Over the past 15 years, memory researchers have published consistent evidence of the impact of eye movements (EMs) on working memory (Andrade, Kavanagh, & Baddeley, 1997; Engelhard et al., 2011; Engelhard, van Uijen, & van den Hout, 2010; Gunter & Bodner, 2008; Lilley, Andrade, Turpin, Sabin-Farrell, & Holmes, 2009; Maxfield, Melnyk, & Hayman, 2008; van den Hout et al., 2010; van den Hout et al., 2011). This evidence supports the hypothesis that working memory is critical in explaining the documented effects of eye movement desensitization and reprocessing (EMDR; Bisson & Andrew, 2007; Schubert & Lee, 2009) on the intrusive memories of patients with posttraumatic stress disorder (PTSD).
In their article on the effects of EMs on positive memories, Hornsveld et al. (2011) provide additional evidence of the impact of EMs on selected aspects of positive memory recall but overstate the relevance of their findings to resource development and installation (RDI; Korn & Leeds, 2002) as well as to the interhemispheric interaction hypothesis (Propper & Christman, 2008). Their study design carefully and effectively investigates the impact of EMs similar to those used during EMDR on the “vividness, pleasantness, and experienced strength” of positive emotional memories. They do so by specifically removing their subjects from a therapeutic setting, working with an undergraduate population, and excluding all elements of the RDI protocol except those specifically related to episodic recall of the memory. They also specifically avoid critical aspects of the RDI protocol designed to enhance vividness of recall and to facilitate associative processing. All of these decisions enhance the study’s ability to specifically measure the impact of EMs, and just EMs, on selected aspects of immediate memory recall. The result is a powerful design, freed from the complications (and goals) of clinical use, which allows them to conclude that EMs act to reduce the vividness, pleasantness, and experienced strength of recently recalled positive memories. But, at the same time, the design disqualifies the authors from making any claims about the relevance of their findings to the clinical usage of EMs in EMDR and, more specifically, in RDI.
Hornsveld et al. (2011) dramatically overstate the implications of their findings when they claim that the “effectiveness of bilateral stimulation in RDI is questionable” (p. 146). Because their research design specifically excluded essential elements of the full RDI procedure and failed to measure clinical outcomes, it cannot indicate whether or not EMs significantly add to RDI’s effectiveness in the stabilization phase of treatment of patients with Disorders of Extreme Stress Not Otherwise Specified (DESNOS; also referred to as “Complex PTSD”) or of any other clinical or nonclinical population.
In fact, their findings of the impact of isolated EMs on positive memories in college students do not contradict our clinical observation that many DESNOS patients experience an increased sense of physical and emotional well-being during the RDI procedure, as the goal of the RDI procedure is not (as Hornsveld et al.  would have us believe) to install positive memories or to make positive memories more vivid or emotional. Rather, the positive memories and imagined scenarios that are accessed during RDI help the patient create and rehearse new positive coping skills constructed from a range of associations linked to remembered and imagined images, feelings, sensations, beliefs, and actions. These new memories form the resources, which, when unconsciously activated or deliberately recalled, allow patients to access an adaptive state (comprising a complex network of recalled memories, feelings, and action tendencies) that can help them face both the stressors of day-to-day life and the challenges of EMDR trauma-focused therapy. This is why the process is called resource development and installation and not simply “positive memory recall.” Within the framework of the AIP model (Shapiro, 2001), the RDI protocol (Korn & Leeds, 2002) postulates that these adaptive states support new coping responses, although new resources also can be thought of as similar to the new “pathways” to “discrete behavioral states” described in Putnam’s (1997) model of discrete behavioral states.
We acknowledge that some patients report decreased vividness for sensory qualities in their positive memories and images after EMs. (Hornsveld et al’s  subjects actually showed no significant decrease in pleasantness after horizontal EMs compared to no EMs [p = 0.16], and based on their Cohen’s d score of 0.57, 28%, showed increased vividness.) When decreased vividness does occur during RDI, the RDI protocol directs clinicians to repeat the subject’s sensory descriptors to reinforce their recall. Indeed, our personal clinical observations are that many patients report at least some immediate, additional, emotionally salient, sensory details during the RDI process and that most report an experience of entering into the world of their resource memories and images in a way that leaves a lasting sense of their increased accessibility. These two observed features of the RDI process—increased sensory detail and increased accessibility—are not evaluated by the research design selected by Hornsveld et al. (2011).
