The contributions of level and near-field head-related transfer functions cues on auditory distance perception in a free field

In a free field, distance-dependent level (or loudness) and near-field HRTF (head-related transfer functions) are considered to be two primary cues for auditory distance perception. However, some recent experiments using virtual auditory display (VAD) have exhibited inconsistent or even controversial results, especially regarding with the contribution of near-field HRTF cues to distance perception. Possible reasons for the inconsistency may be that static VAD with coarse approximation of near-field HRTFs were used in these experiments, which cause poor perception of externalization and error in HRTF-related cues. To address this problem, a set of psychoacoustic experiment using dynamic VAD with accurate near-field HRTFs is conducted in present work. The perceived distances of virtual source at target distance less than 1.0 m and with or without level normalization are evaluated. The results indicate that HRTF cue alone enable distance perception in the lateral region. In contrast, HRTF cue alone is insufficient for distance perception in the front region. A collaboration of HRTF and level cue enhances distance perception in all directions. Therefore, the present experiment yields results similar to previous experiment using real source and validate the contribution of level and near-field HRTF cues to distance perception.