6 - (IOP 6) Dual-task Interventions Reduce Vividness and Unpleasantness in Both Old and New Memories

Eye Movement Desensitization and Reprocessing (EMDR) is an evidence-based psychological therapy for individuals with posttraumatic stress disorder (PTSD). A core element of EMDR therapy is recalling a traumatic memory while concurrently making horizontal eye movements. Experimental studies using EMDR lab analogues show that recalling a negative autobiographical memory while making eye movements (i.e., Recall+Dual-Task) reduces memory vividness and unpleasantness compared to control (i.e., Recall Only) (Mertens et al., 2021).

Over the last 15 years, disentangling studies have critically tested why eye movements (and other tasks) in EMDR are effective. Their effectiveness is now frequently explained by taxation of working memory (van den Hout & Engelhard, 2012). According to this theory, the processes of both memory recall and making eye movements vie for finite working memory resources. Memory recall, specifically visually imagining the event, requires maintenance and active rehearsal of visuospatial elements that are necessary for imagery. Executing eye movements requires the same storage capacity. As a result, this competition disrupts the maintenance and rehearsal of visuospatial memory elements necessary for imagery. This subsequently diminishes the vividness and unpleasantness of the memory during future recalls.

Memory age may limit intervention effectiveness, as older memories undergo greater consolidation and strengthening over time, making them less susceptible to change. However, this contrasts with clinical observations showing that EMDR effectively treats PTSD symptoms from older traumas, including childhood trauma. Thus, this topic is not only theoretically relevant but also practically significant, particularly because EMDR has recently been recommended as an early intervention within the first three months after trauma, highlighting its effectiveness for relatively new memories (Roberts et al., 2019).

To investigate this, participants aged 18 to 80 from diverse backgrounds were recruited from the general population to increase the generalizability of the results and ensure a broad range of memories, including those that could be classified as old. In Experiment 1, participants (N = 195) were instructed to recall a new or old negative autobiographical memory and were randomly assigned to a Recall+Dual-Task intervention or a Recall Only intervention. Before and after the intervention the memory was rated on vividness and unpleasantness. In Experiment 2 (N = 356), the same design as Experiment 1 was used, with the addition of a follow-up assessment one day later to examine potential delayed effects of memory age on intervention effectiveness and to assess the persistence of these effects.

Collectively, the two experiments show that Recall+Dual-Task immediately reduces memory vividness and unpleasantness compared to Recall Only. For unpleasantness this differential effect remained one day later. However, none of the effects were moderated by memory age. These findings indicate that memory age does not limit the effectiveness of dual-task interventions. Therefore, dual-task interventions, as used in EMDR, may be equally effective for treating traumatic memories of different ages.