types of testing
Several methods can be used to test hearing, depending on a child's age, development, and health status.
Behavioral tests involve careful observation of a child's behavioral response to sounds like calibrated speech and pure tones. Pure tones are the distinct pitches (frequencies) of sounds. Sometimes other calibrated signals are used to obtain frequency information.
The behavioral response might be an infant's eye movements, a head-turn by a toddler, placement of a game piece by a preschooler, or a hand-raise by a gradeschooler. Speech responses may involve picture identification of a word or repeating words at soft or comfortable levels. Very young children are capable of a number of behavioral tests.
Physiologic tests are not hearing tests but are measures that can partially estimate hearing function. They're used for kids who can't be tested behaviorally (due to young age, developmental delay, or other medical conditions) and at any age to find which function of the auditory system is at fault.
auditory brainstem response (ABR) test
For this test, tiny earphones are placed in the ear canals and small electrodes (which look like small stickers) are placed behind the ears and on the forehead. Usually, click-type sounds are introduced through the earphones, and the electrodes measure the hearing nerve's response to the sounds. A computer averages these responses and displays waveforms.
An infant may be sleeping naturally or may have to be sedated for this test. Older cooperative kids may be tested in a silent environment while they're visually occupied.
Because there are characteristic waveforms for normal hearing in portions of the speech range, a normal ABR can predict fairly well that a baby's inner ear and lower part of the auditory system (brainstem) is functioning normally in that part of the range. An abnormal ABR may be due to hearing loss, but it may also be due to some medical problems.
otoacoustic emissions (OAE) test
This brief test is performed with a sleeping infant or an older child who may be able to sit quietly. A tiny probe is placed in the ear canal, then many pulse-type sounds are introduced and an "echo" response from the outer hair cells in the inner ear is recorded. These recordings are averaged by a computer.
A normal recording is associated with healthy outer hair cell function. In some cases, despite a healthy outer hair cell function, a hearing loss may be present if it's due to problems in other parts of the hearing pathways.
ABR or OAE tests are used at hospitals to screen newborns. If a baby fails a screening, the test is usually repeated. If the screening is failed again, the baby is referred for full hearing evaluation.
Tympanometry is not a hearing test but a procedure that can show how well the eardrum moves when a soft sound and air pressure are introduced in the ear canal. It's helpful in identifying middle ear problems, such as fluid collecting behind the eardrum.