Towards understanding the limits of distortion product otoacoustic emission measurements

Abstract

Distortion product otoacoustic emission (DPOAE) data were obtained with a custom-designed system from 20 subjects with normal hearing. Cavity measurements, using this system and an Etymotic ER-10B low-noise microphone system, resulted in estimates of recording system distortion of -20 dB SPL for f2 frequencies ranging from 500 to 8000 Hz, and primary levels ranging from 20 to 75 dB SPL (L2 = L1-10 dB). Using this system it was possible to automatically adjust averaging time in order to obtain the same residual noise levels across frequencies. In all subjects with normal hearing, DPOAEs were measurable over a wide range of primary levels for octave f2 frequencies from 1000 to 8000 Hz, but not at 500 Hz. At 500 Hz, only half of the normal-hearing subjects produced DPOAEs that were above the noise floor. When they did, DPOAE amplitude was less than that observed at higher f2 frequencies. While the cause for response absence in some normal ears may have been due to residual noise, the reduced amplitude suggests that the other factors influence the measurement of DPOAEs at low frequencies. This result may be due to reduced cochlear production of DPOAEs at lower frequencies or reduced transmission through the middle ear.

Input–output functions for stimulus-frequency otoacoustic emissions in normal-hearing adult ears

“…The first step in this approach is to study the relationship between OAE I/O functions and BM response growth. DPOAE I/O functions have been reported by several investigators ͑Lonsbury- Martin et al, 1990;Gorga et al, 1994;Whitehead et al, 1995;Kummer et al, 1998;Withnell and Yates, 1998;Buus et al, 2001;Dorn et al, 2001͒. Withnell and Yates ͑1998͒, for example, recorded DPOAE I/O functions in guinea pigs that were comparable in form to the BM I/O functions reported in the literature. Their DPOAE I/O functions were characterized by an approximately linear slope at low stimulus levels, a breakpoint of 22 to 33 dB SPL, and an upper slope of 0.14 to 0.27 dB/dB.…”

Determining the Cause of Hearing Loss: Differential Diagnosis Using a Comparison of Audiometric and Otoacoustic Emission Responses

“…In the case of hearing loss, then, one might naively expect that emissions would "predict" or be wellcorrelated with hearing function, for example, as measured by pure-tone thresholds or auditory brain stem response (ABR) thresholds. There is now ample evidence that there is no measure of emissions that does very well in predicting hearing thresholds, both in infants and in adults with impaired hearing (Gorga et al, 1994;Gorga et al, 1999;Gorga et al, 2003;Norton et al, 2000;Stover et al, 1996). For this reason, for example, it can be asserted that no type of emission measurement can adequately replace ABR in infant screening because there may be emissions present even in cases with severe hearing loss.…”

Test-retest reliability of distortion-product otoacoustic emissions in children with normal hearing: A preliminary study

“…They attributed the larger variability in lower frequency regions to environmental and instrumentation noise. Various researchers, on the other hand, have theorized that forward and reverse middle ear transmission and cochlear nonlinear behaviour could explain for the adverse effect of environmental noise on DPOAEs at lower frequencies (Gorga et al, 1994). Roede et al (1993) used the stimulus level of 70 and 55 dB SPL (with primary tones delivered at equal intensities, i.e.…”