Efficient time-domain simulation of nonlinear, state-space, transmission-line models of the cochlea

Nonlinear models of the cochlea are best implemented in the time domain, but their computational demands usually limit the duration of the simulations that can reasonably be performed. This letter presents a modified state space method and its application to an example nonlinear one-dimensional transmission-line cochlear model. The sparsity pattern of the individual matrices for this alternative formulation allows the use of significantly faster numerical algorithms. Combined with a more efficient implementation of the saturating nonlinearity, the computational speed of this modified state space method is more than 40 times faster than that of the original formulation

Theoretical analysis of signal-to-noise ratios for transient evoked otoacoustic emission recordings.

Recordings of transient-evoked otoacoustic emissions (TEOAEs) suffer from two main sources of contamination: Random noise and the stimulus artifact. The stimulus artifact can be substantially reduced by using a derived non-linear recording paradigm. Three such paradigms are analyzed, called here the level derived non-linear (LDNL), the double-evoked (DE), and the rate derived non-linear (RDNL) paradigms. While these methods successfully reduce the stimulus artifact, they lead to an increase in contamination by random noise. In this study, the signal-to-noise ratio (SNR) achievable by these three paradigms is compared using a common theoretical framework. This analysis also allows the optimization of the parameters of the RDNL paradigm to achieve the maximum SNR. Calculations based on the analysis with typical parameters used in practice suggest that when ranked in terms of their SNR for a given averaging time, RDNL performs best followed by the LDNL and DE paradigm

Spontaneous otoacoustic emissions measured using an open ear-canal recording technique

Spontaneous otoacoustic emissions (SOAEs) and synchronized spontaneous otoacoustic emissions (SSOAEs) were recorded using both the standard closed-canal method of recording and a novel open-canal method which involved suspending the probe at the entrance to the ear canal with no occluding tip. In both conditions, a probe tube microphone was inserted down the ear canal to measure the acoustic pressure near the tympanic membrane. Open- and closed-canal recordings were obtained in twelve otologically normal ears, all of which exhibited SSOAEs, and 6 of which exhibited SOAEs. The results were analysed to identify any differences in response to frequency and amplitude. The different recording conditions appeared to have no significant effect on SOAE or SSOAE frequency, suggesting little effect on the SOAE generator within the cochlea. Below about 2 kHz, the amplitude for both types of emission was less for the open-canal recording when compared to the closed-canal recordings. Above 2 kHz, SSOAE amplitudes were greater in the open- than the closed-canal condition. Model stimulations of the ear canal and middle-ear acoustics are presented which were in qualitative agreement with the results shown for the effects on emission amplitudes.<br/

A parametric model of the spectral periodicity of stimulus frequency otoacoustic emissions

A model for estimating the spectral period of stimulus frequency otoacoustic emissions (SFOAEs) is presented. The model characterizes the frequency spectrum of an SFOAE in terms of four parameters which can be directly related to cochlear mechanical quantities featuring in the theory of SFOAE generation proposed by Zweig and Shera [J. Acoust. Soc. Am. 98, 2018–2047 (1995)]. The results of applying the parametric model to SFOAEs generated by cochlear models suggest that it gives a sensitive measure of spectral period. It is concluded that the parametric model may be a useful tool for detecting small changes in cochlear function using SFOAE measurements

Investigating OAEs and audiogram fine structure in the extended high-frequency region

IntroductionSeveral studies suggest that both noise induced hearing loss (NIHL) and age related hearing loss (ARHL) lead to more rapid hearing threshold level (HTL) shifts in the extended-high frequency (EHF) 10-18 kHz region than in the conventional frequency region (0.25 – 8 kHz). It has therefore been hypothesised that the EHF region can provide early signs of hearing damage, before the conventional frequencies. Previous studies at conventional audiometric frequencies (&lt;8 kHz) have found that the presence of audiogram fine structure (AFS) is associated with normal HTL and normal transient evoked otoacoustic emissions (TEOAEs). The main aim of the present study is to investigate whether the relationships between HTL, otoacoustic emissions (OAEs) (TEOAEs and distortion product otoacoustic emissions (DPOAEs)), and audiogram fine-structure obtained in the EHF region are similar to those reported at conventional frequencies.Research Questions1. Do we see a reduction in the depth of the EHF audiogram fine structure with increasing EHF-HTLs and with a reduction in amplitude of EHF-OAEs?2. Do we see an average spectral periodicity in the EHF audiogram fine structure that is consistent with predictions from cochlear mechanical theory?MethodHearing will be assessed in normal otological adults with measurable EHF-HTL. Hearing sensitivity will be assessed using EHF audiometry (10-18 kHz) and EHF-AFS (8-16 kHz), while cochlear function will be evaluated with EHF-TEOAEs, EHF-DPOAEs and spontaneous OAEs.ResultsWithin subject design will be conducted to assess the correlation between EHF-measurements. Results will be present the correlation between the EHF-HTL, TEOAEs, DPOAEs, and AFS at EHF hearinglevel. The average spectral periodicity of the EHF-AFS will also be presented

