How Does the Acoustic Reflex Work?
Reviewed by Dr. Porter on February 11, 2022
The acoustic reflex is an involuntary muscle movement in the middle ear. It’s vital to good hearing because of what it prevents rather than because of what it does.
The acoustic reflex keeps us from hearing ourselves talk or sing, and it also protects the inner ear from the pressure caused by loud sounds.
How the Acoustic Reflex Modifies the Effects of Sound
If you were to Google for more information on the acoustic reflex, you would find article that refer to this phenomenon as the auditory reflex, the middle-ear muscle reflex, the attenuation reflex, the stapedius reflex or stapedial reflex, the intra-aural reflex, or the cochleostapedial reflex.
All of this complicated terminology refers to the way the middle ear shields the inner ear from unwanted sound.
You probably already know that tiny bones in the ear vibrate when sound enters the ear.
Their movements stimulate nerve endings that generate electrical signals that are sent to the brain.
When a really loud sound enters the ear, two muscles around these tiny bones, the tensor tympani and stapedius muscles, contract to block the sound from traveling further into the ear.
The stapedius muscle pulls the “stirrup” bone back from the sound wave front.
The tensor tympani muscle pulls the ear drum in front of the “hammer” bone.
This doesn’t eliminate the sensation of sound, but it greatly reduces the intensity of sound experienced in the brain.
The effect reduces the intensity of sound by 20 decibels—or about 99 percent.
This is the way the acoustic reflex protects you from the shock of an explosive sound and keeps you from being overwhelmed by the sound of your own voice.
As you might imagine, when something goes wrong with your acoustic reflex, hearing problems can result.
What Are the Symptoms of a Problem with the Acoustic Reflex?
When your acoustic reflex isn’t working properly, you hear repeated loud noises without protection to your middle ear.
The result of having to hear lots and lots of loud sounds over an extended period of time is a condition known as listener fatigue.
Listener fatigue can make you feel tired. You may “tune out” not just the problem sound but a lot of the information ordinary sounds convey.
You may lose your sensitivity to timbre, tone, and pitch. You may want to tune out everything you hear.
Acoustic reflex issues often are caused by nerve problems, including a relatively uncommon kind of tumor known as an acoustic neuroma.
When this is the underlying cause of an acoustic reflex problem, symptoms like these may arise:
- Hearing loss in just one ear. Since this kind of tumor most commonly affects just one ear, there will usually be hearing loss in just one ear. Your ability to hear high frequencies will be affected first. There can be a feeling of fullness in just one ear, and tinnitus (ringing in the ear) in just one ear. Acoustic neuromas that affect both ears are rare.
- Hearing loss that comes and goes. Acoustic neuromas don’t always exert the same pressure on structures in the ear. Loss of hearing from acoustic neuromas usually comes on slowly, while other kinds of damage to the acoustic nerve can be more abrupt.
- Headache and problems with equilibrium and balance as the tumor grows. These usually aren’t problems at first. Hearing issues start before headaches and dizziness.
How Does Your Audiologist Test for Problems with Your Acoustic Reflex?
Testing the acoustic reflex is simple, fast, and painless. Your audiologist will inform you that you are going to hear some loud sounds in one ear at a time.
Your audiologist will place a probe in one ear and play a loud sound, about as loud as an excited crowd in a football stadium.
The probe will register whether the muscles in your middle ear responded to the sound.
There are some patients that we don’t test for acoustic reflex issues.
If you have an outer ear infection, or if you have “recruitment” Issues (you have trouble hearing a single voice in a crowd), or if you are very sensitive to sound, or you already have tinnitus, we may do other kinds of testing.
Harbor Audiology Can Help
The hearing specialists at Harbor Audiology are dedicated to providing you with timely care so you can enjoy the best hearing possible.
We offer evening and Saturday appointments, and we are experienced with VA and insurance claims of all kinds.
Harbor Audiology has offices in Gig Harbor, Tacoma, Sequim, Silverdale, Port Angeles, and Bainbridge Island.
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