Abstract
Distortion-product otoacoustic emissions (DPOAEs) emerge from the cochlea when elicited with two tones of frequencies f1 and f2. DPOAEs mainly consist of two components, a nonlinear-distortion and a coherent-reflection component. Input-output (I/O) functions of DPOAE pressure at the cubic difference frequency, fDP=2f1-f2, enable the computation of estimated distortion-product thresholds (EDPTs), offering a noninvasive approach to estimate auditory thresholds. However, wave interference between the DPOAE components and suboptimal stimulus-level pairs reduces the accuracy of EDPTs. Here, the amplitude P of the nonlinear-distortion component is extracted from short-pulse DPOAE time signals. DPOAE level maps representing the growth behavior of P in L1,L2 space are recorded for 21 stimulus-level pairs and 14 frequencies with f2=1 to 14 kHz (f2/f1=1.2) from 20 ears. Reproducing DPOAE growth behavior using a least-squares fit approach enables the derivation of ridge-based I/O functions from model level maps. Objective evaluation criteria assess the fit results and provide EDPTs, which correlate significantly with auditory thresholds (p < 0.001). In conclusion, I/O functions derived from model level maps provide EDPTs with high precision but without the need of predefined optimal stimulus-level pairs.
Highlights
Otoacoustic emissions (OAEs) are sound waves measurable in the ear canal which emerge either in the absence of acoustical stimulation, referred to as spontaneous OAEs (Kemp, 1979; Zurek, 1981), or in response to acoustical stimulation (Kemp, 1978), yielding the class of evoked otoacoustic emissions (EOAEs)
Based on the growth behavior of the amplitude of the nonlinear-distortion component in the L1; L2 space, this paper presents a refined method, which enables the derivation of Distortion-product otoacoustic emissions (DPOAEs) I/O-functions without the need of predefined optimal stimulus-level paths
Model level maps based on six or more valid DPOAE amplitudes could be computed in 73.6% (206/280) of the tested frequencies, 74.8% (154/206) of which were accepted for threshold estimation
Summary
Otoacoustic emissions (OAEs) are sound waves measurable in the ear canal which emerge either in the absence of acoustical stimulation, referred to as spontaneous OAEs (Kemp, 1979; Zurek, 1981), or in response to acoustical stimulation (Kemp, 1978), yielding the class of evoked otoacoustic emissions (EOAEs). One type of EOAE commonly used in research and clinical applications is the distortion-product otoacoustic emission (DPOAE), which arises when simultaneously presenting two tones of different frequencies, f1 and f2, to the cochlea (Avan et al, 2013; Kemp, 1979), typically with f2=f1 1⁄4 1:2 (Gaskill and Brown, 1990). DPOAEs are by-products of the active, nonlinear, and local amplification of traveling waves within the healthy cochlea (Robles and Ruggero, 2001). This nonlinear amplification process establishes the peripheral basis for the high sensitivity, the large dynamic range, and the sharp tuning of the auditory system in mammals (Avan et al, 2013). The amplifier is known to be highly susceptible to noise overexposure (Keithley, 2019) and ototoxic agents (Laurell and Engstr€om, 1989; Sheth et al, 2017)
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