For animals, it is very important to determine the direction of a sound as it can help with survival. This ability is called sound localization and it is a function of the auditory system. The brain is able to localize sound by using several components of the sound wave, such as interaural intensity (the amount of energy flowing in a sound wave between the ears); spectral information (a continuous series); and time differences in sounds, to name a few. Just like how a GPS (global positioning system) works, sound localization uses three dimensions for best results including horizontal (azimuth), vertical (elevation), and distance positions. If a sound is traveling, then velocity is also used for positioning the sound wave.
Humans are able to hear different sound frequencies (or wavelengths, from peak to peak of the sound) ranging from high to low sounds. However, this is dependent on the individual’s hearing ability of each ear and the quality of the sound. Specifically, for high frequencies (shorter wavelengths), the brain can detect the time of arrival by how the sound wave was reflected (or bounced) off the person’s torso, shoulders, and outer ears (pinnae). When the wave is reflected, some of the higher frequencies are lost and the brain can detect the minute differences between the original wave and the reflected wave. This information can help position and localize the sound source. For low frequencies (longer wavelengths), the brain uses the change in phase (peak to peak or valley to valley) of a sound to identify its position. This means that the brain determines if one ear received the sound’s peak and the other ear received the sound’s valley. This difference would be a shift of the phase that is used for localizing the source.
Patricia A. Bloomquist
See also: Auditory System; Cochlea; Cochlear Implants; Deafness; Vestibulocochlear Nerve
Blauert, Jens. (1996). Spatial hearing: The psychophysics of human sound localization (2nd ed.). Cambridge, MA: MIT Press.