It has been now more than 3 centuries since Molyneux, the Irish philosopher, wondered if a blind from birth person can see all of a sudden will that person be able to recognize the difference between the shapes as he used to distinguish the difference by touch when he was blind. Researches have recently reached an answer to that puzzle.
Imagine, Molyneux wrote, that a man blind from birth who has learned to identify objects — a sphere and a cube, for example – only through his sense of touch is suddenly able to see. The puzzle, he continued, is: “Whether he Could, by his Sight, and before he touch them, know which is the Globe and which the Cube?
Empiricists believed that we are born blank slates, and become the sum total of our accumulated experience.
So-called “nativists” countered that our minds are, from the outset, pre-stocked with ideas waiting to be activated by sight, sound and touch. If a blind man who miraculously recovered his sight could instantly distinguish the cube from the globe it would mean the knowledge was somehow innate, they argued. More recently, this “nurture vs. nature” debate has found its counterpart in modern neuroscience.
Recent studies have suggested that the mental images we accumulate through sight and touch do, in fact, form a common pool of impressions that can be triggered and retrieved by one sense or the other. But until now, no one has been able to design a definitive experiment. The problem was finding subjects. They would have to have been blind at birth and then have had their sight restored, but not until they were old enough to reliably participate in tests. Most forms of curable congenital blindness, however, are detected and cured in infancy, so such individuals are extremely rare.
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.