Newborn Infant Hearing Screening (cont.)
What is an ABR test?
In order to process sounds, electrical impulses are transmitted through
nerves from our ears to the brainstem at the base of the brain. An auditory
brainstem response (ABR) is a physiological measure of the brainstem's response
to sound. It tests the integrity of the hearing system from the ear to the
brainstem. The test is performed by placing four to five electrodes on the
infant's head, after which a variety of sounds is presented to the infant
through small earphones. As the hearing nerve fires, the sound stimulus travels
up to the brain. This electrical activity generated by the nerve can be recorded
by the electrodes and is represented as waveforms on a computer screen. The
audiologist can then present different loudness levels of each sound and
determine the softest levels at which the infant can hear. For infant-screening
purposes, only one sound is used to test the hearing, commonly referred to as a
"click." The click is a grouping of several sounds to test a wider
area of the hearing organ at one time. The click is typically presented at a
loud level and a soft one. If a healthy response is recorded, then the infant
has "passed" the hearing screen. Testing usually takes five to 15 minutes to complete.
What is an OAE evaluation?
An otoacoustic emission test (OAE) measures an acoustic response that is produced by the inner ear (cochlea), which in essence bounces back out of the ear in response to a sound stimulus. The test is performed by placing a small probe that contains a microphone and speaker into the infant's ear. As the infant rests quietly, sounds are generated in the probe. Once the cochlea processes the sound, an electrical stimulus is sent to the brainstem. In addition, there is a second and separate sound that does not travel up the nerve but comes back out into the infant's ear canal. This "byproduct" is the otoacoustic emission. The emission is then recorded with the microphone probe and represented pictorially on a computer screen. The audiologist can determine which sounds yielded a response/emission and the strength of those responses. If there is an emission present for those sounds that are critical to speech comprehension, then the infant has "passed" the hearing screen. Testing generally takes about
five to eight minutes.
Next: OAEs and ABRs, is one test better than the other? »
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