嬰兒是天才的語言學習者 -Patricia Kuhl
Iwant you to take a look at this baby. What you're drawn to are her eyes and theskin you love to touch.
Buttoday I'm going to talk to you about something you can't see -- what's going onup in that little brain of hers. The modern tools of neuroscience aredemonstrating to us that what's going on up there is nothing short of rocketscience. And what we're learning is going to shed some light on what theromantic writers and poets described as the "celestial openness" ofthe child's mind.
Whatwe see here is a mother in India, and she's speaking Koro, which is a newlydiscovered language. And she's talking to her baby. What this mother -- and the800 people who speak Koro in the world -- understands [is] that, to preservethis language, they need to speak it to the babies.
Andtherein lies a critical puzzle. Why is it that you can't preserve a language byspeaking to you and I, to the adults? Well, it's got to do with your brain.What we see here is that language has a critical period for learning. The wayto read this slide is to look at your age on the horizontal axis.
Andyou'll see on the vertical your skill at acquiring a second language. Babiesand children are geniuses until they turn seven, and then there's a systematicdecline. After puberty, we fall off the map. No scientists dispute this curve,but laboratories all over the world are trying to figure out why it works thisway
Workin my lab is focused on the first critical period in development -- and that isthe period in which babies try to master which sounds are used in theirlanguage. We think, by studying how the sounds are learned, we'll have a modelfor the rest of language, and perhaps for critical periods that may exist inchildhood for social, emotional and cognitive development.
Sowe've been studying the babies using a technique that we're using all over theworld and the sounds of all languages. The baby sits on a parent's lap, and wetrain 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 lightsup and a panda bear pounds a drum. A six-monther adores the task.
我們一直研究嬰兒使用的技巧，也是全世界使用的語言技巧和所有語言的聲音技巧。嬰兒坐在父母的膝上，我們訓練他們，當聽到一個聲音從“ah”到 “ee” 他們就轉頭。如果他們一聽到就轉頭，黑盒子就會亮、會出現一只敲鼓的熊貓。六個月大的嬰兒喜歡這個測試。
Whathave we learned? Well, babies all over the world are what I like to describe as"citizens of the world." They can discriminate all the sounds of alllanguages, no matter what country we're testing and what language we're using,and that's remarkable because you and I can't do that.
We'reculture-bound listeners. We can discriminate the sounds of our own language,but not those of foreign languages. So the question arises: when do thosecitizens of the world turn into the language-bound listeners that we are?
Andthe answer: before their first birthdays. What you see here is performance onthat head-turn task for babies tested in Tokyo and the United States, here inSeattle, as they listened to "ra" and "la" -- soundsimportant to English, but not to Japanese. So at six to eight months the babiesare totally equivalent. Two months later something incredible occurs. Thebabies in the United States are getting a lot better, babies in Japan aregetting a lot worse, but both of those groups of babies are preparing forexactly the language that they are going to learn.
Sothe question is: what's happening during this critical two-month period? Thisis the critical period for sound development, but what's going on up there? Sothere are two things going on. The first is that the babies are listeningintently to us, and they're taking statistics as they listen to us talk --they're taking statistics. So listen to two mothers speaking motherese -- theuniversal language we use when we talk to kids -- first in English and then inJapanese.
(Video)English Mother: Ah, I love your big blue eyes -- so pretty and nice.
PatriciaKuhl: During the production of speech, when babies listen, what they're doingis taking statistics on the language that they hear. And those distributionsgrow. And what we've learned is that babies are sensitive to the statistics,and the statistics of Japanese and English are very, very different. Englishhas a lot of Rs and Ls. The distribution shows.
Andthe distribution of Japanese is totally different, where we see a group ofintermediate sounds, which is known as the Japanese "R." So babiesabsorb the statistics of the language and it changes their brains; it changesthem from the citizens of the world to the culture-bound listeners that we are.But we as adults are no longer absorbing those statistics. We're governed bythe representations in memory that were formed early in development.
Sowhat we're seeing here is changing our models of what the critical period isabout. We're arguing from a mathematical standpoint that the learning oflanguage material may slow down when our distributions stabilize. It's raisinglots of questions about bilingual people. Bilinguals must keep two sets ofstatistics in mind at once and flip between them, one after the other,depending on who they're speaking to.
Sowe asked ourselves, can the babies take statistics on a brand new language? Andwe tested this by exposing American babies who'd never heard a second languageto Mandarin for the first time during the critical period. We knew that, whenmonolinguals were tested in Taipei and Seattle on the Mandarin sounds, theyshowed the same pattern.
Sixto eight months, they're totally equivalent. Two months later, somethingincredible happens. But the Taiwanese babies are getting better, not theAmerican babies. What we did was expose American babies during this period toMandarin. It was like having Mandarin relatives come and visit for a month andmove into your house and talk to the babies for 12 sessions. Here's what itlooked like in the laboratory.
(Video)Mandarin Speaker: [Mandarin]
PK:So what have we done to their little brains? (Laughter) We had to run a controlgroup to make sure that just coming into the laboratory didn't improve yourMandarin skills. So a group of babies came in and listened to English. And wecan see from the graph that exposure to English didn't improve their Mandarin.
Butlook at what happened to the babies exposed to Mandarin for 12 sessions. Theywere as good as the babies in Taiwan who'd been listening for 10-and-a-halfmonths. What it demonstrated is that babies take statistics on a new language.Whatever you put in front of them, they'll take statistics on.
Butwe wondered what role the human being played in this learning exercise. So weran another group of babies in which the kids got the same dosage, the same 12sessions, but over a television set and another group of babies who had justaudio exposure and looked at a teddy bear on the screen. What did we do totheir brains?
Whatyou see here is the audio result -- no learning whatsoever -- and the videoresult -- no learning whatsoever. It takes a human being for babies to taketheir statistics. The social brain is controlling when the babies are takingtheir statistics.
Wewant to get inside the brain and see this thing happening as babies are infront of televisions, as opposed to in front of human beings. Thankfully, wehave a new machine, magnetoencephalography, that allows us to do this. It lookslike a hair dryer from Mars. But it's completely safe, completely non-invasiveand silent.
We'relooking at millimeter accuracy with regard to spatial and millisecond accuracyusing 306 SQUIDs -- these are Superconducting QUantum Interference Devices --to pick up the magnetic fields that change as we do our thinking. We're thefirst in the world to record babies in an MEG machine while they are learning.
Sothis is little Emma. She's a six-monther. And she's listening to variouslanguages in the earphones that are in her ears. You can see, she can movearound. We're tracking her head with little pellets in a cap, so she's free tomove completely unconstrained.
It'sa technical tour de force. What are we seeing? We're seeing the baby brain. Asthe baby hears a word in her language the auditory areas light up, and thensubsequently areas surrounding it that we think are related to coherence,getting the brain coordinated with its different areas, and causality, onebrain area causing another to activate.
Weare embarking on a grand and golden age of knowledge about child's braindevelopment. We're going to be able to see a child's brain as they experiencean emotion, as they learn to speak and read, as they solve a math problem, asthey have an idea. And we're going to be able to invent brain-basedinterventions for children who have difficulty learning.
Justas the poets and writers described, we're going to be able to see, I think,that wondrous openness, utter and complete openness, of the mind of a child. Ininvestigating the child's brain, we're going to uncover deep truths about whatit means to be human, and in the process, we may be able to help keep our ownminds open to learning for our entire lives.