1999). More usefully, posthypnotic amnesia has often been shown to be a useful means of
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creating psychological phenomena without individuals’ awareness by providing a suggestion to experience the phenomena and then covering the suggestion with posthypnotic amnesia (Zimbardo, Andersen, & Rabat, 1981, Zimbardo, LaBerge, & Butler, 1993). Importantly, hypnotic suggestion permits a strong sense of involuntariness in the experience of the suggestion, which enhances the comparability of the suggested experience of intrusive thoughts with the involuntary nature of intrusions in clinical populations. In an early application of this approach, Zimbardo et al. (1981) suggested to highly hypnotisable participants that they would experience deafness after hypnosis. Half of the participants were also administered a suggestion for posthypnotic amnesia for the deafness suggestion. This study found that participants who had experienced deafness but lacked the knowledge of why they were deaf reported paranoia reactions on subsequent tests, whereas those who were deaf but realised that this was the result of a direct suggestion did not experience the paranoia (Zimbardo et al., 1981). This study highlights the utility of using hypnosis to create a psychological state and cover the reason for why it is occurring. This paradigm provides a potential means of eliciting intrusive memories in the laboratory setting in that a hypnotic suggestion can be used to instruct individuals to retrieve certain memories, paired with a posthypnotic suggestion to be amnesic of the source of the memory in order to create a sense of involuntariness and intrusion. The present study examined the capacity for hypnosis to elicit involuntary intrusive memories in the laboratory. To test this approach, we focused on highly hypnotisable participants because of their distinctive ability to experience hypnotic suggestions and posthypnotic amnesia (Bryant et al., 1999). Participants were asked to elicit a memory of a distressing event prior to hypnosis. During hypnosis, half of the participants received the suggestion that they would think about the distressing memory after hearing a posthypnotic cue after waking from hypnosis. They were also given a suggestion for posthypnotic amnesia in order to cover the reason for the recollection (posthypnotic amnesia condition). The other half of the participants were instructed during hypnosis that they would be asked to think about their distressing memory after waking (intentional retrieval condition). After the hypnosis session, all participants received the cue midway through a cognitive task. Participants in the intentional retrieval condition were also prompted to retrieve the memory of their distressing event. All participants completed a second version of the cognitive task to index the relative interference of the memories on ongoing task performance. The rationale for administering the cognitive task was that a defining feature of intrusions is that the cognitive load associated with the intrusion interfere with ongoing cognitive functioning. Accordingly, an important index of the load associated with an experimentally-generated intrusion is the extent to which it interferes with cognitive processes. We hypothesised that memories in the posthypnotic amnesia condition would be characterised by greater involuntariness, distress, vividness, and interfere more on a concurrent cognitive task than intentionally retrieved memories. 1. Method 1.1. Participants The sample comprised of 48 (28 female and 20 male) highly hypnotisable undergraduate student participants of mean age 20.29 years (SD ¼ 5.89). Participants were preselected on the basis of their extreme scores on a 10-item version of the group administered Harvard Group Scale of Hypnotic Susceptibility, Form A (HGSHS-A; Shor & Orne, 1962) that was administered to 843
undergraduate students. High hypnotisability was subsequently confirmed by obtaining high scores on a 10-item version of the individually administered Stanford Hypnotic Susceptibility Scale, Form C (SHSS-C; Weitzhenhoffer & Hilgard, 1963). Participants scored in the range 7e10 on the HGSHS-A (M ¼ 8.32, SD ¼ 0.85), and 7e10 on the SHSS-C (M ¼ 8.24, SD ¼ 1.04). Participants were randomly allocated to retrieval conditions. 1.2. Procedure Following written informed consent, the experimenter (ZH or LH) instructed participants to elicit a memory of a distressing event. Participants provided ratings of (a) involuntariness (1 ¼ not at all, 9 ¼ extremely), (b) frequency (1 ¼ not at all, 9 ¼ almost everyday), (c) distress (1 ¼ not at all, 9 ¼ extremely), and (d) vividness (1 ¼ not at all, 9 ¼ extremely) of the memory. The experimenter administered a 20-min hypnotic induction (based on the SHSS-C induction, Weitzenhoffer & Hilgard, 1963) and a number of unrelated hypnotic suggestions (arm rigidity, hand lowering). Participants in the amnesia condition then received the suggestion that “After a while, when you’ve woken up, you will hear me say to you, ‘Let’s move onto something else’. When I say this, you will think about the memory of [the distressing event]. As soon as you hear me say this, you will think about this memory. you will remember this memory. You will think about this memory when you hear me say ‘Let’s move onto something else’ but you will forget that I told you to do so. You will also forget discussing it with me before hypnosis. You will forget anything I said or asked you about this memory just as you will forget the other things until I say to you ‘Now you can remember everything’. Indeed, it will prove to cost so much effort to recall anything I said or asked you about this memory that you will prefer not to try. Even if you do try, you will forget that I told you to think about this memory after