Introduction to Contemporary Linguistics December 9, 1998 Language acquisition OVERVIEW: 1. Why study children's language? 2. Stages in language development 3. The acquisition of grammar 4. Is language innate? 5. Summary ============================================================= 1. Why study children's language? >There are at least three good reasons to study how babies begin to talk: >(1) It's an amazing mystery that deserves as much study as how flowers grow or how stars are born. >(2) Babies can teach us something about how adult language works. >(3) We can test theories that say that much of human nature is not learned, but is innate (天生的). >Nativism: the theory that much of human knowledge (e.g. about language) is innate. >The way you talk about babytalk reveals your theoretical view: >Language learning: emphasizes the importance of experience in beginning to talk. (Used by educators) >Language acquisition: emphasizes the final result: the acquisition (getting) of a complete adult grammar, which may not involve conscious learning. (Used by linguists and many psychologists.) >Language development: emphasizes the change over the child's lifetime, which may be caused by learning or acquisition. (Used by many psychologists.) 2. Stages in language development >The textbook begins when babies begin to produce speech, but actually language acquisition begins much earlier, when infants are learning how to perceive speech. >When do babies begin to perceive speech? In the womb! Here's an experiment that shows this: >Mothers-to-be, 6 weeks before giving birth, read a children's story aloud. >When their babies were born, half of the babies were read the same story, while the other half were read a new story. >The babies were sucking on a pacifier connected to a computer that measured the sucking rate. >Results: The babies who had already heard the same story in the womb increased their sucking rate, as if they recognized it. >How? Sound can filter into the womb, especially prosody: rhythm, loudness, vowel duration, pitch. >Amazingly, even very young infants have categorical perception: if you gradually change [ba] into [pha], they perceive a categorical jump, just as you did in our experiment. >4-month-old American babies heard syllables that varied VOT (voice onset time), from /ba/ to /pa/: VOT (msec)= 0 20 40 60 80 Adult perception:[------ba-------][-------pa------] >Babies were sucking on pacifiers connected to a computer. >First they were played one syllable over and over. >Then the experimenters changed the syllable. >Results: 0-20: no change in sucking rate 60-80: no change in sucking rate 20-40: an increase in sucking rate >The babies noticed the change in the same place as adults! >The beginnings of speech (6-7 months): babbling: meaningless syllables, with sounds that may not be phonemic in the parents' language >Babies babble MORE when adults are NOT around! That means they are not communicating, but practicing. >By 11-12 months, babbling is restricted just to the phonemes of the parents' language. >The beginnings of words: >First words: around 12 months. >Around 16-18 months there is a sudden explosion in vocabulary. >From then on, infants learn OVER EIGHT WORDS A DAY up through 6 years old (=14,000 words). >The earliest words are concrete, dealing with the here-and-now, especially words describing things that they can directly affect: (e.g. "ball" is learned before "chair"). >One-word stage: babies talk in one-word sentences (holophrases): >"Water!" can mean "I want water" or "There is water" or "Give me water" or.... >Do they know syntax at this stage? >It doesn't show up in their speech [OVERHEAD] >But maybe they understand more than they can say: >In an experiment, 17-month-old American babies in the one-word stage were tested. [OVERHEAD] >They watched two TV's which showed familiar characters from the Sesame Street TV show: Cookie Monster and Big Bird. >One TV showed CM tickling BB; the other TV showed BB tickling CM. >The babies heard one of these sentences: (1) "Cookie Monster is tickling Big Bird." (2) "Big Bird is tickling Cookie Monster." >Results: the babies looked longer at the correct TV scene, showing that they understood the basics of English syntax: Subject-Verb-Object. >Two-word stage (starting about 24 months). >The babies use two-word sentences, though their grammar still doesn't match that of their parents: Adults Baby The sock is gone Allgone sock >After this, the children's sentences get longer and more complex: >The Mean Length of Utterance (MLU) gradually increases. 3. The acquisition of grammar >Children actually acquire grammars, not languages. >Children's speech has systematic rules, even if the rules are different from those of their parents. >Children DON'T just imitate what their parents say, but instead try to figure out the correct grammar. >Children have their own syntactic rules: >If they say Allgone sock, they may never say *Sock allgone. >They may form relative clauses differently from their parents, but still in a consistent way: Child's speech Adult's speech "This [my made it]" = "This is [what I made]" This American child is basically using Chinese syntax! [my made it] = [wo zuo t ] de >Children also learn the grammatical rules for the lexicon: >English-acquiring children can say the correct plural form even for a fake noun they never heard before: [OVERHEAD] >Children overregularize: they apply a regular rule to words that are supposed to be exceptions: >Morphology: American kids say "breaked" or "goed" >Semantics: Chinese kids overuse 個 (e.g. 那個蠟筆) >Children have their own phonological rules, too: [OVERHEAD] 4. Is language innate? >The mystery: >How do babies know that language has grammar? >How do they figure out the parents' grammar so fast? >How come people talk, but chimpanzees don't? >The answer of nativism: >In some way, human language is like an instinct: babies are born already "knowing" a lot about what human language is like, just as birds are born knowing a lot (but not everything) about how to sing. >Of course, some things must be learned from experience: >Chinese babies growing up in the USA acquire English; American babies in Taiwan can acquire Chinese. >Many parents and educators feel that parents must "teach" language. (From Kelly & Parson 1975 The Mother's Almanac ) "Say a word over and over, slowly and distinctly, the way you would teach a foreign language.... Do this as many as twelve times at a stretch, and in a matter of weeks your child will try to imitate you.... "In another year your child will wrestle with difficult sounds better if you use props -- a candle flame or a feather to emphasize the breathy 