Auditory Brainstem Response
Unlike a hearing evaluation, which evaluates how well you hear sound, an auditory brainstem response test (ABR) evaluates how well the sounds travel along the auditory pathways to a particular part of the brain called the brainstem.
An ABR may be recommended for a variety of reasons. It may be used to estimate the sensitivity of the ear to sound, such as in the testing of newborns or in a child or adult who is unable to accurately complete a hearing evaluation. For adults, the most common reason an ABR is recommended is to help eliminate the possibility of a disorder along the hearing nerve or in the brain itself.
To complete the ABR test, electrodes are pasted and taped to the scalp and earlobes and soft foam tips are inserted into the ear canals. Clicking sounds then are delivered through the ear tips at a comfortable-to-fairly-loud level. These sounds cause nerve responses that are picked up by the electrodes and passed on to sophisticated equipment to record these responses. The audiologist then measures the responses to determine if they are normal or abnormal.
Today, audiologists have many tools at their disposal to help identify and assess hearing loss.
Otoacoustic emissions (OAEs) are clinically important because they are the basis of a simple, non-invasive, test for hearing defects in newborn babies and in children who are too young to cooperate in conventional hearing tests. An otoacoustic emission test 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. Placing a small probe that contains a microphone and speaker into the ear performs the test. As the patient rests quietly, sounds are generated in the probe and responses that come back from the cochlea are recorded. 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 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.
OAEs can be recorded on people at virtually any age, from shortly after birth to well above age 80. For example, research has shown that babies with normal hearing have measurable OAEs as soon as six hours after birth.
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