hypnosis until I say to you, ‘Now you can remember everything’. You will not remember anything until then. When you hear me say ‘Let’s move onto something else’ you will think about this memory.” Participants in the intentional retrieval condition were informed that “After a while, when you’ve woken up, I will ask you to think about the memory of [the distressing event].” All participants then underwent a deinduction procedure to finish the hypnosis session. Following deinduction, participants completed a sustained attention task that required them to quickly and accurately scan through a list of paired names of neutral objects or number sequences and indicate whether the pairs were the same of different (e.g., “1027” vs. “1072”) for 1 min (names or numbers were presented alternately). Two versions of the pairs were created and participants received Version A or Version B prior to the intrusion cue, and the alternate version following the intrusion cue in a counterbalanced order. After one minute, the experimenter provided the posthypnotic cue phrase (i.e., “let’s move onto something else”). Participants in the intentional retrieval condition were further instructed “to think about the memory of [the distressing event] you told me about earlier, and as you think about it I want you to continue with the task”. The experimenter then instructed the participants to continue with the cognitive task for one additional minute. The order of the task versions was counterbalanced across retrieval conditions. At the end of the second task, the experimenter asked “What were you thinking about during that task?” If the target memory was not mentioned, participants were specifically asked “Did you have any thoughts of the distressing memory?” If participants indicated they experienced the target memory, the experimenter asked participants to briefly describe their memory and provide another set of ratings of how involuntary the memory was (1 ¼ meant to think about it, 9 ¼ did not mean to think about it), how distressing the memory was
Z. Hill et al. / J. Behav. Ther. & Exp. Psychiat. 41 (2010) 433e437
(1 ¼ not at all, 9 ¼ extremely), and how vivid the memory was (1 ¼ not at all, 9 ¼ extremely). The experimenter also asked participants to explain why they had thought about the memory, and cancelled the posthypnotic amnesia instructions for participants in the posthypnotic amnesia condition by saying “Now you can remember everything. You don’t need to think about that memory any more”. Participants then viewed a video recording of the experimental phase and were informed that this would help them to recall their experiences of hypnosis. The experimenter used the Experiential Analysis Technique (EAT; Sheehan, McConkey, & Cross, 1978) to explore the nature of participants’ thoughts and expectations at particular points of the experimental session. The experimenter paused the recording at a number of points to ask specific questions, but also allowed participants to pause at any other point and comment on their experiences. Video recordings were examined by the experimenter and an independent rater. The experimenter and the rater independently coded participants according to four variables: (a) involuntariness of the memory (1 ¼ took effort to retrieve, 5 ¼ memories occurred spontaneously), (b) distress associated with the memory (1 ¼ no emotional reaction, 5 ¼ extremely distressed), (c) vividness of the memory (1 ¼ no visual information, 5 ¼ a lot of visual information), and (d) attributions for experiencing the memory (due to instructions, or unsure). The interrater agreement was satisfactory for all variables (r’s > .82). Analyses of ratings were based on the independent rater’s coding. 2. Results 2.1. Preliminary analyses Table 1 presents the means for participant characteristics across retrieval conditions. Separate one-way analyses of variance (ANOVA) indicated that groups did not differ on age, HGSHS:A scores, or SHSS:C scores. All participants reported a distressing memory (relationship separation ¼ 25; death of loved one/ pet ¼ 12; accident ¼ 7; other ¼ 4). Table 1 presents the means for participants’ ratings of the qualities of the memory they nominated prior to hypnosis. There were no differences in terms of type of event reported, or involuntariness, frequency, distress, or vividness across retrieval conditions. Performance on the sustained attention task was not associated with any participant characteristics of hypnotisability score. 2.2. Manipulation checks Comparable numbers of participants did not recall the target memory in the experimental posthypnotic phase in posthypnotic amnesia (n ¼ 4) and intentional retrieval condition (n ¼ 6) conditions, c2 (1, n ¼ 10) ¼ 0.51, p > 0.05. These 10 participants were excluded from subsequent analyses. In terms of the reported reason for recalling the memory, more participants in the posthypnotic Table 1 Participant characteristics.
Age HGSHS:A SHSS:C Memory involuntariness Memory frequency Memory distress Memory vividness
Posthypnotic amnesia
Intentional retrieval
19.33 8.00 8.09 4.97 4.96 6.54 7.12
21.25 8.69 8.42 5.11 4.60 5.69 6.75
(1.61) (0.63) (0.98) (2.63) (2.36) (1.89) (1.60)
(8.16) (0.93) (1.12) (2.65) (2.78) (2.24) (1.85)
Note. Standard deviations appear in parentheses. HGSHS:A ¼ Harvard Group Scale of Hypnotic Susceptibility, Form A. SHSS:C ¼ Stanford Hypnotic Susceptibility Scale, Form C.
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Table 2 Mean ratings of memory qualities. Posthypnotic amnesia
Intentional retrieval
8.44 (0.65) 6.35 (1.73) 6.41 (2.06)
5.71 (2.66) 5.12 (1.93) 6.68 (1.88)
Postexperimental ratings Involuntariness 4.56 (1.10) Distress 2.80 (1.36) Vividness 3.35 (1.37)
2.87 (1.77) 2.39 (1.50) 3.13 (1.36)
Experimental ratings Involuntariness Distress Vividness
Note: Standard deviations in parentheses.
