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 localizat ion 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 consist ently opposite to the direction of eccentric gaze, i.e. to the left wh en gaze was to the right and vice versa. This shift resembled an appro ximately linear function of horizontal gaze direction. The mean magnit ude of the shift was 3.1 degrees when the gaze was 45 degrees to the s ide (mean slope 0.069 degrees per degree eccentricity in gaze directio n). 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 resul ts indicate a shift in the same direction as the auditory shift (oppos ite to the direction of eccentric gaze). but with a significantly grea ter magnitude, which was 5.7 degrees for 45 degrees eccentricity in ga ze direction. The perceived shifts of sound direction depending on gaz e eccentricity may result from incomplete transformations of the audit ory spatial coordinates from a craniocentric to an oculocentric frame of reference within neural maps of space, as has been suggested by pre vious neurophysiological investigations. (C) 1998 Elsevier Science B.V .