Do you remember learning to

CS 621 Artificial Intelligence

Lecture 35 - 11/11/05

Guest Lecture by

Prof. V Sarma

Human Cognition: The issue of Language Acquisition

Do you remember learning to...

• tie your shoe laces?• ride a bicycle?• to march?• speak?You may recall the first three. But not the fourth

– other than anecdotes of baby talk from parents

And you received explicit instruction and training to perform the first three but not to speak your first language(s)

How is this possible?

What does the child do or not do in acquiring a language?

• Children do not and cannot store all possible words and sentences since children learn to understand and produce (an infinite number) of novel sentences.

• Children learn the “rules” to use their language creatively even though no one teaches them these rules (cf. explicit instruction).

• Children learn the words, sound and sentence structure of their native language(s).

.

Stages of language acquisition-1

Language acquisition follows predictable sequences but the absolute ages varies from child to child

Stage Age Description

Babbling 0;6 - 0;8 repetitive CV patterns

One-word 0;9 - 1;6 Single words or word stems

Two-word 1;6 - 2;0 mini-sentences

Multiword 1 2;0 - 2;6 telegraphic" sentences with lexical not functional/grammatical morphemes

Multiword 2 2;6 on Grammatical/functional morphemes

Stages of language acquisition-2

What do children know at various stages of development? Is their production a direct representation of their perception/knowledge?

What is innate and what is learned? We discuss examples from the grammatical modules of

• Phonology• Lexicon, word learning• Morphology• Syntax

Phonology: Categorization - 1

Phoneme categorization (Eimas, Siqueland, Jusczyk, and Vigorito 1971):

Issue: Do infants perceive speech sounds categorically?Subjects: 1 and 4-month-old babies acquiring EnglishStimuli: tokens on the /ba/-/pa/ continuum (<25ms /b/)

VOT (msec)= 0 20 40 60 80Adult perception: [------ba-------][-------pa------]

Babies sucked on pacifiers connected to a computer. First one syllable was played over and over, then the stimulus changed.

Pairs of input: [20, 40], [60, 80], [0,20]Results: increase no change no change

Phonology: Categorization - 2Are these categories learned or innate? Lasky,

Syrdal-Lasky, and Klein (1975)Subjects: 4-6.5-mo old Guatemalan babies acquiring Spanish

Stimuli: tokens on the /ba/-/pa/ continuum

[20, 60] voiced-voiceless boundary for English speakers

[-20, 20], boundary between voiced-voiceless stops of Spanish

[-60, -20] boundary between Thai pre-voiced and voiced stops

Do the infants’ responses change because Spanish VOT is different from English VOT? Are they sensitive to categorization (prevoicing)that is not seen in their language


VOT= -60 -20 20 60Spanish adults: [-------ba-------][-------pa-------]English adults: [--------ba-------------][--pa--]Thai adults: [--bba--][-------ba-------][--pa--]Results: 20/60 Voiced-voiceless Increase in

English stops heartbeat-60, -20 Prevoiced-voicedIncrease in

Thai stops heartbeat(Same results found with Kikuyu and English speaking children)

-20, 20 Voiced-voiceless NO CHANGE

Spanish stops


The effect of language experience on perception (Werker and Tees 1984)

• 6-8 month-old infants discriminate between contrasts not made in English (retroflexes in Hindi) like Hindi speaking adults do but not English-speaking adults; 95% accuracy

• 8-10 months decline in discrimination ability, 60-70% accuracy

• 10-12 months apparent loss of ability, 20% accuracy

Phonology - Production

Production lags behind perception: ‘Fis’ phenomenon (Berko and Brown 1960)

• Child (pointing at aquarium): /fis/

Adult: Huh?

C: /fis/

A: Oh, fis.

C: No fis

A: Oh! Fish!

C: Ye fis

Learning word meaning

Innate biases or expectations that constrain the hypothesis space for learning word meaning

• Whole object bias: Nouns must refer to whole objects.• Taxonomic bias: Nouns refer to classes of objects and

not to one specific example. But children only hear specific examples!

• Shape bias: shape plays a more important role in defining object categories than color, size, material, etc.

