A new study has revealed that echoes and fluctuations in volume help humans figure out how far away sounds are.
Researchers from UConn Health reported that echoes and fluctuations in volume (amplitude modulation) are the cues people use to figure the distance between them and the source of a noise.
Reverberations, or echoes, tend to degrade amplitude modulation, smoothing out the amplitude's peaks and valleys. Almost any environment has echoes as sounds bounce off of objects such as walls or trees, the ground, et cetera. The farther away the source of a sound would be from a listener, the more echoes there would be, and the more degraded the depth of amplitude modulation gets. The neurons fired less and less when the sound moved further away and the depth of amplitude modulation degraded more and more.
Pavel Zahorik, a researcher at the University of Louisville School of Medicine, tested the same amplitude modulated noise using human volunteers and got the same results; people need both amplitude modulation and reverberation to figure out how far away a sound is. Without amplitude modulation, a person can't tell how far away that noise is. Neither can she do it in an anechoic (echo-free) room.
