The hearing test: Part of this complete speech-language evaluation
I always recommend including a hearing test as part of a speech-language evaluation, because a hearing loss may cause, or contribute to, a speech-language disorder. Speech-language pathologists are qualified to administer a hearing screen (a simple pass-fail procedure); a child who fails the screening is referred to an audiologist for a full evaluation.
You may remember the sort of "hearing test" you had at school, where you wore headphones and raised your hand when you heard a "beep". This was actually not a real hearing test, but a screening. It was probably performed, or at least supervised, by a speech-language pathologist. Public school SLPs typically provide hearing screenings for all students every few years (the exact requirements vary from state to state).
A screening does not provide a lot of information, compared to a full hearing test administered by an audiologist. Usually in a screening, all of the "beeps" are at 20 decibels, so if the child does not respond to one or more of the beeps, all we know is that s/he cannot hear sounds at that level or quieter. We don't know how loud the tone has to be for the child to hear it. Screenings are strictly pass/fail, so if the child passes (responds to all the beeps), nothing further is done. If s/he fails to respond to one or more of the tones, a referral is made for a more extensive hearing test with an audiologist.
It is important to remember that a child cannot be diagnosed as having a hearing loss based on a screen. For a diagnosis, there has to be further testing done by an audiolologist.
Sometimes a pediatrician will refer a child to an otolaryngologist if there are hearing concerns, or if the child has had a lot of ear infections. The otolaryngologist in turn may make a referral to the audiologist.
A full audiological exam may include some combination of the following, depending on your child's age and the exact nature of your concerns with his or her hearing. It probably will not include all of them.
Case history: This may consist of an interview, a written form that you fill out, or (usually) a combination of both.
A physical examination focusing the outer ear and ear canal. The audiologist will use an otoscope to check the inside of the ear canal for excess ear wax, foreign objects (you'd be amazed at what they sometimes find), structural abnormalities, signs of infection or inflammation, and damage to the ear drum.
Immittance: This is a test of middle ear function. The word immittance is actually a combination of the terms impedence (the extent to which sound vibrations are prevented from traveling through the middle ear to the cochlea) and admittance (the extent to which they are allowed through). The audiologist uses immittance testing to check for signs of fluid in the middle ear or a perforated eardrum.
Another thing this test can detect is the presence of the acoustic reflex, a sudden involuntary contraction of the stapedius and tensor tympani muscles in the middle ear in response to a loud noise (about 110 dB). These tiny muscles attach to the stapes and the malleus, two of the bones of the inner ear (ossicles). When activated, the acoustic reflex briefly dampens the vibrations transmitted through the middle ear to the inner ear by the ossicles. If the acoustic reflex is absent, this could be a sign of neural damage.
Pure tone audiometry: This is the classic "Raise your hand when you hear a beep" test, but an audiologist will go into more detail than the 20 dB screenings you get in the schools. For one thing, the audiologist will test more frequencies (in my school screens I do only four). Also, s/he will test for thresholds at each frequency. Which frequencies are affected by how much can tell a lot about what's wrong and how to address it.
An audiologist's pure tone audiometry usually includes a bone conduction test, where a vibrator is placed on the mastoid process, a bony formation just behind the ear. Actually, it can be placed anywhere on the skull, but the mastoid process is the most common site. The sound is transmitted through the bones of the skull directly to the inner ear, bypassing the outer and middle ear. This tells us specifically how well the inner ear is working, even if there is a conductive hearing loss.
What you can't do with a bone conduction hearing test is present the tone to just one ear at a time. No matter where on the skull you place the vibrator, the entire skull will vibrate and the sound will go into both ears. To get around this and test each ear individually, the audiologist may use masking. This involves inserting an earphone into one of the ears and playing "white noise" that is louder than the beep, preventing the patient from hearing the beep in that ear. Since the masking is presented by air conduction, the unmasked ear will be able to hear the tone when it is at or above the patient's hearing threshold. Then the process is repeated with masking in the other ear.
Speech Audiometry: Instead of "beeps," the child hears recorded words and responds appropriately, e.g., pointing at a picture that matches the word. Results of speech audiometry may include Speech recognition threshold, the lowest level at which the person can accurately hear 2-syllable words like baseball and airplane. This type of hearing test may also include word recognition results, the percentage of one-syllable words correctly identified when presented at normal talking level, about 60-70 dB.
Auditory Evoked Potentials (AEP): sometimes called auditory brainstem besponse (ABR) or brainstem auditory evoked response(BAER), this type of hearing test involves placing electrodes on the scalp to detect electrical fluctuations caused by brain activity. A click or tone is played through an ear phone, and the changes in electrical charge are recorded. This is a useful hearing test for young children, including newborns, because it is completely passive. In fact, it works best if the patient is asleep. In some cases, children may even be given a sedative, because it is so important to remain still and calm during the procedure.
The drawback of an AEP hearing test is that it is not very specific. It's kind of like looking out a window that's covered with a layer of ice--you can tell whether it's light or dark, and you can sort of see some colors and shapes and things moving, but there's a lot you can't tell.
Otoacoustic Emissions (OAE): Did you know your ear has an echo? And here you thought it was because your head was empty! When you put a sound into the cochlea, the sound is echoed back into the middle ear. This echo is called an otoacoustic emission, and it can actually be picked up by a small microphone inserted into the ear canal. The ear plug used for this test contains both a speaker and a microphone. A click is played through the speaker, and the microphone picks up the click as it echoes back milliseconds later. A good OAE response indicates that the cochlea is in good working order; if you have a hearing loss but good OAEs, the problem is probably retrocochlear, meaning after sound signals pass through the cochlea--either the auditory nerve or somewhere in the brain. This is important to know, because a retrocochlear loss may be a sign of a medical contition such as a lesion or tumor.
Nystagmus testing: If you are having difficulty with balance along with hearing, the audiologist may do a test to see how the semicircular canals are working. This involves putting very cold water into your ear canal and seeing if you get dizzy. If you do, it means that your semicircular canals are working the way they should. The cold water causes the fluid in the canals to flow inside them due to a process called thermosiphoning. The flowing of the fluid moves the hair cells inside the canals and gives you the sensation that your head is spinning. The audiologist will watch your eyes for back-and-forth movement (nystagmus) that indicates you're trying to compensate for your dizziness by fixing your position in space visually. I've never had this done to me, and frankly, that's okay. I'm getting a little nauseated just writing about it.
Although not actually a hearing test, this involves the ears, so it's often an Audiologist who does the testing. Because the semicircular canals are so close to the parts of the ear involved in hearing, they are often damaged by the same things that damage the hearing organs, especially the chochlea, such as viruses, toxins, and trauma.
If your child comes home from school with a note saying that s/he failed a "hearing test", please take it seriously, but don't panic. The kind of screening provided by schools cannot determine whether or not a child has a hearing loss, so it's important to follow up with an audiologist. An undiagnosed hearing loss can have a negative impact on a child's academic success and quality of life, but appropriate treatment can make a huge difference.
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