What Is Bilateral Stimulation in EMDR Therapy?

Updated 2026-08-16 · For EMDR-trained clinicians

Bilateral stimulation (BLS) is the rhythmic left–right sensory input used during EMDR therapy while a client holds a distressing memory in mind. This guide covers the three delivery modalities, how clinicians choose between them, and what the research does and does not establish.

The basic definition

Bilateral stimulation means alternating sensory input between the left and right sides of the body at a steady rhythm. In EMDR it is applied during the reprocessing phases while the client attends to a target memory, the associated body sensation, and the negative belief attached to it.

The original protocol developed by Francine Shapiro used guided horizontal eye movements. Auditory and tactile forms were added later and are now standard clinical options, particularly in remote work.

The three modalities

Visual (eye movements)

The client tracks a moving stimulus — the therapist's hand, a light bar, or a dot moving across a screen — while holding the target in mind. This is the modality used in most of the original research base. It requires the client to be able to sustain visual tracking, which makes it harder in low-vision, migraine-prone, or heavily dissociative presentations.

Auditory (alternating tones)

A tone alternates between the left and right ear through stereo headphones. It frees the client's gaze entirely, which many clients find less effortful, and it lets them close their eyes — often useful when eye contact itself is activating. It is also the modality that travels best: it needs only headphones and a phone.

Tactile (alternating taps or buzzes)

Alternating physical taps, delivered by handheld pulsers, by the therapist tapping the client's knees or hands, or by the client crossing their arms and tapping their own shoulders (the butterfly hug). Useful when auditory and visual channels are both unavailable or overwhelming.

Choosing a modality in practice

There is no clinical consensus that one modality outperforms the others across the board, so the choice is usually driven by the client and the setting:

• Client preference and tolerance. A client who finds tracking tiring or who reports headaches after eye-movement sets will usually process more comfortably with tones.
• Remote sessions. Visual BLS delivered over a video call is at the mercy of frame rate and connection quality; a dropped frame breaks the rhythm at exactly the wrong moment. Auditory BLS played locally on the client's own device is unaffected by connection quality.
• Dissociation. Some clinicians prefer tactile or auditory input when grounding is a concern, since it keeps a body-based anchor available.
• Environment. In a shared or noisy clinic, headphones give a boundary that hand movements do not.

Many clinicians switch modality mid-course rather than committing to one — for example, using eye movements in the consulting room and tones for remote sessions with the same client.

Speed, sets and tone

Beyond modality, three parameters shape how a set feels:

• Speed. Faster alternation is generally used during desensitisation; slower rhythms are typical for resource installation, calm-place work and closure.
• Set length. Set length is adjusted continuously in response to what the client reports between sets, rather than fixed in advance.
• Tone or pitch. With auditory BLS, a lower tone is often experienced as less intrusive; a client who winces at a bright tone will process differently once it is softened.

The clinically important point is that all three are adjusted during processing, not set once at the start. That is why therapist-side control of the stimulation matters in remote sessions: if the client is the one holding the controls, each adjustment interrupts the very state you are trying to maintain.

What the evidence says

EMDR itself is recommended for post-traumatic stress disorder in major clinical guidelines, including those of the World Health Organization and the UK's National Institute for Health and Care Excellence. That recommendation is for the full eight-phase protocol delivered by a trained clinician.

The specific mechanism by which bilateral stimulation contributes is still debated. The main hypotheses are working-memory taxation (the dual task reduces the vividness and emotional charge of the recalled image) and an orienting-response account. Studies comparing modalities have generally not found large differences between visual, auditory and tactile delivery.

What follows practically is that a therapist can choose the modality that best fits the client and the setting without treating it as a compromise on fidelity — provided the rest of the protocol is delivered as trained.