amnesia condition (95%) than intentional retrieval condition (12%) reported not knowing why they had recalled the memory [c2 (n ¼ 47) ¼ 14.39, p < 0.001]. One participant in the posthypnotic amnesia condition reported explicitly remembering the memory suggestion, and accordingly was excluded from subsequent analyses. The resulting sample comprised of 19 participants in the posthypnotic amnesia condition and 18 participants in the intentional retrieval condition. 2.3. Qualitative features of recalled memories Table 2 presents the mean ratings for involuntariness, distress, and vividness of memories made during the experimental phase. Participants in the posthypnotic amnesia condition reported that the memory was more involuntary [F(1,35) ¼ 14.85, p < 0.001, ή ¼ 0.32], and more distressing [F(1,35) ¼ 1.96, p ¼ 0.05, ή ¼ 0.11] than participants in the intentional retrieval condition. Table 2 also presents the mean ratings of memory qualities made by the independent rater of the postexperimental ratings. Participants in the posthypnotic amnesia condition reported that the memory was more involuntary [F(1,35) ¼ 11.27, p < 0.005, ή ¼ 0.27]. No differences were noted for vividness or distress ratings by participants or by independent raters. 2.4. Cognitive task performance Table 3 presents participants’ mean performance on the cognitive task before and after recall of the memory. A 2 (Retrieval Condition) 2 (Task Order) 2 (Time) ANOVA of correct responses on the cognitive task indicated a significant Retrieval Condition Time interaction effect [F (1, 35) ¼ 4.35, p < 0.05, ή ¼ 0.12], a significant Task Order Time interaction effect [F (1, 35) ¼ 12.53, p < 0.001, ή ¼ 0.28], and a significant three-way Retrieval Condition Task Order Time interaction effect [F (1, 35) ¼ 4.22, p < 0.05, ή ¼ 0.12]. To clarify the three-way interaction, we conducted separate 2 (Retrieval Condition) 2 (Time) ANOVAs for participants who performed Task A or Task B, initially. For participants who completed Task B first, there were no significant main or interaction effects. For participants who completed Task A first, there was a significant main effect for Time [F (1, 16) ¼ 26.32, p < 0.001, ή ¼ 0.62] and a significant Time Retrieval Condition interaction effect [F (1, 16) ¼ 17.28, p < 0.001, ή ¼ 0.52]. Follow-up Table 3 Mean performance on cognitive task.
Pre-recall Post-recall
Posthypnotic amnesia
Intentional retrieval
Order 1
Order 2
Order 1
Order 2
17.55 (5.18) 12.09 (5.41)
14.71 (2.06) 15.86 (3.29)
17.14 (3.43) 16.57 (3.87)
15.55 (3.83) 16.73 (3.85)
Note: Standard deviations appear in parentheses.
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comparisons indicated that after the memory retrieval cue, participants in the posthypnotic amnesia condition had a greater decrement in performance relative to their pre-retrieval cue than participants in the intentional retrieval condition (p < 0.05). 3. Discussion The present study explored the capacity for hypnosis to elicit and index intrusive autobiographical memories in controlled laboratory settings. The majority of participants across retrieval conditions reported experiencing the target memory upon hearing the cue phrase posthypnotically. Significantly, all participants except one in the posthypnotic amnesia condition indicated that they did not know why they had recalled the memory both at the point of recall and during the postexperimental inquiry, indicating posthypnotic amnesia for the memory suggestion and the posthypnotic amnesia suggestion. This extends past studies that have elicited psychological states and precluded awareness of the cause of the phenomena (Zimbardo et al., 1981, Zimbardo et al., 1993), and represents a novel application in the study of autobiographical memories. Our first hypothesis predicted that memories recalled after posthypnotic amnesia would be experienced as more involuntary compared to those that were intentionally retrieved. This was supported by ratings given at the point of recall as well as comments provided during the postexperimental inquiry phase (e. g., “It just popped into my head randomly”, “I have no idea why I just thought of that”). Our second hypothesis predicted that involuntary memories would be experienced differently to intentionally retrieved memories. As predicted, memories recalled after posthypnotic amnesia were more distressing than intentionally retrieved memories. Comments provided by participants in the posthypnotic amnesia condition during the postexperimental inquiry supported this trend (“I was really confused as to why I was thinking about that now. It was pretty upsetting”, “I just wanted to stop thinking about it”). This is consistent with previous studies that suggest the distress associated with intrusive memories is dependent not only on the negative content of the memories, but also on the degree to which they are unexpected (Berntsen, 2001; Dougall et al., 1999). Distress may also be related to individuals’ attributions of control regarding the unwanted experience of the target memory. Ehlers and Clark (2000) posit that negative appraisals regarding one’s control over the emergence and duration of intrusive phenomena result in increased levels of distress. Future research could elucidate upon the role of controllability in intrusive experiences by including measures of control appraisal. Contrary to predictions, memories experienced after posthypnotic amnesia were no more vivid than intentionally retrieved memories. There are several factors that may account for this. First, there is some evidence that differences in vividness between intrusive and non-intrusive memories occur along a continuum of psychopathology status. Across different types of memories (intrusive vs. non-intrusive), types of events (traumatic vs. non-traumatic), and across populations (trauma survivors with vs. without PTSD, and non-clinical populations) studies offering the greatest support for heightened vividness in intrusive memories are based on intrusive memories of traumatic events experienced in PTSD populations (Berntsen et al., 2003). These differences have been less pronounced for non-traumatic memories in non-clinical samples (e.g., Porter & Birt, 2001), such as those studied in the present experiment. Consistent with previous work on intrusions (Dougall et al., 1999; Hellawell & Brewin, 2002; Wegner, 1994), we expected that involuntary memories would interfere with ongoing task performance more so than memories that were intentionally retrieved. Results demonstrated partial support for this hypothesis in that participants in the posthypnotic amnesia condition demonstrated
