You might be surprised to learn that sightless people can avoid large obstacles and make their way through unfamiliar buildings by clicking their tongues and listening to the reflections in order to build up a mental image of their surroundings, just like bats. But people are far better at it than just walking down the street: This kid can can ride a bike on the street. Once sight is removed, we pay greater attention to our other senses. And because sight is so powerful when it comes to orienting ourselves in the world, it can be surprising how much information we can gather without it.
While this bat mimicry is already in use by many blind people as a way to get around, researchers at the Ludwig Maximilians University (LMU) in Munich have been teaching it to people with normal vision in order to find out how it works.
The LMU team hasn’t quite got their test subjects sinking baskets from the three-point line, but–using fMRI scans–they managed to see how the brain works on echolocation, and how it processes the echoes.
First, let’s take a look at how the experiment was set up. After all, it’s tricky to put a person inside a giant, clanking fMRI and also have them listen to clicks bouncing off the walls of an unknown room. So the researchers faked the room. They modeled a small chapel in a computer, choosing a chapel for its hard surfaces and plentiful echoes.
Then they put headphones on the participants while in the fMRI machine, and had them click their tongues. The clicks were processed through the model of the chapel, and the echoes played through the headphones. Another test used prerecorded vocalizations instead of the subjects making their own clicks. Subjects were then asked to estimate the size of the room.
The results showed that people learn to echolocate pretty fast, and sometimes to an extraordinary degree of accuracy. One participant managed to estimate the size of the virtual room to within 4% of its actual size. Overall, participants were way better at estimating distance when using their own clicks, rather than passively listening to computer-generated or recorded clicks, and louder clicks gave better results than quiet ones.
Inside the brain, the auditory cortex fires when it receives the echoes. “In sighted subjects, this is followed shortly afterwards by activation of the motor cortex, which stimulates the tongue and the vocal cords to emit new clicking sounds,” says a report from LMU. But the researchers threw in a wild card, in the form of a congenitally blind expert echolocator. The expert’s auditory cortex activated, just like in the sighted subjects, but upon hearing the reflected sounds, their visual cortex activated, as if they were actually seeing the reflections.
The study is fascinating, if only as a demonstration of how flexible the brain is when it comes to routing around damage and obstructions to its regular functions. One also wonders why more blind people don’t employ active echolocation as a way to get around.