It's a beautiful afternoon in the hills of Mission Viejo. A light breeze provides relief from the high sun and cools my already moist face. The sound of birds mixes with the breeze rushing through the oaks. And as the sun warms their needles, the pines give off their familiar scent.
“Is everyone ready?” Daniel Kish, our guide, asks. “Remember to stay behind each other, but not too close.”
Megan O’Rourke, who is new at this, says: “This is kinda scary. But fun!”
“Fun until you crash into me!” Brian Bushway says. We all laugh.
As we leave the safety of Bushway’s driveway, we enter the street and hear the plastic pull-ties we’ve connected to our bike frames clicking against our tire spokes. The sound is very much like that made by the baseball cards kids fasten to their bike wheels to make a faux-motorcycle sound. But today this clicking sound has a very adult purpose.
“Now, Megan, follow the clicking of my wheels so you stay on the side of the road,” Kish says.
We turn a corner and I look up at an imposing, apparently endless, upward slope. I think that I wish I were in better shape. I also think that, right now, I am the least fortunate one of our group. I am, after all, the only one who can actually see how much effort we’re about to exert. My companions—Daniel Kish, Brian Bushway, and Megan O’Rourke—are blind.
I reach the top of the hill first, while Kish and Bushway stay back to instruct O’Rourke. As the three of them climb the hill and get closer to me, I start to hear sharp intermittent clicks—different from those of the bike wheels. These sharp clicks are emanating from the mouths of Kish and Bushway, who are using them to hear what I can see. They click with their tongues, about once every two seconds, so that they can hear the sounds refl ect back from nearby curbs, shrubs, parked cars, and other obstacles. This method of navigation is known as echolocation, and it enables Kish and Bushway to lead these mountain bike excursions. They both click using the side of their tongues, as if coaxing a horse to gallop.
As we ride, I ask Bushway, “So what parts of the trail can you perceive from echolocating?”
He responds: “I can hear the sides of the trail where the brush meets the dirt. I can also hear if there are big rocks or trees in or near the path. All the important stuff about the trail—except maybe the horse droppings. I use another sense for that.”
We all laugh.
Kish and Bushway have been leading mountain bike trips for about 10 years. Their “Team Bat” usually includes 3 to 5 students, but they’ve led groups as large as 12. All of the participants are severely visually impaired, and most have little, if any, light sensitivity. Besides giving the students a roaring great time, Kish and Bushway believe that these outings build their confi dence. They’ve also been teaching blind students to echolocate, which they feel is one of the most effective means by which students can gain independence. Kish actually conducted scientific research on echolocation for his master’s thesis in 1995.
Daniel Kish and Brian Bushway are particularly adept echolocators. Besides mountain biking, they’ve used echolocation to hike, roller-skate, skateboard, and play basketball. Along with his cane, echolocation is Kish’s principal way of navigating the world. Kish and Bushway’s echolocation skills have also made them celebrities of sorts, landing them on national news and talk shows; in magazine features; and on the lecture circuit, making instructive and inspirational presentations to numerous organizations. In the media, they are often portrayed as “medical mysteries,” or as possessing a “special gift.” This fact is unfortunate because, while Kish and Bushway’s skills are certainly impressive, human echolocation is neither mysterious nor special. And, as you’ll soon learn, you too can echolocate, and you do it all the time.
Daniel Kish was never able to see. At the age of 4 months, he was diagnosed with retinoblastoma in both eyes. Retinoblastomas are cancerous tumors of the retina. They are potentially fatal, and treatment often requires complete removal of the affected eye. In Kish’s case, one eye was removed when he was 7 months old and the second when he was 13 months old. Before then, the blastomas were so large that it is unlikely that he was ever able to visually discriminate anything more than light from dark.
After his eyes were removed, Kish’s parents staunchly encouraged his independence. They refused to restrict his activity in any way, despite his potential for bumps and bruises. They also refrained from acting as guides, allowing him to locomote and explore the world on his own. He attributes much of his adult navigation skill, including his expertise with echolocation, to his parents’ approach and the confidence it provided him.
Kish remembers himself always echolocating. His parents claim that he started clicking even before his eyes were removed and that he later did it to guide his crawling, cruising, and early walking. By the time he was 7, he used echolocation to bike ride and roller-skate. Like most kids, he loved riding his bike around the neighborhood. He was able to hear oncoming traffic and pedestrians by listening for the sounds they emitted and stayed safely to the side of the street by echolocating to follow the curb and locate parked cars. Perhaps most impressively, he could judge where he was in the neighborhood by echolocating the driveways between the lawns: hearing the difference in textures, and counting them as he rode. These days, his riding skills are astounding. During production of a television segment about Kish, he was asked to ride his bike around a playground basketball court. The resulting videotape shows him easily riding within the boundaries of the concrete court and deftly circling the poles that hold up the basket and backboard.