a greater decrease in cognitive performance after recall compared to participants in the intentional retrieval condition, but only for the first counterbalancing order. Intrusive memories compete for cognitive resources (Clark & Rhyno, 2005; Lynch et al., 2007), perhaps as a paradoxical result of attempts to inhibit or suppress negative content (Rassin, Merckelbach, & Muris, 2001). For participants in the posthypnotic amnesia condition, tendencies to suppress may have arisen automatically given the unwanted nature of the experience. In contrast, participants in the intentional retrieval condition were specifically asked to think about the memory. As such, the motivation to remember may have superseded motivation to avoid the content of the memory. This effect was not found in the second counterbalancing order, which may reflect ceiling effects for the first version of the task. We note that our cognitive task did not employ an established measure of working memory. Future studies may wish to increase the cognitive load to ensure tasks are sufficiently demanding to index impairment on cognitive resources using more structured cognitive tasks. It is probable that the mechanisms underpinning hypnoticallyinduced intrusions are not the same as though occurring in clinical intrusions. Some models suggest that intrusive memories are the result of encoded information that is poorly elaborated and inadequately integrated into the general database of autobiographical knowledge (Ehlers & Clark, 2000). Although this information is potentially accessible via voluntary routes of retrieval, poor elaboration enhances the ease by which this information is retrieved via direct or automatic cues and consequently experienced as intrusive (Conway & Pleydell-Pearce, 2000; Ehlers & Clark, 2000). This view posits that although cues are initially specific, cues generalise over time to stimuli loosely connected with the event so that individuals are often unaware of cues and memories appear to come ‘out of the blue’ (Foa & Kozak, 1986). In contrast, hypnosis theories would propose that experiences following posthypnotic amnesia occur as a result of intention that is perceived as involuntary because of a dissociated control process that permits attributions of involuntariness to the experience. According to this perspective, hypnotic intrusions are more parsimoniously explained as memories that are misattributed to involuntariness rather than memories that are triggered by cues associated with a closely integrated network of representations pertaining to the memories. Several factors limit the generalisability of the current findings. First, we recruited from a non-clinical student sample and did not include psychopathology measures; conclusions regarding the experience of intrusive memories in clinical populations are therefore limited. Future research could replicate the current design with a clinical population to determine whether experimentally manipulating the route of retrieval demonstrates the same pattern of results. Second, we specifically recruited highly hypnotisable participants to maximise the success of the posthypnotic suggestion. We note that highly hypnotisable individuals differ along several dimensions compared to medium or low hypnotisable individuals. For example, highly hypnotisable individuals display higher levels of imagination (Lynn & Rhue, 1986), absorption (Roche & McConkey, 1990), and divided attention (Bowers & Brennenman, 1981). The extent to which the findings are generalizable to less hypnotisable individuals remains to be tested. Third, we recognise that participants may have been responding to the demand characteristics of the experiment; replication is required that utilises the real-simulating paradigm (Orne, 1979) in which unhypnotised individuals are asked to simulate the experience of a hypnotised person, which provides an index of demand characteristics and employs implicit measures of thought accessibility. Fourth, as the experimenters were aware of the study hypotheses, the possibility of experimenter bias cannot be ruled out.
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These limitations notwithstanding, this paradigm provides an alternate means to elicit intrusions under experimental conditions. Future studies could use this approach to elicit intrusions in the context of neuroimaging, during different mood states, following attempted thought suppression, and with varying instructions to manage intrusive thoughts.
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A hypnotic paradigm for studying intrusive memories Zoe Hill, Lynette Hung, Richard A. Bryant* School of Psychology, University of New South Wales, Sydney, NSW 2052, Australia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 April 2009 Received in revised form 24 April 2010 Accepted 4 May 2010
Despite the importance of intrusive memories in clinical disorders, research has been limited by a dearth of paradigms that permit experimental study of intrusions. This study describes a hypnotic paradigm for eliciting intrusive memories. Forty-nine highly hypnotisable participants nominated a distressing memory prior to being hypnotised. During hypnosis, they received the suggestion that they would remember the memory in response to a designated cue after the hypnosis session. Half of the participants also received a posthypnotic amnesia suggestion for the source of the memory. Following hypnosis, all participants completed a cognitive task and during the task received the cue to recall the memory. Results demonstrated that memories experienced after posthypnotic amnesia were experienced as more involuntary and more distressing than those that were knowingly retrieved. Participants in the posthypnotic amnesia condition also demonstrated greater interference on the cognitive task after the retrieval cue was given than those who intentionally retrieved the memory. These findings suggest that posthypnotic suggestion provides a useful paradigm to elicit intrusive memories under experimental conditions. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Intrusions Hypnosis Unwanted thoughts
