By Lawrence Rosenblum, published on March 1, 2010 - last reviewed on May 4, 2010
"Is everyone ready?" asks Daniel, our mountain biking guide. "Remember to stay behind each other, but not too close."
"This is kinda scary," says Meagan, who is new at this. "But fun!"
"Fun until you crash into me!" Brian says.
As we leave the safety of Brian's driveway and head toward the trail, Daniel, Brian, and Meagan start making loud, sharp clicking sounds with their tongues. They're doing this so that they can hear what I can see.
Daniel, Brian, and Meagan are blind. They're using echolocation to detect sounds reflected from parked cars, trash cans, and other silent obstacles along the street. Daniel and Brian are experienced echolocators and can actually hear the location of the curbs, driveways, and even hedges.
Like bats, dolphins, and whales, humans can echolocate. The skill involves implicitly listening to how objects reflect sounds in distinct ways. It helps if the emitted sound is produced by the listeners themselves, but this isn't necessary. There's evidence, in fact, that blind individuals can perceive the location of a wall based only on how it reflects the normal, quiet ventilation sounds in a room.
Sighted individuals can also echolocate. In experiments conducted in my lab, we teach blindfolded college freshman to successfully echolocate the position of a movable wall within 10 minutes. And with practice, many listeners can roughly determine the shapes, sizes, and even textures of objects.
To get a sense of how echolocation works, hold your hand up about one foot in front of your face with your palm facing your mouth. Put your front teeth together, open your lips, and make a continuous shhhh sound. Slowly bring your palm toward your mouth. You will hear the shhhh change as the sound reflecting from your hand collides with the sound leaving your mouth. This interference is one of the most important sound dimensions we use to echolocate objects at close distances.
But this demonstration is exaggerated. The interference patterns used for echolocation are usually too subtle to be heard consciously. Still, your brain is able to use the almost imperceptible changes in sound. And there's evidence that echolocation skills can be improved with practice. Daniel and Brian have successfully trained other blind individuals to use clicks to guide biking and hiking.
Back on the bike trail, I hear clicks approaching from behind and Brian zooms past me. I realize that when it comes to our riding, our most important difference is that he's in much better shape.
Read Lawrence Rosenblum's PT Blog.
Daniel Kish: president of The World Organization for the Blind