DP Otoacoustic Emissions
zhaof at cf.ac.uk
Fri Mar 7 09:13:27 EST 1997
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Otoacoustic emissions (OAEs) are the low intensity sounds emitted from the ear canal and generated within the normal cochlear, either spontaneously or in response to acoustic stimulation. They are thought to reflect the activity of active biological mechanisms within the cochlear responsible for the exquisite sensitivity, sharp frequency selectivity and wide dynamic range of the normal auditory system. Because the measurement of OAEs is simple, fast, objective, reproducible and non-invasive, and because reduced OAE amplitudes are associated with certain types of hearing impairment, OAEs have great potential for use in the audiology clinic.
Distortion-product otoacoustic emissions (DPOAEs) are defined as acoustic energy in the ear canal arising from the non-linear interaction of two simultaneously applied pure tones of frequency f1 and f2 within the cochlea. The stimulus are often referred to as "primary" tone. In human ears, as well as in the ears of many animals species, the cubic difference intermodulation DP at the frequency of 2f1-f2 is the most prominent OAE and is therefore, the most thoroughly examined.
Furthermore, there is considerable evidence that DPOAEs are generated from very specific cochlear sites. This cochlear specification of DPOAEs may lead to a frequency-specific relationship with cochlear function. The implication of the frequency-specific properties of DPOAEs is that each part of the cochlea can be characterised by looking at the amplitude on the DP-gram. Due to their greater inherent frequency-specificity than TEOAEs, DPOAEs have attracted special interest for their potential use as objective predictors of the pure tone hearing thresholds.
However, towards this end, there are still several questions hampering the extensively clinical application of DPOAEs, such as (1) unclear mechanism of DPOAEs although it is now generally accepted that DPOAEs represent important aspects of cochlear function; (2) limited knowledge on interpreting the DP-grams and their phases; (3) limited assessment on the reliability and sensitivity of amplitude and latency of DPOAEs. Therefore, DPOAEs are still undergoing evaluation for clinical use.
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