Paul Bach-y-Rita and Sensory Substitution
Updated: Oct 29, 2021
Excerpted from the book: The Brain That Changes Itself
Stories of Personal Triumph from the Frontiers of Brain Science
By Norman Doidge, MD, Penguin Publishing, December, 2007
"I can connect anything to anything." Paul Bach-y-Rita claims. "We see with our brains, not with our eyes," he says.
How a sensation enters the brain is not important to Bach-y-Rita.
''When a blind man uses a cane, he sweeps it back and forth, and has only one point, the tip, feeding him information through the skin receptors in the hand. Yet this sweeping allows him to sort out where the doorjamb is, or the chair, or distinguish a foot when he hits it, because it will give a little. Then he uses this information to guide himself to the chair to sit down. Though his hand sensors are where he gets the information and where the cane 'interfaces' with him, what he subjectively perceives is not the cane's pressure on his hand but the layout of the room: chairs, walls, feet, the three-dimensional space. The actual receptor surface in the hand becomes merely a relay for information, a data port. The receptor surface loses its identity in the process,"
Bach-y-Rita determined that skin and its touch receptors could substitute for a retina, because both the skin and the retina are two-dimensional sheets, covered with sensory receptors, that allow a "picture" to form on them.
It's one thing to find a new data port, or way of getting sensations to the brain. But it's another for the brain to decode these skin sensations and turn them into pictures. To do that, the brain has to learn something new, and the part of the brain devoted to processing touch has to adapt to the new signals. This adaptability implies that the brain is plastic in the sense that it can reorganize its sensory-perceptual system.
Bach-y-Rita's deepest interest became explaining plasticity, but he continued to invent sensory-substitution devices. He worked with engineers to shrink the dentist-chair-computer-camera device for the blind. The clumsy, heavy plate of vibrating stimulators that had been attached to the back has now been replaced by a paper-thin strip of plastic covered with electrodes, the diameter of a silver dollar, that is slipped onto the tongue.
The tongue is what he calls the ideal "brain-machine interface," an excellent entry point to the brain because it has no insensitive layer of dead skin on it. The computer too has shrunk radically, and the camera that was once the size of a suitcase now can be worn strapped to the frame of eyeglasses. p.20
Bach-y-Rita also got his vestibular device small enough so that it is hidden in the mouth, like an orthodontist's mouth retainer. And he has been working on other sensory-substitution inventions as well.
He received NASA funding to develop an electronic "feeling" glove for astronauts in space. Existing space gloves were so thick that it was hard for the astronauts to feel small objects or perform delicate movements. So on the outside of the glove he put electric sensors that relayed electrical signals to the hand.
Then he took what he learned making the glove and invented one to help people with leprosy, whose illness mutilates the skin and destroys peripheral nerves so that the lepers lose sensation in their hands. This glove, like the astronaut's glove, had sensors on the outside, and it sent its signals to a healthy part of the skin — away from the diseased hands — where the nerves were unaffected. That healthy skin became the portal of entry for hand sensations.
He then began work on a glove that would allow blind people to read computer screens, and he even has a project for a condom that he hopes will allow spinal cord injury victims who have no feeling in their penises to have orgasms. It is based on the premise that sexual excitement, like other sensory experiences, is "in the brain," so the sensations of sexual movement, picked up by sensors on the condom, can be translated into electrical impulses that can then be transmitted to the part of the brain that processes sexual excitement. Other potential uses of his work include giving people "super senses," such as infrared or night vision. p.20
Before he did this work, it was acceptable to say, as most neuroscientists do, that we have a "visual cortex" in our occipital lobe that processes vision, and an "auditory cortex" in our temporal lobe that processes hearing. From Bach-y-Rita we have learned that the matter is more complicated and that these areas of the brain are plastic processors, connected to each other and capable of processing an unexpected variety of input.
Paul Bach-y-Rita's importance lies in his being the first of his generation of neuroscientists both to understand that the brain is plastic and to apply this knowledge in a practical way to ease human suffering. Implicit in all his work is the idea that we are all born with a far more adaptable, all-purpose, opportunistic brain than we have understood.
When Cheryl's brain developed a renewed vestibular sense — or blind subjects' brains developed new paths as they learned to recognize objects, perspective, or movement — these changes were not the mysterious exception to the rule but the rule: the sensory cortex is plastic and adaptable.
Recently Bach-y-Rita's work has inspired cognitive scientist Andy Clark to wittily argue that we are "natural-born cyborgs," meaning that brain plasticity allows us to attach ourselves to machines, such as computers and electronic tools, quite naturally. But our brains also restructure themselves in response to input from the simplest tools too, such as a blind man's cane.
Plasticity has been, after all, a property inherent in the brain since prehistoric times. The brain is a far more open system than we ever imagined, and nature has gone very far to help us perceive and take in the world around us. It has given us a brain that survives in a changing world by changing itself.
If this post strikes a chord with you, we take brain plasticity possibilities a step further in Impossible Dream, the extraordinary story of triumph over disability told from the first-person perspective of a young woman living with autism.