Threshold and TEOAEs
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- Parent Category: Basics of OAEs
- Category: TEOAEs
- Last Updated on Saturday, 29 December 2012 15:13
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The relationship between TEOAEs and Audiometric outcomes (mainly with the Pure Tone Audiometry) has been a debating issue from the early days of otoacoustic emissions. The first author presenting evidence on the relationship between TEOAEs and auditory threshold, was David Kemp. According to his studies the TEOAE responses were present when the threshold levels of the tested subject were better or equal than 30 dB HL. This estimate refers to the average hearing threshold at the audiometric frequencies of 0.5 1.0, 2.0 and 4.0 kHz. Latter studies have presented evidence that the threshold level cut-off for the presence of TEOAEs is approximately from 35 to 40 dB HL.
Although the above statements hold true for the majority of clinical cases, there are examples where the TEOAE responses exist despite the observed hearing impairment. These are mostly cases where there is residual hearing at 1.0 or 2.0 kHz. The cochlear zones corresponding to these frequencies are favored by the resonant frequency of the forward and reverse middle ear transduction. Therefore for clinical cases showing a hearing level at 1.0 kHz and 2.0 kHz better than 30 dB HL and worst than 30 dB in the higher octaves (so than the average is around 35-40 dB) it is possible to record TEOAEs
The true debate on the issue of threshold and TEOAEs revolves around the prediction of the auditory threshold by the signal values of the TEOAEs. In this context it can be said that in general the TEOAEs cannot predict the auditory threshold. The reason for the latter is the fact that auditory perception involves more parts of the auditory system than just the periphery whose function is reflected by the TEOAE measurements.
Nevertheless when:
- The external and middle ear functions are normal.
- There are no retrocochlear hearing complications
the audiometric outcomes and the information from the TEOAEs are in agreement. Any deviation from this scenario causes a disagreement between the TEOAEs and the audiometric outcomes.