Blind from infancy due to retinal cancer, Daniel Kish learned as a young boy to judge his height while climbing trees by making rapid clicking noises and listening for their echoes off the ground. No one taught him the technique, which is now recognized as a human form of echolocation. “He just used it, without knowing that he behaved like a bat,” says Lutz Wiegrebe, a neurobiologist at the Ludwig Maximilian University in Munich, Germany.
Like Kish, a handful of blind echolocators worldwide have taught themselves to use clicks and echoes to navigate their surroundings with impressive ease—Kish can even ride his bike down the street, as his daring YouTube videos show. A study of sighted people newly trained to echolocate now suggests that the secret to Kish’s skill isn’t just supersensitive ears. Instead, the entire body, neck, and head are key to “seeing” with sound—an insight that could assist blind people learning the skill.
Bats and other animals that rely on sounds to detect prey in the dark move their ears much like humans use their eyes to track an object of interest, making constant adjustments to their ear positions. When bats echolocate, they emit rapid-fire, high-frequency clicks (usually out of range of human hearing), then swivel their ears like radar dishes to catch the echoes, a system sensitive enough to detect objects as thin as a human hair and tiny, night-flying insects. Unlike bats’ large, mobile ears, however, human ears are small and fixed—an obstacle to blind people who use their ears to “see.”
To test the extent to which people can compensate for this immobility, Wiegrebe and colleagues recruited eight undergraduates with normal vision to don blindfolds and learn some basic echolocation skills. The students were first taught to produce sharp, high-frequency clicks with their tongues. Then they were blindfolded and led into a long, narrow corridor, where they practiced sensing the position of the walls based on how long it took for an echoed click to reach their ears. Although some people are more naturally talented than others at echolocation, most got “quite good” after 2 to 3 weeks of training, Wiegrebe says, and could reliably orient themselves to walk down the corridor without running into any walls using just clicks and echoes.
Next, the researchers created a virtual version of the corridor to test how important head and body movements, rather than hearing alone, had been to the students’ accuracy. Blindfolded subjects sat in a chair wearing headphones while a computer program simulated the acoustics of the real-life corridor when they clicked into a microphone. To ensure that the acoustics of the simulated room were realistic, the researchers asked two blind echolocation experts to navigate it first; both were quickly able to orient their bodies toward the center of the aisle.
The blindfolded students were also instructed to use their clicks and echoes to line up their bodies with the center of the corridor. In one test, they were told to rotate the virtual corridor without making any head or body movements, using a joystick. In another, the corridor was fixed and participants were allowed to swivel their chairs and heads to determine their position in the room.
The difference between the two conditions was stark, Wiegrebe says. When the participants couldn’t move their heads or torsos, they zigzagged down the virtual hall and were unable to self-correct before hitting a “wall.” When the corridor’s position was fixed and their bodies and heads were free to move, however, the novice echolocators soon righted themselves, the team reports online today in the Proceedings of the Royal Society B.
The virtual corridor is a “very creative” way to determine just how important body movements are to echolocation, says Lore Thaler, a psychologist at Durham University in the United Kingdom. The findings fit well with her own recent study, which showed that head movements can enable blind echolocation experts to sense an object’s contours, she says. The research also provides a new way of studying echolocation that can’t be done in animals, she notes. After all, “a bat can’t use a joystick.”
Echolocation is a skill that has evolved independently several times in the animal kingdom in response to low visibility conditions—whether at night, as with bats and a few nocturnal birds, or in murky water, as with whales and dolphins, Wiegrebe notes. “It’s not magic.” Though the research is still in its early stages, he hopes that a virtual reality program similar to that used in the study will eventually help blind people learn to use echolocation in the safety and privacy of their homes.