Volume 126, Issue 6, December 2009
Index of content:
- PHYSIOLOGICAL ACOUSTICS 
126(2009); http://dx.doi.org/10.1121/1.3243310View Description Hide Description
Sound pressure level in-situmeasurements are sensitive to standing-wave pressure minima and have the potential to result in over-amplification with risk to residual hearing in hearing-aid fittings. Forward pressure level (FPL) quantifies the pressure traveling toward the tympanic membrane and may be a potential solution as it is insensitive to ear-canal pressure minima. Derivation of FPL is dependent on a Thevenin-equivalent source calibration technique yielding source pressure and impedance. This technique is found to accurately decompose cavitypressure into incident and reflected components in both a hard-walled test cavity and in the human ear canal through the derivation of a second sound-level measure termed integrated pressure level (IPL). IPL is quantified by the sum of incident and reflected pressure amplitudes. FPL and IPL were both investigated as measures of sound-level entering the middle ear. FPL may be a better measure of middle-ear input because IPL is more dependent on middle-ear reflectance and ear-canal conductance. The use of FPL in hearing-aid applications is expected to provide an accurate means of quantifying high-frequency amplification.
Postnatal development of sound pressure transformations by the head and pinnae of the cat: Binaural characteristics126(2009); http://dx.doi.org/10.1121/1.3257234View Description Hide Description
There are three acoustical cues to sound location: Interaural time differences(ITDs), interaural level differences (ILDs), and monaural spectral shape cues. During development, the increasing interaural distance and pinnae size associated with a growing head and pinnae result in localization cues that change continuously until maturation is complete. Here the authors report measurements of both the physical dimensions of the head and pinnae, as well as acoustical measurements of the binaural localization cues of cats aged 1.3 weeks to adulthood. For a given source location, ILD magnitude tended to increase with both frequency and age. Moreover, the range of significant ILD production shifted with age from higher to lower frequencies. ITD magnitude increased with age. Partial correlation analyses revealed that increasing pinnae size accounted for of the variance in the development of ILDs while increasing head size accounted for virtually none. On the other hand, increases in both the head and pinnae sizes contributed to the development of the ITD cues accounting for and of the variance, respectively. ILD and ITD cues in cats reach maturity by and , respectively, which match the time period over which the pinnae and head dimensions reach maturity.
Use of the matching pursuit algorithm with a dictionary of asymmetric waveforms in the analysis of transient evoked otoacoustic emissions126(2009); http://dx.doi.org/10.1121/1.3243294View Description Hide Description
Transiently evoked otoacoustic emissions (TEOAEs) are normally modeled as the sum of asymmetric waveforms. However, some previous studies of TEOAEs used time-frequency (TF) methods to decompose the signals into symmetric waveforms. This approach was justified mainly as a means to reduce the complexity of the calculations. The present study extended the dictionary of numeric functions to incorporate asymmetric waveforms into the analysis. The necessary calculations were carried out using an adaptive approximation algorithm based on the matching pursuit (MP) numerical technique. The classic MP dictionary uses Gabor functions and consists of waveforms described by five parameters, namely, frequency, latency, time span, amplitude, and phase. In the present investigation, a sixth parameter, the degree of asymmetry, was added in order to enhance the flexibility of this approach. The effects of expanding the available functions were evaluated by means of both simulations using synthetic signals and authentic TEOAEs. The resulting analyses showed that the contributions of asymmetric components in the OAE signal are appreciable. In short, the expanded analysis method brought about important improvements in identifying TEOAE components including the correct detection of components with long decays, which are often related to spontaneous OAE activity, the elimination of a “dark energy” effect in TF distributions, and more reliable estimates of latency-frequency relationships. The latter feature is especially important for correct estimation of latency-frequency data, which is a crucial factor in investigations of OAE-generation mechanisms.