Blind people use brain’s visual cortex to help do maths | New Scientist
Subtract 8 from 52. Did you see the calculation in your head? While a leading theory suggests our visual experiences are linked to our understanding of numbers, a study of people who have been blind from birth suggests the opposite.
The link between vision and number processing is strong. Sighted people can estimate the number of people in a crowd just by looking, for instance, while children who can mentally rotate an object and correctly imagine how it might look from a different angle often develop better mathematical skills.
“It’s actually hard to think of a situation when you might process numbers through any modality other than vision,” says Shipra Kanjlia at Johns Hopkins University in Baltimore, Maryland.
But blind people can do maths too. To understand how they might compensate for their lack of visual experience, Kanjlia and her colleagues asked 36 volunteers – 17 of whom had been blind at birth – to do simple mental arithmetic inside an fMRI scanner. To level the playing field, the sighted participants wore blindfolds.
We know that a region of the brain called the intraparietal sulcus (IPS) is, and brain scans revealed that the same area is similarly active in blind people too.
“It’s really surprising,” says Kanjlia. “It turns out brain activity is remarkably similar, at least in terms of classic number processing.”
This may mean we have a deep understanding of how to handle numbers that is entirely independent of visual experience. This suggests we are all born with a natural understanding of numbers – an idea many researchers find difficult to accept.
The idea that visual experience is important for numerical processing might generally be preferred because it’s easier to explain, says Kanjlia. “But that doesn’t mean that alternative theories aren’t true.”
That wasn’t the only surprise to emerge from the study. Kanjlia and her colleagues also discovered that the volunteers who had been blind since birth seemed to recruit an extra area of the brain to work on mental arithmetic problems.
In people with sight, the visual cortex is responsible for processing visual information and is not involved in maths. But this brain area, which is not needed for vision by people who have never had sight, seems to have been assigned a new function in these blind people.
The team had earlier found evidence that people blind since birth can recruit their visual cortex . “Experience changes the brain in really unexpected ways,” says Kanjlia. “The visual cortex is this ancient structure that’s always processed vision, you would think that could never change. But then you find it does.”
But we don’t know yet if using the visual cortex in this way gives blind people an advantage in arithmetic or language. “It’s like they have this extra bit of brain that’s active during a mathematics test,” says Kanjlia. “Does it help?”
It might: the blind volunteers who gave the most correct answers to the maths questions also had the most brain activity in the visual cortex. But the effect might be subtle: Kanjlia and her colleagues didn’t find any evidence that the blind volunteers in general were significantly better at mental arithmetic than those who could see.