How do babies
learn to talk?

The full narration of the video.

You talk to a baby, and he doesn't understand a word. Yet two years later, he's talking back. So how did he learn? No textbooks. No teachers. He does four things. One, listen. He starts listening before he's even born.

In the last ten weeks or so of pregnancy, a baby can already hear his mother talk. Scientists played sounds to babies less than three days old. When they heard sounds from a foreign language, they sucked their pacifiers harder. As if to say: that's new! He already knows what his mother's language sounds like.

Two: count. Grown-ups talk in one long stream, with no gaps between words. So the baby quietly keeps track of which sounds always stick together. Take "little doggy." "Little" is often followed by "doggy." But what comes after "doggy" could be anything.

Sounds that always stick together are probably one word. In one experiment, eight-month-olds needed just two minutes to work out which sounds belonged together. Three: pick the sounds that matter. Newborns can tell apart the sounds of every language in the world.

Take two sounds English keeps apart but Japanese doesn't. At six to eight months, American and Japanese babies both hear the difference. By ten to twelve months, the American babies get even better. The Japanese babies lose it. The brain is tidying up: it keeps the sounds it hears every day, and sets the rest aside.

Four: he needs a real person to talk with. Nine-month-old American babies played with Mandarin-speaking teachers twelve times, and learned to hear Mandarin sounds. Same teachers, same words, but on video, they learned nothing.

When adults talk to babies, we stretch our words out and raise our pitch. That helps babies hear clearly. After all that listening, he starts practicing. At four to six months, he babbles: ba-ba-ba, ma-ma-ma. Around his first birthday, his first word. Between one and two, two words together: "More cookie."

So babies aren't memorizing words. They listen, count, and choose. And they need someone to talk back and forth with. Next time you meet a baby, look him in the eye and talk slowly. When he says "ah," answer him. What was your first word? Tell me in the comments.