Bilateral stimulation is the use of visual, auditory, or tactile external stimuli occurring in a rhythmic side-to-side pattern.
Bilateral Stimulation Effects
Research has indicated that horizontal eye movement effects memory; improving episodic memory retrieval and reducing false memories, and reducing the vividness and emotional valence for both positive and negativeautobiographical memories. These effects have been shown to be achieved by horizontal eye movements, and also by alternating headphone beeps. However the quality of these results has been questioned. Poorer episodic retrieval is correlated with a high level of handedness. Eye movement has been found to improve communication between the brain hemispheres. This may cause the memory impacts above, and give benefits in handling difficult tasks, and in emotional processing. Ineffective coordination of brain hemispheres has been found to correlate with worrying. A high level of handedness is associated with poorer hemisphere communication,. Bilateral eye movements have been found to reduce asymmetries in hemispheric activation. Asymmetry in hemisphere activity has been found to be associated with depression, and anger. Some results have found that bilateral eye movements give increased EEG coherence between brain hemispheres, although others question this finding. One small study found a reverse result if eyes were kept open after the eye movement, but this study had several methodological limitations. One 2018 contribution questioned whether eye movements could facilitate accepting false information about an event, but others have rejected this concern.
Role of Bilateral Stimulation in EMDR
Bilateral stimulation is a core element ofeye movement desensitization and reprocessing therapy, a common treatment for post traumatic stress disorder. While the client thinks about distressing memories and feelings, the therapist uses external stimuli to facilitate bilateral stimulation. The treatment originally used only left-to-right eye movements as the bilateral stimulus but other forms of stimuli, often physical vibration in combination with binaural sounds, are now commonly being used as alternatives. Proponents of EMDR therapy hypothesize that bilateral stimulation assists clients in the processing of painful or traumatizing memories. In the most common form of treatment, the client focuses on a traumatic memory and the negative thoughts or feelings associated with that memory. The client then follows with their eyes while the therapist moves their finger or some other object in front of them from left to right. Alternatively, the therapist may choose to use other types of bilateral stimuli. The hypothesis is that doing this allows the client to access and reprocess negative memories, eventually leading to decreased psychological arousal associated with the memory. Therapy then focuses on fostering a positive belief or emotion in the client.
Types of bilateral stimulation
Eye movements are the main form of bilateral stimulation used for EMDR. Originally EMDR used only visual stimuli and the resulting eye movements to facilitate the therapy process. The creator of EMDR therapy, Francine Shapiro, postulated that eye movements in particular were a necessary part of the treatment. However, research found similar efficacy using other types of stimulation and other stimuli are now commonly used by EMDR practitioners. These alternative stimuli include auditory stimuli that alternate between left and right speakers or headphones, and physical stimuli such as tapping of the therapist’s hands.
