Otoacoustic Emissions

Susan Moreland smorelan at magnus.acs.ohio-state.edu
Wed Mar 1 14:04:24 EST 1995

In article <acampane.377.2F54BB11 at postbox.acs.ohio-state.edu> acampane at postbox.acs.ohio-state.edu (Angelo Campanella) writes:

>As a matter of starting a dialogue, I introduce some questions about
>otoacoustic emissions.

I'll give this my best shot and count on the lurkers to catch me in any errors 
I make.  ;)

>1/ Where are they detected?  (just outside the eardrum)?

In the ear canal, but the probe doesn't have to be very deep inside.  The 
important thing is that the seal between the probe and the canal wall is tight.

>2/ Are they steady state (can be detected any time without provocation), 
>   or are they always evoked (result of a stimulus)?  If so what stimulus.

Emissions are divided into two major categories -- spontaneous (SOAE) and 
evoked (EOAE).  SOAE's are emissions that occur in the absence of 
auditory stimulation. Their presence or absence is non-diagnostic since 
less than 50% of normally-hearing people have them.  

EOAE's occur (as you might expect) following stimulation.  Their absence is 
indicative of outer hair cell damage/death.  EOAE's are present in 
the ears of virtually people with thresholds better than 30 dB HL.  There are 
three types of transient emissions: 

1)  Stimulus-frequency (SFOAE) -- the stimulus is a continuous tonal stimulus 
that is usually swept across a wide range of freq's.  

2)  Transient-evoked (TEOAE) -- the stimulus is a transient signal.  Clicks 
and tone bursts are often used, and there is research being done re: the use 
of chirps, as well.

3)  Disortion-Product (DPOAE) -- the stimuli are two pure tones, f1 and f2.

>3/ What level, SPL, (broadband or on octave/third octave) are 

SOAE's vary in intensity from person to person and over time.  They are almost 
always inaudible to the "naked ear" -- that is, it would be extremely rare for 
you to stand beside someone and be able to hear their SOAE's.  However, I was 
told that there have been isolated cases of animals (I seem to remember a dog) 
with emissions that were loud enough to be heard without amplification.

Regarding the intensity of evoked emissions, it will vary depending upon the 
type and intensity of the stimulus used.  Typically a response must be at 
least 3 dB above the noise floor before it will be considered to be an EOAE.

Anyone have anything to add or correct?

And Ang, thanks for jumping right in there!

Ang. C.

Susan Moreland

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