Time-frequency domain filtering of evoked otoacoustic emissions

Abstract

Time-domain filtering is a standard analysis technique, which is used to disentangle the two main vector components of the distortion product otoacoustic emission response, exploiting their different phase-frequency relation. In this study, a time-frequency filtering technique based on the continuous wavelet transform is proposed to overcome the intrinsic limitations of the time-domain filtering technique and to extend it also to the analysis of stimulus-frequency and transient-evoked otoacoustic emissions. The advantages of the proposed technique are first discussed on a theoretical basis, then practically demonstrated by applying it to the analysis of synthesized and real otoacoustic data. The results show that the time-frequency approach can be empirically optimized to get effective separation of the components of the otoacoustic response associated with either different generation mechanisms or different generation places. Focusing on a single component of the otoacoustic response with a given time-frequency signature may also improve significantly the signal-to-noise ratio, because the random noise contribution tends to be uniformly distributed on the time-frequency plane.

Oxidative stress biomarkers and otoacoustic emissions in humans exposed to styrene and noise

“…For simplicity, in this study, we will define as long-latency (LL) the rotating-phase reflection component. The LL and ZL components are characterized by very different phase-gradient delays, so they can be effectively separated by time-frequency domain filtering (Moleti et al, 2012). They also have potentially different diagnostic power, because the distortion mechanism is sensitive to the level and to the nonlinear behavior of the basilar membrane (BM) response in the x(f 2 ) region, whereas the reflection mechanism is sensitive to the strength of the cochlear amplifier in the x(f DP ) region.…”

Level dependence of the nonlinear-distortion component of distortion-product otoacoustic emissions in humans

“…This fitting approach mimics narrow, band-pass filtering and yields suppression of long-latency contributions to the DPOAE signal, such as the coherent-reflection component. Recently, Moleti et al (2012) adapted the stimulation paradigm from Long et al (2008) to separate the DPOAE components by means of a continuous wavelet transform, which enables visualization of the nonlinear-distortion and coherent-reflection components in the time-frequency domain.…”

Intensimetric detection of distortion product otoacoustic emissions with ear canal calibration

“…It is well-known 7 that the DPOAE spectral fine-structure is due to interference between two components with different phase-frequency relation, a (typically dominant) nonlinear distortion component, generated by a wave-fixed mechanism, with almost constant phase (as a consequence of the cochlear scaling symmetry), and a reflection component, generated by a place-fixed mechanism, with rapidly rotating phase. Time-frequency filtering 8 allows one to separate the two DPOAE components in the time-frequency domain. Even if intensimetric quantities neglect the phase information, DPOAE amplitude spectra possess the information necessary to separate the components in the time or (better) in the time-frequency domain, because phase and amplitude fluctuations are intrinsically related to each other in causal systems.…”