Daredevil - Ver con el sonido

Articulo publicado en New Scientist
Echo vision: The man who sees with sound


Material interesante en:
Echolocation in World Access for the Blind





Curioso que este joven se llame Daniel y en España Daredevil fue presentado como Dan Defensor. Les dejo un fragmento del articulo:

I am 6 years old and it's my first day at school. The bell rings for recess and all my classmates run gleefully away. But unlike them I cannot see. At least, not with my eyes. Instead, I click my tongue, listening for echoes from the wall to my left. I walk with my hands slightly outstretched to keep me from running into chairs that may have been left askew. I hear kids laughing and shouting through the open door, and by clicking I also hear the presence of the sides of the doorway in front of me. I go through it to the playground for the first time.

Clicking my tongue quickly and scanning with my head, I move cautiously forward, catching fleeting images of bodies darting hither and thither. I follow spaces that are clear, avoiding clusters of bodies, keeping my distance from bouncing balls. I am not afraid - to me, this is a puzzle. I turn my head and click over my shoulder. I can still hear the wall of the building. As long as I can hear that, I can find my way back.

At the time I went to school, blind kids either waited for people to take us around, or we taught ourselves to strike out on our own. My way was by clicking my tongue and listening for the patterns of reflections from objects around me. By doing this, I could get 3D images of my surroundings.

I am certainly not the first person to teach myself echolocation. In fact, human sonar has probably been around for as long as humans. There are two types of sonar: passive and active. Passive sonar exploits sounds made for other purposes to get a sense of the environment, and everyone does it to some extent. We can hear our voice change depending on the kind of space we are in, for instance.

Humans probably used to rely on echolocation far more in the days before artificial lighting, when we had to find our way round in the dark. The readiness with which people learn sonar suggests to me it may be an inbuilt skill.

The first documented case of a blind person using sonar dates back to the mid-18th century. The French philosopher Denis Diderot wrote in 1749 of a blind friend so sensitive to his surroundings that he could distinguish an open street from a cul-de-sac. In the 19th century, the famous "Blind Traveller", James Holman, was reported to sense his surroundings by tapping his stick or listening to hoof beats.

At the time, no one understood the basis of this skill. Some thought it relied on the skin on the face and called it "facial vision". Only in the 1940s did "series of experiments" prove this ability relies on hearing echoes.

Echoes can be used to perceive three characteristics of objects: where they are, their general size and shape and, to some extent, what they are like - solid versus sparse, sound-reflective versus sound-absorbent. This allows the brain to create an image of the environment.

For example, I perceive a parked car as a large object that starts out low at one end, rises in the middle and drops off again. The difference in the height and slope pitch at either end helps me identify the front from the back end; typically, the front will be lower, with a more gradual slope up to the roof.

Distinguishing between types of vehicles is also possible. A pickup truck, for instance, is usually taller, with a hollow sound reflecting from its bed. An SUV is usually taller and sounds blockier.

A tree has narrow and solid characteristics at the bottom - the trunk - broadening and becoming more sparse towards the top. More specific characteristics, such as the size, leafiness or height of the branches, can also be determined.

Passive sonar that relies on incidental noises such as footsteps produces relatively vague images. Active sonar, in which a noise such as a tongue click is produced specifically to generate echoes, is much more precise. My colleagues and I use the term FlashSonar for active sonar, because for us each click is similar to the brief glimpse of the surroundings sighted people get when a camera flash goes off in the dark.