A commonly proposed hypothesis is that dual attention stimulation elicits an orienting response. The orienting response is a natural response of interest and attention that is elicited when attention is drawn to a new stimulus. There are three different models for conceptualizing the role of the orienting response in EMDR: cognitive/information processing (Andrade et al., 1997; Lipke, 1999), neurobiological (Bergmann, 2000; Servan-Schreiber, 2000; Stickgold, 2002) and behavioral (Armstrong & Vaughan, 1996; MacCulloch & Feldman, 1996). These models are not exclusive; to some extent, they view the same phenomenon from different perspectives. Barrowcliff et al. (2001) posit that the orienting in EMDR is actually an “investigatory reflex,” that results in a basic relaxation response, upon determination that there is no threat; this relaxation contributes to outcome through a process of reciprocal inhibition. Others suggest that the inauguration of an orienting response may disrupt the traumatic memory network, interrupting previous associations to negative emotions, and allowing for the integration of new information. A study by Kuiken, Bears, Miall & Smitth (2001-2002) which tested the orienting response theory indicated that the eye movement condition was correlated with increased attentional flexibility. It is further possible that the orienting response induces neurobiological mechanisms, which facilitate the activation of episodic memories and their integration into cortical semantic memory (Stickgold, 2002). This theory has recently received experimental support (Christman and Garvey, in press). Further research is needed to test these hypotheses.
There are several research studies (e.g., Andrade et al., 1997; Kavanaugh et al., 2001; van den Hout et al., 2001) indicating that EMs and other stimuli have an effect on perceptions of the targeted memory, decreasing image vividness and associated affect. Two possible mechanisms have been proposed to explain how this effect may contribute to EMDR treatment. Kavanaugh et al. (2001) hypothesize that this effect occurs when EMs disrupt working memory, decreasing vividness, and that this results in decreased emotionality. They further suggest that this effect may contribute to treatment as a “response aid for imaginal exposure” (p. 278), by titrating exposure for those clients who are distressed by memory images and/or affect. Van den Hout et al. (2001) hypothesize that EMs change the somatic perceptions accompanying retrieval, leading to decreased affect, and therefore decreasing vividness. They propose that that this effect “may be to temporarily assist patients in recollecting memories that may otherwise appear to be unbearable” (p. 129). This explanation has many similarities to reciprocal inhibition.