Auditory distance perception in front and rear space

The distance of sound sources relative to the body can be estimated using acoustic level and direct-to-reverberant ratio cues. However, the ability to do this may differ for sounds that are in front compared to behind the listener. One reason for this is that vision, which plays an important role in calibrating auditory distance cues early in life, is unavailable for rear space. Furthermore, the filtering of sounds by the pinnae differs if they originate from the front compared to the back. We investigated auditory distance discrimination in front and rear space by comparing performance for auditory spatial bisection of distance and minimum audible distance discrimination (MADD) tasks. In the bisection task, participants heard three successive bursts of noise at three different distances and indicated whether the second sound (probe) was closer in space to the first or third sound (references). In the MADD task, participants reported which of two successive sounds was closer. An analysis of variance with factors task and region of space showed worse performance for rear than for front space, but no significant interaction between task and region of space. For the bisection task, the point of subjective equality (PSE) was slightly biased towards the body, but the absolute magnitude of the PSE did not differ between front and rear space. These results are consistent with the hypothesis that visual information is important in calibrating the auditory representation of front space in distance early in life.