When the blind gain sight, the brain rewires to build a visual world
For the newly-sighted, the hardest part isn’t opening their eyes — it’s teaching the brain how to see.
By Sachin Rawat
Sharon Gilad-Gutnick has witnessed many children see for the first time. After having their cataracts surgically removed, the children can see the world but don’t recognize faces well. Even among those who can recognize the faces of their parents or others they know well, most don’t look at the faces of the people they speak with.
“If we told them to look at the face, they could usually manage it,” Gilad-Gutnick told Big Think. “But they were mostly looking at the hands.”
A former research scientist at MIT, Gilad-Gutnick worked with these children as part of Project Prakash, an initiative that provides care to children and adults with congenital blindness in India and investigates the neuroscience of sight restoration. Congenital cataracts are a preventable cause of blindness and are often treatable within two months of birth. However, due to a lack of access to cataract screening and surgery, many children in developing countries are often treated too late, if at all.
The Prakash children eventually learn to look at faces when spoken to — usually a few months after their surgeries. Their experiences reveal that seeing doesn’t come naturally the moment a person is cured of blindness. Newly-sighted people must learn to see.
With advances in sight-restoration technologies, such as gene and stem cell therapies, and greater access to cataract surgery, many more people may gain sight even after decades of blindness. Understanding how and why vision works differently for those who gain sight later in life, as compared to those who can see from birth, could help the newly-sighted see better.
At first sight
A newborn’s vision is blurry. It takes time before things come into focus. Binocular vision develops by the third month, and it takes a couple more months before babies can perceive distances. They gain the hand-eye coordination required to grasp things by their first birthdays. These milestones are driven by specializations of the visual cortex, the part of the brain that processes visual inputs, and visual input from both eyes is critical for the development of the brain’s visual system.
For people born blind or those who lose sight as infants, the lack of early visual experiences explains many of the differences in how the newly-sighted see when compared to those who can see since birth.
For instance, after sight restoration, newly-sighted people have low visual acuity and find it hard to identify shapes or perceive details. Gilad-Gutnick mentioned a child who used the researchers’ camera to take pictures of what he saw. He snapped a picture of his friend and correctly identified what he saw. He then took a picture of a hand sanitizer bottle and said it showed his friend. Both the bottle and his friend’s shirt were blue, suggesting that he relied heavily on color.
Newly-sighted people also find it difficult to estimate distances or depths and have a high sensitivity to light. These challenges often last, to some degree, years after sight restoration. However, the newly-sighted are quick to correctly interpret biological motion — such as the Prakash children looking at the speakers’ hands.
Even as their visual acuity improves and they get better at identifying faces, as opposed to things that look like faces, they can still have difficulty telling faces apart. This suggests that a sensitive period might exist in the development of the visual system. During this period, if not stimulated by visual input, the brain doesn’t develop face perception capabilities, even if the individual can see later in life.
“The issue isn’t necessarily in the area [of the brain] that processes faces or depth,” Ella Striem-Amit, a neuroscientist at Georgetown University, told Big Think. “It can be anywhere in the processing chain from the eyes to that area.”
The newly-sighted get better at perceiving differences in color, shape, and size — even if they were treated for their congenital cataracts after years of blindness—but not so much at spotting differences in shading or contours. This could partly be responsible for the persistent difficulty in distinguishing faces.
Sight deprivation in early years may also shape how people see the world in the long term. Scottish artist Tansy Lee Moir, who was treated for congenital cataracts as a child in the 1970s, draws exclusively in monochrome. Her charcoal sketches of ancient trees evoke a sense of fluidity that defies their rootedness.
“However hard I try to make things very soft and undefined, I always want to put edges in,” Moir told me.
The visual functions that do improve do so to a considerably different degree in newly-sighted people. That’s mainly because patients had varying levels of residual vision before their treatment and lost sight at different points in their lives. Those who became blind later had more visual experience to draw from, but how much vision improves, and to the degree it enables a newly-sighted person, depends as much on non-visual experience.
The plastic visual system
In the absence of visual input, parts of the visual cortex come to specialize in processing non-visual stimuli. “It can take on or respond to other senses because our brains receive information from other senses, even when we are sighted,” Striem-Amit said. For instance, the visual cortex uses sounds to predict what the eyes will see, and the brain combines information from all senses to create a coherent multisensory experience of the world.
In blind people, even those who lost their sight later in life, neural circuits responsible for vision can reorganize to perform other functions. There is also evidence showing that “circuits [typically associated with vision] are doing auditory or tactile processing, or even higher cognition functions, like language and math,” Rashi Pant, a cognitive neuroscientist at the University of Hamburg, told Big Think.
The non-visual parts of the brain adapt, too. Because they rely more on touch and hearing, blind people often have heightened sensitivity to tactile and auditory stimuli. A blind person will often estimate the relative location of two sounds better than sighted people. Such adaptations in non-visual senses have been noted to persist even after sight recovery.
