Asymmetries in human judgements of distance for approaching and receding sounds are predicted by a loudness model for time-varying sounds

Judging the distance of approaching threats is fundamental to an organism's survival. The adaptive looming bias theory posits that the auditory system evolved to produce a bias for approaching sounds, predicting: (1) judged start/end distances of approaching sounds will be smaller than the judged end/start distances of receding sounds moving over equivalent distances; (2) such asymmetries will be larger for closer than for farther distances; (3) asymmetries will be greater for tones than broadband noise; and (4) approaching sounds will be judged to travel a greater distance than receding sounds. Blindfolded participants judged starting and end distances for virtual anechoic approaching or receding tones and white noise, moving 11 m over three distance ranges (close, middle and far). Participants also judged static sound distances. The results were consistent with predictions (1) and (2), but not (3) and (4). The pattern of results was accurately predicted using a model of loudness for time-varying sounds, suggesting that when level is the primary distance cue, distance judgements for static and dynamic sounds are based on loudness; it is not necessary to invoke the adaptive perceptual bias theory to account for asymmetries in loudness and distance judgements between approaching and receding sounds.