Human echolocation is the ability of humans to detect objects in their environment by sensing echoes from those objects, by actively creating sounds: for example, by tapping their canes, lightly stomping their foot, clapping their hands, snapping their fingers, or making clicking noises with their mouths. People trained to orient by echolocation can interpret the sound waves reflected by nearby objects, accurately identifying their location, size and density. That is, the echoes allow detailed information about the object's location (where it is), dimension (size and shape), and density (solidity) to be identified. For example, they provide information about the location and nature of objects and their environment, such as walls, doorways, recesses, overhangs, pillars, ascending curbs and steps, fire hydrants, pedestrians, parked or moving vehicles, trees and other foliage. Some of them can perform tricks such as running, basketball, rollerblading, football and skateboarding, and can safely navigate wilderness areas by hiking or mountain biking.
Overview Many blind individuals passively use natural environmental echoes to sense details about their environment (passive echolocation); however, others actively produce mouth clicks (palatal click) and are able to gauge information about their environment using the echoes from those clicks (active echolocation). Both passive and active echolocation help blind individuals sense their environments. Those who can see their environments often do not readily perceive echoes from nearby objects, due to an echo suppression phenomenon brought on by the precedence effect. However, with training, sighted individuals with normal hearing can learn to avoid obstacles using only sound, showing that echolocation is a general human ability. John Levack Drever refers to echolocation in humans an example of panacusi loci, spatial hearing that exceeds the prescribed normative mode.
Discrimination ability Echoes and other sounds can convey spatial data that are comparable in many respects to those conveyed by light. A blind traveler using echoes can perceive very complex, detailed, and specific features of the world from distances far beyond physical reach. Echoes can make information available about the nature and arrangement of objects and environmental features such as walls, doorways, recesses, overhangs, pillars, ascending curbs and steps, fire hydrants, pedestrians, parked or moving vehicles, trees and other foliage, and much more. Echoes can give detailed information about location (where objects are), dimension (how big they are and their general shape), and density (how solid they are). Location is generally broken down into distance from the observer and direction (left/right, front/back, high/low). Dimension refers to the object's height (tall or short) and breadth (wide or narrow). By understanding the interrelationships of these qualities, much can be perceived about the nature of an object or multiple objects. For example, an object that is tall and narrow may be recognized quickly as a pole. An object that is tall and narrow near the bottom while broad near the top would be a tree. Something that is tall and very broad registers as a wall or building. Something that is broad and tall in the middle, while being shorter at either end may be identified as a parked car. An object that is low and broad may be a planter, retaining wall, or curb. And finally, something that starts out close and very low but recedes into the distance as it gets higher is a set of steps. Density refers to the solidity of the object (solid/sparse, hard/soft). Awareness of density adds richness and complexity to one's available information. For instance, an object that is low and solid may be recognized as a table, while something low and sparse sounds like a bush; but an object that is tall and broad and very sparse is probably a fence.
Mechanism Vision and hearing are akin in that each entails detection of reflected waves of energy. Vision processes light waves that travel from their source, bounce off surfaces throughout the environment and enter the eyes. Similarly, the auditory system processes sound waves as they travel from their source, bounce off surfaces and enter the ears. Both neural systems can extract a great deal of information about the environment by interpreting the complex patterns of reflected energy that their sense organs receive. In the case of sound these waves of reflected energy are referred to as echoes.
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