| Definition: |
Audiology tests your ability to hear sounds.
Sounds vary according to the intensity (volume or loudness) and the tone (the speed of sound wave vibrations). Hearing occurs when sound waves are conducted to the nerves of the inner ear and from there to the brain. Sound waves can travel to the inner ear by air conduction (through the ear canal, eardrum, and bones of the inner ear) or bone conduction (through the bones around and behind the ear).
The intensity of sound is measured in decibels (dB). A whisper is about 20 dB, loud music (some concerts) is around 80 to 120 dB, and a jet engine is about 140 to 180 dB. Usually, sounds greater than 85 dB can cause hearing loss in a few hours; louder sounds can cause immediate pain, and hearing loss can develop in a very short time.
The tone of sound is measured in cycles per second (cps) or Hertz. Low bass tones range around 50 to 60 Hz, while shrill, high - pitched tones range around 10,000 Hz or higher. The normal range of human hearing is about 16 Hz to 16,000 Hz. Some people can hear within a slightly higher range, and animals can hear up to about 50,000 Hz.
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| Alternative Names: |
Audiometry; Hearing test; Audiography; Audiogram
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| How the test is performed: |
General screening may be used to estimate the need for audiography. Specific procedures may vary, but they generally involve occluding one ear at a time and checking for the ability to hear whispers and then spoken words or the sound of a ticking watch. A tuning fork may be used to test your general ability to hear by air conduction and bone conduction. The tuning fork is tapped and held in the air on each side of the head to test the ability to hear by air conduction. It is tapped and placed against the mastoid bone behind each ear to test bone conduction.
Audiography provides a more precise measurement of hearing. Air conduction is tested by having you wear earphones attached to the audiometer. Pure tones of controlled intensity are delivered, usually to one ear at a time. You are asked to indicate (by raising a hand, pressing a button, or other means) when they hear a sound, and the minimum intensity (volume) required to hear each tone is graphed. An attachment is placed against the bone behind each ear to test bone conduction. |
| How to prepare for the test: |
Adults:
There is no special preparation.
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
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| How the test will feel: |
| There is no discomfort. The length of time varies. Screening may take about 5 to 10 minutes; detailed audiography may take about 1 hour. |
| Why the test is performed: |
| This may be a screening test to detect a hearing loss at an early stage. It may also be used when there is difficulty in hearing from any cause. Common causes of hearing loss include chronic ear infections, a ruptured eardrum, acoustic trauma, an occupational hearing loss, a head injury, inherited conditions, diseases of the inner ear, and complications of ototoxic medications (medications that can be toxic to the nerve of the inner ear, including certain antibiotics such as neomycin, diuretics such as Lasix, and large doses of salicylates such as aspirin). |
| Normal Values: |
The unimpaired ability to hear a whisper, normal speech, and a ticking watch is normal. The unimpaired ability to hear a tuning fork through air and bone is normal.
Audiography screening usually includes 2 tones of 256 Hz and 4,096 Hz delivered at 5 and 10 dB (the normal speech range). Detailed audiography shows normal hearing, with low tones (around 64 Hz) heard at 1 or 2 dB and high tones (11,584 Hz) heard at around 10 dB, and tones in between this range all heard at less than 10 dB. |
| What abnormal results mean: |
There are many different kinds and extents of hearing loss. Some include only the loss of the ability to hear high or low tones, or the loss of only air or bone conduction. The inability to hear pure tones below 10 dB indicates some extent of hearing loss. The extent and kind of hearing loss may give clues to the cause and the prognosis (probable outcome).
Conditions that may affect test results:
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| What the risks are: |
| There is no risk. |
| Special considerations: |
| There are many hearing function tests, from simple screenings (such as producing a loud noise and observing the test subject for a startle response) to complex, detailed measurements such as the auditory evoked responses test (BEAR), in which an electroencephalogram is used to detect brain wave response to sounds. |
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