EMDR (Eye Movement Desensitization and Reprocessing) is an exposure-based procedure for the treatment of patients with post-traumatic stress disorder (PTSD). Although the efficiency of EMDR-treatment is empirically proven, it remains unclear whether the bilateral stimulation triggered via eye movements has specific effects on treatment outcome. Hypothesis explaining the efficacy of the EMDR treatment are: focussing on the moving hand triggers an orientation reaction, and the duality of alertness focus during trauma exposition causes a distraction of the traumatic topic.