Hearing Testing

There are various types of hearing loss, most falling into one of two categories depending upon the origin of the loss. Conductive hearing loss can be localized to the outer or middle ear including the visible ear, the ear canal, eardrum, middle ear bones or any combination thereof. Sensorineural hearing loss involves the inner ear (cochlea/auditory nerve) and occurs when the hair cells, neural fibers or their connections to the cochlea are damaged or do not function properly. One can have both a conductive and sensorineural hearing loss which is then referred to as a mixed loss.MCZCarol

Our audiologists employ a variety of methods for identifying and diagnosing hearing loss in adults and children. These include pure tone testing, speech testing, testing of the middle ear, auditory brainstem response and otoacoustic emissions.

A pure-tone conduction hearing test determines the faintest tones a person can hear at selected pitches or frequencies, from low to high. During this test, earphones are worn so that information can be obtained for each ear. Sometimes, use of earphones is not possible, such as when a child refuses to wear them. In these cases, sounds are presented through speakers inside a sound booth (called sound-field screening).

The person participating in the test may be asked to respond to the sounds in a variety of ways, including raising a finger or hand, pressing a button or pointing to the ear in which they hear the sound or simply by stating yes, the sound was heard.  During the test, each test frequency (or pitch) is varied by intensity (or loudness) to determine the softest sound that can be heard. Thresholds for each ear are plotted on a graph or “audiogram”.

The audiologist will also conduct tests of listening and speech. These results are also recorded on the audiogram. One test that the audiologist conducts during a hearing test is the speech reception threshold (SRT). This is used with older children and adults, and helps to confirm the pure-tone test results. The SRT records the faintest speech that can be heard half the time. Then the audiologist will also record word recognition or the ability to correctly repeat back words at a comfortable loudness level.  Speech testing may be done in a quiet or noisy environment. Difficulty understanding speech in background noise is a common complaint of people with hearing loss, and this information is helpful. 

Hearing loss is measured in decibels (dB) and is typically described in the following general categories:

Normal Hearing (0 to 25 dB HL)
Mild Hearing Loss (26 to 40 db HL)
Moderate Hearing Loss (41 to 70 db HL)
Sever Hearing Loss (71 to 90 dB HL)
Profound Hearing Loss (greater than 91 dB HL)

If there is a blockage such as wax or fluid in the outer or middle ears, a method called pure-tone bone conduction testing may be employed. Here, the blockage is bypassed by sending a tone through a small vibrator placed behind the ear (or on the forehead). The signal reaches the inner ear (or cochlea) directly through gentle vibrations of the skull. The testing can measure response of the inner ear to sound independently of the outer and middle ears and can help determine the type of hearing loss being measured.


 Testing Hearing in Children

AHS employs audiologists that specialize in diagnosing and treating adult as well as pediatric hearing loss. Children present different challenges and require alternative testing methods. 
Our audiologists employ two primary types of hearing screening methods for newborns:  evoked otoacoustic emissions and visual reinforcement audiometry.
Evoked otoacoustic emissions (EOAE) is a test that uses a tiny, flexible plug that is inserted into the baby's ear. Sounds are sent through the plug. A microphone in the plug records the otoacoustic emissions (responses) of the normal ear in reaction to the sounds. There are no emissions in a baby with hearing loss. This test is painless and is usually completed within a few minutes, while the baby sleeps. 
Visual reinforcement audiometry is the method of choice for screening children between the ages of 6 months and 2 years of age. Here, the child is trained to look toward a sound source. When the child gives the correct response (e.g. looking toward the source of the sound when it is presented), the child is rewarded through a visual reinforcement such as watching a toy that moves or watching a flashing light.  This process is repeated at multiple sound frequencies.  The level at which the child stops responding determines the hearing threshold. 

Conditioned play audiometry is used for older children such as toddlers and preschoolers (ages 2-5). The child is trained to perform an activity each time a sound is heard. Such activities may include putting a block in a box, placing pegs in a hole, putting a ring on a cone, etc.

Tympanometry (also called impedance audiometry) is a test used to determine how the middle ear is functioning. It does not tell if the child is hearing or not, but helps to detect any changes in pressure in the middle ear and is used to help diagnose the type of hearing loss. 

Infants (under the age of six months) do best with testing when they have not napped or eaten prior to testing. If the screening tests identify that your child has a hearing loss, further testing is needed. It is recommended that all babies with hearing loss be identified by 3 months of age so that treatment can begin before the baby is 6 months old, an important time for speech and language development.  






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