An infant child possesses an amazing, and fleeting, gift: the ability to master a language quickly. At six months, the child can learn the sounds that make up English words and, if also exposed to Quechua and Tagalog, he or she can pick up the unique acoustic properties of those languages, too. By age three, a toddler can converse with a parent, a playmate or a stranger

I still marvel, after four decades of studying child development, how a child can go from random babbling to speaking fully articulated words and sentences just a few years later — a mastery that occurs more quickly than any complex skill acquired during the course of a lifetime. Only in the past few years have neuroscientists begun to get a picture of what is happening in a baby’s brain during this learning process that takes the child from gurgling newborn to a wonderfully engaging youngster.

At birth, the infant brain can perceive the full set of 800 or so sounds, called phonemes, that can be strung together to form all the words in every language of the world. During the second half of the first year, our research shows, a mysterious door opens in the child’s brain. He or she enters a “sensitive period,” as neuroscientists call it, during which the infant brain is ready to receive the first basic lessons in the magic of language. ...