AUDITORY BLS · 17
Auditory bilateral stimulation, in perfect stereo.
A clinician-facing reference to auditory BLS — when to use it, how it works, and how BilateralSync delivers it online with the same fidelity as in-room hardware.
DEFINITION
Auditory bilateral stimulation is a form of BLS in which a tone alternates between the left and right ear, typically through stereo headphones, providing the dual-attention task without requiring the client to track a visual target.
What is auditory BLS?
Alternating stereo tones deliver bilateral stimulation to the auditory system. The therapist controls speed, tone frequency, volume and the depth of the left-right pan.
When to choose auditory over visual
When oculomotor tracking is fatiguing, when the client wants to close their eyes, or by preference. Auditory BLS also frees the client's gaze for interoceptive attention.
Delivering auditory BLS online
BilateralSync generates the audio through the Web Audio API directly in the client's browser, so latency is essentially the latency of the client's own audio subsystem — not the network. Visual and auditory BLS stay in perfect sync when used together.
Frequently asked questions
What is auditory bilateral stimulation?＋
Auditory BLS is a form of bilateral stimulation in which a tone alternates between the left and right ear, typically through headphones. It is used when eye tracking is uncomfortable or when the client prefers to close their eyes.
Why use alternating audio during EMDR?＋
Alternating stereo audio provides the same dual-attention task as visual BLS while allowing the client to close their eyes. It is useful when oculomotor tracking is fatiguing, for clients with visual conditions, or by client preference.
Does auditory BLS work as well as visual?＋
Studies comparing modalities have not consistently favoured one over another. Auditory BLS is a validated modality within standard EMDR protocol.
Do clients need headphones?＋
Yes. Stereo panning depends on the left and right channels being separated at the ear — laptop speakers do not reliably deliver the effect. Any wired or wireless stereo headphones work.
Related reading
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Auditory Bilateral Stimulation
Auditory bilateral stimulation uses tones alternating between the left and right ear. Learn how stereo BLS is used in EMDR and how to configure it online.
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How bilateral stimulation music and stereo-panned tones work in EMDR. Evidence, use cases and how to deliver auditory BLS reliably online.
Theory & Research
How Bilateral Stimulation Works
How does bilateral stimulation work in EMDR? A clear overview of working-memory theory, orienting response and current evidence for the mechanism of BLS.