The Effect of Hemispace, Velocity, and Direction on Spatial Localization of Moving Sounds

Motion influences the spatial localization of objects, with offset points overestimated in the direction of motion ("representational momentum" RM). Most RM studies use visual stimuli, but RM is also present for auditory stimuli. This study examined auditory RM in front vs. back hemispace to examine moving sounds that are in vs. out of the visual field. Sound movement velocity and direction were also tested. Participants (n=30) heard virtual sounds in the horizontal plane that moved towards midline. The sounds had an offset at one of 7 locations at or flanking midline (0° midline, ±4°, ±8°, ±16°), and participants made left/right judgments about offset location relative to midline. The dependent variable was the point of subjective equality (PSE), calculated by a psychometric function (offset location x % right). Analysis examined factors of hemispace (front, back), velocity (20°/s, 40°/s), and movement direction (leftward, rightward). A PSE was also calculated for static sounds as a control, which was subtracted from the motion PSEs. Results showed that the PSEs for static front and back sounds were nearly identical, and slightly to the left of midline (-1.3±0.2°). For moving stimuli, the offset location was overestimated at 20°/s (p=.009), indicating RM, and underestimated at 40°/s (p<.001). The velocity differences were slightly greater in the front vs. back hemispace (p<.05), and sounds moving rightward had greater underestimations than leftward sounds (p=.002). The velocity effect is similar to reports of decreased RM with increased velocities, but here the effect shifted from overestimations at 20°/s (RM) to underestimations at 40°/s, suggesting representational lag. Our results suggest that the properties of moving sounds determined how motion influences spatial localization of offset points. Applications of understanding the natural perceptual processes include improvement of spatial localization training and virtual reality experiences.