Volume 120, Issue 1, July 2006
Index of content:
- PHYSIOLOGICAL ACOUSTICS 
The effect of superior-canal opening on middle-ear input admittance and air-conducted stapes velocity in chinchilla120(2006); http://dx.doi.org/10.1121/1.2204356View Description Hide Description
The recent discovery of superior semicircular canal (SC) dehiscence syndrome as a clinical entity affecting both the auditory and vestibular systems has led to the investigation of the impact of a SC opening on the mechanics of hearing. It is hypothesized that the hole in the SC acts as a “third window” in the inner ear which shunts sound-induced stapes volume velocity away from the cochlea through the opening in the SC. To test the hypothesis and to understand the third window mechanisms the middle-ear input admittance and sound-induced stapes velocity were measured in chinchilla before and after surgically introducing a SC opening and after patching the opening. The extent to which patching returned the system to the presurgical state is used as a control criterion. In eight chinchilla ears a statistically significant, reversible increase in low-frequency middle-ear input admittance magnitude occurred as a result of opening the SC. In six ears a statistically significant reversible increase in stapes velocity was observed. Both of these changes are consistent with the hole creating a shunt pathway that increases the cochlear input admittance.
120(2006); http://dx.doi.org/10.1121/1.2205130View Description Hide Description
When distortion product otoacoustic emissions (DPOAEs) are measured with a high-frequency resolution, the DPOAE shows quasi-periodic variations across frequency, called DPOAE fine structure. In this study the DPOAE fine structure is determined for 50 normal-hearing humans using fixed primary levels of . An algorithm is developed, which characterizes the fine structure ripples in terms of three parameters: ripple spacing, ripple height, and ripple prevalence. The characteristic patterns of fine structure can be found in the DPOAE of all subjects, though the DPOAE fine structure characteristics are individual and vary from subject to subject. On average the ripple spacing decreases with increasing frequency from oct at to oct at . The ripple prevalence is two to three ripples per oct, and ripple heights of up to could be detected. The 50 normal-hearing subjects were divided into two groups, the subjects of group A having slightly better hearing levels than subjects of group B. The subjects of group A have significantly higher DPOAE levels. The overall prevalence of fine structure ripples do not differ between the two groups, but are higher and narrower for subjects of group B than for group A.
120(2006); http://dx.doi.org/10.1121/1.2204437View Description Hide Description
In a longitudinal study with 338 volunteers, audiometric thresholds and otoacoustic emissions were measured before and after 6 months of noise exposure on an aircraft carrier. While the average amplitudes of the otoacoustic emissions decreased significantly, the average audiometric thresholds did not change. Furthermore, there were no significant correlations between changes in audiometric thresholds and changes in otoacoustic emissions. Changes in transient-evoked otoacoustic emissions and distortion-product otoacoustic emissions were moderately correlated. Eighteen ears acquired permanent audiometric threshold shifts. Only one-third of those ears showed significant otoacoustic emission shifts that mirrored their permanent threshold shifts. A Bayesian analysis indicated that permanent threshold shift status following a deployment was predicted by baseline low-level or absent otoacoustic emissions. The best predictor was transient-evoked otoacoustic emission amplitude in the 4-kHz half-octave frequency band, with risk increasing more than sixfold from approximately 3% to 20% as the emission amplitude decreased. It is possible that the otoacoustic emissions indicated noise-induced changes in the inner ear, undetected by audiometric tests. Otoacoustic emissions may therefore be a diagnostic predictor for noise-induced-hearing-loss risk.
120(2006); http://dx.doi.org/10.1121/1.2204438View Description Hide Description
The aim of this paper is the introduction and comparison of consistent albeit passive mechanical models for the whole cochlea. A widely used transmission line filterbank, which hydrodynamically speaking is a long wave approximation (L model), suffers from a well-known inconsistency: its main modeling assumption is not valid within the resonance region, where most of the overall excitation takes place. In the present paper two approaches to overcome this inconsistency are discussed. One model is the average pressure (AP) model by Duifhuis, the other is obtained by a combination of a long and a short wave approximation (LS model). Considerable differences between the L and the LS model are observed. All models are compared by inserting them into the full integral equation obtained from the hydrodynamicequations and the boundary conditions. Here the LS model fares better than the AP model for small damping, whereas the opposite is true for higher damping. As expected, the L model fails badly in the resonance region.