Humans, when you train them, can be phenomenally good at pattern recognition. Our long history as the descendants of organisms who could spot a predator in dappled grass probably has something to do with it, but today, this ability makes all manner of things possible. For instance, people who have lost their vision, or never had any to begin with, can learn to echolocate, using the sound bouncing off of the world around them to navigate. This peculiar skill is of abiding interest to many scientists, who are curious as to how the brain spatially interprets information carried by sound. A group at Ludwig-Maximilians-Universitaet in Munich has now published the results of a small study in which they trained a blind person and 11 sighted people to use sound to deduce the size of a room, scanning their brains in the process.
For this experiment, the group created a digital version of a nearby church. If a subject lying in an MRI machine hummed or clicked their tongue or made any other sound, they would hear, through headphones, a simulation of the echoes made by that noise in the church. At first, in a heavily padded room with almost no echoes of its own, the researchers trained their subjects to tell which of two generic computer-generated rooms was bigger using the sounds the rooms made, among other tasks. They were allowed to make whatever noises they wanted to elicit the echoes. Then, for the main experiment, the researchers had the subjects do the same with various versions of the church, which were shrunk or digitally enlarged to make rooms of different sizes, to see how close rooms could get in size before subjects stopped being able to tell the difference.
The results were surprising. “We thought, ‘If it’s sighted people, it’s not going to be something we’ve ever learned to do,’” reflects Virginia Flanagin, a neuroscientist and first author of the study. “‘So probably we’re really bad at it.’” But the sighted subjects had little trouble figuring out the relative sizes of the spaces. The person who grew the most skilled at it could tell if there was as little as a 4 percent difference in the size of the room. Even the people who did less well could still often tell apart differences of 6 to 8 percent, with the least skilled bottoming out at a 16 percent difference. Overall, that actually is about the same level of acuity—ability to distinguish differences—that you find in some visual tests, says Flanagin.
Additionally, the brain scans showed something odd: The sound of the echoes was activating sighted subjects’ motor cortex, the part of the brain that handles movements. The researchers had the subjects make their echolocation sound—usually a click with their tongues—without playing them back any echoes, then subtracted that scan from the scans taken when they heard the noise reverberating in the church, to get rid of any motor cortex activation from moving the tongue. But it still lit up, even with the tongue movement removed. In fact, the brain region was more active with large versions of the church than smaller ones. “It seems like the motor cortex is somehow involved in the sensory processing,” says Flanagin. In the blind subject, the echoes caused the activation of the visual cortex instead.
These results lay the groundwork for future studies investigating whether sighted people can be trained to do more complicated kinds of echolocation, like navigating down a virtual hallway. The idea, Flanagin says, is to understand at what level of complexity blind people start being able to do things that sighted people can’t and what might have changed in their brains to allow them to do that. In general, the resilience of the human brain and the readiness with which we can learn new skills when circumstances demand it is impressive. Quoting the blind advocate Daniel Kish, who uses echolocation himself to walk around every day, Flanagin remarks, “The only reason sighted people can’t do it is they don’t have to.”