Human echolocation
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, dimension, and density 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 ; however, others actively produce mouth clicks and are able to gauge information about their environment using the echoes from those clicks. 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 the reach of the longest cane or arm. 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, dimension, and density. Location is generally broken down into distance from the observer and direction. Dimension refers to the object's height and breadth.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. 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
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.Brain areas associated with echolocation
Some blind people are skilled at echolocating silent objects simply by producing mouth clicks and listening to the returning echoes. Although few studies have been performed on the neural basis of human echolocation, those studies report activation of primary visual cortex during echolocation in blind expert echolocators. The driving mechanism of this brain region remapping phenomenon is known as neuroplasticity.In a 2014 study by Thaler and colleagues, the researchers first made recordings of the clicks and their very faint echoes using tiny microphones placed in the ears of the blind echolocators as they stood outside and tried to identify different objects such as a car, a flag pole, and a tree. The researchers then played the recorded sounds back to the echolocators while their brain activity was being measured using functional magnetic resonance imaging. Remarkably, when the echolocation recordings were played back to the blind experts, not only did they perceive the objects based on the echoes, but they also showed activity in those areas of their brain that normally process visual information in sighted people, primarily the primary visual cortex or V1. This result is surprising, as visual areas are normally only active during visual tasks. The brain areas that process auditory information were no more activated by sound recordings of outdoor scenes containing echoes than they were by sound recordings of outdoor scenes with the echoes removed. Importantly, when the same experiment was carried out with sighted people who did not echolocate, these individuals could not perceive the objects and there was no echo-related activity anywhere in the brain. This suggests that the cortex of blind echolocators is plastic and reorganizes such that primary visual cortex, rather than any auditory area, becomes involved in the computation of echolocation tasks.
Despite this evidence, the extent to which activation in the visual cortex in blind echolocators contributes to echolocation abilities is unclear. As previously mentioned, sighted individuals have the ability to echolocate; however, they do not show comparable activation in visual cortex. This would suggest that sighted individuals use areas beyond visual cortex for echolocation.
Background
The term "echolocation" was coined by zoologist Donald Griffin in 1944. But the phenomenon was known about earlier, for example, Denis Diderot reported in 1749 that blind people could locate silent objects. Human echolocation has been known and formally studied since at least the 1950s. The field of human and animal echolocation was surveyed in book form as early as 1959.In earlier times, human echolocation was sometimes described as "facial vision" or "obstacle sense", as it was believed that the proximity of nearby objects caused pressure changes on the skin. Only in the 1940s did a series of experiments performed in the Cornell Psychological Laboratory show that sound and hearing, rather than pressure changes on the skin, were the mechanisms driving this ability.
Notable cases
Daniel Kish
Echolocation has been further developed by Daniel Kish, who works with the blind through the non-profit organization World Access for the Blind. He leads blind teenagers hiking and mountain-biking through the wilderness, and teaches them how to navigate new locations safely, with a technique that he calls "FlashSonar". Kish had his eyes removed at the age of 13 months due to retinal cancer. He learned to make palatal clicks with his tongue when he was still a child, and now trains other blind people in the use of echolocation and in what he calls "Perceptual Mobility". Though at first resistant to using a cane for mobility, seeing it as a "handicapped" device, and considering himself "not handicapped at all", Kish developed a technique using his white cane combined with echolocation to further expand his mobility.Kish reports that "The sense of imagery is very rich for an experienced user. One can get a sense of beauty or starkness or whatever—from sound as well as echo." He is able to distinguish a metal fence from a wooden one by the information returned by the echoes on the arrangement of the fence structures; in extremely quiet conditions, he can also hear the warmer and duller quality of the echoes from wood compared to metal.
Thomas Tajo
Thomas Tajo was born in the remote Himalayan village of Chayangtajo in the state of Arunachal Pradesh in the north-east India. He became blind around the age of 7 or 8 due to optic nerve atrophy and taught himself to echolocate. Today he lives in Belgium and works with Visioneers or World Access to impart independent navigational skills to blind individuals across the world. Tajo is also an independent researcher. He researches the cultural and biological evolutionary history of the senses and presents his findings to scientific conferences around the world.Ben Underwood
Ben Underwood was born on January 26, 1992, in Riverside, California. He was diagnosed with retinal cancer at the age of two, and had his eyes removed at the age of three.He taught himself echolocation at the age of five, becoming able to detect the location of objects by making frequent clicking noises with his tongue. This case was explained in 20/20: Medical Mysteries. He used it to accomplish feats such as running, playing basketball, riding a bicycle, rollerblading, playing football, and skateboarding. Underwood's childhood eye doctor claimed that Underwood was one of the most proficient human echolocators.
He inspired other blind people to follow his lead. He died of cancer in 2009.