• Mutual exclusivity bias: words always have different meanings (ranked above Whole object bias)

Acquiring morphological rules -1

This was the first evidence that psycholinguists found that kids are developing a grammar; they can produce new words that they never heard before. (Jean Berko 1958)

Test: “Here is a wug. Now there are two of them. There are two ...?” (Answer, /wugz/)

(English plural rule, with allomorphic variation)

heafs, wugs, luns, tors, cras, tasses, gutches, kashes, nizzes

Results: Three year olds perform with great accuracy


English past tense morphemes• My teacher holded the baby rabbits and we

patted them• Hey, Horton heared a Who• I finded the ball• The alligator goed kerplunk.

Not produced by adults, over-regularization.


Compound formation: Kiparsky noted that compounds can be formed from irregular but not regular plurals:

• men-bashing *gays-bashing

• mice-infested *rats-infested

• teethmarks *clawsmarks

Irregular plurals are stored in the mental dictionary as roots or stems and can enter word-formation; compounding takes place with stored words.

Acquiring morphological rules -4Gordon 1986Subjects: 3-5 year olds“Here is a monster that eats mud. He is called a mud-eater.”“… who likes to eat mice” MICE-EATER (MOUSE-EATER)“… who likes to eat rats” RAT-EATER“… who likes to eat purple people” PURPLE-PEOPLE-EATER“… who likes to eat purple lions” PURPLE-LION-EATERQuestion: Learning from parents by looking at plural-

compounds?No plural compounds in motherese (poverty of stimulus)Automatically distinguish between stored and derived items.

Acquiring syntax - 1

Do children have syntax in the one-word stage? (Hirsh-Pasek et al. 1985)

Subjects: 17-mo-olds, one-word stage, using few/no verbs.They watched two TV's showing familiar characters from the

Sesame Street TV show: Cookie Monster and Big Bird.Task: 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


(Hirsh-Pasek et al. 1988)

Found the same result for 24-month-olds with more subtle syntactic cues, and without any lexical cues:

• “Big Bird is flexing Cookie Monster.” [CAUSE TO]• “Big Bird is flexing with Cookie Monster.” [ALONG

WITH]

Thus young kids can use syntactic cues in comprehension even before they can produce whole sentences.


Children make certain errors (goed, holded, oxes etc.) but never certain others are logically plausible

In all languages it is impossible to move a "wh-phrase" out of a conjoined noun phrase (as in 2b)

• 1a. John ate eggs with toast

1b. What did John eat eggs with? • 2a. John ate eggs and toast?

2b. *What did John eat eggs and?


Knowledge of wanna-contraction in English• 1a I want to eat a cookie.

1b I wanna eat a cookie. • 2a What do you want to eat?

2b What do you wanna eat? • 3a You want who to eat a cookie?

3b Who do you want to eat a cookie?

3c *Who do you wanna eat a cookie.

Generalization: contraction is not possible when questioning the subject of the subordinate clause.


An Experiment to test wanna-contraction in children aged 3-5 years. The experimental protocol is designed to elicit questions in which the object of the subordinate clause is questioned

Exp: The rat looks hungry. I bet he wants to eat something. Ask

Ratty what he wants.

Child: What do you wanna eat?

Rat: Some cheese would be good.


The next protocol is used to elicit questions about the subject of the subordinate clause

Exp: There are three guys in this story: Cookie Monster, a dog, and this baby. One of them gets to take a walk, one gets to take a nap, and one gets to eat a cookie. And the rat gets to choose who does each thing. So, one gets to take a walk, right? Ask Ratty who he wants.

Child: Who do you want (*wanna) to take a walk?

Rat: I want the dog to take a walk.

The following video illustrates this performance.

Theories of language acquisition

Imitation Theory: Children produce what they hear. • Child: My teacher holded the baby rabbit and we patted

them.

Adult: Did you say that your teacher held the baby rabbit?

Child: Yes

Adult: What did you say she did?

Child: She holded the baby rabbit and we patted them

Adult: Did you say she held them tightly?

Child: No, she holded them loosely.

Imitation Theory: Problems

• Non-imitation of parents

• Systematic errors across children and languages: hitted, goed (overgeneralization)

no drink (He does not want a drink)

dog toy (That’s the dog’s toy)

• Acquiring complex rules and producing novel sentences

Reinforcement, explicit instruction

Reinforcement Theory: Children learn through explicit teaching with positive/negative reinforcement

• Child: Want other one spoon, Daddy.Daddy: You mean, you want THE OTHER SPOON?Child: Yes, I want other one spoon, please, DaddyDaddy: Can you say ‘the other spoon’?Child: Other…one…spoon.Daddy: Say ‘other’Child: OtherDaddy: ‘Spoon’Child: SpoonDaddy: ‘Other…Spoon’Child: Other…spoon. Now give me other one spoon?

