Otoacoustic Emission Testing

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Otoacoustic Emission Testing

The cochlea is the sensory organ for hearing contained in the inner ear.  It is housed within the temporal bone which is the hardest bone in the human body. 

Within the cochlea is a structure called the Organ of Corti.  This structure contains the inner and outer hair cells.  The outer hair cells act like a pre-amplifier with an output limiter  in our ear. They enhance our ability to hear soft sound and inhibit loud sounds.  When the inner ear is damaged, you lose both the ability to hear soft sound as well as the ability to tolerate loud sound.  You also lose the fine tuning structure, so sound may be distorted and not clear. 

Otoacoustic emissions are acoustic signals generated by the normal inner ear, either in the absence of acoustic stimulation (spontaneous emissions) or in response to acoustic stimulation (acoustically-evoked emissions) or electrical stimulation (electrically-evoked emissions). Acoustically evoked otoacoustic emission testing allows the audiologist to understand how the outer hair cells of your inner ear are working.  There are three types of Otoacoustic emission testing: Spontaneous, Transient, and Distortion Product.  

We will only discuss Distortion Product testing (DPOAE) here.  To obtain DPOAE measurements, the audiologist will position an earplug in your outer ear.  The earplug houses the measuring microphone and sound emitting speakers for the DPOAE measurements.  Moderate level tones are presented in pairs (f1 and f2) over a range from low to high frequency.  The sounds enter the outer, middle, and inner ear.  Recording microphones pick up the small sounds coming back from the inner ear, and the computer averages and processes the responses, displaying the results on the computer screen for the patient and audiologist.   Here is an example of the DPOAEs from a musician who has played in loud bands for many years:

   

The solid lines show the normal range where the DPOAEs should be present.  The Xs and Os show the responses obtained from the outer hair cells in the inner ears of this musician. The green line is the background physiologic noise.

In addition to being used for measuring hearing loss in musicians, OAEs are used to screen newborn infants for hearing loss.

For more images and information on the cochlea, visit: http://ctl.augie.edu/perry/ear/hearmech.htm

Copyright 2001 Audible Difference

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