What’s the News: Neuroscientists have found a preliminary answer to a question that has puzzled philosophers for centuries: If someone who has always been blind is one day able to see, can they recognize by sight objects they already know by touch? In a new study published online by Nature Neuroscience, patients who had been blind since birth underwent sight-restoring surgeries as children or adolescent. In the day or two following surgery, patients seemed unable to match what they felt with their hands with what they saw, the researchers found, but a week later, they could.
This results suggests that the brain doesn’t have the innate ability (or maybe has limited innate ability) to tie input from different senses to the same concept—but that it can learn, and pretty fast. Just how fast, the researchers wrote, suggests that the neuronal machinery needed to bring together visual and tactile information may already be there; it just has to be started up.
How the Heck:
- The researchers worked with five patients, aged 8 to 17, who had recently had surgeries to remove congenital cataracts or correct a cloudy cornea. The patients were all part of Project Prakash, a program one of the researchers began that works to restore sight to blind children in India.
- Within 48 hours of the surgery, the researchers presented each child with a distinctively shaped object made of Lego-like blocks to feel without looking at. Afterwards, they gave the child two objects—one the same shape as the first and one a new shape–and had them say, again by feel and not sight, which was the object they’d just held.
- Then, using a new set of objects, the researchers did the same thing—only this time the child could see the two objects but not touch them and asked which was the one they’d previously felt. (The scientists also tested whether the kids could see well enough to distinguish between the objects—which they could—to rule out the possibility that their vision wasn’t yet up to the task.)
- The children were great at identifying the objects by feel, but when they identifying objects by sight, they were right just 58% of the time: not much better than chance.
- Five days to a week later, the researchers had the children do the same tests, with new sets of objects. Now, they found, the children could visually recognize the object they’d touched about 80% of the time.
What’s the Context:
- The history of this scenario goes back to 1688, when Irish natural philosopher William Molyneux first posed the question of whether people blind from birth could visually recognize familiar objects—now called Molyneux’s Problem—in a letter to John Locke.
- Harvard neuroscientist Alvaro Pascual-Leone agrees that the change happens too quickly for the brain to undergo significant rewiring. When the children switch from recognizing objects by feel to recognizing them by sight, he told ScienceNOW, “they’re not starting from zero.”
Reference: Richard Held, Yuri Ostrovsky, Beatrice deGelder, Tapan Gandhi, Suma Ganesh, Umang Mathur & Pawan Sinha. “The newly sighted fail to match seen with felt.” Nature Neuroscience online, April 10, 2011. DOI:10.1038/nn.2795
Image: Flickr / GaelG