Problems with explicit instruction

• Parental reinforcement /instruction is seldom seen

• Parents correct for meaning, not form (Brown & Hanlon 1969)

• Child: Mama isn’t boy, he a girl. Adult: That’s right

Child: Walt Disney visits on Tuesday.

Adult: No, he doesn’t.

• Much of adult’s knowledge is NOT explicit• When parents do correct, children don’t get it

Learning by analogy

Analogy Theory: Children learn language by hearing a sentence and creating analogous sentences

Problems:• I painted a red barn.

I painted a barn red.• I saw a red barn.

I saw a barn red (not possible, not produced) • sun → sunny

moon → moony (not possible)

Innateness Hypothesis

• Humans are born ‘ready’ for language – Universal Grammar is hardwired.

• Acquisition is rapid and completed by age four-five

• Poverty of the stimulus – lack of negative evidence and sometimes positive evidence

• Input may be fallible: speech errors, false starts, ungrammatical and incomplete sentences

Exposure combined with UG leads children to construct a grammar

Evidence for IH• universals in acquisition• children neither imitate nor are they instructed• innate perceptual categories• ‘invention’ of language by children deprived of real

input• critical age – normal cognition but abnormal language• abnormal cognition and normal language (William’s

syndrome, hydrocephalics)• Inherited language deficiencies (Special Language

Impairment)

The Critical Period HypothesisThe difference between adults and children is in

the ease of language learning – the effect of ‘accent’, ‘grammatical mistakes’ etc. are attributed to the critical period

• Acquisition by the age of 7 yields native command

• Acquisition between the ages of 8 and 15 yields progressively less perfect command

The innate ability to acquire language degrades with age

Evidence for CPH: Feral children

Genie, isolated until the age of 13.5, never learned to produce more than telegraphic speech.

• Applesauce buy store.• Neal come happy; Neal not come sad.

Isabelle, isolated until the age of 6.5, mastered grammar within on year

• Why does the paste come out if one upsets the jar?

• Do you go to Miss Mason's school at the university?

CPH is not restricted to language

Aspects of maturation are seen in humans and animals.

• in ducklings: imprinting, ability to identify and follow the mother

• in kittens: ability to perceive visual images• in sparrows: ability to learn the father's songs

Developing the neural circuits for such skills is an expensive allocation of developmental resources and evolution favours individuals who lose this once learning has (normally) occurred

Abnormal cognition, normal language

Williams Syndrome (Chr. 11, IQ of 50):Cannot tie shoe-laces, tell right from left, retrieve things from the cupboard, add two numbers, find their way, draw a bicycle. Understand complex sentences and fix ungrammaticalities. Fondness for unusual words.

Crystal (U. Bellugi): This is a story about chocolates. Once upon a time in Chocolate World there used to be a Chocolate Princess. She was such a yummy princess. She was on her chocolate throne and then some chocolate man came to see her. And the man bowed to her and he said these words …

Inherited language deficiences -1

Specific Language Impairment (KE family, 3 generations, 30 members, 16 affected, M. Gopnik)

Impairment uniform across affected members, randomly distributed; Impervious to teaching and correction; Persists through life; Problems with inflections (plural, tense, agreement); non verbal IQ tests normal, hearing normal.

• The boys eat four cookie• Carol is cry in the church• It’s a flying finches, they are

Inherited language deficiences -2

• No plausible environmental causes• 53% of family but 3% of the total population• Syndrome all or none, so likely one gene is the

cause rather than several genes, no graded disability

• Autosomal gene – affects both sexes• Dominant gene (not recessive) – one copy

Led to the isolation of the FOXP2 gene by Lai et al which is implicated evolutionarily also in the leap to language

Conclusion

Language experience is a mere "trigger"

Claim: children only use linguistic experience to choose among a very narrow range of possible hypotheses given to them by the innate language module – universal grammar.

Plato’s paradox is explained by the richness of the innate structures.

Documents

Do you remember learning to