Would a blind person, on regaining sight, be able to immediately visually recognise an object previously known only by touch? This question, now known as the “Molyneux Problem” was first formulated by Dubliner, William Molyneux to the English philosopher John Locke in a letter from Dublin on March 2nd 1693. Three centuries later, a team of MIT researchers are attempting to answer it. Their question is: How does the human brain “learn” to see? If the brain is deprived of visual input early in life, can it later learn to see at all?

However, the recent case study by Pawan Sinha, associate professor of brain and cognitive sciences at MIT and his team found that a woman who had her vision restored at the age of 12 performed almost normally on a range of high-level vision tests when they studied her at the age of 32. Known by her initials, S.R.D., the woman was the first subject of this kind who has been extensively studied, but there are other patients like her in India, says Yuri Ostrovsky, a graduate student in brain and cognitive sciences.

Before her surgery, at age 12, S.R.D. could distinguish between light and dark but could not make out form or pattern. Twenty years after the surgery, S.R.D.’s visual acuity was only 20/200, but the researchers were surprised to find that she showed normal or near normal abilities on most tests of high-level vision, including recognising objects and faces, judging depth order and matching 2-D and 3-D shapes.

One task where she did not do well was the gaze-estimation test, where she based her answers on where people’s heads were pointed, rather than where their eyes were looking. She also seemed to take longer to perform some of the tasks, and she had trouble visualizing objects with her eyes closed. S.R.D. had no explicit training after her surgery, so she had to learn by experience. Because of the 20-year lag between her sight restoration and initial testing by the researchers, they don’t know how much time it took her to reach her present level. “It’s hard to get the full picture,” said Ostrovsky.

The new research “shows that the brain is still malleable” in older children, says Pawan Sinha. “The findings have significant implications for the idea of a ‘critical period’ for learning how to see”, says Sinha. There are few data from human subjects regarding such a critical period, but studies with other animals, such as kittens, have suggested that visual recovery is very limited following a few initial months of rearing in complete darkness. This knowledge could benefit thousands of blind children around the world, who were previously thought to be too old to receive eye treatment.

Extrapolating from these findings to humans would lead one to conclude that treating blind children after a few years of age would be of very limited use. However, evidence from the case of S.R.D. and others suggests that the visual cortex retains its plasticity, or ability to learn new functions, well into childhood.

These early results have already had an impact on how doctors view childhood blindness. Ophthalmologists working with the MIT team in India are now more willing to treat older patients, whom they previously thought would be hopeless. In other ongoing studies, the researchers hope to track the precise order and mechanism of visual skill development following sight restoration.

Childhood blindness is a huge problem, and professor Sinha recently launched a humanitarian initiative, Project Prakash, to help expand the reach of eye care facilities. Through Project Prakash (Prakash means “light” in Sanskrit), the MIT researchers are making eye care available to blind children who would otherwise go untreated. About 450,000 children in India are blind, and many of those cases are preventable.

(Tragically, shortly after this study S.R.D. was fatally injured in a bus accident. The MIT team will help support her nine-year-old daughter.)