Last week we introduced Echolocation and this week we will focus on how this procedure has been used with visually impaired humans. Since bats, dolphins and others are able to use echolocation, it is possible to see with your ears. Although most audiologists understand the physics of sound and its echoing possibilities, it is still foreign to consider that humans could actually navigate using echolocation.
Supa et al (1944) describes that Diderot in 1749 (other sources say it was in 1789) recorded that the blind had an amazing ability to not only perceived objects but to accurately judge distance as well. At the time Diderot dubbed this capability “facial hearing” as it was thought to be the result of an air disturbance that stimulated an extra sensitive facial nerve. Since Diderot’s first account, numerous cases possessing this special ability have been reported and fostering theories to explain the phenomenon. Hayes (1935) lists 14 different theories as to how this echolocation is possible dividing them into the general categories of sensory, perception, and the occult. In the current century, however, Schwitzgebel and Gordon (2000) offer that humans do echo locate and it is very much a part of the normal human experience. They further describe that echolocation ability may be due, in part, to several sources of information. If a listener produces a sound, they may be able to use the time delay and loudness differences between production and reception to determine the distance of reflective surfaces. Reflected sound from any source can provide the listener with distance and object property information using timbrel and pitch variations. They further suggest that a moving listener may also use:
- Timbre Changes – Interference of sound reflecting back on itself.
- Motion Parallax – Closer objects change their position relative to the listener faster than distant objects.
- Tau – Objects expand more rapidly as they get closer.
- Doppler Shift – Change in the apparent frequency of the waveform as the observer moves toward or away from an object.
For example, a walk down a long tiled hallway each step creating a small burst of noise radiating from the shoes. In listening to this the listener not only hears the shoes on the floor of the hallway but the reflections of that sound on nearby surfaces. Other spaces like bathrooms would have different noises create by the shoes and reflected from the surfaces. Hallways sound different than bathrooms and this can be used as information. Schwitzgebel and Gordon suggest that we all use these clues to ambulate through our environment as they are the sounds and reflections that offer us clues in everyday communication and interaction with the world.
Kish and Bleier (1994) have developed a program for training instructors to teach blind individuals to echo locate. They feel that these echolocation skills vary widely among students. They base their opinion on a combination of psycho-physical research, theoretical knowledge, observation of dozens of students over many years, and over 30 years of personal experience. They feel that using echolocation a pole of about an inch diameter can be perceived at about two feet while a fire hydrant may be perceived from several feet away, but not up close unless the student is very short. Likewise, a 4 inch curb is also easier to detect from distances of about 3 to 10 feet, but not too close. A chainlink fence may be detectable at 6 to 10 feet. A parked car may be perceived at 10 or 15 feet; add another 5 feet for a van or truck. A tree may be detectable from 15 or 20 feet. A large building is detectable for hundreds of feet with a strong echo signal. While features in terrains such as mounds, large rocks, up-curbs, or mud puddles may be detectable, drop-offs are almost impossible to detect. Low objects such as curbs seem taller than they are from several feet away. These may be difficult to perceive up close. Although echoes are quiet and subtle, echoes from large, hard, nearby objects are extremely pronounced once you know what to listen for and they feel that it becomes ridiculous for blind people to run into a wall as it is for sighted people. In their opinion, teaching this technique to the blind is not “rocket science” but rather intuitive once certain principles are kept in mind.
Does Anyone Really Use This Technique?
These days Kish is an instructor for the echolocation and teaches his technique to the blind. Pictured left, Daniel Kish (Click for Video) is often called “Batman” as he uses his technique to ride bikes, and move throughout the world by making a clicking noise and listening.
Pictured right is Ben Underwood (Click for video) who learned to use echolocation as a young child and was highly capable of moving through the world at age 14 and his story was picked up by ABC News. Although a sad story of a young person that ultimately was taken too soon by cancer at age 16, he was a great example to many blind children that can now learn this new technique to SEE WITH SOUND!