Intrusive thoughts and memories are common in many clinical disorders, including posttraumatic stress disorder (Brewin, 1998), obsessive compulsive disorder (Salkovskis, 1985), depression (Brewin, 1998), social phobia (Hackmann, Clark, & McManus, 2000), and agoraphobia (Day, Holmes, & Hackmann, 2004). Across all these disorders, intrusions share the common properties of occurring involuntarily and causing significant distress (Clark & Rhyno, 2005). In general, intrusive memories are experienced as more vivid and distressing than non-intrusive memories (Berntsen, Willert, & Rubin, 2003). They are also experienced as spontaneous, repetitive, and difficult to control, regardless of the content (Clark & Rhyno, 2005; Dougall, Craig, & Baum, 1999). Since the early proposals of Janet (1904), theorists have asserted that intrusive memories of trauma are different from ordinary autobiographical memories (e.g., Brewin, Dagleish, & Joseph, 1996; Ehlers & Clark, 2000). Such memories have been described as being more vivid and more emotionally intense than voluntary memories of traumatic or non-traumatic events (Bryant & Harvey, 1998). Intrusive memories have also been shown to be difficult to control (Wegner, 1994), and to interfere with ongoing task performance (Hellawell & Brewin, 2002). Most research has relied on retrospective reports of intrusive memories (e.g., Brewin, 1998; Bywaters, Andrade, & Turpin, 2004; Hackmann, Ehlers, Speckens, & Clark, 2004;
* Corresponding author. Tel.: þ61 2 93853640; fax: þ61 2 93853641. E-mail address: [email protected] (R.A. Bryant). 0005-7916/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jbtep.2010.05.001
Reynolds & Brewin, 1998) or diary methods (e.g., Berntsen, 2001). Other studies have studied intrusions by presenting participantsS200 with evocative stimuli (Lynch, Schneider, Rosenthal, & Cheavens, 2007) or reminders of traumatic events (Bryant & Harvey, 1998). All of these approaches are potentially confounded by retrospective bias or by extraneous environmental factors (Clark & Purdon, 1995). There is a need to develop new paradigms to examine intrusions under experimental conditions. There are several reasons to suggest that hypnosis may provide a useful model for studying intrusions. Hypnotisability is associated with susceptibility to intrusive thoughts (Bryant & Idey, 2001) and a tendency to attribute involuntariness to internal experiences (Kirsch & Lynn, 1999). Numerous clinical disorders that are characterised by intrusive memories are associated with elevated levels of hypnotisability, including PTSD (Spiegel, Hunt, & Dondershine, 1988), acute stress disorder (Bryant, Guthrie, Moulds, Nixon, & Felmingham, 2003), and phobias (Frankel & Orne, 1976). One of the classic responses during hypnosis is posthypnotic amnesia. Posthypnotic amnesia involves suggesting to hypnotised persons that following hypnosis they will be unable to recall particular aspects of the hypnotic experience until they receive a cancellation instruction. A number of studies have demonstrated that a suggestion for posthypnotic amnesia can alter an individual’s access to autobiographical memories to create profound but reversible forgetting in highly hypnotisable individuals (Barnier, 2002; Bryant, Barnier, Mallard, & Tibbits, 1999). More usefully, posthypnotic amnesia has often been shown to be a useful means of
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creating psychological phenomena without individuals’ awareness by providing a suggestion to experience the phenomena and then covering the suggestion with posthypnotic amnesia (Zimbardo, Andersen, & Rabat, 1981, Zimbardo, LaBerge, & Butler, 1993). Importantly, hypnotic suggestion permits a strong sense of involuntariness in the experience of the suggestion, which enhances the comparability of the suggested experience of intrusive thoughts with the involuntary nature of intrusions in clinical populations. In an early application of this approach, Zimbardo et al. (1981) suggested to highly hypnotisable participants that they would experience deafness after hypnosis. Half of the participants were also administered a suggestion for posthypnotic amnesia for the deafness suggestion. This study found that participants who had experienced deafness but lacked the knowledge of why they were deaf reported paranoia reactions on subsequent tests, whereas those who were deaf but realised that this was the result of a direct suggestion did not experience the paranoia (Zimbardo et al., 1981). This study highlights the utility of using hypnosis to create a psychological state and cover the reason for why it is occurring. This paradigm provides a potential means of eliciting intrusive memories in the laboratory setting in that a hypnotic suggestion can be used to instruct individuals to retrieve certain memories, paired with a posthypnotic suggestion to be amnesic of the source of the memory in order to create a sense of involuntariness and intrusion. The present study examined the capacity for hypnosis to elicit involuntary intrusive memories in the laboratory. To test this approach, we focused on highly hypnotisable participants because of their distinctive ability to experience hypnotic suggestions and posthypnotic amnesia (Bryant et al., 1999). Participants were asked to elicit a memory of a distressing event prior to hypnosis. During hypnosis, half of the participants received the suggestion that they would think about the distressing memory after hearing a posthypnotic cue after waking from hypnosis. They were also given a suggestion for posthypnotic amnesia in order to cover the reason for the recollection (posthypnotic amnesia condition). The other half of the participants were instructed during hypnosis that they would be asked to think about their distressing memory after waking (intentional retrieval condition). After the hypnosis session, all participants received the cue midway through a cognitive task. Participants in the intentional retrieval condition were also prompted to retrieve the memory of their distressing event. All participants completed a second version of the cognitive task to index the relative interference of the memories on ongoing task performance. The rationale for administering the cognitive task was that a defining feature of intrusions is that the cognitive load associated with the intrusion interfere with ongoing cognitive functioning. Accordingly, an important index of the load associated with an experimentally-generated intrusion is the extent to which it interferes with cognitive processes. We hypothesised that memories in the posthypnotic amnesia condition would be characterised by greater involuntariness, distress, vividness, and interfere more on a concurrent cognitive task than intentionally retrieved memories. 1. Method 1.1. Participants The sample comprised of 48 (28 female and 20 male) highly hypnotisable undergraduate student participants of mean age 20.29 years (SD ¼ 5.89). Participants were preselected on the basis of their extreme scores on a 10-item version of the group administered Harvard Group Scale of Hypnotic Susceptibility, Form A (HGSHS-A; Shor & Orne, 1962) that was administered to 843
