Auditory localization of a nearby point source

Abstract

Although human auditory localization has been studied extensively in the past century, little is known about the localization of nearby sound sources. The head-related transfer function (HRTF) contains all relevant localization information and has been thoroughly examined for relatively distant sources, but may exhibit unique properties in the ‘‘near-field’’ region within 1 m of the center of the head. A rigid-sphere computational model of the head has been used to estimate near-field HRTFs, and a KEMAR manikin and a specialized acoustic ‘‘point’’ source have been used to measure HRTFs for sources as close as 0.25 m. For a fixed source direction, the interaural time delay is roughly independent of distance, but the interaural amplitude difference increases dramatically as the source approaches within 1 m of the head. When the source is near one ear, the interaural amplitude difference exceeds 20 dB across the audio spectrum. The differences between near-field and more distal HRTFs will be discussed, including comments on how near-field effects may facilitate three-dimensional localization judgments. In addition, preliminary results of a psychoacoustic experiment designed to measure human localization performance for sources within ‘‘arm’s reach’’ of the listener may be presented. [Work supported by AFOSR and NIDCD].