How come humans can’t use sonar in the dark, like bats?
How come humans can’t use sonar in the dark, like bats? asks Kevin Guan, via email.
Listening for the echoes of their own rapid-fire, high-pitched calls, bats navigate the night, while snatching tiny insects from the air. Dolphins (along with many whales and shrews) are also skilled “echolocaters.” And it turns out that we humans, too, are capable of using a kind of sonar, and getting better with practice. In fact, in the 1800s, one blind man used a kind of echolocation as he traveled the world, mostly on foot, writing about his adventures in a series of books.
Bats are the experts at traveling — and hunting — by listening. Like submarines in the murky ocean depths, bats move through a sea of echoes, “picturing” objects in their way.
Bats emit high-pitched sounds through their mouths or noses, using their big, oddly-shaped ears to listen for sound reflections. A bat may sweep your dark yard with sound at 10 blips a second. When the sounds echo off an insect, the bat increases the rate, giving it a better sense of the bug’s size and location. As the bat zeroes in, it chirps faster and faster, up to 200 times a second.
While human beings would lose a sonar throwdown with bats, some sight-impaired people do develop the ability to echolocate. The simplest form of echolocation is tapping a cane or stick while listening for the echoes. This gives the walker a sense of the changing terrain, as well as objects along the path. But some people also use clicking or other sounds, much like bats, to determine the location, size, shape, and composition (hard or soft) of objects around them.
California teenager Ben Underwood, blind since he was a toddler, navigates using a series of fast tongue clicks. Underwood says he began using clicking as a young child, and can even sink baskets by listening for echoes from the basketball pole and backboard. One scientist estimated that Ben’s sonar clocks in at about 120 clicks a second.
Daniel Kish, a California psychologist who is also blind, practices and teaches echolocation. His students have even learned to mountain-bike using the human form of sonar.
The first well-known human practitioner of echolocation was James Holman, born in 1786 with normal vision. James was only 12 years old when he enlisted in the British navy, rising to lieutenant by his 20s. Then, after an illness involving severe joint pain, Holman lost his vision at 25.
Holman decided to travel the world, using a walking stick and listening for resounding clicks as he trekked through Europe, Asia, Africa, and South America. The books he wrote about his sometimes-perilous journeys were bestsellers in the 1800s. After his death in 1857, the so-called “Blind Traveler” was gradually forgotten. His story is recounted in the book “A Sense of the World: How a Blind Man Became History’s Greatest Traveler,” by Jason Roberts.
For more on Holman, listen to an interview with Roberts at www.npr.org/templates/story/story.php?storyId=5675082. For more on Ben Underwood and Daniel Kish, go to http://abcnews.go.com/Primetime/story?id=2283048.
