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Otoacoustic Emissions Testing Valuable for Musicians

Laura E. Gifford

Everyone knows that loud sound can cause hearing loss. This situation is particularly touchy for musicians, whose careers frequently demand high levels of sound exposure when performing and sensitive hearing for creating music. While noise or music exposure and sensitive hearing may seem mutually exclusive, a new type of audiological test can detect hearing damage before it becomes audibly noticeable.

When we hear, a signal travels through the outer and middle ear to the cochlea, or inner ear. In the cochlea, there are two types of cells that process sound, outer hair cells and inner hair cells. The inner hair cells are largely responsible for hearing sounds, while the outer hair cells work to clarify the signals before they are sent to the brain. Otoacoustic emissions (OAEs) are a response, similar to an echo, to sounds heard by the ear. These "echoes" can now be recorded. Using equipment developed especially for OAE recording, clicking sounds or tones are presented through a probe tip held in the ear canal. When the tones reach the inner ear, movement of the outer hair cells generates a very soft sound. These sounds exit through the middle ear into the ear canal. A microphone in the probe tip records these responses, measuring frequencies from about 500 through 8000 Hertz.

Measurement of the presence, absence or abnormality of OAEs can identify subtle problems in the hearing system. Outer hair cells are arranged in the cochlea by frequency, so if there is damage in some area, there may be no emissions at that frequency. Since OAEs are measured at individual frequencies, specific areas of damage can be discerned. For people who feel that their hearing has suffered but have not been diagnosed with hearing loss through a routine audiogram, this is an excellent way to asses the whole ear . In the event that injury to the hearing mechanism is very slight and restricted primarily to the outer hair cells, such as is common in the early stages of sound-induced hearing loss, the audiologist may not be able to detect dysfunction without testing otoacoustic emissions. Early identification of impairment is always important, so that special care can be taken to avoid any additional hearing loss. For example, further exposure to loud sounds can add to the damage until a significant hearing loss develops.

Prior to the measurement of OAEs, a person's hearing sensitivity would have to worsen by 20 decibels or more before it was considered a significant difference. By measuring OAEs, audiologists can tell patients early on that they have suffered some decline in outer hair cell function before there is any noticeable hearing change. An audiologist can also fit patients with special hearing protection to guard against damage without distorting sound.

Laura E. Gifford, BS, is a graduate student in the Division of Hearing and Speech Sciences at Vanderbilt Univrersity. Correspondence to Ms. Gifford at Vanderbilt Balance and Hearing Center, 1500 21 st Avenue South, Suite 2600, Nashville, TN 37212-3102.

 





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