Working memory refers to the processing when we bring information stored in our long-term memory into present and active use. Whereas long-term memory has limitless storage potential, our working memory is limited. In EMDR therapy, the dual task of bringing up the memory in our mind while simultaneously moving our eyes taxes the limits of working memory, thus making the memory less vivid and less emotional.
In application, the more dual tasks we add while maintaining focus on the traumatic memory, the easier it is for the brain to process the negative material and desensitize. The desensitized memory is then stored into long-term memory in its new, less intense state.