PHOTOGRAPH BY PAUL FUSCO/MAGNUM

In 2011, Dr. Pawan Sinha, a professor of vision and computational neuroscience at M.I.T., published his answer to an almost-four-hundred-year-old philosophical problem_._ The philosopher William Molyneux, whose wife was blind, had proposed a thought experiment in the seventeenth century about a person, blind from birth, who could tell apart a cube and a sphere by touch: If his vision were restored and he was presented with the same cube and sphere, would he be able to tell which was which by sight alone? The philosophical camps on Molyneux’s question divided roughly through the centuries into those who believe that certain qualities, such as the roundness of spheres, are innate and shared among the senses (the Yeses), and those who insist that, to understand roundness, the eyes must have already seen roundness (the Nos). The longevity of many other philosophical thought experiments—Schrödinger’s cats, twin Earths, what it's like to be a bat—relies on their impermeability, but, after the discovery in the early eighteenth century that a simple cataract surgery could lift the curtain of blindness for some, Molyneux’s thought experiment became, simply, an experiment.

Since 2003, Sinha, through a non-profit that he founded called Project Prakash, has organized and supervised sight-restoration surgeries for more than two hundred blind children from some of the poorest regions in India. The surgeries were given to any child who medically qualified, a subset of whom had been blind since birth with cataracts. After sight had been restored, Sinha posed Molyneux’s question.

The results might have disappointed those in Molyneux’s Yes camp. Sinha showed me a video in which a teen-age boy, blind since birth because of opaque cataracts, sees for the first time. The boy sits still and blinks silently, the room around him reflecting in his eyes as a kind of proof of their new transparency. Sinha believes these first moments for the newly sighted are blurry, incoherent, and saturated by brightness—like walking into daylight with dilated pupils—and swirls of colors that do not make sense as shapes or faces or any kind of object. “The moments immediately following bandage removal are not quite as ‘magical’ as Hollywood movies would have us believe,” Sinha told me. To answer Molyneux, then: No. A cube and a sphere are both lost in this confusion.

Stephen Kosslyn, a pioneer in the field of vision and mental imagery, told me that he was not surprised by Sinha’s results—many of the seemingly natural qualities in everyday vision are not innate but are instead learned through experience. Kosslyn gave the example of stereo vision, which requires the eyes to combine the two slightly different images that they receive into a single, sharp percept. “In order for stereo vision to work, the brain has to know something about how far apart the eyes are,” he said. Factors like prenatal nutrition can influence bone growth, which can set the eyes varying distances apart. “The brain can't possibly know that in advance of being born,” he said, and so, in those first moments of new sight—even with two good eyes—the incoming light will be mishandled by an unprepared brain.

How quickly, if at all, does the brain adapt and vision return after surgery? A simple answer, and a correct one, is that it depends entirely on circumstance. Back in 1993, Oliver Sacks wrote a story in the magazine about Virgil, a man with limited to no vision as a child who had developed cataracts at the age of six. After his cataracts were removed, fifty years later, Virgil had trouble adjusting. (For example, he could not always distinguish the letter “A” from the letter “H” and, when given Molyneux’s test, could not tell a square he felt from a square he saw.)*

Since the surgeries, Sinha has followed up with the Prakash children and found that, while they continued to suffer from poor acuity, many higher-order aspects of vision seemed to be improving. Within a week to a few months after surgery, the children could match felt objects to their visual counterparts. They also improved on spatial-navigation tasks requiring mental imagery, which tested their ability to follow a series of up, down, left, and right directions on a visually imagined game board. This finding was particularly important because previous work by Kosslyn and others had found that the congenitally blind have a capacity for mental imagery, but it is limited in some ways and becomes increasingly poor as the task becomes more complex. (In one example, a sighted person will imagine a typewriter a few feet away as larger than the same one imagined a hundred feet away. Among the congenitally blind, however, the imagined typewriter—a composite of experiences of touch and sound alone—is the same size at all distances.)

Kosslyn believes that any improvements in mental imagery will require a “catalogue of visual memories” that can then be used to build expectations about the visual world. “When you develop expectations, you can use the fruits of previous experience to help you process what's coming in now,” Kosslyn said. “But you need to have had that experience.” An example is depth perception: to the sighted, with a lifetime of practice, rules about occlusion (if A occludes B, object A is closer) and foreshortening (objects farther away appear smaller) are continually used to combine incoming light into a rich, three-dimensional world. The absence of these rules can frustrate the newly sighted, whose visual world can be both blurry and two-dimensional—paintings and people are often described as “flat, with dark patches”; a far-away house is “nearby, but requiring the taking of a lot of steps”; streetlights seen through glass are “luminous stains stuck to the window”; sunbeams through tree branches collapse into a single “tree with all the lights in it.” (The writer Jorge Luis Borges, who went blind at age fifty-five, described going blind as a process by which “everything near becomes distant.” In the newly sighted, without depth perception, the opposite seems true: the distant—tiny houses on the horizon, clouds in the impossibly high sky—suddenly looks nearby.)

Still, Sinha believes that surgery is the best option for young candidates. “A remarkable thing about the brain's processing capabilities is that, even with less than perfect image quality, it can extract a great deal of meaning about the visual world,” he said. “The Prakash children learn to recognize objects and people, and also move around under visual guidance. These abilities confer a tremendous amount of independence, confidence, and happiness on the children."

*Update, 10:20 A.M.: This post has been revised to include information about Oliver Sacks’s 1993 article.