undergraduate students. High hypnotisability was subsequently confirmed by obtaining high scores on a 10-item version of the individually administered Stanford Hypnotic Susceptibility Scale, Form C (SHSS-C; Weitzhenhoffer & Hilgard, 1963). Participants scored in the range 7e10 on the HGSHS-A (M ¼ 8.32, SD ¼ 0.85), and 7e10 on the SHSS-C (M ¼ 8.24, SD ¼ 1.04). Participants were randomly allocated to retrieval conditions. 1.2. Procedure Following written informed consent, the experimenter (ZH or LH) instructed participants to elicit a memory of a distressing event. Participants provided ratings of (a) involuntariness (1 ¼ not at all, 9 ¼ extremely), (b) frequency (1 ¼ not at all, 9 ¼ almost everyday), (c) distress (1 ¼ not at all, 9 ¼ extremely), and (d) vividness (1 ¼ not at all, 9 ¼ extremely) of the memory. The experimenter administered a 20-min hypnotic induction (based on the SHSS-C induction, Weitzenhoffer & Hilgard, 1963) and a number of unrelated hypnotic suggestions (arm rigidity, hand lowering). Participants in the amnesia condition then received the suggestion that “After a while, when you’ve woken up, you will hear me say to you, ‘Let’s move onto something else’. When I say this, you will think about the memory of [the distressing event]. As soon as you hear me say this, you will think about this memory. you will remember this memory. You will think about this memory when you hear me say ‘Let’s move onto something else’ but you will forget that I told you to do so. You will also forget discussing it with me before hypnosis. You will forget anything I said or asked you about this memory just as you will forget the other things until I say to you ‘Now you can remember everything’. Indeed, it will prove to cost so much effort to recall anything I said or asked you about this memory that you will prefer not to try. Even if you do try, you will forget that I told you to think about this memory after hypnosis until I say to you, ‘Now you can remember everything’. You will not remember anything until then. When you hear me say ‘Let’s move onto something else’ you will think about this memory.” Participants in the intentional retrieval condition were informed that “After a while, when you’ve woken up, I will ask you to think about the memory of [the distressing event].” All participants then underwent a deinduction procedure to finish the hypnosis session. Following deinduction, participants completed a sustained attention task that required them to quickly and accurately scan through a list of paired names of neutral objects or number sequences and indicate whether the pairs were the same of different (e.g., “1027” vs. “1072”) for 1 min (names or numbers were presented alternately). Two versions of the pairs were created and participants received Version A or Version B prior to the intrusion cue, and the alternate version following the intrusion cue in a counterbalanced order. After one minute, the experimenter provided the posthypnotic cue phrase (i.e., “let’s move onto something else”). Participants in the intentional retrieval condition were further instructed “to think about the memory of [the distressing event] you told me about earlier, and as you think about it I want you to continue with the task”. The experimenter then instructed the participants to continue with the cognitive task for one additional minute. The order of the task versions was counterbalanced across retrieval conditions. At the end of the second task, the experimenter asked “What were you thinking about during that task?” If the target memory was not mentioned, participants were specifically asked “Did you have any thoughts of the distressing memory?” If participants indicated they experienced the target memory, the experimenter asked participants to briefly describe their memory and provide another set of ratings of how involuntary the memory was (1 ¼ meant to think about it, 9 ¼ did not mean to think about it), how distressing the memory was
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(1 ¼ not at all, 9 ¼ extremely), and how vivid the memory was (1 ¼ not at all, 9 ¼ extremely). The experimenter also asked participants to explain why they had thought about the memory, and cancelled the posthypnotic amnesia instructions for participants in the posthypnotic amnesia condition by saying “Now you can remember everything. You don’t need to think about that memory any more”. Participants then viewed a video recording of the experimental phase and were informed that this would help them to recall their experiences of hypnosis. The experimenter used the Experiential Analysis Technique (EAT; Sheehan, McConkey, & Cross, 1978) to explore the nature of participants’ thoughts and expectations at particular points of the experimental session. The experimenter paused the recording at a number of points to ask specific questions, but also allowed participants to pause at any other point and comment on their experiences. Video recordings were examined by the experimenter and an independent rater. The experimenter and the rater independently coded participants according to four variables: (a) involuntariness of the memory (1 ¼ took effort to retrieve, 5 ¼ memories occurred spontaneously), (b) distress associated with the memory (1 ¼ no emotional reaction, 5 ¼ extremely distressed), (c) vividness of the memory (1 ¼ no visual information, 5 ¼ a lot of visual information), and (d) attributions for experiencing the memory (due to instructions, or unsure). The interrater agreement was satisfactory for all variables (r’s > .82). Analyses of ratings were based on the independent rater’s coding. 2. Results 2.1. Preliminary analyses Table 1 presents the means for participant characteristics across retrieval conditions. Separate one-way analyses of variance (ANOVA) indicated that groups did not differ on age, HGSHS:A scores, or SHSS:C scores. All participants reported a distressing memory (relationship separation ¼ 25; death of loved one/ pet ¼ 12; accident ¼ 7; other ¼ 4). Table 1 presents the means for participants’ ratings of the qualities of the memory they nominated prior to hypnosis. There were no differences in terms of type of event reported, or involuntariness, frequency, distress, or vividness across retrieval conditions. Performance on the sustained attention task was not associated with any participant characteristics of hypnotisability score. 2.2. Manipulation checks Comparable numbers of participants did not recall the target memory in the experimental posthypnotic phase in posthypnotic amnesia (n ¼ 4) and intentional retrieval condition (n ¼ 6) conditions, c2 (1, n ¼ 10) ¼ 0.51, p > 0.05. These 10 participants were excluded from subsequent analyses. In terms of the reported reason for recalling the memory, more participants in the posthypnotic Table 1 Participant characteristics.
