Upper hemisphere sound localization using head-related transfer functions in the median plane and interaural differences

Morimoto and Aokata [J. Acoust. Soc. Jpn. (E), 5, 165–173 (1984)] clarified that the same directional bands observed on the median plane by Blauert occur in any sagittal plane parallel to the median plane. Based upon this observation, they hypothesized that the spectral cues that help to determine the vertical angle of a sound image may function commonly in any sagittal plane. If this hypothesis is credible, sound localization in any direction might be simulated by using head-related transfer functions (HRTFs) measured on the median plane to determine the vertical angle, and by using frequency-independent interaural differences to determine the lateral angle. In this paper, a localization test was performed to evaluate the hypothesis, and to examine a simulation method based on the hypothesis. For this test, stimuli simulating HRTFs measured on the median sagittal plane combined with interaural differences measured on the frontal horizontal plane were presented to the subjects. The results supported the hypothesis and confirmed that the experimental simulation was not only possible, but also quite effective in controlling sound image location.