Spectral cues in human sound localization

The differential contribution of the monaural and interaural spectral cues to human sound localization was examined using a combined psychophysical and analytical approach. The cues to a sound's location were correlated on an individual basis with the human localization responses to a variety of spectrally manipulated sounds. The spectral cues derive from the acoustical filtering of an individual's auditory periphery which is characterized by the measured head-related transfer functions (HRTFs). Auditory localization performance was determined in virtual auditory space (VAS). Psychoacoustical experiments were conducted in which the amplitude spectra of the sound stimulus was varied independently at each ear while preserving the normal timing cues, an impossibility in the free-field environment. Virtual auditory noise stimuli were generated over earphones for a specified target direction such that there was a "false" flat spectrum at the left eardrum. Using the subject's HRTFs, the sound spectrum at the right eardrum was then adjusted so that either the true right monaural spectral cue or the true interaural spectral cue was preserved. All subjects showed systematic mislocalizations in both the true right and true interaural spectral conditions which was absent in their control localization performance. The analysis of the different cues along with the subjects' localization responses suggests there are significant differences in the use of the monaural and interaural spectral cues and that the auditory system's reliance on the spectral cues varies with the sound condition.