In compensating for the loss of sight, the visual cortices of blind people can also perform similar functions as those of sighted people, but for non-visual stimuli. “If you have an area that’s supposed to be dedicated to reading, it would still be performing its reading function, just in this case using Braille,” Striem-Amit said. After sight recovery, the area can retain some of this non-visual function while still reorganizing to gain visual function.
However, a lack of vision early in life does lead to irreversible changes in the brain structure. For instance, the visual cortices of congenitally blind people who had their sight restored are thicker and have a lower surface area than those of sighted people.
Early blindness even changes the population composition of neurons in the brain. As each brain system develops, it settles into a balance of excitatory and inhibitory neurons, which fire up and calm down other neurons, respectively. In a 2025 study published in eLife, Pant and colleagues found that early blindness led to an irreversible change in the relative abundance of these neurons.
“We found that this ratio in the visual cortex for the newly-sighted is not the same as in sighted people,” Pant said. For them, she added, the visual cortex probably didn’t develop the typical excitation-inhibition ratio within the sensitive period in visual development.
Learning to see
Newborns have months of experience seeing before they need to act on what they perceive, and unlike newborns, the newly-sighted have a lot of experience navigating the world through senses other than vision.
“If you were blind throughout your life, learning to see isn’t trivial,” Striem-Amit said.
Having relied only on non-visual stimuli, their mental models of the world are likely to be considerably different from those of sighted people. Even after prolonged blindness, these models can still act as a scaffold over which the brains of the newly-sighted can learn to see. A transfer of abilities from non-visual senses to sight could enable the newly-sighted to draw on their non-visual experience to interpret what they see.
For example, many newly-sighted people recognize things better when they can touch them. In his 1971 book, Sight Restoration After Long-Term Blindness, ophthalmologist Alberto Valvo provides one such example of a man who was blind for 34 years following a case of corneal ulcers at the age of eight months. He could read numbers much faster when touching them with his finger, even though the figures weren’t etched on the surface.
Sight can feel like an extension of touch. As Moir told me, “The process of drawing feels as if I’m touching the surface of the tree with my eyes.”
Rehabilitative strategies that rely on multisensory processing could boost outcomes, such as using canes for mobility or auditory aids that allow the newly-sighted to simultaneously use cues from other senses while learning to see. “It makes sure that they navigate the world in a way that they are comfortable with,” Pant said.
From a clinical care perspective, follow-ups are necessary to monitor improvements in visual acuity and prevent other sight disorders, such as lazy eye, where one eye is used more than the other. They also keep newly-sighted people inspired to use their vision to the fullest. The man from Valvo’s book used his newly gained vision primarily for moving around before sessions with a psychologist motivated him to use it more broadly.
As Valvo wrote: “He was eventually brought to the point where he could grasp the principle of sight, and he understood that he could improve his ability to see. When he started, he had a double representation of objects: a very confused visual image, and a purely intellectual concept of the same object that was acquired by touch. He said that he had great difficulty in putting two ‘things’ together.”
For a long time, congenital cataracts in older children or adults were rarely treated due to a belief that they would have difficulty adapting, and therefore, the surgery wouldn’t be worth the risk. Despite a large and growing body of research showing that people who are congenitally blind can learn to see even after years of blindness, a significant gap persists between research on sight recovery and ophthalmological practice.
“Even though people have moved away from the notion that they’re not going to learn, there’s still this really widespread thought that they’re not going to improve much,” Gilad-Gutnick said. If more people understood how much their sight can improve, more congenitally blind adults could likely benefit from sight restoration procedures.
Making a visual mind
In An Essay Concerning Human Understanding, the philosopher John Locke described a puzzle posed to him by his friend William Molyneux: If a man born blind, who learned to distinguish between a cube and a sphere by touch, were to gain sight as an adult, would he be able to tell the shapes apart by only looking at them?
Locke and Molyneux thought he wouldn’t, and many researchers today do too, but the puzzle remains unsolved three centuries later. A 2011 study tested it with a few Project Prakash children, and the answer was a “likely no.” As with many other visual functions, congenitally blind children treated for their cataracts found it hard to distinguish shapes solely by sight early on, but performed much better when tested a few days later.
Arguably, those children didn’t make for a good test for Molyneux’s problem, mainly because the newly-sighted don’t gain vision exactly as it is for those who could always see. Regardless of whether the problem can be empirically solved, further research into how the brains of the newly-sighted begin to integrate shapes, colors, contrast, and other visual features with their non-visual experiences could help researchers understand how the brain makes the mind.
For the newly-sighted, it could inform better strategies to ease their transition to living with vision. The ability of the newly-sighted to use vision improves gradually over months and years after sight restoration. But some aspects of their lives improve dramatically, pretty quickly.
“A few days later, they all seem to gain a lot of confidence,” said Gilad-Gutnick. “They like to tell you a lot about what they can see.”
Correction, March 5: A previous version of this story said Sharon Gilad-Gutnick was a researcher at MIT. In fact, she is a former researcher with the institute.
It would be interesting to know if people who've learned to see after having been born blind can recall images or whether they have aphantasia