Article summary by EMDR: Eye movements superior to beeps in taxing working memory and reducing vividness of recollections by Van den Hout & Engelhard - 2010

What is EMDR?

EMDR (eye movement desensitization and reprocessing) was introduced about twenty years ago as a treatment method for PTSD. EMDR appears to be effective for PTSD, just as effective as cognitive behavioral therapy. In addition, significant effects of eye movements have been found, whereby eye movements during the recall of aversive memories diminish the vividness and emotionality of the memories. They are "labile" during recalling memories, which means they are influenced by the experiences they have during recalling. We use our working memory to recall memories, and the capacity of this working memory is limited. If we perform a second task while recalling a reminder, there is less capacity available for recalling. This reduces the liveliness and emotionality. Eye movements are such a "second task". EMDR uses the unstable state of reminders during recall and the fact that reconsolidation is influenced by the nature of recall reminders.

Horizontal and vertical eye movements are equally effective. Tasks that hardly need any capacity (such as simple finger tapping) have no effect, but more complex movements do. Not only can EMDR be used for traumas, it can also deal with negative ideas about future events. In addition, people who are bad at multitasking benefit more from, for example, eye movements while calling.

The main memory consists of three subsystems:

• Central executive (CE): the allocation and distribution of attention between tasks, activation of memory, recall of memories, inhibition of distraction and selection of retrieval strategies.
• Visuospatial sketchpad (VSSP): implement visuospatial information.
• Phonological loop (PL): implement verbal information.

Which components are influenced by tasks such as eye movements? In general, the theory states that there is modality specificity. Eye movements should affect the VSSP and verbal tasks on the PL. Research has found that eye movements reduce the vividness of images because they temporarily disrupt the preservation and manipulation of traumatic images in the VSSP. In general, it has been found that eye movements and counting, for example, have memory effects. These effects are both general, with influence on the CE, and modality-specific, with influence on the VSSP or PL.

An alternative to eye movements is binaural stimulation: the patient wears headphones and hears beeps right and left. No verified data has been reported for this method. The question is whether this way appeals to the WM because it does not require active cognitive or motor actions.

In five experiments the researchers of this article look at the effect of binaural stimulation and eye movements.

• In experiment 1 it was found that eye movements cause a substantial delay in the reaction time (in response to an auditory stimulus), which implies that eye movements influence the CE.
• In experiment 2 it was found that doing sums reduces the response time to visual stimuli.
• In experiment 3, a random interval repetition task (RIR) was used, in which reaction times were viewed, and the auditory stimuli were randomly offered. Response times for such a task are shorter than for other tasks. Substantially shorter reaction times were indeed found in this experiment than in experiments 1 and 2. This task may therefore be more sensitive to CE taxing. In this experiment it was also found that eye movements cause interference. CE sources also use binaural stimulation, but this effect is small compared to eye movements.
• In experiment 4 it was found that eye movements and the accompanying taxing of the WM decrease the liveliness and emotionality. Binaural stimulation has relatively little effect on the vividness of memories.

About 50% of EMDR treatments are performed using binaural information instead of eye movements. Binaural stimulation does indeed use the CE, but four times as little as eye movements do. Eye movements do not have stronger effects for emotionality than other methods, but for liveliness they do. Binaural stimulation also has an effect here, but this is only one third of the effect of eye movements. EMDR sessions are much longer in clinical practice, and it seems logical that the effects are also increased. It is not logical that an auditory task uses the VSSP, just as it is not logical that a visual task uses the PL. The data found in the experiments support the CE explanation of the eye movement part of EMDR.

There are a number of limitations to the experiments performed here. First, the clinical effects of binaural stimulation on eye movements are not tested. In addition, the quality of negative memories is assessed by self-reporting. Moreover, the long-term effects have not been tested.