The effect of gaze eccentricity on perceived sound direction and its relation to visual localization.

This study investigates the influence of eye position on the localization of a free-field sound source by employing a pointing method. While fixating visual targets in various directions, the subjects indicated the perceived direction of a sound source by adjusting the azimuthal angle of a swivel pointer. The perceived sound azimuth shifted consistently opposite to the direction of eccentric gaze. i.e. to the left when gaze was to the right and vice versa. This shift resembled an approximately linear function of horizontal gaze direction. The mean magnitude of the shift was 3.1 degrees when the gaze was 45 degrees to the side (mean slope 0.069 degrees per degree eccentricity in gaze direction). An additional experiment investigated the relation of this effect to visual localization. Using the same method, the shift of perceived visual azimuth was measured as a function of gaze direction. The results indicate a shift in the same direction as the auditory shift (opposite to the direction of eccentric gaze), but with a significantly greater magnitude, which was 5.7 degrees for 45 degrees eccentricity in gaze direction. The perceived shifts of sound direction depending on gaze eccentricity may result from incomplete transformations of the auditory spatial coordinates from a craniocentric to an oculocentric frame of reference within neural maps of space, as has been suggested by previous neurophysiological investigations.