Newborn Infant Hearing Screening (cont.)

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How is hearing in infants tested?

Hearing in infants can be tested using two different methods: the auditory brainstem response (ABR) evaluations or the otoacoustic emission (OAE) measures. Both tests are accurate, noninvasive, automated, and do not require any observable response from the infant. Which test is used depends on the screening program's choice of instrumentation and training. For a screening tool, both methods are extremely effective. There are, however, some distinct differences in how the hearing is measured using an ABR versus an OAE.

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.

Medically Reviewed by a Doctor on 2/18/2014

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