A newborn's world is a blur that clears up in about 6 months--unless a baby is born with cataracts. Removing cataracts without delay can allow a baby to develop decent vision; waiting on surgery more than a few years can mean banishing a child to a netherworld of vague shapes for the rest of its life, as the brain misses out on a critical period in the early months during which it learns how to interpret sensory input. Now scientists have revealed the stunning speed with which a young brain learns to comprehend visual input once the blinders are removed.
Researchers from the Hospital for Sick Children in Toronto and McMaster University in Hamilton tested the eyesight of 28 babies who had just had surgery to remove cataracts. Led by psychologist Daphne Maurer, the team showed the babies striped patterns of various widths on a plain background. If the infants are able to make out the black and white lines, they will stare at them; otherwise their attention wanders.
Immediately after surgery, the babies, who ranged in age from a few weeks to 9 months old, saw about as clearly as newborns. But barely an hour had passed before the babies' visual acuity had doubled--they could see stripes half as wide as those they registered right after surgery, the researchers report in the current issue of Science. Once the cataracts are removed, Maurer says, the babies are "racing to catch up" with others their own age. After 1 month, the babies' vision is close to normal.
"It came as a big surprise" that babies could recover so quickly, says neuroscientist Donald Mitchell of Dalhousie University in Canada. No one knows, he says, how months-old babies seeing the world for the first time can improve their vision so rapidly--much faster than newborns do. Somehow, says Maurer, "the brain is primed and ready to see."