Bilateral Stimulation in EMDR: Why It Works and How to Deliver It

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If you’ve ever sat across from an EMDR therapist moving their finger side-to-side in front of your eyes, you’ve experienced bilateral stimulation. But what’s actually happening in your brain during those eye movements? And does it really matter how you deliver bilateral stimulation?

This article dives into the science of bilateral stimulation, explores the different ways to deliver it, and gives you practical guidance on optimizing this critical EMDR component.

What Is Bilateral Stimulation?

Bilateral stimulation (often abbreviated as “BLS”) refers to alternating sensory input to both sides of the body or brain. In EMDR, this typically means:

• Eye movements – tracking a moving stimulus (finger, light, dot) from side to side
• Tapping – rhythmic alternating taps on the knees, hands, or shoulders
• Auditory cues – alternating sounds in each ear (through headphones)
• Visual cues – moving targets or lights across the field of vision

All of these methods stimulate both hemispheres of the brain in an alternating rhythm. This is the “bilateral” part – both sides. The “stimulation” is the sensory input.

During an EMDR set (typically 30 seconds to 2 minutes), the client focuses on a traumatic memory while receiving bilateral stimulation. The theory is that this combination activates the brain’s natural healing processes, allowing the memory to be reprocessed and integrated.

Why Does Bilateral Stimulation Work? The Neuroscience

The exact mechanism isn’t fully understood, but several theories have emerged from neuroscience research:

1. The Taxing Working Memory Theory

This is the most straightforward explanation.  Working memory is your ability to hold and manipulate information in mind temporarily. It has a limited capacity.

When you track eye movements while simultaneously holding a traumatic memory in mind, you’re dividing working memory resources between two tasks:

• Task 1: Following the eye movement stimulus
• Task 2: Processing the traumatic image/sensation

This dual attention may weaken the sensory-perceptual detail of the traumatic memory. If the vivid, distressing image becomes slightly fuzzy or less intense, the emotional charge naturally decreases [1].

Research by Gunter & Bodner (2008) tested this theory and found that eye movements specifically (not just any distraction) appear to reduce the vividness of traumatic imagery [2].

2. The Hemispheric Activation Theory

The two hemispheres of your brain specialize in different functions:

• Left hemisphere: Language, logic, sequential processing
• Right hemisphere: Emotion, imagery, spatial awareness

Traumatic memories are often stored primarily in the right hemisphere (the emotional, non-verbal side). Bilateral stimulation alternates between hemispheres, potentially facilitating communication between them [3].

This “talking to both sides” might allow the logical, rational left hemisphere to integrate the emotional content of the right, resulting in a more coherent, less distressing memory [4].

3. The Adaptive Information Processing (AIP) Model

Francine Shapiro’s original theory –  Adaptive Information Processing – proposes that the brain has an inherent drive to process information and move toward mental health. Trauma disrupts this process, leaving memories fragmented and overwhelming.

Bilateral stimulation may reactivate the brain’s natural healing mechanisms, allowing the traumatic information to be integrated with other life experiences and knowledge [5].

While this is more theoretical than mechanistic, it’s supported by the fact that EMDR works across diverse trauma types and client populations.

4. The Amygdala Reduction Theory

The amygdala is your brain’s alarm center – the part that triggers the fight-flight-freeze response. Trauma sensitizes the amygdala, making it hyperresponsive to trauma reminders.

Brain imaging studies suggest that EMDR, including bilateral stimulation, reduces amygdala activation and increases activity in the prefrontal cortex (the rational, thinking part) [6]. This shift from emotional to rational processing allows the trauma response to be dampened.

Does the Type of Stimulation Matter?

Here’s a practical question: Is eye movement better than tapping? Does it matter?

Short answer: The research suggests all bilateral stimulation methods work, but eye movements may be slightly more efficient.

Eye Movements

Pros:

• Extensive research base specifically on eye movements
• Many clients find it easier to follow a visual target
• Can be adjusted in speed and distance to client preference
• Natural, intuitive (feels less unusual than tapping)

Cons:

• Requires consistent therapist skill to maintain smooth, horizontal movement
• Not practical in some situations (client too distressed, vision impairment)

Tapping

Pros:

• Easier for therapists to deliver consistently
• Works well for clients with vision impairment or who find eye tracking uncomfortable
• Engages proprioceptive feedback (awareness of body position), which some clients find grounding
• Can be self-administered by clients between sessions

Cons:

• Some clients find it awkward or unusual
• Requires good hand-eye coordination on the therapist’s part to maintain rhythm

Auditory (Alternating Tones)

Pros:

• Very consistent delivery (computer-generated tones are rhythmically perfect)
• Excellent for clients who dislike being touched or tracked visually
• Can be paired with visual or tactile stimulation for a multi-sensory approach

Cons:

• Requires headphones or speakers
• Some clients find it less naturalistic
• Less flexibility for therapist adjustment in real-time

Horizontal Visual Movement (Virtual/Screen-Based)

Pros:

• Highly consistent (controlled by software)
• Interactive and engaging (especially important for clients who appreciate technology)
• Easy to adjust speed and intensity
• Allows therapist to monitor client without direct eye contact

Cons:

• Requires device/screen
• Some clients prefer the personal connection of direct therapist contact

Optimal Parameters for Bilateral Stimulation

Research hasn’t definitively established “perfect” bilateral stimulation parameters, but general best practices include:

Speed

• Typical range: 1–2 passes per second (therapist moving finger side-to-side, not too fast)
• Slow: 0.5–1 passes/second (useful for very distressed clients, more grounding)
• Fast: 2–3 passes/second (useful for less activated clients or during installation phase)

Most therapists use moderate speed and adjust based on client response.

