EMDR FORUM ARCHIVE, 2000
Re: differential mechanism
Cahill · 11/04/01 at 1:49 PM ET
Part 6: (you) From my point of view the dismantling studies are not convincing. The major problem here is that the so-called control condition of eye fixation actually evokes similar patterns of brain activation as eye-movements (see Corbetta M, Akbudak E, Conturo TE, Snyder AZ, Ollinger JM, Drury HA, Linenweber MR, Petersen SE, Raichle ME, Van Essen DC, Shulman GL. 1998. A common network of functional areas for attention and eye movements. Neuron, 21: 761-73.) Shapiro tries to account for this in the recent revision of her textbook my referring to dual attention rather than bilateral stimulation. First, going back to the distinction I discussed earlier between operational uses of terms vs. functional uses of terms, I think it's pretty clear that my comments were on the operational aspects of eye movements or other bilateral stimulation (i.e., the things therapists do to instantiate bi-lateral stimulation or dual attnention). Dismantling studies investigate whether removing particular therapist activities designed to induce bilateral stimulation (telling participants to track the therapists fingers as they are moved rapidly back and forth across the participants' visual field, telling participants to alternate tapping left and right fingers, the therapist alternating left-right finger snaps, etc.) significantly alters the efficacy of the treatment. To date, there are no convincing data to indicate that such procedures contribute significantly to treatment outcome. Your response, however, proposes that because similar patterns of brain activation are obtained in eyes fixed conditions as in eye movement conditions. In other words, the eyes fixed conditions were functionally eye movement conditions despite the differential therapist procedures. This kind of argument is similar to exposure therapist who have "explained" failures of exposure therapy in terms of "functional exposure" (or the lack thereof): Despite the therapist activities, some people engage in subtle forms of avoidance or safety behaviors that reduce the actual exposure to the feared stimulus and thereby prevent habituation/emotional processing/ extinction (or whatever) from occurring. Although I think such explanations warrant consideration, we also need to be careful that such "explanations" do not degenerate to circular reasoning. For example, I treat an OCD patient with intensive exposure and response prevention and they don't get better. Why didn't they get better? Because they didn't achieve functional exposure (despite all my efforts to get them into their feared situations and despite my efforts to block their rituals). How do I know they didn't achieve functional exposure? Because they didn't get better. And around and around it goes. To prevent such circular reasoning, we must be able to assess the whether or not the behavioral intervention alters the hypothesized underlying mechanisms in the desired direction that is independent of outcome. At present, the explanation that these alternative activate small eye movements or the same brain states as eye movements and that this "explains" the current data remains post-hoc at this time. Second, let's consider the data that need explaining and see if this hypothesis provides an adequate account of the extant dismantling studies. Dismantling studies have compared EMDR with a variety of control procedures. A. Eye movements vs. other forms of laterally alternating: 2. Bauman & Melnyk (1994) - participants engaged in alternate finger tapping with eyes open. Evidence of improvement, but no untreated control group. No difference between conditions. Perhaps alternate tapping or focusing eyes ahead engaged either small eye movements or dual attention. 3. Foley & Spates (1995) - a spatially moving tone. Both groups superior to waitlist, no difference between groups. Best evidence so far…Treatment worked and alternating spatial tones constitutes bilateral stimulation and dual attention. 4. D. Wilson et al. (1996) - participants engaged in alternate thumb tapping in time with a metronome. EMDR was superior to tapping on increasing VoC and skin temperature, decreasing SUDs and GSR. No outcome data (e.g., diagnostic status) were reported. Tapping in this study involved both bilateral stimulation and dual attention, but had no effect on the dependent measures. Theoretically, why should this be the case? Unfortunately, the lack of outcome data preclude knowing whether there were any group differences on the effectiveness of treatments on the target condition. How does your (or Shapiro's) hypothesis account for the discrepancy between D. Wilson et al. and all the other studies? B. Eye movements vs. Eyes open and fixed: 2. Gosselin & Mathews (1995) - eyes fixed on stationary finger. Evidence of improvement over time, but no waitlist control group and no difference between conditions. 3. Dunn et al. (1996) - eyes focussed on a fixed dot. Reduction in SUDs and reduction in heartrate over the course of treatment, but no difference between groups despite using a yoking procedure that potentially biases results in favor of the index (or "master") treatment (EMDR in this case). No waitlist control group. 4. Devilly et al. (1998) - eyes focused on a stationary flashing light. Some evidence that EMDR and the eyes fixed condition were slightly better than a standard psychiatric support group immediately after treatment, but the differences disappeared at 6 month follow-up. No differences between EMDR and eyes fixed. 5. Foley & Spates (1995)- participants were instructed to "rest his/her eyes on his/her hands." Both EMDR and no eye movemnts more effective than no treatment, but no difference between treatments. 6. D. Wilson et al. (1996) - this condition differed from EMDR only in that "subjects performed no eye movements." This description does not make clear whether subjects eyes were open or closed, whether they fixed on a particular point, or whether the therapists moved their fingers across the participants' visual field. Results were the same as for the alternate tapping condition described above: EMDR superior on SUDs, VoC, skin temperature and GSR during treatment, but no outcome data available. 