Age HGSHS:A SHSS:C Memory involuntariness Memory frequency Memory distress Memory vividness
Posthypnotic amnesia
Intentional retrieval
19.33 8.00 8.09 4.97 4.96 6.54 7.12
21.25 8.69 8.42 5.11 4.60 5.69 6.75
(1.61) (0.63) (0.98) (2.63) (2.36) (1.89) (1.60)
(8.16) (0.93) (1.12) (2.65) (2.78) (2.24) (1.85)
Note. Standard deviations appear in parentheses. HGSHS:A ¼ Harvard Group Scale of Hypnotic Susceptibility, Form A. SHSS:C ¼ Stanford Hypnotic Susceptibility Scale, Form C.
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Table 2 Mean ratings of memory qualities. Posthypnotic amnesia
Intentional retrieval
8.44 (0.65) 6.35 (1.73) 6.41 (2.06)
5.71 (2.66) 5.12 (1.93) 6.68 (1.88)
Postexperimental ratings Involuntariness 4.56 (1.10) Distress 2.80 (1.36) Vividness 3.35 (1.37)
2.87 (1.77) 2.39 (1.50) 3.13 (1.36)
Experimental ratings Involuntariness Distress Vividness
Note: Standard deviations in parentheses.
amnesia condition (95%) than intentional retrieval condition (12%) reported not knowing why they had recalled the memory [c2 (n ¼ 47) ¼ 14.39, p < 0.001]. One participant in the posthypnotic amnesia condition reported explicitly remembering the memory suggestion, and accordingly was excluded from subsequent analyses. The resulting sample comprised of 19 participants in the posthypnotic amnesia condition and 18 participants in the intentional retrieval condition. 2.3. Qualitative features of recalled memories Table 2 presents the mean ratings for involuntariness, distress, and vividness of memories made during the experimental phase. Participants in the posthypnotic amnesia condition reported that the memory was more involuntary [F(1,35) ¼ 14.85, p < 0.001, ή ¼ 0.32], and more distressing [F(1,35) ¼ 1.96, p ¼ 0.05, ή ¼ 0.11] than participants in the intentional retrieval condition. Table 2 also presents the mean ratings of memory qualities made by the independent rater of the postexperimental ratings. Participants in the posthypnotic amnesia condition reported that the memory was more involuntary [F(1,35) ¼ 11.27, p < 0.005, ή ¼ 0.27]. No differences were noted for vividness or distress ratings by participants or by independent raters. 2.4. Cognitive task performance Table 3 presents participants’ mean performance on the cognitive task before and after recall of the memory. A 2 (Retrieval Condition) 2 (Task Order) 2 (Time) ANOVA of correct responses on the cognitive task indicated a significant Retrieval Condition Time interaction effect [F (1, 35) ¼ 4.35, p < 0.05, ή ¼ 0.12], a significant Task Order Time interaction effect [F (1, 35) ¼ 12.53, p < 0.001, ή ¼ 0.28], and a significant three-way Retrieval Condition Task Order Time interaction effect [F (1, 35) ¼ 4.22, p < 0.05, ή ¼ 0.12]. To clarify the three-way interaction, we conducted separate 2 (Retrieval Condition) 2 (Time) ANOVAs for participants who performed Task A or Task B, initially. For participants who completed Task B first, there were no significant main or interaction effects. For participants who completed Task A first, there was a significant main effect for Time [F (1, 16) ¼ 26.32, p < 0.001, ή ¼ 0.62] and a significant Time Retrieval Condition interaction effect [F (1, 16) ¼ 17.28, p < 0.001, ή ¼ 0.52]. Follow-up Table 3 Mean performance on cognitive task.
Pre-recall Post-recall
Posthypnotic amnesia
Intentional retrieval
Order 1
Order 2
Order 1
Order 2
17.55 (5.18) 12.09 (5.41)
14.71 (2.06) 15.86 (3.29)
17.14 (3.43) 16.57 (3.87)
15.55 (3.83) 16.73 (3.85)
Note: Standard deviations appear in parentheses.
