Blind since birth, Marie-Laure Martin had always thought that candle flames were big balls of fire. The 39-year-old woman couldn’t see the flames themselves, but she could sense the candle’s aura of heat.
Last October, she saw a candle flame for the first time. She was stunned by how small it actually was and how it danced. There’s a second marvel here: She saw it all with her tongue.
The tongue, an organ of taste and touch, may seem like an unlikely substitute for the eyes. After all, it’s usually hidden inside the mouth, insensitive to light, and not connected to optic nerves. However, a growing body of research indicates that the tongue may in fact be the second-best place on the body for receiving visual information from the world and transmitting it to the brain.
Researchers at the University of Wisconsin Madison are developing this tongue-stimulating system, which translates images detected by a camera into a pattern of electric pulses that trigger touch receptors. The scientists say that volunteers testing the prototype soon lose awareness of on-the-tongue sensations. They then perceive the stimulation as shapes and features in space. Their tongue becomes a surrogate eye.
Earlier research had used the skin as a route for images to reach the nervous system. That people can decode nerve pulses as visual information when they come from sources other than the eyes shows how adaptable, or plastic, the brain is, says Wisconsin neuroscientist and physician Paul Bach-y-Rita, one of the device’s inventors.
“You don’t see with the eyes. You see with the brain,” he contends. An image, once it reaches an eye’s retina, “becomes nerve pulses no different from those from the big toe,” he says. To see, people rely on the brain’s ability to interpret those signals correctly.