- Category: DPOAEs
- Last Updated on Tuesday, 11 December 2012 09:15
- Written by Editorial Board
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Editor's Note:A portion of the material presented has appeared in the NATASHA (Network and Tools for the Assessment of Speech/Language and Hearing Ability) project web pages.
- Set-up (equipment, test environment, etc.):
Since no patent was deposited for the DPOAE stimulation scheme, a large number of manufacturers have developed DPOAE devices.
The DPOAE stimulus consists of two pure tone signals of which the frequency ratio varies from 1.20 to 1.22.
The L1 and L2 values vary from 75 to 55 dB SPL. For screening applications a small number of frequencies is tested, such as 2.0, 3.0 and 4.0 kHz (referenced to F2). For ototoxicity- monitoring applications the bandwidth of the measurements extends up to 8-10 kHz (referenced to F2).
The probe positioning is an equally crucial procedure as with TEOAE testing. An erroneous position of the probe CAN block or severely alter the shape of the DP-gram. Usually an erroneous position results in a blockage in one of the two microphones which emits the F1 or the F2 tone.
It is well known that the cochlear-amplifier is more vulnerable at lower stimulus intensities and for the detection of light cochlear insults primary intensities in the range of 50 - 55 dB SPL should be used.
- Interpretation of results
From the information presented in the Introduction page on DPOAEs, it might be clear that it is difficult to optimize a DPOAE protocol, as different setting affects different frequencies. In this context any DPOAE protocol represents a clinical compromise.
Neonatal subjects (pre or full-term) often show in their DP-grams a notch (an abrupt decrease of the 2F1 - F2 amplitude) around 3 kHz. This phenomenon is probably related to the interaction between the DPOAE response and a standing wave in the external meatus.
The level of the DPOAEs or the S/Ns of the DP-gram or the IO plots do not have a precise clinical significance. The observed fine structure (caused by interactions of the DPOAE components) of the "DP-gram" clearly limits the extensive clinical application of DPOAEs. Different methods have been introduced to eliminate this effect either by masking ("Single Generator DPOAE") or by determining the level-dependencies of these components. See Mauermann et al. (1999) for a review of these effects.