Volume 126, Issue 3, September 2009
Index of content:
- PHYSIOLOGICAL ACOUSTICS 
Fast multipole boundary element method to calculate head-related transfer functions for a wide frequency range126(2009); http://dx.doi.org/10.1121/1.3177264View Description Hide Description
Head-related transfer functions (HRTFs) play an important role in spatial sound localization. The boundary element method(BEM) can be applied to calculate HRTFs from non-contact visual scans. Because of high computational complexity, HRTF simulations with BEM for the whole head and pinnae have only been performed for frequencies below . In this study, the fast multipole method (FMM) is coupled with BEM to simulate HRTFs for a wide frequency range. The basic approach of the FMM and its implementation are described. A mesh with over 70 000 elements was used to calculate HRTFs for one subject. With this mesh, the method allowed to calculate HRTFs for frequencies up to . Comparison to acoustically-measured HRTFs has been performed for frequencies up to , showing a good congruence below . Simulations with an additional shoulder mesh improved the congruence in the vertical direction. Reduction in the mesh size by 5% resulted in a substantially-worse representation of spectral cues. The effects of temperature and mesh perturbation were negligible. The FMM appears to be a promising approach for HRTF simulations. Further limitations and potential advantages of the FMM-coupled BEM are discussed.
126(2009); http://dx.doi.org/10.1121/1.3168508View Description Hide Description
Different attempts have been made to directly measure frequency specific basilar membrane (BM) delays in animals, e.g., laser velocimetry of BM vibrations and auditory nerve fiber recordings. The present study uses otoacoustic emissions(OAEs) and auditory brainstem responses (ABRs) to estimate BM delay non-invasively in normal-hearing humans. Tone bursts at nine frequencies from served as stimuli, with care taken to quantify possible bias due to the use of tone bursts with different rise times. BM delays are estimated from the ABR latency estimates by subtracting the neural and synaptic delays. This allows a comparison between individual OAE and BM delays over a large frequency range in the same subjects, and offers support to the theory that OAEs are reflected from a tonotopic place and carried back to the cochlear base via a reverse traveling wave.
126(2009); http://dx.doi.org/10.1121/1.3192220View Description Hide Description
Behavioral and objective estimates of cochlear response times (CRTs) and traveling-wave (TW) velocity were compared for three normal-hearing listeners. Differences between frequency-specific CRTs were estimated via lateralization of pulsed tones that were interaurally mismatched in frequency, similar to a paradigm proposed by Zerlin [(1969). J. Acoust. Soc. Am.46, 1011–1015]. In addition, derived-band auditory brainstem responses were obtained as a function of derived-band center frequency. The latencies extracted from these responses served as objective estimates of CRTs. Estimates of TW velocity were calculated from the obtained CRTs. The correspondence between behavioral and objective estimates of CRT and TW velocity was examined. For frequencies up to 1.5 kHz, the behavioral method yielded reproducible results, which were consistent with the objective estimates. For higher frequencies, CRT differences could not be estimated with the behavioral method due to limitations of the lateralization paradigm. The method might be useful for studying the spatiotemporal cochlear response pattern in human listeners.