Healthy infants start learning to discern objects, typically by their form and colour, from the moment they open their eyes. By the time a baby is a year old vision development is more or less complete, although refinements continue through childhood. But as the brain grows older, it becomes less adaptable, neuroscientists generally believe. "The dogma is that after a certain age the brain is unable to process visual inputs it has never received before," explains cognitive scientist Amy Kalia of the Massachusetts Institute of Technology (MIT) in Cambridge.

Consequently, eye surgeons in India often refuse to treat children blinded by cataracts since infancy if they are over the age of seven. Such children are not usually found in wealthier countries such as the United States — where cataracts are treated as early as possible — but are tragically plentiful in India.

In the study, which was published last week in Proceedings of the National Academy of Sciences, Kalia and her collaborators followed 11 children enrolled in Project Prakash, a humanitarian and scientific effort in India that provides corrective surgery to children with treatable cataracts and subsequently studies their visual abilities. ('Prakash' is Sanskrit for light.)