An area of reduced sound intensity around the ear that is further from a sound source, as a result of reflection and absorption of sound waves by the head, leading to a binaural difference in loudness that is used as a cue (2) for localizing sounds above about 1,000 hertz (about two octaves above Middle C), which have wavelengths shorter than the diameter of the head, but not for longer waves that bend round the head and do not produce sonic shadows. It is less accurate than localization based on transient disparity and phase delay, except for very high-pitched sounds with frequencies above 8,000 hertz, when the pinna becomes effective as a focusing device. Animals with very small heads, such as rodents, cannot use transient disparity or phase delay, because the time differences are too tiny to be detected accurately, but their ears are sensitive to very high-pitched sounds whose wavelengths are shorter than the diameter of their heads, which enables them to use sonic shadows to locate sounds. Also called a binaural intensity difference, an interaural intensity difference, or a sound shadow. See also binaural ratio, biosonar, cone of confusion, sound localization.