I didn't know that! Issue# 23- Audiometry

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Pure-tone audiometry is completed in a soundproof booth—a room with special treatment to the walls, ceiling, and floor to ensure that background noise does not affect test results. Only those sounds that the audiologist introduces into the room, either through earphones or through speakers located in the room, will be heard. Sounds may also be sent through a special headset "vibrator" that has been placed just behind the ear or on the forehead.

In testing hearing for tones, a pure tone air conduction hearing test is given to find out the faintest tones a person can hear at selected pitches (frequencies) from low to high. During this test, earphones are worn and the sound travels through the air in the ear canal to stimulate the eardrum and then the auditory nerve. The person taking the test is instructed to give some type of response such as raising a finger or hand, pressing a button, pointing to the ear where the sound was received, or saying "yes" to indicate that the sound was heard.

Sometimes children are given a more play-like activity (conditioned play audiometry) to indicate response. They may be instructed to string a peg, drop a block in a bucket, or place a ring on a stick in response to hearing the sound. Infants and toddlers are observed for changes in their behavior such as sucking a pacifier, quieting, or searching for the sound and are rewarded for the correct response by getting to watch an animated toy (visual reinforcement audiometry).

The audiologist uses a calibrated machine called an audiometer to present tones at different frequencies (pitches) and at different intensity (loudness) levels. A signal of a particular frequency (something like a piano note) is presented to one ear, and its intensity is raised and lowered until the person no longer responds consistently. Then another signal of a different frequency is presented to the same ear, and its intensity is varied until there is no consistent response. This procedure is done for at least six frequencies. Then the other ear is tested in the same way.

The frequency or pitch of the sound is referred to in Hertz (Hz). The intensity or loudness of the sound is measured in decibels (dB). The responses are recorded on a chart called an audiogram that provides a graph of intensity levels for each frequency tested.

In some cases, it is necessary to give a pure tone bone conduction hearing test. In this test, the tone is introduced through a small vibrator placed on the temporal bone behind the ear (or on the forehead). This method "bypasses" blockage, such as wax or fluid, in the outer or middle ears and reaches the auditory nerve through vibration of skull bones. This testing can measure functionality of the inner ear independently of the functionality of the outer and middle ears.

Air conduction test results indicate hearing losses that are either conductive or sensorineural. Bone conduction test results reflect only the sensorineural component. By comparing air conduction and bone conduction test results, the audiologist can determine whether there is a hearing loss due to a problem in the outer or middle ear. If air and bone conduction thresholds are the same, the loss is sensorineural. If there is a difference between air and bone thresholds (an air-bone gap), the loss is conductive or mixed.

American Speech-Language-Hearing Association