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comparisons indicated that after the memory retrieval cue, participants in the posthypnotic amnesia condition had a greater decrement in performance relative to their pre-retrieval cue than participants in the intentional retrieval condition (p < 0.05). 3. Discussion The present study explored the capacity for hypnosis to elicit and index intrusive autobiographical memories in controlled laboratory settings. The majority of participants across retrieval conditions reported experiencing the target memory upon hearing the cue phrase posthypnotically. Significantly, all participants except one in the posthypnotic amnesia condition indicated that they did not know why they had recalled the memory both at the point of recall and during the postexperimental inquiry, indicating posthypnotic amnesia for the memory suggestion and the posthypnotic amnesia suggestion. This extends past studies that have elicited psychological states and precluded awareness of the cause of the phenomena (Zimbardo et al., 1981, Zimbardo et al., 1993), and represents a novel application in the study of autobiographical memories. Our first hypothesis predicted that memories recalled after posthypnotic amnesia would be experienced as more involuntary compared to those that were intentionally retrieved. This was supported by ratings given at the point of recall as well as comments provided during the postexperimental inquiry phase (e. g., “It just popped into my head randomly”, “I have no idea why I just thought of that”). Our second hypothesis predicted that involuntary memories would be experienced differently to intentionally retrieved memories. As predicted, memories recalled after posthypnotic amnesia were more distressing than intentionally retrieved memories. Comments provided by participants in the posthypnotic amnesia condition during the postexperimental inquiry supported this trend (“I was really confused as to why I was thinking about that now. It was pretty upsetting”, “I just wanted to stop thinking about it”). This is consistent with previous studies that suggest the distress associated with intrusive memories is dependent not only on the negative content of the memories, but also on the degree to which they are unexpected (Berntsen, 2001; Dougall et al., 1999). Distress may also be related to individuals’ attributions of control regarding the unwanted experience of the target memory. Ehlers and Clark (2000) posit that negative appraisals regarding one’s control over the emergence and duration of intrusive phenomena result in increased levels of distress. Future research could elucidate upon the role of controllability in intrusive experiences by including measures of control appraisal. Contrary to predictions, memories experienced after posthypnotic amnesia were no more vivid than intentionally retrieved memories. There are several factors that may account for this. First, there is some evidence that differences in vividness between intrusive and non-intrusive memories occur along a continuum of psychopathology status. Across different types of memories (intrusive vs. non-intrusive), types of events (traumatic vs. non-traumatic), and across populations (trauma survivors with vs. without PTSD, and non-clinical populations) studies offering the greatest support for heightened vividness in intrusive memories are based on intrusive memories of traumatic events experienced in PTSD populations (Berntsen et al., 2003). These differences have been less pronounced for non-traumatic memories in non-clinical samples (e.g., Porter & Birt, 2001), such as those studied in the present experiment. Consistent with previous work on intrusions (Dougall et al., 1999; Hellawell & Brewin, 2002; Wegner, 1994), we expected that involuntary memories would interfere with ongoing task performance more so than memories that were intentionally retrieved. Results demonstrated partial support for this hypothesis in that participants in the posthypnotic amnesia condition demonstrated
a greater decrease in cognitive performance after recall compared to participants in the intentional retrieval condition, but only for the first counterbalancing order. Intrusive memories compete for cognitive resources (Clark & Rhyno, 2005; Lynch et al., 2007), perhaps as a paradoxical result of attempts to inhibit or suppress negative content (Rassin, Merckelbach, & Muris, 2001). For participants in the posthypnotic amnesia condition, tendencies to suppress may have arisen automatically given the unwanted nature of the experience. In contrast, participants in the intentional retrieval condition were specifically asked to think about the memory. As such, the motivation to remember may have superseded motivation to avoid the content of the memory. This effect was not found in the second counterbalancing order, which may reflect ceiling effects for the first version of the task. We note that our cognitive task did not employ an established measure of working memory. Future studies may wish to increase the cognitive load to ensure tasks are sufficiently demanding to index impairment on cognitive resources using more structured cognitive tasks. It is probable that the mechanisms underpinning hypnoticallyinduced intrusions are not the same as though occurring in clinical intrusions. Some models suggest that intrusive memories are the result of encoded information that is poorly elaborated and inadequately integrated into the general database of autobiographical knowledge (Ehlers & Clark, 2000). Although this information is potentially accessible via voluntary routes of retrieval, poor elaboration enhances the ease by which this information is retrieved via direct or automatic cues and consequently experienced as intrusive (Conway & Pleydell-Pearce, 2000; Ehlers & Clark, 2000). This view posits that although cues are initially specific, cues generalise over time to stimuli loosely connected with the event so that individuals are often unaware of cues and memories appear to come ‘out of the blue’ (Foa & Kozak, 1986). In contrast, hypnosis theories would propose that experiences following posthypnotic amnesia occur as a result of intention that is perceived as involuntary because of a dissociated control process that permits attributions of involuntariness to the experience. According to this perspective, hypnotic intrusions are more parsimoniously explained as memories that are misattributed to involuntariness rather than memories that are triggered by cues associated with a closely integrated network of representations pertaining to the memories. Several factors limit the generalisability of the current findings. First, we recruited from a non-clinical student sample and did not include psychopathology measures; conclusions regarding the experience of intrusive memories in clinical populations are therefore limited. Future research could replicate the current design with a clinical population to determine whether experimentally manipulating the route of retrieval demonstrates the same pattern of results. Second, we specifically recruited highly hypnotisable participants to maximise the success of the posthypnotic suggestion. We note that highly hypnotisable individuals differ along several dimensions compared to medium or low hypnotisable individuals. For example, highly hypnotisable individuals display higher levels of imagination (Lynn & Rhue, 1986), absorption (Roche & McConkey, 1990), and divided attention (Bowers & Brennenman, 1981). The extent to which the findings are generalizable to less hypnotisable individuals remains to be tested. Third, we recognise that participants may have been responding to the demand characteristics of the experiment; replication is required that utilises the real-simulating paradigm (Orne, 1979) in which unhypnotised individuals are asked to simulate the experience of a hypnotised person, which provides an index of demand characteristics and employs implicit measures of thought accessibility. Fourth, as the experimenters were aware of the study hypotheses, the possibility of experimenter bias cannot be ruled out.
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These limitations notwithstanding, this paradigm provides an alternate means to elicit intrusions under experimental conditions. Future studies could use this approach to elicit intrusions in the context of neuroimaging, during different mood states, following attempted thought suppression, and with varying instructions to manage intrusive thoughts.
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