Imagine picturing a table without constructing a visual image.
Credit: Public domain
Paul Gabias has never seen a table. He was born prematurely and went blind shortly thereafter, most likely because of overexposure to oxygen in his incubator. And yet, Gabias, 60, has no trouble perceiving the table next to him. "My image of the table is exactly the same as a table," he said. "It has height, depth, width, texture; I can picture the whole thing all at once. It just has no color."
If you have trouble constructing a mental picture of a table that has no color — not even black or white — that's probably because you're blinded by your ability to see. Sighted people visualize the surrounding world by detecting borders between areas rich in different wavelengths of light, which we see as different colors. Gabias, like many blind people, builds pictures using his sense of touch, and by listening to the echoes of clicks of his tongue and taps of his cane as these sounds bounce off objects in his surroundings, a technique called echolocation.
"There's plenty of imagery that goes on all the time in blind people," he told Life's Little Mysteries. "It just isn't visual."
As well as being blind himself, Gabias is an associate professor of psychology at the University of British Columbia who conducts research on perceptual and cognitive aspects of blindness. His personal and professional experience leads him to believe that the brains of blind people work around the lack of visual information, and find other ways to achieve the same, vitally important result: a detailed 3D map of space.
The brain region neuroscientists normally think of as the "visual" cortex, rather than being left to languish, plays a key role in the blind's mental mapping process. [Do Colorblind People Dream In Color?]
In sighted people, visual information first goes to the visual cortex, which is located in the occipital lobe at the back of the brain. From there, it goes to the parietal lobe, sometimes referred to as the "where system" because it generates awareness of a sensed object's location. Next, the information is routed to the temporal lobe, also known as the "what system" because it identifies the object.
Evidence from recent brain-imaging experiments indicates that blind people's brains harness this same neural circuitry. "When blind people read Braille using touch, the sensory data is being sent to and processed in the visual cortex," said Morton Heller, a psychologist who studies spatial cognition and blindness at Eastern Illinois University. "Using touch, they get a sense of space" — and the relative locations of the raised dots that form Braille letters — "that's not visual, it's just spatial."
For blind people who are adept at echolocation, sound information routes through the visual cortex as well. Their brains use echoes to generate spatial maps, which are sometimes so detailed that they enable mountain biking, playing basketball and safely exploring new environments. In fact, last year, Canadian researchers discovered that even when blind echolocation experts listened to audio recordings of their tongue clicks echoing off different objects, they could easily identify the objects that had been present at the time of the recordings. Scans with functional magnetic resonance imaging (fMRI) showed activity in areas of their brains associated with visual processing. In other words, their brain scans resembled those of a sighted person identifying an object in a photo.
Clearly, detecting visual contrasts is only one method of many for perceiving reality. But when trying to imagine a world perceived using hearing or touch, one tends to automatically picture echoes and textures generating a visual image built out of contrasts between light and dark. Gabias cannot conceive of light and dark. So what, exactly, are his mental images like?
"I just picture tables. We have no idea what our brain is doing. We just perceive — that's the wonderful thing about it. This is all 'psychologization' that has made it complicated to explain, but simple to do. You don't know how you perceive. You just do it," he said.
"If you know that blind people know where to put their plates on their table, and you know that blind people deal with tables in the exactly the same way you do, then you presume that they imagine them in the same way you do. You have got to presume that what's inside their head is like yours."
This story was provided by Life's Little Mysteries, a sister site to LiveScience. Follow Natalie Wolchover on Twitter @nattyover or Life's Little Mysteries @llmysteries. We're also on Facebook & Google+.