Much confusion tends to result when the outcomes of the three types of component studies (see What has research determined about EMDR's eye movement component) are combined. Because these studies differ substantially in design, purpose, participants, and outcome measures, they have produced a wide range of results: (1) In dismantling studies with analogue participants, EMs do not contribute to outcome, possibly because of a floor effect. (2) In clinical dismantling studies with diagnosed participants, there has been a consistent nonsignificant trend for a treatment effect. (3) In the component action studies a consistent significant effect for EMs in isolation was found in reducing the vividness of, and affect associated with, autobiographical memories; it is possible that such effects may contribute to treatment outcome. In the Davidson and Parker (2001) meta-analysis, no effects were found for EMDR-with-EMs compared to EMDR-without-EMS, when all types of studies were included. However, when the results of the clinical dismantling studies were examined, EMDR-with-EMs was significantly superior to EMDR-without-EMs.
Various reviews of the related EM research have provided a range of conclusions. Some reviewers (e.g., Lohr, Lilienfeld, Tolin, & Herbert, 1999; Lohr, Tolin, & Lilienfeld, 1998) stated that there is no compelling evidence that eye movements contribute to outcome in EMDR treatment and the lack of unequivocal findings has led some reviewers to dismiss EMs altogether (e.g., McNally, 1999). Other reviewers (e.g., Chemtob et al., 2000; Feske, 1998; Perkins & Rouanzoin, 2002) identified methodological failings (e.g., lack of statistical power, floor effects) and called for more rigorous study.
Numerous controlled studies have also indicated that eye movements cause a decrease in imagery vividness and distress, as well as increased memory access.
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