What is Bilateral Stimulation?

Bilateral stimulation (BLS) is the rhythmic, alternating left–right sensory input used during Eye Movement Desensitization and Reprocessing (EMDR) therapy. It can be delivered visually (a moving target the client tracks with their eyes), auditorily (tones alternating between the left and right ear), or tactually (alternating taps or vibrations on the hands, shoulders or knees). BLS is one of the defining procedural elements of EMDR and is used across all eight phases of the standard protocol.

Bilateral stimulation was introduced by Francine Shapiro in 1987 and has since been studied extensively. Meta-analyses of randomized controlled trials show EMDR — of which BLS is a core procedural element — is an effective treatment for post-traumatic stress disorder and is recommended in guidelines from the World Health Organization, the American Psychological Association and the UK National Institute for Health and Care Excellence (NICE). Dismantling studies suggest the alternating stimulation contributes to working-memory taxation and vividness/emotionality reduction of target memories, though the exact mechanisms remain an active research area.

In clinical practice, therapists select the BLS modality that best fits the client's presentation, comfort and clinical context. Visual eye movements are the classical default; auditory or tactile BLS is preferred when eye tracking is uncomfortable, when the client wants to close their eyes, or during online sessions where camera bandwidth is limited. Speed and duration of sets are adjusted iteratively during Phase 4 (Desensitization) based on the client's SUD (Subjective Units of Disturbance) and observed processing. BilateralSync provides synchronized visual and stereo-panned auditory BLS with sub-100 ms latency, which lets clinicians apply the same procedural rigor online as in the room.