AUDITORY-VISUAL SPATIAL INTEGRATION - A NEW PSYCHOPHYSICAL APPROACH USING LASER POINTING TO ACOUSTIC TARGETS

The alignment of auditory and visual spatial perception was investigat ed in four experiments, employing a method of laser pointing toward ac oustic targets in combination with various tasks of visual fixation in six subjects. Subjects had to fixate either a target LED or a laser s pot projected on a screen in a dark, anechoic room and, while doing so , direct the laser beam toward the perceived azimuthal position of the sound stimulus (bandpass-filtered noise; bandwidth 1-3 kHz; 70 dB sou nd pressure level, duration 10 s). The sound was produced by one of ni ne loudspeakers, located behind the acoustically transparent screen be tween 22 degrees to the left and 22 degrees to the right of straight a head. Systematic divergences between sound azimuth and laser adjustmen t were found, depending on the instructions given to the subjects. The eccentricity of acoustic targets was generally overestimated by up to 10.4 degrees with an only slight influence of gaze direction on this effect. When the sound source was straight ahead, gaze direction had a substantial influence in that the laser adjustments deviated by up to 5.6 degrees from sound azimuth, toward the side to which the gaze was directed. This effect of eye position decreased with increasing eccen tricity of the sound. These results can be explained by the interactiv e effects of four distinct factors: the lateral overestimation of the auditory eccentricity, the effect of eye position on sound localizatio n, the effect of the retinal eccentricity on visual localization, and the extraretinal effect of eye position on visual localization. (C) 19 98 Acoustical Society of America. [S0001-4966(98)06308-5]