1,721,157 research outputs found
Comparison between otoacoustic and auditory brainstem response latencies supports slow backward propagation of otoacoustic emissions
No full textExperimental measurements of the latency of transient evoked otoacoustic emission and auditory brainstem responses are compared, to discriminate between different cochlear models for the backward acoustic propagation of otoacoustic emissions. In most transmission-line cochlear models otoacoustic emissions propagate towards the base as a slow transverse traveling wave, whereas other models assume fast backward propagation via longitudinal compression waves in the fluid. Recently, sensitive measurements of the basilar membrane motion have cast serious doubts on the existence of slow backward traveling waves associated with distortion product otoacoustic emissions [He et al., Hear. Res. 228, 112-122 (2007)]. On the other hand, recent analyses of "Allen-Fahey" experiments suggest instead that the slow mechanism transports most of the otoacoustic energy [Shera et al., J. Acoust. Soc. Am. 122, 1564-1575 (2007)]. The two models can also be discriminated by comparing accurate estimates of the otoacoustic emission latency and of the auditory brainstem response latency. In this study, this comparison is done using human data, partly original, and partly from the literature. The results are inconsistent with fast otoacoustic propagation, and suggest that slow traveling waves on the basilar membrane are indeed the main mechanism for the backward propagation of the otoacoustic energy. (C) 2008 Acoustical Society of America
DPOAEs evoked by different stimulus paradigms in a fully nonlinear cochlear model
No full textThe DPOAE generation is a consequence of the intrinsically nonlinear nature of the cochlear dynamics. Different stimulus paradigms have been proposed for using DPOAE measurements as a diagnostic test of the hearing function. In particular, Kummer et al. [1] proposed a method for measuring the hearing threshold by extrapolating the growth rates of the linear DPOAE response at zero response magnitude, and defining this level as the best estimate of the audiometric threshold level. This method requires the so called “scissors” paradigm for evoking DPOAE. The scissors paradigm is considered capable of approximately maximizing the DPOAE response at any saturation regime, in all frequency ranges. In the scissors paradigm the L2 stimulus grows much faster than L1. A higher L1 level is generally needed because, in the “overlap” nonlinear distortion generation place, x(f2), the basilar membrane (BM) response to f2 is fully resonant whereas that to f1 is not. On the other hand, the nonlinearity of the BM response implies that the “advantage” of the f2 component decreases with increasing stimulus level, as the bandwidth of the response also increases. Different growth rates are obviously associated to DPOAE evoked by different paradigms. In addition, it is quite difficult to interpret the DPOAE growth curves when complex protocols are used to evoke them. In this work, a nonlinear non-local cochlear model is proposed to simulate otoacoustic emissions. The presence of strong nonlinearity, as a physical non-perturbative property of the system, requires a time domain solution of the equations representing the cochlea from a micromechanical point of view. The cochlear equations are solved in time domain by means of the state space variables mathematical formalism [2]. The model parameter space has been explored in order to generate DPOAE levels and growth rates compatible with experimental data on human subjects. The main properties of the DPOAE generated by the different paradigms have been reproduced. In particular, the “scissors” paradigm was able to maximize the DP amplitude at each L2 stimulus level, in agreement with the experimental evidence. The proposed model represents a useful tool for studying OAE evoked by complex protocols in strongly nonlinear regime
Estimating cochlear tuning dependence on stimulus level and frequency from the delay of otoacoustic emissions
No full textAn objective technique based on the time-frequency analysis of otoacoustic emissions is proposed to get fast and stable estimates of cochlear tuning. Time-frequency analysis allows one to get stable measurements of the delay/frequency function, which is theoretically expected to be a function of cochlear tuning. Theoretical considerations and numerical solutions of a nonlinear cochlear model suggest that the average phase-gradient delay of the otoacoustic emission single-reflection components, weighted, for each frequency, by the amplitude of the corresponding wavelet coefficients, approximately scales as the square root of the cochlear quality factor. The application of the method to human stimulus-frequency and transient-evoked otoacoustic emissions shows that tuning decreases approximately by a factor of 2, as the stimulus level increases by 30 dB in a moderate stimulus level range. The results also show a steady increase of tuning with increasing frequency, by a factor of 2 between 1 and 5 kHz. This last result is model-dependent, because it relies on the assumption that cochlear scale-invariance breaking is only due to the frequency dependence of tuning. The application of the method to the reflection component of distortion product otoacoustic emissions, separated using time-frequency filtering, is complicated by the necessity of effectively canceling the distortion component
