Learning word meanings

Concept learning review

Simple associations not enough• Goal direction / determining tendency• Essences for some types of concept

(“natural kinds”)• Defining features present early for some

concepts (robber)• Characteristic defining for others

(uncle)

Concept learning review ctd

Concept of race

Interaction of universal / innate part with social learning

A “developmental” approach

Concept learning review ctd

But:

• Simple associationism illuminates asymmetric category learning

• Its failures highlight what remains to be explained

• Its limitations don’t mean we can’t model concept learning

Overview of lecture

A. The computational problem

B. Constraints that might help

C. Summary

A. The computational problem

1. Quine’s rabbit

2. Searching a concept space

3. Winston’s arch

Gavagai

Inductive concept learning

(eats-meat fluffy small red) +(eats-meat fluffy big red) -(eats-fruit fluffy small red) -(eats-fruit smooth small red) -(eats-meat fluffy small red) +

What's the concept?(eats-meat fluffy small)

Can a concept like this be learned automatically?

A search problem

For a given number of attributes, a space can be defined of possible concepts

()

(eats-meat) (eats-fruit) (fluffy) (smooth) ...

(eats-meat fluffy) (eats-meat smooth) (eats-fruit fluffy)...

(eats-meat fluffy small)(eats-meat smooth small) ...

etc.

Operators: generalisation & specialisation

Generalisation

Cover more examples:

drop an attribute from a concept

First positive case initialises concept:

(eats-meat fluffy small red) +

(eats-meat fluffy small blue) +

Generalise: (eats-meat fluffy small)

This is a 'move in concept space'

Specialisation

Cover fewer examples:

add an attribute to a concept

(eats-meat fluffy) +

(eats-meat fluffy) -

Specialise: try (eats-meat fluffy small)

… a 'move in concept space'

Winston's arch learnersupports(block1, obj) support(block2, obj) flat(obj) roof(obj)

Ex 1 [+]

Ex 2 [+] supports(block1, obj) support(block2, obj) roof(obj)

DEFINE

GENERALISE

supports(block1, obj) support(block2, obj) roof(obj) not touch(block1, block2)

SPECIALISE

Ex 3 [-]

B. Constraints that might help

1. General expectations

2. Cognitive constraints

3. Language form (syntax) constraints

4. Pragmatic constraints

5. World knowledge

Balaban & Waxman (1997) 9 month old childrenprediction - if child forms category while viewing instance:

1. they get bored (habituate)2. they'll show a novelty preference

is the effect greater with naming?9 rabbits then a pig and a rabbit

More children showed pig preference (sig.)with words than tones accompanying

Waxman & Markow (1995)novelty preference method

12-13 mths - N or Adj (novel word), or no label

Train: 4 instances (eg. 4 animals)

Test: choice of new instance, or non-member

This one is an X Novelty preference

This one is X-ish Novelty preference

Look at this No novelty preference

Waxman & Markow ctd

Words prompt (very young) children to form conceptsA general expectation about word forms

The infants didn’t differentiate between the noun and adjective form

However:Children with a high vocabulary

facilitated superordinate but not basic level category formation

Children with a low vocabularyneither clearly assisted

Booth & Waxman (2002)

Stages 1 and 2: Training

Stage 1 Familiarisation

4 novel objects with characteristic shape & colourThis one is a dax, and this one,…

Look what I can do with this one… [demo]

Look at this one…

Stage 2 Contrast

Booth & Waxman ctd

Stage 3: Generalisation

Forced choice between a new instance and a non-memberCan you find me another one of these?

At 14 mths, demo of function helps

- because it focuses child on a relevant subset of properties

Cognitive constraints

• Perceptual constraints eg. shape

• Constraints can be learned

• Ontological constraint

• Taxonomic constraint

• Mutual exclusivity

Landau, Smith & Jones (1988)

YES NO

Is this a Dax?

YES NO

Does this one match?

Jones, Smith & Landau (1991)Trained example

.50 .53

.76

.82

.48

.80

Soja, Carey, & Spelke (1991)

2 yrs

Novel object introduced, described, and handled

My blicket, this blicket

Then a forced choice: point to the blicket

Soja et al. ctd

Object learned:another same shape different stuff

or three little chunks same stuff

Substance learned:another pile or slick the same

shape, but different stuffor three blobs the same stuff

Soja et al. ctdIf just ask to choose (no trained item, no word)

responses were at chance

another same shape different stuff= three little chunks same stuff

and another pile or slick the same shape,

but different stuff= three blobs the same stuff

Soja et al. ctd

By 2 years

Children know about the distinction between objects and substances

And they use it to organise the generalisation of word meanings

Colunga & Smith (2003)

Previously(Soja, Carey, & Spelke, 1991, Cognition, 38, pp179-211)

Children aged 24/30 monthssolid objects same shapenon-solid objects same materialBut not at 18 months…

Hypothesis: learn this pattern by associationFirst 300 wordsMost denote solid objects, objects that have a consistent shape… and non-solid mostly denote substances i.e. child learns to apply this mapping pattern from associations

present in first words learned

Colunga & Smith (2003)Output units [words]

Hidden units […]

Inputs [shape] [substance] [solid, not s.]

