Original EMDR therapy involved a subject with open eyes tracking a target that moves side to side.
It is now common for EMDR to use devices like electronic "tappers" to alternately stimulate the left and right sides of the subject's body, leaving the subject free to close his eyes and engage in visualizations related to the trauma being treated.
In general, during wakeful visualizations with my eyes closed I often move my eyes in a manner similar to REM sleep. I have tried a few sessions of EMDR and found it to be uncannily effective. During closed-eye EMDR I sometimes find myself engaging in REM based on my visualizations, and other times find my eyes moving side to side in synchrony with the "tappers."
My question: Are there any studies or theories that suggest eye movement in closed-eye EMDR is relevant to the efficacy of the therapy? E.g., does it matter whether the closed eyes move side to side if there is some other bilateral stimulation?