Investigating measures of high-frequency hearing function and noise-exposure in a longitudinal study

IntroductionSome studies suggest that both noise induced hearing loss (NIHL) and age related hearing loss (ARHL) lead to relatively rapid hearing threshold level (HTL) shifts in the extended-high frequency (EHF) 10-18 kHz region. It has therefore been hypothesised that NIHL may first show up as HTL elevations in the 10-18 kHz frequency range, before showing up as a 4-kHz notch. This poster is presented with two main research questions: 1. Can we detect a difference in EHF hearing function between a low- and high-noise exposure group of young adults? 2. Can we detect any changes in EHF hearing function over 12-14 month period that depend on noise-exposure? (result for this RQ are not yet avalible)MethodHearing function was assessed in 58 participant with normal hearing, subjects were assigned to either high or low noise exposed group, based on the results of noise-exposure interview. Hearing was assessed using EHF audiometry (10-18 kHz) and extended high frequency otoacoustic emissions (OAEs) (EHF- distortion product otoacoustic emissions (EHF-DPOAEs) EHF- transient evoked otoacoustic emissions (EHF-TEOAEs).Results Between-group comparisons were conducted to assess the impact of noise on hearings. Measurements will be conducted at three time points: baseline; 6 months; 12 months to allow any changes over time to be assessed.Results of ANCOVA (with age as the covariate) for comparisons: Differences in measures of EHF-hearing function at baseline between low- and high-noise exposure groups, revealed that ; 1. Hearing threshold level at the EHF showed that there are no statistically significant differences between groups. 2. EHF-distortion product otoacoustic emissions showed statistically significant differences between groups. 3. EHF TEOAEs means were statistically difference between groups.ConclusionEHF Hearing threshold level was not statistically different between the groups. While EHF-TEOAEs and EHF DPOAEs showed statistical difference between groups.<br/

Transient otoacoustic emissions and audiogram fine structure in the extended high-frequency region

Objective: previous studies at conventional audiometric frequencies found associations between the rip-ple depth seen in audiogram fine structure (AFS) and amplitudes of both transient evoked otoacoustic emissions (TEOAEs) and overall hearing threshold levels (HTLs). These associations are explained by the cochlear mechanical theory of multiple coherent reflections of the travelling wave apically by reflections sites on the basilar membrane and basally by the stapes.Design: the aim was to investigate whether a similar relationship is seen in the extended high-frequency (EHF) range from 8–16 kHz. Measurements from 8–16 kHz were obtained in normal-hearing subjects com-prising EHF HTLs, EHF TEOAEs using a double evoked paradigm, and Bekesy audiometry to assess AFS ripple depth and spectral periodicity.Study Sample: twenty eight normal-hearing subjects participated.Results: results showed no significant correlation between AFS ripple depth and either frequency-aver-aged EHF HTLs or EHF TEOAE amplitudes. The amplitude of AFS ripple depth was also lower than that seen in the conventional frequency region and spectral periodicity in the ripple more difficult to discern. Conclusion: the results suggest a weaker interference pattern between forward and reverse cochlear travelling waves in the most basal region compared to more apical regions, or a difference in cochlear mechanical properties

The effect of suppression on the periodicity of stimulus frequency otoacoustic emissions: experimental data

In a companion paper [Lineton and Lutman, J. Acoust. Soc. Am. 114, 859–870 (2003)], changes in the spectral period of stimulus frequency otoacoustic emissions (SFOAEs) during self-suppression and two-tone suppression were simulated using a nonlinear cochlear model based on the distributed roughness theory of otoacoustic emission generation [Zweig and Shera, J. Acoust. Soc. Am. 98, 2018–2047 (1995)]. The current paper presents the results of an experimental investigation of SFOAE suppression obtained from 20 human subjects. It was found that, in most subjects, the spectral period increased during self-suppression, but reduced during high-side two-tone suppression. This pattern of results is in close agreement with the predictions of the cochlear model, and therefore strongly supports the distributed roughness theory of Zweig and Shera. In addition, the results suggest that the SFOAE spectral period is sensitive to changes in the state of the cochlear amplifier