Research on bats has shown that these animals use a process of echolocation to determine the position of objects in the dark by emitting high-pitched chirps that reflect off nearby objects and return to their ears. By comparing the time, energy, and frequency differences between the emitted and returning sound, bats are able to determine the location and characteristics of the objects (moths, trees, telephone wires). At Cornell University, Karl Dallenbach’s team ran a series of experiments to see whether humans echolocated like bats and determined that, indeed, the blind could and did.
Since Dallenbach’s work, other laboratories have shown that humans can use echolocation to hear more detailed properties of objects. These properties include an object’s horizontal position, relative distance, and relative size. Astonishingly, humans also have the ability to identify the general shape of an object (square, triangle, disk) and even an object’s material composition (wood, metal, cloth) using echolocation. Blind subjects are generally better at echolocating, but untrained sighted subjects are also able to perform all of these tasks with some success and to improve their accuracy with practice. In my own lab’s research, we find that sighted subjects can learn to accurately echolocate the position of a movable board after just 10 minutes of practice.
Guided by Echoes
How does your brain use sound to echolocate? Like a bat, you probably use the time delay between an emitted sound and its returning reflected sound to gauge your distance from an object—the farther the object, the longer the delay. The difference in intensity (loudness) between emitted and reflected sound is also most likely used for this purpose—the farther the object, the quieter the returning sound.
However, these types of sound cues are limited in their use for two reasons. First, once you are within two meters of an object, your ear is physiologically unable to resolve the very small time and intensity differences between emitted and returning sounds. Second, you don’t need to actually emit a sound to “echolocate.” Many echolocation experiments have shown that the skill can be accomplished with sounds emitted by sources other than the echolocator. This makes it unlikely that comparisons between emitted and reflected sounds are necessary.
It is likely that your brain is often using other types of sound cues for echolocation. One of the most important is the sound wave interference patterns that occur in front of sound-reflecting objects. The best way to understand this is to try a quick demonstration: Hold your hand up about one foot in front of your face with your palm facing your mouth. Now put your front teeth together, open your lips, and make a continuous shhhhh sound. As you make this sound, slowly bring your hand toward your mouth. You will hear the shhhhh change systematically as you bring your hand closer. To really hear the sound change, repeatedly move your hand back and forth, closer and farther from your mouth. You will hear a whooshing sound that changes with your hand position.
What you’re hearing is the sound reflecting from your hand colliding with the sound leaving your mouth. And as your hand moves, the sound interference patterns change with the distance. You can hear these sound interference patterns change—the whooshing sounds—even if you are not the one emitting the sound. Ask your friend to perform this demonstration near you, and you should have no problem hearing the interference whooshes. If you have no friend nearby, turn on your radio or TV to an unused channel so you hear noise. Move your hand toward the speaker, and again, you should hear the whooshing interference patterns.
Glimpses of Light
Daniel Kish is now the president of the World Organization for the Blind, an association dedicated to helping blind individuals and their sighted friends and family understand the capabilities of the visually impaired. Brian Bushway is also a charter member. A cornerstone of its approach is teaching echolocation for mobility purposes and educating the general public about its potential. Kish and Bushway travel the world consulting with institutes for the blind and tutoring blind individuals. They have trained over 100 people to use echolocation with good to excellent success.
After our mountain bike ride, I asked Daniel Kish how he would describe the experience of being an expert echolocator to a sighted person. He provided a lovely analogy: He often camps in the mountains with both blind and sighted friends. His group enjoys late-night hikes and sometimes a sighted friend will bravely forgo a flashlight and let him lead the way. The friend will hold his arm as they walk the trail under the mountain sky and the thick oak canopy that renders the path pitch-black. But now and then, the canopy will reveal enough starlight to dimly illuminate the path for a moment. Kish believes that he recognizes these moments by sensing a brief boost in his sighted companion’s confidence, which then shows him the frequency and duration of these illuminations. Based on this knowledge, Kish believes that his companion is experiencing something like a visual version of echolocation. Expert echolocation, like night hiking under a thick tree canopy, affords dim “glimpses” of the environment that permit identification of major obstacles and establish the direction to head until the next glimpse comes. Of course, Kish has an advantage: By echolocating at will, he can decide when and how often these glimpses occur.
Excerpted from See What I’m Saying: The Extraordinary Powers of Our Five Senses by Lawrence D. Rosenblum. Copyright 2010 by Lawrence D. Rosenblum. With permission of the publisher, W. W. Norton & Co.