Index of content:
Volume 119, Issue 5, May 2006
- PHYSIOLOGICAL ACOUSTICS 
Middle ear ossicles motion at hearing thresholds with air conduction and bone conduction stimulation119(2006); http://dx.doi.org/10.1121/1.2184225View Description Hide Description
Hearing threshold data with bone conduction and air conduction stimulation are combined with physiological and mechanical measurements of the middle ear ossicles vibration to compute the vibration level of the ossicles at threshold stimulation. By comparing the displacements of the stapes footplate with the two stimulation modalities and assuming the vibration of the stapes footplate to be the input to the cochlea when stimulation is by air conduction, the importance of middle ear ossicles inertia with bone conduction stimulation is evaluated. Given the limitations of the analysis, the results indicate that the inertia of the middle ear is not an important contribution to the perception of BC sound for frequencies below ; it seems to contribute to perception of bone conducted sound between the frequencies 1.5 and . At frequencies above , the analysis failed since the input to the cochlea is probably not through the oval window with bone conduction stimulation. Comparison of basilar membrane vibration data verified the calculations for frequencies between 0.8 and . It was also found that the fluid flow at the round window, rather than at the oval window, reflects the stimulation of the basilar membrane with bone conduction stimulation.
119(2006); http://dx.doi.org/10.1121/1.2188370View Description Hide Description
Current finite-element(FE) models of the eardrum are limited to low pressures because of the assumption of linearity. Our objective is to investigate the effects of geometric nonlinearity in FE models of the cat eardrum with an approximately immobile malleus for pressures up to , which are within the range of pressures used in clinical tympanometry. Displacements computed with nonlinear models increased less than in proportion to applied pressure, similar to what is seen in measured data. In both simulations and experiments, there is a shift inferiorly in the location of maximum displacement in response to increasingly negative middle-ear pressures. Displacement patterns computed for small pressures and for large positive pressures differed from measuredpatterns in the position of the maximum pars-tensa displacement. Increasing the thickness of the postero-superior pars tensa in the models shifted the location of the computed maximum toward the measured location. The largest computed pars-tensa strains were mostly less than 2%, implying that a linearized material model is a reasonable approximation. Geometric nonlinearity must be considered when simulating eardrum response to high pressures because purely linear models cannot take into account the effects of changing geometry. At higher pressures,material nonlinearity may become more important.
Simultaneous latency estimations for distortion product otoacoustic emissions and envelope following responsesa)119(2006); http://dx.doi.org/10.1121/1.2191616View Description Hide Description
The purpose of this research was to simultaneously estimate processing delays in the cochlea and brainstem using the same acoustic stimuli. Apparent latencies were estimated from ear canal measurements of distortion product otoacoustic emissions (DPOAEs), and scalp recordings of the envelope following response (EFR). The stimuli were equal level tone pairs (SPL) with the upper tone set at either 900 or to fix the initiation site of the DPOAE and EFR. The frequency of was swept continuously between frequency limits chosen to keep the EFR response between 150 and . The average DPOAE latencies were 9.6 and for and , and the corresponding EFR latencies were 12.4 and . In a control condition, a third (suppressor) tone was added near the DPOAE response frequency to evaluate whether the potential source at was contributing significantly to the measured emission. DPOAE latency is the sum of both inward and outward cochlear delays. The EFR apparent latency is the sum of inward cochlear delay and neural processing delay. Neural delay was estimated as approximately for both frequencies of stimulation.
Signal to noise ratio analysis of maximum length sequence deconvolution of overlapping evoked potentials119(2006); http://dx.doi.org/10.1121/1.2191609View Description Hide Description
In this study a general formula for the signal to noise ratio (SNR) of the maximum length sequence (MLS) deconvolution averaging is developed using the frequency domain framework of the generalized continuous loop averaging deconvolution procedure [Özdamar and Bohórquez, J. Acoust. Soc. Am.119, 429–438 (2006)]. This formulation takes advantage of the well known equivalency of energies in the time and frequency domains (Parseval's theorem) to show that in MLS deconvolution, SNR increases with the square root of half of the number of stimuli in the sweep. This increase is less than that of conventional averaging which is the square root of the number of sweeps averaged. Unlike arbitrary stimulus sequences that can attenuate or amplify phase unlocked noise depending on the frequency characteristics, the MLS deconvolution attenuates noise in all frequencies consistently. Furthermore, MLS and its zero-padded variations present optimal attenuation of noise at all frequencies yet they present a highly jittered stimulus sequence. In real recordings of evoked potentials, the time advantage gained by noise attenuation could be lost by the signal amplitude attenuation due to neural adaptation at high stimulus rates.
119(2006); http://dx.doi.org/10.1121/1.2169918View Description Hide Description
The time-course of the human medial olivocochlear reflex (MOCR) was measured via its suppression of stimulus-frequency otoacoustic emissions (SFOAEs) in nine ears. MOCR effects were elicited by contralateral, ipsilateral or bilateral wideband acoustic stimulation. As a first approximation, MOCR effects increased like a saturating exponential with a time constant of , and decayed exponentially with a time constant of . However, in ears with the highest signal-to-noise ratios , onset time constants could be separated into “fast,” , “medium,” , and “slow,” components, and there was an overshoot in the decay like an under-damped sinusoid. Both the buildup and decay could be modeled as a second order differential equation and the differences between the buildup and decay could be accounted for by decreasing one coefficient by a factor of 2. The reflex onset and offset delays were both . Although changing elicitor level over a SPL range produced a consistent systematic change in response amplitude, the time course did not show a consistent dependence on elictor level, nor did the time-courses of ipsilaterally, contralaterally, and bilaterally activated MOCR responses differ significantly. Given the MOCR’s time-course, it is best suited to operate on acoustic changes that persist for 100’s of milliseconds.