The isoazimuthal perception of sounds across distance: A preliminary investigation into the location of the audio egocenter

Evidence indicates that both visual and auditory input may be represented in multiple frames of reference at different processing stages in the nervous system. Most models, however, have assumed that unimodal auditory input is first encoded in a head-centered reference frame. The present work tested this conjecture by measuring the subjective auditory egocenter in six blindfolded listeners who were asked to match the perceived azimuths of sounds that were alternately played between a surrounding arc of far-field speakers and a hand-held point source located three different distances from the head. If unimodal auditory representation is head centered, then "isoazimuth" lines fitted to the matching estimates across distance should intersect near the midpoint of the interaural axis. For frontomedially arranged speakers, isoazimuth lines instead converged in front of the interaural axis for all listeners, often at a point between the two eyes. As far-field sources moved outside the visual field, however, the auditory egocenter location implied by the intersection of the isoazimuth lines retreated toward or even behind the interaural axis. Physiological and behavioral evidence is used to explain this change from an eye-centered to a head-centered auditory egocenter as a function of source laterality.