Motion parallax serves as an independent cue in sound source disambiguation

In the absence of dominant cues to the distance of a sound source from the observer, estimating absolute or relative distance becomes difficult. Motion parallax may contribute to this estimation. However, its role as an independent cue has not yet been investigated. To address this issue, we designed an experiment that included logarithmically varying distance of sound source along the depth plane of the observer, elimination of distance related loudness using perceptual loudness equalization and to and fro (laterally) movement of subjects while the sounds were generated in three conditions a simultaneous playback, sequential playback and simultaneous playback of phase-interrupted sounds. Sequential presentation of the low and high sound subjects showed a substantial improvement in distance estimates relative to the baseline static condition. Improvement was also observed for the simultaneous phase interrupted sound condition. Here we demonstrate for the first time the existence of auditory motion parallax from lateral self- motion and show that it aids distance estimation of sound position. Interestingly, a bias to perceive low frequency sounds as farther away was also observed. Auditory depth perception is improved by lateral observer motion, which alters the inter-aural difference cues available