Module 5 — Bilateral Stimulation | EMDR Course
- Jun 5
- 7 min read
Updated: Jun 8
Free Course by Everything IFS Academy | Therapeutic Modalities Series
Module 5 — Bilateral Stimulation
Of everything in EMDR, one element is the most recognizable and the most asked about: the back-and-forth eye movements, and the wider family of techniques they belong to. This is bilateral stimulation, the engine of the whole method. It is what people picture when they picture EMDR, and it is the part that has drawn both the most fascination and the most argument. This lesson covers what it is, the forms it takes, how it is delivered, and the leading ideas about why it does anything at all.
What Bilateral Stimulation Is
Bilateral stimulation, often shortened to BLS, is rhythmic, alternating left-right sensory input applied while a person holds a memory in mind.
The key word is alternating. The stimulus moves steadily from one side to the other and back, left, right, left, right, at a regular pace. On its own, that would be nothing more than a metronome for the senses. What makes it bilateral stimulation in the EMDR sense is that it happens while the person's attention is also turned toward the target memory. This pairing has its own name: dual attention. The person keeps one foot in the present, tracking the external rhythm in the safety of the room, while the other foot stays in the past, in contact with the memory being worked on. Because of this, the technique is also called dual attention stimulation. Holding both at once, the now and the then, is the active ingredient, and it is what separates EMDR's eye movements from simply watching a moving object.
The Three Forms of Bilateral Stimulation
Bilateral stimulation does not have to mean eye movements. It comes in three main forms, and all three deliver the same alternating left-right rhythm through a different sense.
Eye movements. The original form, and the most studied. The person tracks a moving target with their eyes, traditionally the therapist's fingers sweeping side to side, or a light moving along a bar, while keeping the head still. This is the version EMDR is named for and the one most of the research has examined.
Tactile, or tapping. Alternating taps delivered to the two sides of the body, for example on the backs of the hands or the tops of the knees, or through small handheld devices that buzz gently in turn. Touch carries the same left-right rhythm for people who find eye movements uncomfortable or hard to sustain.
Auditory tones. Soft tones that alternate between the left and right ear, usually through headphones, so the rhythm arrives as sound. This form is easy to use at a distance and is common in remote sessions.
The three forms give EMDR its flexibility, letting the work fit the person and the setting. In practice they are largely treated as interchangeable, chosen for fit; all three are widely used and regarded as effective, with the eye movements the most heavily researched, since they are the original form and the one most studies have tested.
The Butterfly Hug
One form of tactile stimulation deserves its own mention, because it is the piece of EMDR most likely to be useful outside a therapist's office: the butterfly hug.
It is a way of giving bilateral stimulation to oneself. The arms are crossed over the chest, each hand resting on the opposite upper arm or shoulder, so the position itself looks a little like a hug. From there, the hands tap the shoulders alternately, left, then right, in a slow, steady rhythm, the crossed arms suggesting the butterfly the technique is named for.
Its origins are humanitarian. It was originated by Lucina Artigas, with her colleague Ignacio Jarero, while working with survivors of Hurricane Pauline in Acapulco, Mexico, in 1998, as a way to bring bilateral stimulation to large groups of distressed people at once, including children, without a therapist needing to guide each person's eyes. That heritage is exactly why it travels so well. It needs no equipment, no partner, and no special setting, which makes it one of the few EMDR-derived tools a person can genuinely use on their own to steady themselves. It is now widely taught as a self-soothing and grounding technique, and it turns up well beyond formal EMDR, in classrooms, in disaster relief, and in ordinary moments of stress.
How It Is Delivered: Sets, Passes, and Speed
Bilateral stimulation is not one continuous stream. It is delivered in sets, short bursts of the back-and-forth rhythm with brief pauses between them. A single left-to-right-and-back movement is one pass, and a set is a series of passes strung together, after which the stimulation stops for a moment before the next set begins. The number of passes in a set, and how many sets are used, vary with the person and the work.
Speed varies too, and it is not arbitrary. Faster, more demanding stimulation tends to be used during active reprocessing, when the goal is to keep the system moving. Slower, gentler stimulation is used when the goal is to settle and steady, for instance when reinforcing a calm internal state. The pace is matched to the purpose.
Underneath all of it sits that same dual attention, the split focus between the safe present and the memory being worked on. That focus is the real demand bilateral stimulation places on the mind, and it sits at the center of the leading explanations for why the technique works.
Why It Might Work
This is where EMDR gets most interesting, and most contested. No one can yet say with certainty why bilateral stimulation helps. Several explanations have been proposed, each with some support, and they are not mutually exclusive. These are the leading ideas.
Working memory taxation. This is the best-supported explanation. Working memory is the mind's small, short-term workspace, where it holds and juggles information in the moment, and it has a strict limit on how much it can hold. Recalling a vivid memory uses that workspace, and so does tracking a moving target or a rhythm. Doing both together forces them to compete for the same limited space. Something has to give, and what gives is the vividness of the memory. As it loses detail and intensity in the crowded workspace, its emotional charge drops with it. Laboratory studies have repeatedly shown this dual-task effect: a disturbing image recalled while doing a demanding tracking task becomes less vivid and less upsetting.
The orienting response. Any new or alternating stimulus triggers a built-in reflex of attention, an automatic turn toward the input to check what it is, sometimes called the orienting response. As the brain examines the rhythmic stimulus and finds no threat in it, a relaxation response can follow. Some researchers think this repeated cycle of alerting and finding safety helps the nervous system treat the old memory as something that is over rather than something still dangerous.
REM and sleep-like processing. The eye movements of EMDR resemble those of REM sleep, the dreaming stage in which the brain naturally sorts and integrates emotional memories. The idea here is that bilateral stimulation may nudge the waking brain into a similar memory-processing mode, doing in a session something like what the sleeping brain does on its own. A related version points to the slow brain waves of deep sleep, which also play a part in consolidating memory.
Interhemispheric communication. The brain has two hemispheres that tend to specialize, very roughly, in the more logical and the more emotional sides of experience. Because bilateral stimulation alternates left and right, some have proposed that it increases the traffic between the hemispheres, helping the thinking and feeling parts of the brain work together so a memory can be processed in a more integrated way.
These explanations overlap, and several may be partly true at once. The most likely picture is a combination, with working memory the strongest single thread and the rest still under study.
What the Evidence Shows
It would be easy to come away from the debate about mechanism thinking the whole therapy is shaky. That would be a mistake, and the distinction is what clears it up. Two separate questions are in play. One is whether EMDR works. The other is exactly how the bilateral stimulation contributes.
On the first question, the evidence is strong. A large body of trials supports EMDR as an effective treatment for trauma, which is why major health organizations recommend it. On the second, the picture is less settled. Studies comparing reprocessing with and without the stimulation often find an advantage when it is present, especially for how vivid and disturbing a memory feels, so the stimulation does seem to add something. But the working-memory account suggests it is not the eye movement itself that is magical: what matters is a demanding task competing with the memory for mental space. That cuts two ways. It is not that any idle distraction would do, since a wandering mind is not the same demand, but it is also probably not the case that left-right eye movement is uniquely and exclusively powerful. How much the stimulation adds, and through exactly which mechanism, is what researchers continue to argue about.
Holding both at once is the fair position. The therapy's results are well established. The precise reason the stimulation helps is not yet pinned down. A method can be reliably effective while its inner workings are still being mapped, and bilateral stimulation is a clear case of exactly that.
Below this lesson, you'll find an EMDR practice along with a few ways to begin noticing and practicing it in everyday life this week.
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