Journal of Behavior Therapy and Experimental Psychiatry
The impact of eye movements and tones on disturbing memories involving PTSD and other mental disorders
Introduction
Posttraumatic stress disorder (PTSD) is an anxiety disorder that is rooted in the experience of events involving actual or threatened death or serious injury, or the threat to the physical integrity of oneself or others (American Psychiatric Association, 2000). Individuals with PTSD repeatedly experience their traumatic event in the form of aversive and disturbing memories, nightmares, distressing dreams, hallucinations, and flashbacks. One of the most effective therapies for the treatment of such unpleasant memories is eye movement desensitization and reprocessing (EMDR). Clinical trials and meta-analyses demonstrate that EMDR is an evidence based treatment for PTSD, and equally effective as trauma-focused cognitive behavioral therapy (Bisson et al., 2007; Seidler & Wagner, 2006).
A core feature of EMDR therapy is that the patient is asked to hold a disturbing memory in mind while engaging in sets of eye movements or other bilateral stimuli, such as taps or tones (Lee & Cuijpers, 2013; Shapiro, 2001). In the original description of EMDR it was assumed that the bilaterality of the presented stimulus was a necessary factor to stimulate trauma recovery. However, evidence is mounting to support an explanation based upon a working memory model. The theory underpinning this model states that recalling an episode uses working memory capacity, which in itself is limited (Baddeley, 2012). Since a traumatic memory is inherently intense, vivid and emotionally charged, it taxes working memory resources when it is recalled. If at the same time another task (i.e. client's eyes following the therapist's hand back and forth) is executed during recall, fewer resources would be available for the memory (Baddeley, 2012). This competition within the working memory results in less memory resources for the vividness and the disturbance or emotionality of the memory (e.g. Andrade, Kavanagh, & Baddeley, 1997; Gunter & Bodner, 2008; Hornsveld et al., 2010). Consistent with hypotheses from a working memory theory, memories have been found to not only becoming less disturbing, and less vivid, during execution of an eye-movement task (e.g. Gunter & Bodner, 2008), but also during a range of other working memory taxing tasks (for an overview see van den Hout et al., 2012).
Two studies have investigated the effects of taxing working memory with trauma images using a clinical population with a PTSD diagnosis. Lilley and his colleagues used a within-subjects design in which 18 patients completed an imagery task under three concurrent task conditions: eye movements (following a letter flashing up on alternate sides of computer screen), counting, and exposure only (without a concurrent task) (Lilley, Andrade, Turpin, Sabin-Farell, & Holmes, 2009). The participants selected three distressing images each. Each image was assigned to a condition that comprised eight trials in which the participants were asked to recollect the image for 8 s while performing one of the three tasks. Vividness and emotionality of each of the images was assessed before and after the intervention. The eye-movement task reduced vividness and emotionality of the distressing images relative to the counting task and exposure only. In the other study (van den Hout et al., 2012) 12 PTSD patients were asked to recall the traumatic event while performing three tasks in counterbalanced order: eye movements (visually tracking the therapist's fingers), listening to tones, and just recalling the event. The results showed that eye movements were superior to tones in reducing emotionality and vividness of the trauma memories, whereas tones and ‘recall only’ had both similar, negligible effects. Interestingly, despite the fact that the application of eye movements was (far) more effective than auditory tones in almost all patients, eight out of 12 patients preferred the tones, while only three preferred the eye movements.
Key to the working memory explanation of EMDR therapy is the question of whether the findings observed translate to other memories than those involving PTSD per se. To this end, EMDR is increasingly applied as a treatment for other (anxiety) disorders (De Jongh and Ten Broeke, 2009a, De Jongh and Ten Broeke, 2009b), such as driving phobias (De Jongh, Holmshaw, Carswell, & van Wijk, 2011), and other conditions and symptoms that developed following an adverse event (see for instance De Jongh & Ten Broeke, 2009b; Maxfield & Melnyk, 2000). If the working memory model is a valid explanation for what occurs during EMDR, it would mean that taxing working memory is effective in resolving negative memories that play a role in, or underlie, a broad variety of psychological symptoms and conditions.
The purpose of the present study is two-fold. First, it was aimed at replicating previous clinical studies that tested the working memory explanation of EMDR, using a larger sample size to increase statistical power, thereby lending more credibility to the conclusions. As eye movements have been found to tax working memory more than tones, and tones more than ‘recall only’ (van den Hout et al., 2011), it was predicted that eye movements would outperform tones, whereas tones would outperform ‘recall only’ in diminishing emotionality and vividness of patients' crucial upsetting memories. As van den Hout et al. (2012) found that treatment efficacy did not coincide with preference of the patients, patients were not only asked for preferences, but also for the reason a particular task was evaluated as most effective. The second main aim of the study was to investigate whether results found in PTSD patients could be extrapolated to patients with other mental health conditions. It was hypothesized that the experimental tasks would have similar effects on memories of patients with other diagnoses than PTSD.
Section snippets
Participants
Inclusion criteria for patients were at least 18 years old, indicated by their therapist for EMDR, but never having received EMDR treatment before, good command of the Dutch language and any valid clinical diagnoses based on the DSM-IV-TR (American Psychiatric Association, 2000) as determined by their therapist. The final sample consisted of 64 patients (50 females; mean age = 35.6 yrs, SD = 11.2; range = 19–61 yrs; education levels: 9.4% low, 48.4% middle, 39.1% high, and 3.1% unknown). It appeared
General effects on emotionality and vividness
First, it was tested whether the procedure as a whole was effective in terms of reduction of emotionality and vividness. Main effects of time on emotionality (F (1.98, 114.80) = 60.27, p < .001, ηp2 = .51) and on vividness (F (2.08, 122.66) = 27.49, p < .001, ηp2 = .32) were significant, indicating a decrease across the four measurement points. Posthoc analyses examining the decline per time-block showed that all decreases were significant (see Table 2).
Differences between eye movements, auditory tones, and ‘recall only’
Table 3 shows the emotionality and vividness scores.
Discussion
In this study all patients underwent two widely used variations of EMDR (eye movements and bilateral tones via a headphone), and a control (‘recall only’) condition. The results showed that eye movements outperformed ‘recall only’ in diminishing emotionality of patients' crucial upsetting memories. This is in accordance with van den Hout and his colleagues who performed a similar clinical study in 12 PTSD patients (van den Hout et al., 2012). Both studies showed a mean decrease of about 1 SUD
Conflict of interest
None.
Acknowledgments
We are grateful to Francine Shapiro for providing helpful comments on an earlier draft of this paper, Irene Aartman for statistical advice, and Marieke Meijerink for providing language help.
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