So, we've talked about the structure of languages, what they have in common and how they're different. Now, let's turn to the question of language acquisition. How is it that we get from a baby who doesn't know any language, all the way through an adult who does know language. Now, one radical perspective on this has been proposed by the linguist Noam Chomsky, who we met in our discussion of behaviorism, who was one of the major critics of skinner's Siri. Chomsky is probably the best known linguists in the world. He is strongly identified to School of philosophical and psychological thought known as nativism. Nativism has another meaning in a political context. What it means for a psychologist or philosopher, is the idea that we're born with a lot of knowledge, a lot of knowledge is innate. Chomsky has argued this particularly in the domain of languag. In fact, he says, that we should see the development of language not so much as learning, but as growth and so here's a quote, "No one would take seriously the proposal that the human organism learns through experience to have arms rather than wings, or that the basic structure of particular organs results from accidental experience. [Language] proves to be no less marvelous and intricate than these physical structures.. Why, then, should we not study the acquisition of a cognitive structure like language more or less as we study some complex bodily organ?" Now, I have some sympathy for this view and I want to later on present some evidence that language does seem to show certain patterns that hint at universality. Hint that in some way we can see language as akin to a bodily organ and different from a product of culture like baseball games or British history. But at the same time, it's clear that language development does involve learning, that is, it's impossible to explain how we come to know language without accepting that we attend to what others around us do and do as they do and pick up the way they speak. This has to be the case, because language is differ. So, consider an example from each of our three domains. In English, there's a phonetic distinction between L and R. So, I'm giving you the letters, but it's really the sounds associated with them. We know this because words can differ in meaning, depending on whether it's which phoneme is used. There's a different in lip, which is a part of the mouth versus rip. Which means to tear up something. The other languages don't make this distinction. Some languages have a sound [inaudible]. that will distinguish certain words. Other languages just use tonal distinctions to make distinction in words and English doesn't have those. So, plainly part of what it is to come to know a language has come to learn their phonetic properties language. Another thing is part of what is to know a language is to learn the meanings of words, morphology. An English child has to know that this is a dog, while a French child has to know this is a chien, [inaudible]. while a child learning one of the thousands of other languages has to pick up the corresponding sound of those with it. Finally, there's syntax. So, in English, if you wanted to say that Bill hit John, that Bill was to hitter and John was hit, you'd say in this order, Bill hit John. If all you knew was English you would think this is inevitable, how else would you do it? But in fact, other languages just do it differently. Some languages would say, Bill hit John, by saying, Bill John hit, or even John hit Bill, where the phrases are in different order to capture the same meaning. All of this phenology, morphology and syntax has to be learned. But, as Chomsky points out, if it is learning is learning of a fundamentally different character than other forms of learning. For one thing as mentioned before, everybody learns language, it's a universal part of development, all normal children come to have it and this is true in every human society. More interestingly, there are specific impairments of language. So, things can happen to you as an adult, like brain damage, or trauma, or stroke, or as a child as an a developmental disorder, or a genetic disorder, that could leave you bereft of language. It could leave you unable to speak or understand. This is relevant because many people believe that all that you need to learn language is, for instance, to be very smart, or to want to communicate. But plainly, that can't be true, because there are people who are walking around who are very smart and desperately want to communicate and they can't learn language. This supports the idea, that language is to some degree special, it iss not reducible to other human capacities. Also, on the theme of learning, language is learned, but it's not learned in through feedback or specific training. There are many people who believe that if you don't really teach your kid to talk, your kid won't talk. Just as in other societies, people would believe that if you don't teach your kid to stand up or walk, he'll never walk. There are some societies, for instance, where they pile up sand under the kids butt so they could gradually gets more and more upright until he's walking. Anything if you didn't do that he never learned to walk. We look at that and say that's silly, you don't need it, kids learn to walk on their own. But, those societies would look at our society with this obsession with flashcards, and drills, and learning how to calibrate your speech to the kid, and tremendous focus on what you say to a kid to make them learn to speak, and they'd say that's silly, you don't need to do that. They're right, cross-cultural leaders, great differences in how we speak to our children, or whether we speak to our young children and all. This seem to have little or no effect on whether or not kids talk, all kids talk regardless. Now, it's also true that in Western societies people give feedback to their children. So, often you'll correct your child if he says something. Some people have speculated along lines of behaviorism, that this feedback perhaps as a reward and punishment, shapes the child's learning. But, we now know that this isn't true. For one thing, you don't need