Sound localization is the ability to pinpoint the source and location of a sound, using input from the ears, as well as cognitive processes. Hearing animals are all capable of this to some extent, although some are better at it than others; owls, for example, have excellent sound localization abilities because they rely on sound to locate and track their prey. Errors with sound localization can cause disorientation and confusion.
When sound enters the ears, it goes through a complex filtering process. The ear can return information to the brain on roughly where sounds come from, as well as providing data about volume and frequency of the sound. The brain can process this information extremely rapidly to provide input about what is happening in the surrounding environment. These reactions occur in fractions of a second, providing a nearly real-time feed of information about noise. As animals develop, they also learn to distinguish fine details; humans, for instance, learn to recognize speech at a very early age.
Evolutionwise, sound localization has a number of advantages. Predators use sound, among other senses, to find their prey and rely on the ability to precisely fix locations on the basis of sound alone when other senses may not be available or may be compromised. Prey need an excellent sense of hearing and a keen sense of location and distance so they can avoid predators. A horse grazing in a pasture, for example, can hear the sound of approaching feet, determine what kind of animal is nearing, and find out where the animal is coming from, all without looking up to get visual information.
Neurologically, the processes involved in sound localization are very complex. People can experience a variety of problems along the way when they attempt to localize sounds. Losing hearing, even partially, in one ear can throw off the brain's calculations, returning bad information. Likewise, errors in the pathways to the brain may distort sensory information and the brain can also scramble up sound data when it is processing it, returning bad information.
Tricks can be played with sound localization to create the illusion of sounds originating from a different or unusual location. Ventriloquism involves making people believe a sound is coming from the mouth of a dummy instead of its handler, for example. Distorted sound designed to confuse and imbalance people may be used in funhouses, theatrical films, and even interrogation rooms, with the goal of making people feel unsettled and nervous.