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Human echolocation is the ability of humans to sense objects in their environment by hearing echoes from those objects. This ability is used by some blind people to navigate within their environment. They actively create sounds, such as by tapping their canes or by making clicking noises with their mouths. Human echolocation is similar in principle to active sonar and to the animal echolocation employed by some animals, including bats and dolphins.

By interpreting the sound waves reflected by nearby objects, a person trained to navigate by echolocation can identify the location and sometimes size of nearby objects and use this information to steer around obstacles and travel from place to place. However, since humans make sounds with much lower frequencies and slower rates, human echolocation can only picture comparatively much larger objects than other echolocating animals.

Contents 1 Background 2 Mechanics 3 Notable individuals who employ echolocation 3.1 James Holman 3.2 Daniel Kish 3.3 Ben Underwood 4 See also 5 References 6 External links

[edit] Background

Human echolocation has been known and formally studied since at least the 1950s.^[1] Before it was known to be based on localization of echoes, human echolocation was sometimes described as "facial vision".^[2][3][4] The field of human and animal echolocation was surveyed in book form as early as 1959.^[5]

Some blind people have described the phenomenon not as a learned method of navigation, but as an inherent and intuitive extra sense. For example, a blind person could walk past a line of trees and feel a "pressure" at their side as they passed each tree. The cause of this would be the echo of the sound of their footsteps; however, they may not consciously be aware of this mechanism, only that the phenomenon exists and can often be relied upon to detect obstacles.

[edit] Mechanics

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Vision and hearing are close cousins in that they both can process reflected waves of energy. Vision processes light waves as they 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 systems can extract a great deal of information about the environment by interpreting the complex patterns of reflected energy that they receive. In the case of sound, these waves of reflected energy are called "echoes".

Echoes and other sounds can convey spatial information that is comparable in many respects to that conveyed by light. With echoes, a blind traveler can perceive very complex, detailed, and specific information from distances far beyond the reach of the longest cane or arm. Echoes make information available about the nature and arrangement of objects and environmental features such as overhangs, walls, doorways and recesses, poles, ascending curbs and steps, planter boxes, pedestrians, fire hydrants, 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.

- "Echolocating Distance by Moving and Stationary Listeners", Lawrence D. Rosenblum, Michael S. Gordon and Luis Jarquin‌, in Ecological Psychology, 2000, Vol. 12, No. 3, pages 181-206.

- "Evaluation of an echo-Mobility training program for Young blind people", Daniel Kish, Master Thesis. 1982, University of Southern California.

[edit] Notable individuals who employ echolocation

[edit] James Holman

One of the earliest documented cases of echolocation was "the blind traveler" James Holman (1786-1857), who used the sound of a tapping cane to travel the world. Journalist William Jerdan wrote, "From Marco Polo to Mungo Park, no three of the most famous travelers, grouped together, would exceed the extent and variety of countries traversed by our blind countryman."^[6]

[edit] Daniel Kish

Echolocation has been further developed by Daniel Kish, who works with the blind, leading blind teenagers hiking and mountain-biking through the wilderness and teaching them how to navigate new locations safely, through the non-profit organization World Access for the Blind.^[7] He has developed a click-emitting device and trains other blind people in the use of echolocation and in what he calls "echo-mobility".^[8][9][10]

Daniel has taught many blind people to utilize echolocation and expand their mobility. He has shared his experiences with Ben Underwood.^{[11] [9][10]}

[edit] Ben Underwood

Diagnosed with retinal cancer at the age of two, American Ben Underwood had his eyes removed at the age of three.^[12]

He discovered echolocation at the age of five. He was able to detect the location of objects by making frequent clicking noises with his tongue. This case was explained in 20/20:medical mysteries. ^[13] He used it to accomplish such feats as running, basketball, rollerblading, playing foosball, and skateboarding.^[14][15]

Though at first resistant to using a cane for mobility, seeing it as a "handi-capped" device, and considering himself "not handicapped at all", Daniel Kish demonstrated to Ben how he utilized his white cane combined with echolocation to further expand his mobility, though Ben never adopted this method.^[11]

Ben died on January 19, 2009 at the age of 16. He died from the same cancer that took his sight.^[16]

[edit] See also

• Animal echolocation
• Acoustic location
• Sensory substitution

[edit] References

[edit] External links

• How to see with sound Article by Daniel Kish in the New Scientist
• Harvard historical study and bibliography
• World Access for the Blind
• Blind Kid Uses Echo Location! - CBS video from YouTube.
• Seeing with Sound project
• BBC Science item "Sound of the Future"