The Linguistic Gift of Babies Ⅰ. Critical age Decline of babies’ language learning ability occurs at the age of 【T1】______.

The Linguistic Gift of Babies
    Good morning, everyone. In today’s lecture, I’m going to talk about something you can’t see. That is, what’s going on in the little brain of a baby, for example, how babies learn a language. It is always a question people show great interest in. (1) Babies and children are geniuses until they turn seven, and then there’s a systematic decline. (2) Work in my lab is focused on the first critical period in development, and that is the period in which babies try to master which sounds are used in their language. (3) We think, by studying how the sounds are learned, we’ll have a model for the rest of language, and perhaps for critical periods that may exist in childhood for social, emotional and cognitive development. So we’ve been studying the babies by conducting an experiment. (4/5) During our experiment, the baby, usually a six-months, sits on a parent’s lap, and we train them to turn their heads when a sound changes—like from "ah" to "ee". If they do so at the appropriate time, the black box lights up and a panda bear pounds a drum.
    What have we learned? Well, babies all over the world are what I like to describe as "citizens of the world". (6) They can discriminate all the sounds of all languages, no matter what country we’re testing and what language we’re using, and that’s remarkable because yoUKnow, I can’t do that. We’re culture-bound listeners. We can discriminate the sounds of our own language, but not those of foreign languages. So the question arises: When do those citizens of the world turn into the language-bound listeners that we are? (7) And the answer: before their first birthdays. What you see here is performance on that head-turn task for babies tested in Tokyo and the United States, here in Seattle, as they listened to the "ra" and "la"—sounds important to English, but not to Japanese. (8) So at six to eight months, the babies are totally equivalent. (9) Two months later, something, something incredible occurs. The babies in the United States are getting a lot better while babies in Japan are getting a lot worse.
    So the question is: What’s happening during this critical two-month period? We know this is the critical period for sound development, but what’s going on up there? Maybe there are two things going on. (10-1) The first is that the babies are listening intently to us, and they’re taking statistics as they listen to us talk—they’re taking statistics. That is to say, the two babies listen to their own mother speaking motherese—the universal language we use when we talk to kids.
    (10-2) During the production of speech, when babies listen, what they’re doing is taking statistics, that is, sound distribution on the language that they hear. And those sound distributions grow and babies absorb more. And what we’ve learned is that babies are sensitive to the statistics, and the statistics of Japanese and English are very, very different. I mean, the sound distribution of both languages is different. So babies absorb the statistics of the language and it changes their brains; it changes them from the citizens of the world to the culture-bound listeners that we are because we as adults are no longer absorbing those statistics. In this case, of course, we’re arguing that the learning of language material may slow down when our distribution stabilizes.
    OK. Today, we just talked about a recent project on babies’ language development. In our next lecture, we will concentrate on bilingual people, how bilinguals keep two sets of statistics in mind at once.