Deriving a cochlear transducer function from low-frequency modulation of distortion product otoacoustic emissions

Abstract

In this paper, a new method is introduced to derive a cochlear transducer function from measuring distortion product otoacoustic emissions (DPOAEs). It is shown that the cubic difference tone (CDT, 2f1-f2) is produced from the odd-order terms of a power series that approximates a nonlinear function characterizing cochlear transduction. Exploring the underlying mathematical formulation, it is found that the CDT is proportional to the third derivative of the transduction function when the primary levels are sufficiently small. DPOAEs were measured from nine gerbils in response to two-tone signals biased by a low-frequency tone with different amplitudes. The CDT magnitude was obtained at the peak regions of the bias tone. The results of the experiment demonstrated that the shape of the CDT magnitudes as a function of bias levels was similar to the absolute value of the third derivative of a sigmoidal function. A second-order Boltzmann function was derived from curve fitting the CDT data with an equation that represents the third derivative of the Boltzmann function. Both the CDT-bias function and the derived nonlinear transducer function showed effects of primary levels. The results of the study indicate that the low-frequency modulated DPOAEs can be used to estimate the cochlear transducer function.

Multiple Indices of the ‘Bounce’ Phenomenon Obtained from the Same Human Ears

“…While hearing thresholds are obtained with acoustic stimuli at levels obviously close to hearing thresholds (usually between about 0 and 10 dB SPL in the present study), DPOAEs were evoked with primary tones of 65 dB SPL. There are indications that the OPs of outer hair cell MET transfer functions shift with stimulus level and are therefore not identical under low and high level stimulation (Dallos 1986;Cody and Russell 1995;Frank and Kossl 1997;Bian et al 2002;Bian et al 2004) which can explain the seemingly opposite behaviour of hearing thresholds and QDP levels. A movement of the OP (which is assumed to be located below the inflection point in the presence of the intense primary tones) away from the inflection point, towards the inflection point and back, would produce the biphasic pattern of QDPs with initial enhancement (see Fig.…”

Low-frequency modulation of distortion product otoacoustic emissions in humans

“…By introducing a high-level low-frequency tone, this method can "slowly" shift the cochlear partition to vary the operating point (OP) of the hair cell transducer and induce an amplitude modulation (AM) of the DPOAEs. For odd-order DPs, the magnitudes are suppressed depending on the phase of the low-frequency bias tone (Bian et al, 2002;Bian, 2006); whereas for even-order DPs, the DPOAE magnitudes are enhanced at maximal displacements of the cochlear partition induced by the bias tone (Bian, 2004(Bian, , 2006. These different DPOAE modulation patterns are intimately related to the cochlear transducer nonlinearity, because in principle these DP magnitudes are proportional to the appropriate derivatives of the cochlear F Tr .…”

“…A low-frequency biasing technique has been used in quantifying a cochlear transducer function (F Tr ) from the DPOAEs measured in gerbils (Bian et al, 2002;Bian, 2004). This technique fully utilizes the nonlinear effects of cochlear transduction, namely suppression and distortion, to estimate the transfer characteristics of the inner ear.…”

Comparing the optimal signal conditions for recording cubic and quadratic distortion product otoacoustic emissions

“…Among other factors ͑Gar-ner, 2008͒, such as hearing sensitivity, middle ear transmission, and inner ear reflections, a source of the variability can be attributed to less optimized signal conditions of the primary tones ͑Johnson et al, 2006;Mills et al, 2007͒ that cannot evoke the largest DPOAEs. Since DP levels are correlated with the nonlinear characteristics of cochlear transduction ͑Lukashkin and Russell, 1999; Fahey et al, 2000;Bian et al, 2002;Bian, 2004͒, maximizing DPOAE magnitudes can improve the signal-to-noise ratio ͑SNR͒ so that more accurate estimates of cochlear function are possible. Therefore, there is a need for standardizing ͑Mills et al, 2007͒ or individualizing ͑Neely et al, 2005͒ the measurement procedures.…”