Objective measurement of cochlear tuning factor by means of time-frequency analysis of oto-acoustic emissions
No full textA new technique is proposed for the objective estimate of cochlear tuning, starting from measurements of the delay function of Stimulus Frequency (SF) and Transiently Evoked (TE) Otoacoustic Emissions (OAEs). The technique is quick and reliable, also in not cooperating subjects, while the psychoacoustic tuning measurements are time consuming and based on a large number of assumptions. It is well known that OAEs originate from two main backscattering mechanisms: coherent reflection and nonlinear wave-fixed distortion. The main TEO-AE and SFOAE sources are supposed to be linear reflection from the peak region, due to randomly distributed roughness. Recent experiments found evidence of OAE sources more basally located with respect to the CP (characteristic place) on the basilar membrane (BM). The origin of the basal sources is due to the multiple-peak nature of the coherent local reflectivity function generated by the roughness. The OAE components generated at different places of the BM can be effectively separated in the time-frequency domain, being characterized by different phase-gradient delay. A time-frequency technique was proposed to identify the curved time-frequency region corresponding to single-reflection SFOAE and TEOAE components, to get, for each frequency, a weighted average of the delay over this region, weighted by the square of the wavelet coefficient. This average delay is assumed to scale as the square root of the tuning factor. The estimated spectral tuning values turned out to decrease significantly with increasing stimulus level, confirming that at high stimulus levels a saturation process occurs in which a widening of the BM excitation patterns takes place. This increase of the BM response width increases the relative importance of the shorter-delay more basal peaks of the reflectance and, consequently, a reduction of the average delay. The proposed technique is based on the idea that a smooth relation exists between the average delay and the BM tuning, which is correctly exploited to get reliable and stable tuning estimates only if: 1) multiple reflections are filtered out, and 2) a weighted average of the delay is considered instead of a single delay value associated with the most intense of the OAE components, which is that picked up by standard measurements of the phase-gradient delay
On the large-scale spectral structure of otoacoustic emissions
No full textTransient evoked and distortion product otoacoustic emission data, showing a characteristic slowly oscillating spectral shape, are presented. Such peculiar behavior had also been observed in earlier studies, and deserves some theoretical explanation. A simple model of the cochlear reflectivity, based on the analogy between the cochlear transmission line equations and the Schrodinger wave equation for the motion of an elementary particle above a one-dimensional potential well, is presented. Wave mechanics predicts indeed reflection from a negative potential well, which is quasiperiodically dependent on the width and depth of the well, i.e., on the quality,factor of the cochlear resonance. The model, whose quantitative predictions are dependent on the rather uncertain level and slope of the cochlear tuning curve, proves capable of explaining, at least qualitatively, the observed experimental behavior. (c) 2005 Acoustical Society of America
On the sensitivity of gravitational wave resonant bar detectors
No full textDifferent theoretical estimates of the sensitivity of gravitational wave resonant bar-detectors, which have been published in the last decades, are reviewed and discussed. The "classical" cross-section estimate is obtained considering the bar as a classical or quantum oscillator, whose initial thermal state is that of a single oscillator driven by a single external stochastic force. Other theoretical studies computed a much larger cross-section, using a variety of quantum-mechanical arguments. The review of the existing literature shows that there is no well established model for the response of a resonant detector to gravitational waves. The resonant, yet random, nature of the Brownian thermal motion may justify considering the bar response at the fundamental longitudinal eigenfrequency as that of a large number of effective quantum mechanical oscillators. Assuming this hypothesis, quantum coherence effects, as first suggested by Weber, lead to a much larger cross-section than that "classically" predicted. The reduction of this amplification due to thermal noise itself is also computed
Use of the organic fraction of municipal solid waste for the production of bioplastics for agricultural use: a supply chain study
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