Blind since the age of two, 14-year-old Ben Underwood uses the same sonar navigation techniques as dolphins.
Credit: Theo Rigby/Austral Press
Ben Underwood is a remarkable teenager, who loves to skateboard, ride his bicycle and play football and basketball. For the most part, the Californian 14-year-old is just like other kids his age. What makes Underwood remarkable is his ability to master these activities despite the fact that he is blind.
Underwood had both eyes removed after being diagnosed with retinal cancer at age two. To most people's amazement upon meeting him, he seems completely unfazed by his lack of sight, defying common stereotypes about blindness as a disability. So how does he do it?
The answer is echolocation: the sonar navigation technique used by bats, dolphins, several other mammals and some birds. As Underwood moves about he habitually makes clicking noises with his tongue; these sounds bounce off surfaces and, with each return, add to Underwood's perception of his surroundings.
He's so good at it that he can tell the difference between a fire hydrant and a rubbish bin, distinguish between parked cars and trucks, and — if you take him to a house he's never been to before — he will tell you he can 'see' a staircase in that corner and a kitchen in the other. He can even distinguish between different materials. As he explains, "Metallic objects have a soft echo. Wood sounds hard and glass sounds sharp."
While Underwood is exceptionally talented at 'seeing with sound' as he calls it (also known as 'facial vision', 'bat-like vision' and an 'extra sense'), he's not the only blind person who uses self-generated sounds to navigate. In fact, researchers believe that all people, even the sighted, use echolocation to varying degrees.
The technique contributes to spatial perception: our awareness of what surrounds us. In our brains, the region that deals with spatial perception is found in a separate zone to that dealing with vision, and receives signals from various sites in the brain including the visual, auditory and tactile centres.
To better understand the concept, close your eyes and ask a friend to guide you through an unfamiliar environment. Touch the objects, furniture and walls around you. Soon you will find yourself with a kind of
three-dimensional map in your mind. This spatial perception is generally created using visual information as well, so you don't notice the contribution made by tactile cues.
We can make a similar 3-D map using auditory cues. In daily life, we use this ability to perceive the direction of sounds coming towards us: a subconscious mechanism in the brain analyses minute differences between sounds as they reach each ear to target a sound's source. In echolocation, the brain also calculates the distance to an object, based on the time it takes for each echo to return.
Although research has shown that echolocation is a normal part of human perception, most people aren't aware of their ability, and rely primarily on vision for orientation. Blind people, however, tend to increase their reliance on auditory feedback, just as their other active senses are heightened.
Since the 1950s, research in echolocation has led to the development of sonar-based devices that emit pulses of ultrasound and convert the returning echoes into meaningful patterns of sound. For example, when one such device detects an obstacle in the user's path, the beeps emitted decrease in tone as the user approaches the object.
Andrew Downie provides technical resources for people with a disability and wrote his psychology thesis on the use of Sonicguide, a sonar-based mobility aid for the blind. Downie, who is blind himself and an avid user of both self-generated and device-aided echolocation, says that despite the technology's potential to enhance the mobility of blind people, many are reluctant to use the technique.
He attributes this to the fact that making clicking or other sounds in public can attract unwanted attention, or be considered socially inappropriate. As a result, he estimates that in Australia fewer than 10 per cent of blind people consciously use some form of echolocation to navigate.
As with any other human ability, echolocation can be enhanced through training and practice. According to Downie, for those without sight, this could be an indispensable skill for improving orientation, navigation and ultimately, independence and self-esteem.
Puya Abolfathi is a biomedical engineer at the Quadriplegic Hand Research Unit of Sydney's Royal North Shore Hospital.
