Input-output functions of the nonlinear-distortion component of distortion-product otoacoustic emissions in normal and hearing-impaired human ears

Abstract

Distortion-product otoacoustic emissions (DPOAEs) arise in the cochlea in response to two tones with frequencies f1 and f2 and mainly consist of two components, a nonlinear-distortion and a coherent-reflection component. Wave interference between these components limits the accuracy of DPOAEs when evaluating the function of the cochlea with conventional continuous stimulus tones. Here, DPOAE components are separated in the time domain from DPOAE signals elicited with short stimulus pulses. The extracted nonlinear-distortion components are used to derive estimated distortion-product thresholds (EDPTs) from semi-logarithmic input-output (I/O) functions for 20 normal-hearing and 21 hearing-impaired subjects. I/O functions were measured with frequency-specific stimulus levels at eight frequencies f2 = 1,…, 8 kHz (f2/f1 = 1.2). For comparison, DPOAEs were also elicited with continuous primary tones. Both acquisition paradigms yielded EDPTs, which significantly correlated with behavioral thresholds (p < 0.001) and enabled derivation of estimated hearing thresholds (EHTs) from EDPTs using a linear regression relationship. DPOAE-component separation in the time domain significantly reduced the standard deviation of EHTs compared to that derived from continuous DPOAEs (p < 0.01). In conclusion, using frequency-specific stimulus levels and DPOAE-component separation increases the reliability of DPOAE I/O functions for assessing cochlear function and estimating behavioral thresholds.

Time-domain analysis of distortion-product otoacoustic emissions using a hydrodynamic cochlea model

“…Exploiting the different latencies of the components, stimulation with short pulses instead of conventional continuous primary tones enables the separation of the DPOAE components in the time domain [5], which significantly increases the accuracy of DPOAEs when used to estimate behavioral thresholds [4,6]. However, there is evidence for additional components in the DPOAE recordings.…”

“…Suitable phase shifts of the stimulus pulses in consecutive acquisition blocks enabled the cancelation of the stimulus pulses after ensemble averaging [13]. Details of the measurement setup and the short-pulse acquisition paradigm are specified elsewhere [6]. For comparison with simulated data, DPOAE components were extracted by fitting the zerophase band-pass filtered signal with a mathematical model using a least-squares approach [5].…”

Comparison of time-domain source-separation techniques for short-pulse distortion-product otoacoustic emissions

“…The primary goal of this study is the comparison of two extraction methods of the nonlinear-distortion component in the time domain. The first method, referred to as onset decomposition (OD), 3,12 samples the envelope of p(t) at a time instant, T OD , before the coherent-reflection component starts to interfere to obtain an estimate of the amplitude,P OD , of the nonlinear-distortion component [ Fig. 1(a)].…”

“…2 Recently, it was shown that the accuracy of the relationship between EDPTs and behavioral thresholds significantly increases when the amplitude of p 1 (t) is extracted from DPOAE time signals evoked by pulsed stimuli using a technique called onset decomposition (OD). 3 In contrast to previously established source separation methods, which rely on either time-consuming recordings of DP-grams with high frequency resolution 2,4 or chirps spanning a frequency range of octaves, 5,6 pulsed stimulation enables estimation of the two DPOAE components at a single f 2 frequency. 7 Utilizing short-pulsed DPOAE recordings, OD extracts the nonlinear distortion component without the necessity of using an individually adapted third tone to suppress the coherent-reflection component.…”

“…7 Utilizing short-pulsed DPOAE recordings, OD extracts the nonlinear distortion component without the necessity of using an individually adapted third tone to suppress the coherent-reflection component. 8 For a more thorough review of the pertinent literature, see Zelle et al 3 Here, the accuracy of OD is analyzed by comparing the estimated amplitudes of the nonlinear-distortion component with the time courses of p 1 (t) and p 2 (t) extracted from pulsed DPOAE signals using a least-squares curve fit 9 as well as with DPOAEs conventionally obtained using Fourier analysis at f DP in response to continuous stimulation. In addition to the expected smoothening of the DP-grams, 4,5 the quality of the extraction is verified by showing that the frequencydependent variation of the DP-amplitude in DP-grams of continuous recordings, commonly known as DPOAE fine structure, can be accurately reconstructed as the sum of the phasor components computed from p 1 (t) and p 2 (t).…”