Swept-sines provide a tool for fast and high-resolution measurement of evoked otoacoustic emissions. During the measurement, a response to swept-sine(s) is recorded by a probe placed in the ear canal. Otoacoustic emissions can then be extracted by various techniques, e.g., Fourier analysis, the heterodyne method, and the least-square-fitting (LSF) technique. This paper employs a technique originally proposed with exponential swept-sines, which allows for direct emission extraction from the measured intermodulation impulse response. It is shown here that the technique can be used to extract distortion-product otoacoustic emissions (DPOAEs) evoked with two simultaneous swept-sines. For proper extraction of the DPOAE phase, the technique employs previously proposed adjusted formulas for exponential swept-sines generating so-called synchronized swept-sines (SSSs). Here, the SSS technique is verified using responses derived from a numerical solution of a cochlear model and responses measured in human subjects. Although computationally much less demanding, the technique yields comparable results to those obtained by the LSF technique, which has been shown in the literature to be the most noise-robust among the emission extraction methods.
- MeSH
- Fourierova analýza MeSH
- kochlea * fyziologie MeSH
- lidé MeSH
- otoakustické emise spontánní * fyziologie MeSH
- zvukovod fyziologie MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Stimulus-frequency otoacoustic emissions (SFOAEs) are generated by coherent reflection of forward traveling waves by perturbations along the basilar membrane. The strongest wavelets are backscattered near the place where the traveling wave reaches its maximal amplitude (tonotopic place). Therefore, the SFOAE group delay might be expected to be twice the group delay estimated in the cochlear filters. However, experimental data have yielded steady-state SFOAE components with near-zero latency. A cochlear model is used to show that short-latency SFOAE components can be generated due to nonlinear reflection of the compressor or suppressor tones used in SFOAE measurements. The simulations indicate that suppressors produce more pronounced short-latency components than compressors. The existence of nonlinear reflection components due to suppressors can also explain why SFOAEs can still be detected when suppressors are presented more than half an octave above the probe-tone frequency. Simulations of the SFOAE suppression tuning curves showed that phase changes in the SFOAE residual as the suppressor frequency increases are mostly determined by phase changes of the nonlinear reflection component.
The amplitudes of distortion-product otoacoustic emissions (DPOAEs) may abruptly decrease even though the stimulus level is relatively high. These notches observed in the DPOAE input/output functions or distortion-product grams have been hypothesized to be due to destructive interference between wavelets generated by distributed sources of the nonlinear-distortion component of DPOAEs. In this paper, simulations with a smooth cochlear model and its analytical solution support the hypothesis that destructive interference between individual wavelets may lead to the amplitude notches and explain the cause for onset and offset amplitude overshoots in the DPOAE signal measured for intensity pairs in the notches.
- MeSH
- akustická stimulace MeSH
- kochlea fyziologie MeSH
- lidé MeSH
- otoakustické emise spontánní * MeSH
- teoretické modely * MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Publikační typ
- časopisecké články MeSH
- tisková chyba MeSH
There is a long-lasting question of how distortion products (DPs) arising from nonlinear amplification processes in the cochlea are transmitted from their generation sites to the stapes. Two hypotheses have been proposed: (1) the slow-wave hypothesis whereby transmission is via the transverse pressure difference across the cochlear partition and (2) the fast-wave hypothesis proposing transmission via longitudinal compression waves. Ren with co-workers have addressed this topic experimentally by measuring the spatial vibration pattern of the basilar membrane (BM) in response to two tones of frequency f(1) and f(2). They interpreted the observed negative phase slopes of the stationary BM vibrations at the cubic distortion frequency f(DP) = 2f(1) - f(2) as evidence for the fast-wave hypothesis. Here, using a physically based model, it is shown that their phase data is actually in accordance with the slow-wave hypothesis. The analysis is based on a frequency-domain formulation of the two-dimensional motion equation of a nonlinear hydrodynamic cochlea model. Application of the analysis to their experimental data suggests that the measurement sites of negative phase slope were located at or apical to the DP generation sites. Therefore, current experimental and theoretical evidence supports the slow-wave hypothesis. Nevertheless, the analysis does not allow rejection of the fast-wave hypothesis.
- MeSH
- biologické modely MeSH
- deformace percepce fyziologie MeSH
- Fourierova analýza MeSH
- interferometrie metody MeSH
- kochlea fyziologie MeSH
- lasery MeSH
- lidé MeSH
- otoakustické emise spontánní fyziologie MeSH
- vibrace MeSH
- vnímání výšky zvuku fyziologie MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- srovnávací studie MeSH
The cubic component of the distortion product otoacoustic emission (DPOAE) in response to two tones of frequency f(1) and f(2) is generated by so-called primary- and secondary-source mechanisms in the cochlea. Interference between the resulting two source components can limit the usefulness of DPOAEs in assessing cochlear function. Although techniques are available for separating the source components, depending on the application, they can be either time-consuming or ineffective without a priori knowledge of optimal parameters. Here, we investigated, in humans, the possibility of separating the source components in the time-domain by sampling the onset and offset of the DPOAE-time signal at appropriate instants. Therefore, a DPOAE paradigm was developed in which the f(2) tone was periodically switched on during the continuous presence of the f(1) tone. F(2) was increased in 20-Hz steps from 1.5 to 2.5 kHz and the ratio f(2)/f(1) held constant at 1.2; measurements were made at six primary tone levels, ranging from L(2)=25 to 65 dB SPL. To investigate the possibility of separating the two sources by appropriate sampling, we developed an algorithm called onset-decomposition. The algorithm is based on the shape properties of DP-grams constructed from DPOAE responses at different time instants in the onset of the DPOAE signal. Thus, at each such time instant, the source components were extracted by time-windowing of the corresponding DP-gram. The time courses of the amplitude onsets of these separated primary- and secondary-source components provided evidence that the primary-source component attained its steady-state before the secondary-source component started to significantly influence the DPOAE by interference with the primary-source component. Consequently, in the final paradigm, the primary-source component is extracted by sampling the DPOAE signal at a single pre-defined time instant after the onset of the f(2) stimulus tone, before the secondary component begins to interfere. Based on the near-absence of interference maxima and minima in the DP-grams, the appropriate sampling instant was 8-10 ms for all frequencies and intensities in the stimulus set. Extracting the primary-source by onset sampling has the advantage that when individual source components for a given f(2) are to be investigated, there is no need to measure a DP-gram. In conclusion, it is shown that the technique can reliably and quickly separate the source components, making it an attractive paradigm for applications in basic research and clinical diagnosis. 2009 Elsevier B.V.
- MeSH
- akustická stimulace MeSH
- akustické impedanční testy MeSH
- algoritmy MeSH
- audiometrie čistými tóny MeSH
- biologické modely MeSH
- časové faktory MeSH
- dospělí MeSH
- Fourierova analýza MeSH
- kochlea fyziologie MeSH
- lidé MeSH
- otoakustické emise spontánní MeSH
- počítačové zpracování signálu MeSH
- reakční čas MeSH
- reflex akustický MeSH
- reprodukovatelnost výsledků MeSH
- sluchová dráha fyziologie MeSH
- sluchové kmenové evokované potenciály MeSH
- sluchový práh MeSH
- tlak MeSH
- zvuková spektrografie MeSH
- Check Tag
- dospělí MeSH
- lidé MeSH
- mužské pohlaví MeSH
- ženské pohlaví MeSH
- Publikační typ
- práce podpořená grantem MeSH
