Auditory localization of nearby sources. II. Localization of a broadband source

Although many researchers have examined auditory localization for relatively distant sound sources, little is known about the spatial perception of nearby sources. In the region within 1 m of a listener's head, defined as the "proximal region," the interaural level difference increases dramatically as the source approaches the head, while the interaural time delay is roughly independent of distance. An experiment has been performed to evaluate proximal-region localization performance. An auditory point source was moved to a random position within 1 m of the subject's head, and the subject responded by pointing to the perceived location of the sound with an electromagnetic position sensor. The overall angular error (17 degrees) was roughly comparable to previously measured results in distal-region experiments. Azimuth error increased slightly as the sound source approached the head, but elevation performance was essentially independent of source distance. Distance localization performance was generally better than has been reported in distal-region experiments and was strongly dependent on azimuth, with the stimulus-response correlation ranging from 0.85 to the side of the head to less than 0.4 in the median plane. The results suggest that the enlarged binaural difference cues found in the head-related transfer function (HRTF) for nearby sources are important to auditory distance perception in the proximal region.