In recent decades, a number of blind people have developed a bat-like method of determining their surroundings using tongue clicks. Following recent success in Berlin, the technique could become more widespread in Germany. Some even use "flash sonar" to ride bikes and go hiking in the mountains.
Two-and-a-half-year-old Juli merrily twirls around, holding a small white cane in her outstretched arm. Every so often, she makes a discreet clicking sound with her tongue. Doing so allows her to see with her ears, her parents say. She just needs more practice.
Four-and-a-half-year-old Frida already knows how it works. If someone holds out a pot lid at arm's length, she can locate it with a fair degree of precision. Using subtle tongue clicks, she scans the space in front of her face. "There it is!" she says. With a few more clicks, she can even determine the contours of the lid. The edge lies where the echo cuts off and she no longer hears a response.
The two girls are learning a method of echolocation known as "flash sonar," which resembles the type of active sonar used by bats. Both were born blind in Berlin, and both have parents who want to spare them from the typical life of a blind person.
"We spent a long time looking for a good replacement for vision," says Steffen Zimmermann, Juli's father. He believes that using flash sonar, blind people can get through life with a surprising degree of independence.
This April two Americans came to Berlin to train Juli and Frida in flash sonar. They toured the city together, had them perform some initial exercises and explained to their parents what seeing with the ears is all about. One of the most important things is making the right sound: a snappy, dry click is best for locating things in the immediate vicinity.
Bats navigate in a similar way. Using only echoes, they can flutter through thick foliage without incident, plucking insects off leaves with precision as they fly by. Though humans don't hear nearly as well, with a little effort they can make a surprising amount of progress with a similar technique.
One of the trainers is Juan Ruiz, a well-known flash-sonar expert. In several YouTube videos he can be seen riding a mountain bike through rough terrain.
Indeed, before making his way to Berlin, Ruiz made a stop in Italy, where he set a new Guinness World Record. A television studio in Milan was outfitted with an obstacle course featuring 10 columns, spread out over a 20-meter (66-foot) path. The cameras rolling, Ruiz mounted his bicycle and pedaled away, constantly clicking. The spellbound audience followed Ruiz's progress as he navigated his way forward guided by what seemed like a sleepwalker's instincts. One column after the next seemed to enter his field of vision. He curved to the left and to the right and, after 48.34 seconds, rolled over the finish line without a single mistake.
Ruiz believes that anyone can learn to do what he does, including his young students in Berlin, Juli Schweizer and Frida Capellmann. "The girls are already doing quite well for their age," he says.
Juli, the youngest, lumbers fearlessly through her parents' apartment. For now, her discovery of the world of echoes is largely based on games. Her parents occasionally encourage her to use tongue clicks to detect a post or a ball, though it doesn't always work.