Train: ball [ball-shape] [random] [ 1 0 ]

Test: novel shapes/materials

Prediction - hidden unit activation patterns ("representations") will be similar for

non-solid / same material or

solid / same shape

Colunga & Smith (2003)Prediction - hidden unit activation patterns ("representations") will be similar when

non-solid and same material

solid and same shape

Testing

Forced choice Pick shape

non-solid / same material 30%

solid / same shape 55%

Markman & Hutchinson (1984)

Taxonomic constraint

words refer to whole objects; of same type

3-4 year old children

Target picture eg. poodle

Test pictures eg. alsation or dog foodGive the puppet the one that’s the same.

without label - prefer thematic

with label - prefer taxonomic

Markman & Wachtel (1988)

mutual exclusivity constraint

- two words don’t mean the same thing

Expt 1 (3 years old)

Offer child choice of objects, one unfamiliar. Familiar object already has a name.

Give me a merk

Children tend to choose the novel object

Markman & Wachtel (1988)Expt 2 to check for response bias

Present one object (with a salient part)FAMILIAR fish (fin)UNFAMILIAR microscope (platform)Which is the fripe, the whole thing or just this part?

- What predictions do the constraints make?whole object constraint?mutual exclusivity?

20% chose part for unfamiliar object57% chose part for familiar object

Syntactic constraints

• General expectation differentiates into more specific, syntactically driven, expectations

• Soja

• Language specificity

Syntax – a very brief intro!

Word order indicates relationships among event participantsThe boy kicked the dog

Part of speech is indicated by word order function words, and morphologyThe boyboy function word (= closed class word)

kickkicked morphology (changes word shape)

Syntax – brief intro ctdWord order indicates relationships among event participants

Part of speech is indicated by word order, function words, and morphology

In some languages, morphology can do nearly all the work, and word order matters less (eg. Latin)

Waxman & Booth (2001; 2003)1. Training on 4 purple animals, presented in 2 pairs (same colour, same category)

2. Contrast example orange carrot

3. Then test generalisation

11 mths 14 mths

Nouns

Category [new animal, purple; or purple plate] 0.57 0.68

Property [new animal, purple; or new animal, blue] 0.55 0.44

Adjectives

Category [new animal, purple; or purple plate] 0.59 0.50

Property [new animal, purple; or new animal, blue] 0.58 0.52

No word

Category [new animal, purple; or purple plate] 0.46 -

Property [new animal, purple; or new animal, blue] 0.49 -

Soja, Carey, & Spelke (1991)

2 yrs

Novel object introduced, described, and handled

My blicket, this blicket

Then a forced choice: point to the blicket

Soja et al. ctd

Object learned:another same shape different stuff

or three little chunks same stuff

Substance learned:another pile or slick the same

shape, but different stuffor three blobs the same stuff

Soja et al. ctdIf just ask to choose (no trained item, no word)

responses were at chance

another same shape different stuff= three little chunks same stuff

and another pile or slick the same shape,

but different stuff= three blobs the same stuff

Soja et al. ctd

By 2 years

Children know about the distinction between objects and substances

And they use it to organise the generalisation of word meanings

Soja et al. (1991)

If the learned object was introduced with selective syntax

a blicket

some blicket

… it made no difference

Soja (1992)

2 and 2.5 year olds who had mastered mass-count syntax in their speaking

Were partly sensitive to syntax in word learning

GENERALISES TO

some [substance] substance

a [substance] bounded pile

Language specificityEnglish, Spanish - plural marks nounEnglish - mass/count distinction

draws attention to shape

Korean - classifier language

Experiment (3-5 years; n = 16)novel word applied to an object: "fep", a magnet

choice: cube of same substancewood block same shape

English, Spanish - prefer shape similarKorean - prefer substance

Language specificity ctd

But, classifiers highlight shape:

Empitsu o gohon kudasi

pencil five long thin given

Yonpil tasot caru

pencil five long thin

Pragmatic influencesPrinciple of contrastClark (1993)

- every difference of form marks difference in meaning

- economical for learning- a pragmatic principle

-- used once understand speaker is intentional

For Clark, contrast means any difference in meaning (including connotation, register & dialect).

Identity of reference is not sufficient

Tomasello & Barton (1994) DevPsych 30 639-650

2 years "Let's go find the toma"

look in one of buckets (5)

Either find it straight away

or

first find and reject two

("oh no", scowl, put back)

then find the right thing

Akhtar & Tomasello (1996) 2 yearsSimilar expt but one (distinctively shaped)

bucket is shut and can't be opened

Pre-play, so that child is familiar with the objects in each bucket (no naming)

Put them backAdult - "Now, let's find the toma!"Adult expresses disappointment at no access,

but plays with other objectsLearned equally well whether no access or did

retrieve

Role of world knowledge Schank, Collins & Hunter (1986)

• Hijackings cubageneralisation? cuba?

• Hijacking libyasyntactically, do what?drop destination as a dimension?or generalise feature content?

e.g. warm country?

Target concept - a model of how terrorists select destinationsWhich are relevant features has to be worked out

often not perceptually available

C. Summary

1. Quine’s rabbit & the problem

2. Constraints guide search of the space

3. A variety of factors influence learning word meanings