Linguistic Theory

1. Linguistic Theory Lecture 12 Language Acquisition

2. Outline of lecture • This lecture will be in three parts: • What children actually do • How to model what children do • Theories about how they do it

3. What children don’t do • Common opinion: children are taught language by their parents • This cannot be true: • The vast majority of children learn language perfectly • Teaching is a skill that has to be learned • Most parents are not trained teachers • You have to know something to be able to teach it • No adult ‘knows’ the language that they have learned • The first fact stands in direct opposition to the following two!

4. What children don’t do • Maybe, parents can teach like this: • Wait until child says something ungrammatical (this often happens) • Provide the grammatical version as a correction • This does not require them to know the grammar – just the difference between grammatical and ungrammatical sentences • But ...

5. For this to work: • Parents must behave consistently • They must correct every error the child makes • They must never correct a grammatical sentence • Children must know: • When a parent repeats one of their sentences it is meant as a correction • What the mistake is in their sentence and how to alter the grammar according to the ‘correct’ sentence provided by the child • The first does not happen, the second is rather much to expect of a child.

6. What children do do • From birth: • They make noise • Soon after: • Babbling • Not reactive/reflexive noises • From about 24 weeks: • Reduplicative babbling • Repetitive CV sequences • Soon after: • Non-reduplicative babbling • Differing CV sequences with intonation contours

7. No one knows why: • It is not essential • Babies who had tracheotomies during the babbling period learn language perfectly well • It is not dependent on environment • Profoundly deaf babies do it • It doesn’t differ depending on language of parents/community

8. First words • From about 1 year (±0;2): • First ‘meaningful’ words appear • One or two to start • Slowly increases over next 4-6 months, then ... • From about 1;6 (±0;2): • Vocabulary spurt • First words in combination (2 word sentences) • Mirrors word order of parent language

9. This continues for nearly a year • Slowly increase in number of words which are combined • But not much syntactic variation • Until ... • From about 2;6 (±0;2): • Syntax spurt • Rapid increase in number of words • Syntactically varied expressions present • This continues to slowly develop for another 2;6 by which time most of the system is in place

10. What do children learn? • Clearly, they do not learn language • We do not know language • We know grammar • That children learn rules is demonstrated by: • Wug experiment (Berko 1958):

11. Here is a Wug:

12. Here are two ................. • All children say [wʊgz] • Not [wʊgs] or [wʊgɪz] • They have never heard the word before • But they know the correct plural form • So they must be able to generate new forms from what they have learned

13. Modelling the acquisition situation • With the onset of the mathematical approach to language in the 1960s, linguists also attempted to set up a mathematical model of language acquisition. • These models were deliberately simplifications with respect to the actual case • The point being that any negative result for the simplified model would carry over to the more complex real situation

14. Assumtpions • What is learned: • Languages (not grammars) • Thus the ‘learner’ does not have to figure out from data what the underlying rules are (a more difficult process) • We can assume that the hypothesis space is limited to mathematically defined languages (context free, context sensitive, etc.)

15. The learning situation • Data from the target language is presented to the learner one bit at a time • On the basis of a datum, the learner makes a guess at the target language • Given the next datum, the learner either sticks with the hypothesis or abandons it in favour of another • This continues for ever (no one tells the learner when to stop) • Learning is successful if in some finite time the learner correctly selects the target language and never rejects it on future data

16. The learning strategy • Conservative learning • Learner rejects a hypothesis only if they receive data to show that it is wrong • Non-conservative learning • A hypothesis can be rejected even if the data is compatible with it • Conservative learning is safer – if the target is selected, it will never be rejected as all data will be compatible.

17. Data presentation • Negative and positive • Both grammatical and ungrammatical sentences are presented properly indicated • Positive only • Only grammatical sentences are presented

18. Gold’s results • Assuming a conservative learning strategy and positive data presentation only finite languages are learnable • Context free, context sensitive, unrestricted re-write systems (formally equivalent to transformational grammars) are unlearnable

19. Theories of language acquisition • Structuralist/behaviourist theory • Child makes noises • Child accidentally makes a noise similar to one of the parent’s language • Parents react to this positively • Child’s behaviour is reinforced and so they are more likely to make the same noise again • Over time and a series of accidents and reinforcements, the child only makes the noises of the language

20. It should be obvious what is wrong with this!

21. Early Chomsky • The child has some species and linguistic specific innate ability which allows her to learn language • The Language Acquisition Device (LAD) • Not much was known about this

22. Mathematical approach • Assuming that human language falls into one of the mathematically defined set of languages, the LAD orders possible languages and the child selects and rejects grammars on the basis of this

23. 1970s - constraints • With constraints came greater generality • Generality allows ‘universal’ principles to be proposed • Universal Grammar became a reachable goal • But how ‘learning’ operated within this was still unsettled

24. 1980s Principles and Parameters • Principles are universal parts of UG • Parameters are variable parts of UG • Parameters can be set differently for different languages • Parameter settings are what needs to be learned

25. E.g. X-bar principles and parameters • English has heads preceding complements (object follows V, prepositions, inflections precede VP, etc.) • Japanese has heads following complements (objects precede V, postpositions, inflections follow VP, etc.) • Both have heads and complements but the order varies:

26. X-bar principle • X’  X, YP (comma indicates no order) • X-bar parameter • A) head first • B) head last • All the child has to hear is one head initial phrase and she will know that the language has prepositions and VO and I-VP word order

27. Problems • Isn’t this a bit too easy? • Why does it take so long to learn language? • Isn’t this too descriptive? • What counts as a parameter? • If any difference between languages can be stated as a parameter we can account for any logically possible amount of variation

28. Restricting parameters • Rich deductive parameters • A simple underlying parameter is responsible for a lot of apparently unconnected surface phenomena because the modules of the grammar interact with each other in complex ways • E.g. Pro-drop • Unfortunately this could not be empirically sustained

29. Restricting parameters • Languages differ only in the behaviour of their functional elements (nouns, verbs, etc. are pretty much universal). • =the functional parameterisation hypothesis (Borer 1986) • This works for some parameters, but it is difficult to see how it can work for all (head left/right parameter)

30. Restricting parameters • Learners have to learn the lexicon of the language • Perhaps parameters are a matter of lexical differences • = the lexical parameterisation hypothesis (Manzini and Wexler 1986) • If this is so, it is difficult to see why there is not more variation within a language with one word conforming to one parameter value and another to another value.

31. Maturation • None of these theories account for the syntax spurt • Why do children all of a sudden learn a lot of syntax? • It has been proposed that what happens at this time is that functional elements enter the child’s grammar: • Before they operate only with thematic categories: nouns, verbs, adjectives, etc. • So the question is: why do they not learn functional categories before 2;6? • The functional maturation hypothesis (Radford 1988) • The notion of a functional category is not available to the child until after a genetically predetermined time (like teeth and puberty)