otometrics Madsen AccuScreen PRO, Руководство пользователя

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14 GN Otometrics A/S
Test Methods AccuScreen PRO User Manual
2.1.2 Types of OAEs
Spontaneous otoacoustic emissions (SOAE)
SOAEs are low level, tonal signals, which are measured in the ear ca-
nal in the absence of any known stimulus. They are usually inaudi-
ble to the persons from whose ears they are detected.
SOAEs are of limited use clinically because they cannot be measured
in all ears, and appear at discrete and unpredictable frequencies.
However, the presence of an SOAE indicates that hearing is within
normal limits near the frequency at which it appears. In addition, it
may influence behavioural testing, as well as measurements of other
types of OAEs.
Transiently evoked otoacoustic emissions (TEOAEs)
This type of emission is elicited by brief stimuli such as clicks or tone
bursts. They can be recorded in nearly all persons with normal hear-
ing. When a click is used to elicit the response, the resultant wave-
form is, like a fingerprint, idiosyncratic.
TEOAEs are extremely non-linear. Their pattern of growth is consist-
ent with the operation of the cochlear amplifier, which provides
most gain for low level inputs, and lends support to the notion that
OAEs arise from outer hair cell activity.
TEOAEs do not correlate with behavioural audiometric thresholds.
Consequently, it is not possible to predict hearing thresholds based
on TEOAE thresholds. However, since the presence of TEOAEs cor-
relates strongly with normal hearing, the most common clinical ap-
plication involves click stimulation at moderate intensity levels for
the purpose of hearing screening or differential diagnosis.
Distortion Product Otoacoustic Emissions (DPOAE)
As with other OAEs, DPOAEs are thought to be generated by the ac-
tive cochlear process, which is responsible for enhancing the basilar
membrane motion.
DPOAEs are tones produced by the ear in response to two simulta-
neous pure-tone stimuli known as primary tones. They are "distort-
ed" in the sense that they are not present in the eliciting pure-tone
stimuli. The lower frequency pure-tone stimulus is called the f1 pri-
mary, and the higher frequency stimulus is called the f2 primary.
The most frequently measured distortion product is at the frequency
2f1-f2, although the cochlea also produces distortion products at
other frequencies. The 2f1-f2-distortion product is the largest distor-
tion product, and is the only one utilised for clinical purposes at
present.