Abstract:
Experiments in a hybrid (natural and virtual) acoustical environment suggest that subjects are largely insensitive to detail in the HRTF magnitude spectra in anechoic space. In the primary experiments, subjects were tested in a 2I, 2AFC discrimination paradigm and were required to judge the order of free-field stimuli (delivered from a loudspeaker) and virtual stimuli (presented from tubephones in the ear canals) for corresponding spatial locations in the horizontal plane. Virtual stimuli were constructed from individually measured HRTFs and delivered near the entrance of the ear canal via tubes that were confirmed to not significantly alter the natural sound field. Each interval consisted of a pair of 80-ms noise bursts separated by 100 ms. Performance of subjects was at chance for all four azimuthal positions tested, even when the HRTF magnitude spectra used for the virtual stimuli were systematically smoothed by large amounts. With extreme smoothing, subjects reported an externalized and elevated sound image, consistent with a natural sound image from a loudspeaker directly overhead. These latter results further suggest that directional features in the HRTF are not responsible for the externalization of sound images. [Work supported by NIDCD.]