Blurring Aversive Memories by Dual Tasking

Background: Vivid intrusive traumatic memories are core symptoms of post-traumatic stress disorder. A technique for manipulating memory vividness and emotionality is used in eye movement desensitization and reprocessing (EMDR). In EMDR, patients are asked to recall traumatic memories while simultaneously making eye movements (EM). EMDR may be debated but, meta-analyses show that EMDR is very effective while EM are an active ingredient. This effect presumably occurs because dual tasks (e.g. making EM) tax working memory (WM), which leaves less WM resources available for simultaneous imagery of the memory, resulting in decreased vividness and emotionality of the memory when it is later recalled again (i.e. ‘blurring’; see van den Hout & Engelhard, 2012). According to WM theory, the blurring effect can be enhanced by adjusting the dual task load to an individual’s WM capacity. This experiment tested whether undergraduates with high WM capacity benefit more from high vs. low WM load during recall, and undergraduates with low WM capacity benefit more from low vs. high WM load. Method: To determine WM capacity, 120 students performed a reading span task. Students with the highest (n=36) and lowest (n =36) scores recalled three negative autobiographical memories in three conditions: recall + high WM load (fast EM), recall + low WM load (slow EM), and Recall Only. Results & Discussion: Results showed that compared to Recall Only performing either type of dual task (i.e. slow or fast EM) during recall reduced vividness and emotionality during later recalls, without dual tasking; an often documented finding. The largest reductions were found for high taxation of WM, followed by low taxation, and no taxation (i.e. recall only). This effect, however, seemed to be independent from WM capacity for vividness. The implications for the WM explanation and the clinical implications will be discussed, as well as directions for future research.