Perceptual bias for rising tones

An approaching sound source creates a pattern of rising intensity that can specify the arrival time of the source1,2,3. Here we found that listeners reliably overestimated the change in level of rising level tones relative to equivalent falling level tones. In a natural environment this overestimation could provide a selective advantage, because rising intensity can signal movement of the source towards an organism. The bias was stronger at higher levels, suggesting that rising loudness is even more critical when a sound source is either close or loud. These results suggest a privileged status of dynamic rising loudness for harmonic tones and an asymmetry in the neural coding of harmonic dynamic intensity change.