Paul Bach-y-Rita:Your Brain Can See With Your Back. So Just What Is Vision?
A question grew in his mind: could the brain substitute one sense for another? Bach-y-Rita decided to try presenting a tactile "display" to blind people. Here's the idea: attach a video camera to someone's forehead and convert the incoming video information into an array of tiny vibrators attached to their back. Imagine putting this device on and walking around a room blindfolded.
At first you'd feel a bizarre pattern of vibrations on the small of your back. Although the vibrations would change in strict relation to your own movements, it would be quite difficult to figure out what was going on. As you hit your shin against the coffee table, you'd think, "This really is nothing like vision."
Or isn't it? When blind objects strap on these visual-tactile substitution glasses and walk around for a week, they become quite good at navigating a new environment. They can translate the feelings on their back into knowing the right way to move. But that's not the stunning part. The stunning part is that they actually begin to perceive the tactile input--to see with it. After enough practice, the tactile input becomes more than a cognitive puzzle that needs translation; it becomes a direct sensation.
If it seems strange that nerve signals coming from the back can represent vision, bear in mind that your own sense of vision is carried by nothing but millions of nerve signals that just happen to travel along different cables. Your brain is encased in absolute blackness in the vault of your skull. It doesn't see anything. All it knows are these little signals, and nothing else. And yet you perceive the world in all shades of brightness and colors. Your brain is in the dark but your mind constructs light.
To the brain, it doesn't matter where these pulses come from--from the eyes, the ears, or somewhere else entirely. As long as they consistently correlate with your own movements as you push, thump, and kick things, your brain can construct the direct perception we call vision. (From Incognito:The Secret Lives of the Brain by David Eagleman)