6
GN Otometrics A/S
User Manual
CAPELLA Cochlear Emissions Analyzer
1.1
Applications of
Capella
CAPELLA Cochlear Emissions Analyzer
is designed to measure the
low-amplitude audio frequencies transmitted from the cochlea
through the middle ear to the external ear canal and known as otoa-
coustic emissions. Otoacoustic emissions (OAE's) were first identi-
fied at the Royal National TNE Hospital, London, and have been
shown to be the result of an active mechanical process in the cochlea.
This process enhances the sound-induced motion of cochlear struc-
tures and increases the sensitivity and frequency selectivity of the
ear. OAE's are typically classified into two broad classes based on
the type of acoustic stimulation that evokes them, as described be-
low.
1.1.1
Spontaneous Otoacoustic Emissions
Spontaneous Otoacoustic Emissions (SOAE's) are low-level narrow-
band signals measured in the absence of deliberate acoustic stimula-
tion. They occur in only about one half of normal-hearing ears, and
at only a few frequencies for ears in which they do occur. Conse-
quently, they are thought to have limited clinical utility although
they may have research implications.
1.1.2
Evoked Otoacoustic Emissions
Evoked emissions, which occur in nearly all normal-hearing ears,
are further divided into three sub-types according to the nature of
the acoustic stimulus used to elicit them. Transient Evoked Otoa-
coustic Emissions (TEOAE's) occur in response to brief acoustic sig-
nals (clicks, tone bursts, etc.). It has been suggested that they may be
particularly well-suited to detection of cochlear disorders, especially
in screening applications.
Stimulus-Frequency Otoacoustic Emissions (SFOAE's) are elicited
by swept pure tone signals and show characteristics similar to those
of transient emissions. However, because their detection is more
complicated and time-consuming than the measurement of TE-
OAE's, they have not yet been incorporated into clinical tests.
Distortion Product Otoacoustic Emissions (DPOAE's or DP's) are
evoked by two simultaneously presented pure tones of different fre-
quencies. They represent the ear's nonlinear response to the stimu-
lus tones, and consist of new frequencies not present in the eliciting
stimuli. Although DPOAE's are somewhat more complex to elicit
and analyze than TEOAE's, they may have greater clinical utility for
some applications.
Capella
currently measures Spontaneous, Transient, and Distortion
Product Otoacoustic Emissions, using synchronous time averaging
(where applicable), correlation techniques and FFT frequency analy-