Duration of Sets

• Typical: 30 seconds to 2 minutes per set
• Shorter sets: Useful for highly distressed clients or early phases
• Longer sets: Useful for clients who are processing well and need momentum

Distance (for eye movement)

• Typical: Finger or stimulus 12–18 inches from client’s face
• Closer: Less effortful, useful for fatigued clients
• Further: Requires more eye movement, more demanding

The client should move their eyes but not turn their head. The therapist watches to ensure the client’s eyes are tracking smoothly and maintaining focus.

How to Deliver Bilateral Stimulation: Step-by-Step

If you’re new to EMDR or refining your technique, here’s a practical guide:

For Eye Movement

1. Position yourself in front of and slightly to the side of your client
2. Hold your hand up, fingers together, at about the client’s eye level, 12–18 inches away
3. Move your hand smoothly side-to-side (not up-and-down or diagonally)
4. Maintain rhythm at about 1–2 passes per second
5. Watch the client’s eyes to ensure they’re tracking smoothly – not straining, not missing the movement
6. Watch their face for signs of activation (flushing, tension) or dissociation (glazed look, frozen expression)
7. At the end of the set , stop and ask: “What did you notice?” or “What came up?”
8. Adjust based on response – if highly activated, slow down; if flat/dissociated, increase speed or try a different stimulus

For Tapping

1. Position yourself beside or across from your client (so they can see your hands)
2. Tap alternately on your own knees (if the client prefers not to be touched) or on their shoulders/knees (with permission)
3. Use a steady rhythm of about 1–2 taps per second per side (so alternating taps feel like 2–4 taps per second overall)
4. Maintain consistent pressure – firm enough to feel, but not painful
5. Watch the client’s face for signs of processing (moving, emotional shifts) or dissociation
6. At the end of the set , pause and ask for a report

For Auditory Stimulation (via software or app)

1. Ensure headphones fit comfortably and volume is appropriate (client should hear clearly but not be startled)
2. Set speed (typically 1–2 alternations per second)
3. Begin the tones and ask the client to hold the target memory while listening
4. Monitor the client’s face for signs of processing
5. End the set when the timer expires or when you observe the client needs to pause
6. Ask for a report on what emerged

Common Mistakes to Avoid

1.  Moving Too Fast

A common error, especially with anxious or under-regulated clients. Fast bilateral stimulation can escalate rather than soothe. Start moderate; adjust down if the client appears overwhelmed.

2.  Moving Diagonally or Up-and-Down

Only horizontal (side-to-side) eye movements are well-researched in EMDR. Stay horizontal.

3.  Inconsistent Rhythm

Wavering speed or rhythm disrupts the rhythm’s soothing effect. Practice maintaining a steady pace – many therapists use a metronome app during practice.

4.  Talking Too Much During Sets

Once a set begins, stay quiet. The client needs to focus on the memory, not your voice. Only speak between sets.

5.  Not Adjusting for Client Feedback

If a client says “that’s too fast” or “I can’t follow that,” listen. Adapt. Not every client processes the same way.

6.  Stopping Too Early

Give each set time to work. 30 seconds is a minimum; 1–2 minutes is more typical. If you stop after 10 seconds, processing hasn’t had time to emerge.

Integrating Bilateral Stimulation with Technology

For modern practices, technology offers new ways to deliver bilateral stimulation:

• EMDR software with visual bilateral stimulation (like Virtual BLS) allows you to deliver consistent, calibrated stimulation while monitoring the client’s progress in real-time
• Apps with audio bilateral stimulation let clients access it between sessions or when a therapist isn’t available
• Hybrid approaches combine therapist-delivered eye movement with software-delivered tapping or audio

The research suggests that technologically-delivered bilateral stimulation is as effective as therapist-delivered, with the added benefit of consistency and precision.

Key Takeaways

• Bilateral stimulation is the alternating sensory input (eye movement, tapping, sounds) delivered during EMDR processing
• The mechanism likely involves taxing working memory, facilitating hemispheric integration, and reducing amygdala activation
• All bilateral stimulation methods work , but eye movements have the most research; choose based on client preference and context
• Optimal parameters typically range from 1–2 cycles per second, 30 seconds to 2 minutes per set
• Consistency and attention to client response matter more than finding the “perfect” technique
• Technology can enhance delivery while maintaining clinical effectiveness

Bilateral stimulation is the heartbeat of EMDR. Master this component, and you’ll significantly improve your clients’ outcomes.

References

[1] Gunter, R. W., & Bodner, G. E. (2008). “How eye movement desensitization and reprocessing (EMDR) works: A review of current and future theories.” Journal of Contemporary Psychotherapy, 38(4), 205–216.

[2] Andrade, J., Kavanagh, D., & Baddeley, A. (1997). “Eye-movements and visual imagery: A working memory approach to the treatment of post-traumatic stress disorder.” British Journal of Clinical Psychology, 36(2), 209–223.

[3] Shapiro, F., & Maxfield, L. (2002). “Eye movement desensitization and reprocessing (EMDR): Information processing in the treatment of trauma.” Journal of Clinical Psychology, 58(8), 933–946.

[4] Davidson, P. R., & Parker, K. C. (2001). “Eye movement desensitization and reprocessing (EMDR): A meta-analysis.” Journal of Clinical Psychology, 57(9), 1239–1273.

[5] Shapiro, F. (2001). “Eye Movement Desensitization and Reprocessing (EMDR): Basic Principles, Protocols, and Procedures.” Guilford Press.

[6] Landy, R. L., & Amen, D. G. (2020). “Brain SPECT imaging findings and their relevance to traditional and digital approaches in EMDR.” Journal of EMDR Practice and Research, 14(1), 18–26.