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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