Still, one can ask, how might we reconcile the findings of Hornsveld et al. (2011) with the clinical success of RDI (Korn & Leeds, 2002; Leeds, 2009)? Of course, one solution is the one Hornsveld et al. champion, namely that RDI works despite the allegedly detrimental effects of the EMs and that RDI would work even better without them. However, their study provides no evidence in support of this solution. It is similar to claiming that because exercise can leave some people feeling weak and exhausted, whatever health benefits accrue from going to the gym would be even greater if one just did not exercise. Extending the metaphor, although some people feel weak and tremulous in overworked muscles after a new exercise program, most feel calmer, more toned, and more alert. One reconciliation might be afforded by assuming, as with the gym analogy, that the apparent weakening of the vividness and emotion of the memory seen in some patients reflects processes that actually increase the effectiveness of RDI. How might this be?
Another proposed mechanism of EMDR, the “REM/Orienting Response” (REM/OR) hypothesis, argues that, as in REM sleep, the goal of the EMs is to facilitate a form of memory processing that “results in the identification, integration, and enhancement of those aspects of memories calculated to be most important” (Stickgold, 2008, p. 290). This integration process includes “the activation [during REM sleep] of more distant associations than seen either in non-REM sleep or in the normal wake state” (Stickgold, 2008, p. 295). Support for these claims can be found in the work of Kuiken et al. (Kuiken, Bears, Miall, & Smith, 2002; Kuiken, Chudleigh, & Racher, 2010) who investigated undergraduates reporting recently experienced significant loss or trauma. Among these students, EMs increased the extent to which metaphoric sentence endings were reported to be “striking.” This increased attentional flexibility provides an explanation for another widely reported effect of BLS in the standard EMDR protocol that is not explained by the working memory hypothesis—namely, that BLS frequently leads to spontaneous positive associations to adaptive memories and to an increased likelihood, during EMDR psychotherapy, of recalling previously forgotten or dissociated disturbing memories (Lipke, 1995; Paulsen, 1995). When following the actual RDI procedure, such increased attentional flexibility may lead patients to recall additional sensory details and associated positive memories. Based on the REM/OR hypothesis, this processing of memories and associations results in clinical RDI patients experiencing increased self-capacities to respond to stressors in a more adaptive and self-affirming ways (Korn & Leeds, 2002; Leeds, 2009).
Hornsveld et al. (2011) do not merely overstate the significance of their findings for the role of EMs in the RDI procedure. They also overstate the implications of their findings for the interhemispheric interaction hypothesis (Propper & Christman, 2008). Although we do not disagree with their statement in the abstract that their findings provide “no support for the interhemispheric hypothesis” (Hornsveld et al., 2011, p. 146), we do take issue with their conclusion that interhemispheric interaction “does not seem to be an important mechanism to strengthen adaptive responses during the resource development protocol” (Hornsveld et al., 2011, p. 153). The study was not designed to test this hypothesis and, in fact, did not.
RDI, with its EMs, does work. Consistent and widespread clinical observations support our contention that the full RDI protocol produces notable gains in coping skills and well-being for DESNOS patients (see review of case reports in Leeds, 2009). Hornsveld et al. (2011) admit that major elements of the full RDI protocol were omitted from their research design including (a) individualized exploration and identification of salient and meaningful qualities needed to address a particular stressor; (b) elicitation of associations via the question, “What are you feeling or noticing now?”; (c) strengthening of the resource; (d) mental rehearsal of installed resources in the context of an identified stressor (future template); and (e) behavioral re-evaluation. Given these omissions from their research protocol, Hornsveld et al. can conclude nothing about the clinical effectiveness of EMs in the context of the full RDI protocol. Given that Hornsveld et al. overreach in their conclusions and disregard the existence of evidence supporting the REM/OR mechanism, EMDR trainers, consultants, and clinicians should feel comfortable in continuing the standard practice of combining EMs with the Calm Place/Safe Place and RDI procedures until such time as direct controlled tests of the full RDI procedure argue otherwise.
It may indeed be true that bilateral EMs lessen the vividness or emotionality of positive memories. The working memory hypothesis may accurately describe the mechanism behind this effect, but there are most likely multiple mechanisms underlying the actions of EMDR and RDI. The possibility that the working memory hypothesis is one of these does not mean that the EMs of RDI are counterproductive. The test that is needed—that has been needed for more than 10 years—is to randomly assign DESNOS patients with identified and measured coping problems to alternate conditions: one an RDI procedure without any bilateral (or other distracting) sensory stimulation and one with bilateral EMs. As we argued in 2002, and continue to believe today, only a study that randomly assigns DESNOS patients to either EM or no-EM conditions, with prebehavioral and postbehavioral measures, can assess the contribution of EMs to RDI. Such research is long overdue.
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