7. Feske & Goldstein (1997) - eyes fixed on a stationary finger. Evidence that both treatments were superior to waitlist control and that EMDR was somewhat more effective immediately after treatment, but the difference disappeared at 3-month follow-up. How does your (or Shapiro's) theory account for the discrepancy between most studies showing no difference between EMDR and eyes fixed and the two studies that show at least some superiority for eye movements on either process measures (D. Wilson et al.) or short-term, but not long-term, outcome (Feske & Goldstein)? C. EMDR vs. eyes closed: 2. Boudewyns & Hyer (1996) - Decrease in HR in both treatment conditions, but not control group (received neither treatment). Significant decrease in SUDs for both treatment groups. Decrease in Profile of Mood States scores for both treatments but not control. No differences between treatments on any of the above. All three groups showed decreases on the CAPS, but no differences among groups. How does your (or Shapiro's) theory account for the pattern of SUDs in Boudewyns et al. (1993) where eye movements reduces SUDs during therapy, but not at the posttest when eye movements were not induced? How does your (or Shapiro's) theory account for the equal efficacy on outcome measures for EMDR and eyes closed in Boudewyns & Hyer (1996)? Third, lets consider an implication of the hypothesis that all of the above variations, when they work, recruit either adequate levels of eye movements (i.e., the nominal no eye movement groups are functionally eye movement groups) or that they in some other way induce similar levels of brain activity (perhaps in the thalamus). If we assume that the Boudewyns & Hyer (1996) results are not a fluke, then it seems your (or Shapiro's) theory would functionally equate EMDR with imagery with eyes closed and no additional procedures by the therapist to induce some kind of bilateral stimulation or some kind of dual attention. At this point, how is EMDR functionally different from any other imagery technique. In other words, this theory reduces exposure therapy to a form of EMDR or (since exposure therapy has a longer history) EMDR to a form of exposure therapy. Yet, many proponents of EMDR absolutely resist the idea that EDMR is fundamentally a form of imaginal exposure with a several add-on elements of no, very limited, or unknown additive efficacy. Finally, Shapiro at one time (Shapiro, 1991) tossed out the possibility that the eye movements served as a distraction. It seems that she and others now reject this position due to evidence to suggest that distraction impedes the efficacy of exposure therapy. According to your post, Shapiro is now entertaining the idea that eye movements and other stimuli constitute a dual task, and that is what is important. How is a "dual task" different from "distraction"? If we view attention as a capacity- limited resource, then how does splitting those resources across two tasks enhance processing of the trauma memory? Perhaps this is addressed in the revised edition of Shaprio's book, but at present I only own the 1995 edition. I realize that in this section, I am in some respects asking you to defend Shapiro's position, rather than your own. If your position is different from hers, please feel free to only address your own position.
From our prior exchange
(me) Dismantling studies have shown that eye movements are not necessary. They have also shown that bi-lateral stimulation of other sorts are also not necessary: one can do "EMDR" with eyes fixed and without replacing it with some other form of laterally alternating stimuli and still get comparable outcome
You have said that you are skeptical of the dismantling studies because "the so-called control condition of eye fixation actually evokes similar patterns of brain activation as eye movements." You then note Shapiro's recent attempt to integrate these findings in terms of dual attention. I have four general reactions to this proposal.
1. Pitman et al. (1996) - although patients were instructed to fix eyes forward, the therapists moved their fingers back and forth across the visual field and participants tapped a finger rhythmically (not alternating). Some evidence of limited improvement, although no untreated control to rule out passage of time, repeated assessments, etc. No difference between conditions. Perhaps just having the therapist move their fingers across the visual induces some small eye movements that are enough to recruit the same brain mechanisms. Or perhaps tapping a single finger engages dual attention, or perhaps attempting to focus straight ahead engages either small eye movements or dual attention.
1. Renfrey & Spates (1994) - eyes fixed on a light. Evidence of improvement over time, but no waitlist control group to rule out passage of time, repeated assessments, etc. No difference between conditions.
1. Boudewyns et al. (1993) - EMDR resulted in greater SUDs reduction during therapy and a greater number of participants rated as "treatment responders" by their therapist. However, there were no differences on standardized outcome measures. Further, neither group was any better than a control group that received neither treatments. The failure to see differences on standardized outcome measures is often explained by the limited number of sessions. However, this doesn't account for the discrepancy between in-session measures that suggested improvement and outcome measures that saw no improvement. More importantly for this discussion, however, is the observation that there were no differences among the three groups at the posttreatment assessment on SUDs that were obtained during script driven imagery of the index trauma (i.e., the memory targeted in treatment) when eye movements were not being induced by the therapist. Certainly, this is not evidence that eye movements enhanced processing of the memory.
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