I expect some stares as we walk into the bike shop, and we get them. My companions are both blind, leading with white canes, and one is rolling in his ailing mountain bike. I’m also not surprised when the salesman approaches me to ask what we need. But then one of my companions, Daniel Kish, answers that he’s looking for a new tube “24 inches, latex, with a Presta valve”. The salesman quickly realizes that despite appearances, Daniel is the experienced rider.
In fact, Daniel has been leading his group of blind mountain bikers and hikers—Team Bat—for over 15 years. Today’s group is small: Daniel, his co-leader Brian Bushway, Daniel’s intern Megan O'Rourke and myself, the only sighted rider. I’m along to document the experience for my book.
We fix Daniel’s bike, and meet Brian at his home in Mission Viejo, California. Once equipped, we leave the safety of Brian’s driveway and turn onto the residential street leading to the mountain trail. That’s when the tongue-clicking begins. Daniel, Brian, and Megan are making loud, sharp clicking sounds with their tongues so that they can hear what I can see. Using this form of human echolocation allows them to detect sounds reflected from parked cars, trash cans, and other silent obstacles along the street. Daniel and Brian are more experienced echolocators and can actually hear the location of the curbs, driveways, and even hedges on the side of the street.
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 listener him or herself, 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 own lab, we’re able to get blindfolded college freshman to successfully echolocate the position of a small wall within 10 minutes. And with practice, both blind and sighted listeners can determine the rough shape, size, and even texture of objects based on how they reflect sound.
To get a sense of how echolocation works, try this. 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 shhhhhh sound. As you make this sound, slowly bring your hand toward your mouth. You will hear the shhhh sound change. What you’re hearing is the sound reflecting from your hand colliding with the sound leaving your mouth. This interference turns out to be one of the most important types of 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 consciously heard. This highlights one of the most amazing aspects of echolocation: It’s rarely experienced as sound. Try using your shhhh sounds to walk slowly toward a wall with your eyes closed. As you come close to the wall, you’ll experience its presence as more of a feeling than a change in sound. It may feel as if there are air pressure changes on your face, an experience also reported by the blind (echolocation was once called “facial vision”). Echolocation is truly one of your implicit perceptual skills: It allows you to detect aspects of your environment without even knowing which sensory system you’re using. And it could very well be that you’re constantly using the skill to recognize properties of the rooms you occupy.
Research on human echolocation has been sporadic since the 1950’s. But a study published last week in Acta Acustica received media attention. The study confirms that the types of tongue clicks used by Daniel Kish and his colleagues are acoustically ideal. In fact, Daniel and Brian have reportedly had good success in training other Team Bat members 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 then realize that when it comes to our riding, our most important difference is that he’s in much better shape. But I’m comforted in knowing that we both have auditory systems that allow us to hear reflections from the silent world.