- Patients with congenital cataracts got visual input for the first time as pre-teens.
- Their brains took time to learn how to process that input.
- After a year, they have visual memory similar to that of individuals with sight since birth.
The brain comes prepared to perceive the world. When babies are born, the optic nerve (which carries signals from the light-sensitive retina at the back of the eye) connects to a nucleus in the thalamus, and, from there, connections go to areas of the brain’s cortex that are responsible for processing visual information. Although this wiring is built in, the areas of the brain need input in order to organize in ways that actually allow the visual world to be perceived.
An amazing thing about the visual system is that it supports incredible visual memory abilities. You are able to recognize large numbers of objects based on brief visual input. You are also able to remember which objects you have seen recently and to differentiate them from other objects you have not seen, even if you only view them briefly.
What would happen to your brain, though, if you did not get early visual input? For people who are blind from birth, their retinas never carry information about the visual world back to the brain, and, so, the brain is unable to organize in a way that would support visual perception. Suppose, though, that a blind person suddenly got the ability to see. Would the brain then adapt to this input and create the same kind of amazing memory abilities that people with sight since birth have?
This question was explored in a fascinating study by a team of nine authors led by Priti Gupta that appeared in the June 2022 issue of Psychological Science.
Study of Patients With Congenital Cataracts
They engaged with a project in India that provides surgery for congenital cataracts that emerged before the age of 1 so that these individuals functionally had no sight since birth. These patients received the surgery on average when they were 13 years old. Their performance was compared to that of a group of normally sighted children of a similar age. These participants wore lenses that blurred their vision to simulate the level of visual clarity that the patients would have after surgery.
All participants did several tests of visual memory in which they saw sets of 10, 20, 40, or 80 pictures and then did a test in which they saw the pictures from the set along with distractor images and had to say which of the pictures they had seen before. Some of the test sets showed real objects, and others showed abstract patterns. Tests were given to patients before the first surgery, once after the surgery on each eye (which were done about a week apart), and then again a month, 6 months, and 12 months after surgery).
Before surgery, some patients did have a little light that would pass through their cataracts. Nonetheless, they were not able to recognize the pictures they were shown during the test before their first operation. Their visual memory test results were also poor (though slightly better) after their first and second surgeries. However, by about a month after surgery, patients were much better at recognizing both the images of real objects and the abstract images.
Results at 12 Months After Surgery
By the time the participants were 12 months after surgery, their performance on the memory test was just as good as the normally sighted individuals whose vision was blurred.
This research suggests that the brain is able to adapt to getting visual input, even after 10 years of blindness. That said, it takes a little while before this ability to really process the images kicks in. Right after the second surgery, patients are getting input to the brain from their retinas, but their visual memory is still poor. After about a month, though, the brain has found ways to process this visual information, and, a year later, their brains do just about as well as those of people who had sight from birth.
Gupta, P., Shah, P., Gutnick, S. G., Vogelsang, M., Vogelsang, L., Tiwari, K., Gandhi, T., Ganesh, S., & Sinha, P. (2022). Development of Visual Memory Capacity Following Early-Onset and Extended Blindness. Psychological Science, 33(6), 847–858. https://doi.org/10.1177/09567976211056664