(This talk was ultimately moved to the Hearing Seminar.)
For commercial applications head-related transfer functions (HRTFs) are typically greatly simplified for more real-time performance with less signal processing power. However, by definition HRTF is a measured response from a point in the free-field space to a point in the ear canal. Hence, it contains all the monaural and binaural cues needed for spatial hearing (for the particular sound incident and person). The essence is to understand in what extent are these auditory cues (perceptually) important, although matters underlying are complex. Author's wide-scaled analyses of carefully measured HRTFs show excellent system quality, high HRTF repeatability and effects of various factors to HRTFs, including ear plug type, experimenter's experience/carefulness, hairstyle and headpieces. The vast inter-person variance makes it difficult to find robust common trends or groups in HRTFs. A mathematical index of deviance helps to segregate atypical responses, hinting to possible artifacts and/or deviating anatomical structures. This measure also relates to quantitative analysis towards a generic HRTF model allowing a deeper understanding of (auditory) spatial hearing. Unfortunately, HRTFs are not sufficient to understand the true multisensory spatial hearing. Its multisensory interactions with vision, motion, bone conduction, tactile and vestibular sensing with their cognitive impacts need also to be considered in order to reveal the true enigma of spatial hearing. Elaborate multimodal perceptual experiments are thus being devised. Brain mechanisms are investigated by magnetoencephalography (MEG) measurements based on individual HRTFs. Results show differences in binaural neural processing between azimuth and elevation angles of 3-D sounds. Related publications available at www.lce.hut.fi/~kar/publications.html
Klaus A. J. Riederer
Helsinki University of Technology
Laboratory of Computational Engineering, Cognitive Science, and Technology
Laboratory of Acoustics and Audio Signal Processing
P.O. Box 9400, FIN-02015 HUT, Finland
E-mail: , URL: http://www.lce.hut.fi/~kar