otometrics Madsen AccuScreen PRO, User Manual

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AccuScreen PRO User Manual Test Methods
GN Otometrics A/S 13
2 Test Methods
2.1 About Otoacoustic Emissions
Congenital hearing impairment has serious consequences for
speech and language acquisition as well as emotional and intellectu-
al development. Recent research has confirmed that this can be min-
imised, when identification and intervention occur, before the
hearing-impaired child reaches 6 months of age. In addition, techno-
logical advances have made automated screening of infants' hearing
possible by a wide range of caregivers. One such automated screen-
ing method makes use of the presence of otoacoustic emissions to
determine its outcome.
Otoacoustic emissions (OAEs) are sounds found in the ear canal that
originate from activity in the cochlea. These sounds are small, but
potentially audible, sometimes amounting to as much as 30 dB SPL.
They are created by motion of the eardrum driven by vibrations in
the cochlea, which are transmitted through the middle ear chain.
Consequently, they can be detected only when the middle ear is op-
erating normally. OAEs are generated only when the Organ of Corti
is in normal or near normal condition. They can emerge spontane-
ously, but more commonly follow acoustic stimulation.
Note that otoacoustic emissions do not contribute to hearing, but are
by-products of an active process in the cochlea, in which motility of
the outer hair cells tunes the basilar membrane and amplifies weak
sounds. They are clinically significant in the sense that they provide
an indication of the integrity of the cochlear amplifier/outer hair
cells.
2.1.1 Recording OAEs
In general, the recording of all OAEs requires that a sensitive, low
noise microphone be sealed in the external ear canal. Recording of
emissions elicited by an acoustic stimulus also requires that there is
one (for TEOAE) or two receivers (for DPOAE) to deliver the stimu-
li. The microphone records the sound present in the external ear ca-
nal in response to the acoustic stimulus. The type of signal analysis
used depends on the type of emissions to be recorded.