The Doppler effect — an evolutionary critical cue for the perception of the direction of moving sound sources

Objects that are about to confront us are crucial for prospective actions. Even if we are not able to see what is approaching, the processing of auditory information enables us to identify the direction of moving sound sources. Various mechanisms allow us to accomplish this task most effectively. To date all of the mechanisms that have been widely discussed are based on sound-level differences or on timing aspects of incoming sounds. We considered sound sources which move radially towards or away from the listener emitting signals with constant amplitudes. If objects are too far away from us to produce any perceivable level differences, we have to rely on other acoustic cues. In an experiment using synthesized sounds in a virtual environment, we show that the so-called Doppler effect, which shifts the frequency of the direct sound and its reflections, is sufficient to identify correctly whether a moving sound source approaches or recedes.