it. Again, even in Western societies some parents don't reinforce and punish their kids for what they say and yet kids nonetheless learn to talk. Moreover, even the parents who do give their kids reinforcement and punishment don't tend to do it for the phenology, or the morphology, or the grammar, but more for the appropriateness or cuteness of what kids say. So, we correct kids if they get their facts wrong. We don't typically correct them if they get their grammar wrong. Just imagine the child who says, "I loves you mommy." It's very unlikely that the kid's mother will say, "Oh, that's terrible, you got your morphology wrong, you got your verb wrong, grow up." We will accept cute, but wrong statements, if a kid says, "I hate your guts mother." The mother is unlikely to shower that kid with praise for his perfectly formed grammatic [inaudible]. So, children learn language by absorbing the language around them, that much has to be true. But, it doesn't seem as if any teaching, certainly any reinforcement or punishment plays a critical role. So, what do we know about language development? Well, what I'll do now is, I'll just kind of walk through this stagees without saying much about the psychological mechanisms that drive kids from one stage to another, but provide you with descriptive overview what happens. So, the child's born and when a child is born, he or she likes listening to his or her own language. There's all sorts of clever studies that explored this. My favorite studies involve putting headphones on the baby and this baby could it be a newborn baby. Then hook the baby up to a pacifier were the baby will suck on a pacifier and gets to hear voices, depending on how long the baby sucks. It turns out that kids who are raised in societies where people speak English, prefer to listen to English than to listen to Russian, and kids raised in Russian speaking society prefer to listen to Russian than to listen to English. What's particularly cool is very early on, children can discriminate all the Phonemes of natural language. I said before there are many many phonemes in English and every other languages just chooses a subset of them. But kids are sensitive to them from the very start your average, your kid born in America to English-speaking parents can distinguish between bar and par, which are English distinctions, but also can make distinctions between Phonemes in Czech and Hindi, which are not expressed in English. What's really cool is, this capacity goes away. So, this is one way in which kids are better than adults. It's that there are not many examples of this, but this is one example. A baby can make distinctions, can hear distinctions that you can't. This capacity you start off oversensitive and then we whittled down our sensitivity until we're just understanding the distinctions made in their own language. Around age seven months starts babbling, kids go Ba-Ba-Ba Pa-Pa-Pa, make sounds like that. Fascinatingly, deaf children learning sign language also babble, they babble with their hands producing the equivalent of Ba-Ba-Ba Pa-Pa-Pa. At around the kids first birthday, and there's quite a lot of variance for this, parents shouldn't panic if kids take longer than 12 months, but you know you get the first words, momma, dadda, typically words for objects, actions, properties, milk, give, up, hot, words like that. Early on using clever methods, it turns out that there are some sensitivity to word order. So, for instance, you could put a kid down at around a one-year-old, even a one-year-old who isn't yet producing sentences, and put the kid down and there's two screens. On one screen, first, you find out the kid can recognize big burden Cookie Monster Sesame Street characters, if not you could use other characters. Then you have two screens, in one screen, big bird is pushing Cookie Monster, in the other screen, Cookie Monster's pushing big bird, and you say to the kids something like, look big birds pushing Cookie Monster and you'll see where the kid looks. Very early on, you find that the kid looks in an appropriate direction, in a screen that matches the English sentence expressing that action, showing that very early on you have some understanding of word order. Around a year and a half, the kid starts to increase the rate of learning words, produces two word sentences, what's called a telegraphic speech. There aren't telegrams anymore, but telegrams used to be ways to communicate where each word you used was very expensive, so you had to kind of put things together, you wouldn't say, "Oh, I'm traveling through Spain and I've lost my wallet please send me money right now", you'd say, "Spain-lost-wallet-need-money." That's how kids talk early on, as if words are very expensive. Then, gradually at this point, function morphemes, we talked about them before like, in, of, a, the plural marker 's', the past tense marker 'ed', gradually begin to appear. Language continues to develop, then at some certain point, it becomes more difficult to learn a language and people are rarely fully successful. This is true both for second languages and also studies of deaf children learning sign language for first languages. For instance, some really interesting studies to illustrate this looked at people and these were all people who have been in America for many many years, I think for about 30 years, so they've learned a language as well as their aboriginal learn it. The comparison was, when did they start? Did they start as babies? Did they start as young children? Did they start as adolescents? Did they start after the age of 17? what you can see in this graph is, that the older you start, past about age three, the less good you are. So, if you start learning English at age three you're fine, but if you start learning English at age 10, at age 15, or age 20, even if you were to speak it for 30 years, you still will not be perfectly fluent. This suggests that, the biological capacity to learn language has a clock on it. Like other capacities psychologists have studied, there's a critical period you have to do it within a certain period of development, or you'll never be fully successful.