A controversial treatment for post-traumatic stress disorder involves the traumatised person holding a painful memory in mind while simultaneously following with their eyes the horizontal movements of their therapist's finger.
Known as Eye Movement Desensitisation and Reprocessing therapy (EMDR), the approach seems to be beneficial and is recommended by the U.K.'s health advisory body NICE. However, EMDR remains controversial largely because experts can't agree on why it works.
Now Raymond Gunter and Glen Bodner have tested three possible explanations. In all the experiments, students were asked to recall an occasion that made them feel anxious, fearful or distressed.
An initial experiment showed that, relative to staring straight ahead, eye-movements increased arousal levels. This seems to undermine the "investigatory-reflex" account for why EMDR works: the idea that eye movements activate an innate investigatory reflex that inhibits fear and provokes relaxation.
A second experiment showed that both horizontal and vertical eye movements reduced the vividness and emotionality of the students' memories. Given that vertical eye movements (unlike horizontal ones) don't enhance hemispheric communication, this finding appears to undermine the "increased hemispheric communication" account for why EMDR works. This is the idea that horizontal eye movements aid interhemispheric communication, thus allowing the more rational left hemisphere to process the right hemisphere's traumatic memories.
A final experiment showed that the students' memories became less vivid and emotional, not only when they performed concurrent horizontal eye movements, but also if they instead performed a simultaneous simple hearing task. This undermines the idea that EMDR works specifically by taxing the so-called "visuo-spatial sketch-pad" of working memory. It suggests instead that the mechanism underlying EMDR is a more general effect based on taxing the big boss of short-term memory - the central executive.
If it's true that taxing the central executive of working memory is key to EMDR's success - what's going on? "The experience of holding a traumatic memory in mind, made more palatable by the central executive's attentional resources being taxed, may ultimately work to foster acceptance of those memories," the researchers said.
In other words, performing a concurrent task, be it eye movements or some other distraction, while also recalling a painful memory, allows a person to be exposed to that memory, without having the mental resources available to get too upset by it. Over time, this process acts like a form of gentle exposure to the memory, as the person learns that they can, after all, cope with their past.
R GUNTER, G BODNER (2008). How eye movements affect unpleasant memories: Support for a working-memory account Behaviour Research and Therapy, 46 (8), 913-931 DOI: 10.1016/j.brat.2008.04.006