'wh' sound of 'what', rather than the flat 'w' sound of 'water'." >In reality, acquiring a first language (L1) is quite different from how people typical learn a second language (L2): >When you learn an L2 (e.g. English), you get a lot of positive evidence (= grammatical examples) but also a lot of negative evidence (= ungrammatical examples and corrections by your teacher). >However, children do NOT get very much negative evidence from their parents, and even when they do get it, they ignore it! [OVERHEAD] >This observation creates an argument for nativism: >Without negative evidence, kids cannot learn if something is truly ungrammatical, or if it is grammatical but they just haven't heard it yet. >So how do children learn what is ungrammatical? They must already innately know something about what is an impossible human language. >Example: In all languages, you can't put regular inflection inside a compound: shoe store (grammatical) *shoes store (ungrammatical) >Even young (American) children know this: >Ask them to name a monster that eats rats, and they will call it a "rat-eater", not a "rats-eater". >How can they learn this? >There is no negative evidence: Children and adults never say things like "rats-eater". >Even the positive evidence is not helpful, since adults very rarely use "N-V-er" compounds. >Conclusion: All children are born knowing that regular inflection must go "outside" compounds >If language is partly innate, then how can learning and experience affect it? >One theory: children go through a biologically determined critical period (or sensitive period) when they are especially sensitive to language information. >This period supposedly starts before birth and gradually fades out through adolescence. >Thus babies don't "learn" language; their grammars "grow" with language input the way plants grow with the sun. >Evidence for sensitive periods in animals: >Male songbirds of many species must "learn" how to sing properly from adult models. >The sensitive period for one bird ends around 10 months; if they don't hear adult models before then, then they will never sing properly. >Is there a sensitive period for human language? >Children who are isolated from language past adolescence never learn to talk properly: >When "Genie" returned to normal human life after 13.5 years of linguistic isolation, she did not acquire English grammar correctly: Applesauce buy store. Genie have Momma have baby grow up. I like elephant eat peanut. >Criticism: such isolated children often do not receive love either; perhaps that's why they don't learn to talk. >However, many children who are born deaf but have hearing parents DO receive lots of love, though they don't learn spoken or sign language during the sensitive period. Just like "Genie", if they learn ASL later in life, they end up using the grammar incorrectly. >There is another interesting argument for innateness from children acquiring sign languages: ignoring iconicity. >Since most languages are spoken languages, and spoken languages use very little iconicity, we can guess that babies innately assume that human language is not iconic. >Sign languages, however, often seem very iconic. Does iconicity help deaf babies or do they ignore it? >They ignore it! Babies acquiring ASL develop language at the same rate as hearing babies acquiring spoken language. >For example, kids acquiring spoken languages get confused by deictic words like "you" and "me". >In sign languages like ASL, the signs YOU and ME are very iconic, so babies should have no trouble, right? >Wrong! Signing babies mix up YOU and ME, too! This implies that the human brain expects human language to have arbitrary connections between words and meanings, not iconic connections. >But what about those signing chimpanzees? Don't they prove that "innate" knowledge is not necessary to learn language? >Since chimpanzees gesture so much to each other, it's natural to try to teach them a gestural language like ASL. >The first chimpanzee was a female named Washoe, who was taught sign language in a loving home environment. >The signing chimp experiments have had a big impact on the public. (Have you seen the movie Congo?) >But most linguists and psychologists are not impressed! >Chimpanzees are our closest relatives (OVERHEAD); their minds are very similar to ours; they are in danger of extinction and should be protected. But their brains do not seem to have the necessary structures to acquire human grammar (just as humans will never learn how to act like chimpanzees!) >Problems with the signing chimpanzee studies: >(1) The Clever Hans phenomenon: >Clever Hans was a horse in Germany in early 1900's who seemed to be able to do math and understand complex sentences. >A scientist studied Clever Hans and found that the horse was merely responding to tiny, unconscious movements made by the people watching him. >To avoid this problem when studying animals (or babies), researchers should not know what response is expected, so they don't "give away" the answers. >However, such controls are not often followed in the chimpanzee studies, and videotaped experiments show that humans do help some chimps "cheat" in this way. >(2) Chimpanzees don't use any syntax at all: (some "sentences" by a chimp named Nim Chimpsky): Nim eat Nim eat Drink eat me Nim Tickle me Nim play Me banana you banana me you give You me banana me banana you Banana me me me eat Give orange me give eat orange me eat orange give me eat orange give me you >(3) Signing chimps use a lot more iconicity than real ASL signers. Thus even people who don't know ASL can often figure out what the chimps are trying to communicate (or at least imagine that the chimps are communicating!) That is, the chimps are not using grammar. >For example, here is the ASL sign for GIVE: it is somewhat iconic, but its use is controlled by the grammar [OVERHEAD] >Here's a native ASL signer on the Washoe project: "When [the chimps] want something, they reach. Sometimes [the trainers would] say, 'Oh, amazing, look at that, it's exactly like the ASL sign for "give"!' It wasn't." (quoted in Pinker 1994, p. 338) 5. Summary: the stages of language development. [as usual, this table is all messed up] Age (月) Speech perception Speech production Lexicon Syntax 0-8 Know prosody; categorical perception of non-native phonemes 8-12 Lose categorical perception of non-native phonemes Babbling; may use non-native phonemes 12-18 Use only native phonemes Produce first words Holophrases; can understand simple sentences 18-24 Vocabulary explosion 24-36 2-word stage >36 Phonological rules become adult-like Learn more morphology Gradual increase in complexity and MLU