Distance discrimination thresholds of proximal sound sources in a real anechoic environment

Abstract

When a sound source off the midline is located close to the head, the interaural level difference changes dramatically with distance. Although distance discrimination thresholds for frontal sound sources have been comprehensively studied, the thresholds for real lateral sound sources in the proximal region have rarely been explored. The present study measured distance discrimination thresholds via a loudspeaker located at different distances and directions, both with fixed-emission and normalized intensities referring to the head center, to confirm the contribution of near-field binaural cues in a quantitative manner. The results demonstrated that the sound level is the main cue for distance discrimination, and binaural cues promote the ability to perceive differences in sound distances for lateral sources located at 0.5 m from the head center. The thresholds for lateral sources were significantly lower than those for sources in the median plane, both with and without level cues. However, when the sound sources were located at a distance of 1.0 m, the promotion of lateral thresholds was not significant. This study provides plausible just-noticeable differences for distance discrimination at various directions and distances from the head.