acoustic continua and phonetic categories

Acoustic Continua andPhonetic Categories

Frequency - Tones

Frequency - Tones

Frequency - Tones

Frequency - Tones

Frequency - Complex Sounds

Frequency - Complex Sounds

Frequency - Vowels

• Vowels combine acoustic energy at a number of different frequencies

• Different vowels ([a], [i], [u] etc.) contain acoustic energy at different frequencies

• Listeners must perform a ‘frequency analysis’ of vowels in order to identify them(Fourier Analysis)

Frequency - Male Vowels

Frequency - Male Vowels

Frequency - Female Vowels

Frequency - Female Vowels

Synthesized Speech

•Allows for precise control of sounds•Valuable tool for investigating perception

Timing - Voicing

Voice Onset Time (VOT)

60 msec

English VOT production

• Not uniform

• 2 categories

Perceiving VOT

‘Categorical Perception’

Discrimination

Same/Different

Discrimination

Same/Different0ms 60ms

Discrimination

Same/Different0ms 60ms

Same/Different

Discrimination

Same/Different0ms 60ms

Same/Different0ms 10ms

Discrimination

Same/Different0ms 60ms

Same/Different0ms 10ms

Same/Different

Discrimination

Same/Different0ms 60ms

Same/Different0ms 10ms

Same/Different40ms 40ms

Discrimination

Same/Different0ms 60ms

Same/Different0ms 10ms

Same/Different40ms 40ms

Why is this pair difficult?

Discrimination

Same/Different0ms 60ms

Same/Different0ms 10ms

Same/Different40ms 40ms

Why is this pair difficult?

(i) Acoustically similar?

(ii) Same Category?

Discrimination

Same/Different0ms 60ms

Same/Different0ms 10ms

Same/Different40ms 40ms

Why is this pair difficult?

(i) Acoustically similar?

(ii) Same Category?

A More Systematic Test

Discrimination

Same/Different0ms 60ms

Same/Different0ms 10ms

Same/Different40ms 40ms

A More Systematic Test

0ms

20ms

40ms

20ms

40ms

60ms

Discrimination

Same/Different0ms 60ms

Same/Different0ms 10ms

Same/Different40ms 40ms

A More Systematic Test

0ms

20ms

40ms

20ms

40ms

60ms

D T

D

T T

D

Within-Category Discrimination is Hard

Cross-language Differences

R L

Cross-language Differences

R L

R L

Cross-Language Differences

English vs. Japanese R-L

Cross-Language Differences

English vs. Hindi

alveolar [d]

retroflex [D] ?

Russian-40ms

-30ms

-20ms

-10ms

0ms

10ms

Development of Speech Perception3 Classics

Development of Speech Perception

• Unusually well described in past 30 years

• Learning theories exist, and can be tested…

• Jakobson’s suggestion: children add feature contrasts to their phonological inventory during development

Roman Jakobson, 1896-1982Kindersprache, Aphasie und allgemeine Lautgesetze,

1941

Developmental Differentiation

0 months 6 months 12 months 18 months

UniversalPhonetics

Native Lg.Phonetics

Native Lg.Phonology

#1 - Infant Categorical Perception

Eimas, Siqueland, Jusczyk & Vigorito, 1971

Discrimination

Same/Different0ms 60ms

Same/Different0ms 10ms

Same/Different40ms 40ms

A More Systematic Test

0ms

20ms

40ms

20ms

40ms

60ms

D T

D

T T

D

Within-Category Discrimination is Hard

English VOT Perception

To Test 2-month olds

Not so easy!

High Amplitude Sucking

Eimas et al. 1971

General Infant Abilities

• Infants’ show Categorical Perception of speech sounds - at 2 months and earlier

• Discriminate a wide range of speech contrasts (voicing, place, manner, etc.)

• Discriminate Non-Native speech contrastse.g., Japanese babies discriminate r-le.g., Canadian babies discriminate d-D

Universal Listeners

• Infants may be able to discriminate all speech contrasts from the languages of the world!

How can they do this?

• Innate speech-processing capacity?

• General properties of auditory system?

What About Non-Humans?

• Chinchillas show categorical perception of voicing contrasts!

#2 - Becoming a Native Listener

Werker & Tees, 1984

When does Change Occur?

• About 10 months

Janet Werker

U. of British ColumbiaConditioned Headturn Procedure

When does Change Occur?

• Hindi and Salishcontrasts testedon English kids

Janet Werker

U. of British ColumbiaConditioned Headturn Procedure

What do Werker’s results show?

• Is this the beginning of efficient memory representations (phonological categories)?

• Are the infants learning words?

• Or something else?

#3 - What, no minimal pairs?

Stager & Werker, 1997

A Learning Theory…

• How do we find out the contrastive phonemes of a language?

• Minimal Pairs

Word Learning

• Stager &Werker 1997

‘bih’ vs. ‘dih’and‘lif’ vs. ‘neem’

Word learning results

• Exp 2 vs 4

Why Yearlings Fail on Minimal Pairs

• They fail specifically when the task requires word-learning

• They do know the sounds

• But they fail to use the detail needed for minimal pairs to store words in memory

• !!??

One-Year Olds Again

• One-year olds know the surface sound patterns of the language

• One-year olds do not yet know which sounds are used contrastively in the language…

• …and which sounds simply reflect allophonic variation

• One-year olds need to learn contrasts

Maybe not so bad after all...

• Children learn the feature contrasts of their language

• Children may learn gradually, adding features over the course of development

• Phonetic knowledge does not entailphonological knowledge

Roman Jakobson, 1896-1982

Connecting Hearing & Speaking

Connecting Hearing & Speaking

Auditory [ba] + Visual [ga] = Perceptual [da]

McGurk Effect

Connecting Hearing & Speaking

Auditory [ba] + Visual [ga] = Perceptual [da]

Evidence for connection

• Infants know connection between visual and auditory speech stimuli

• Mix and match[a] vs. [i]

Questions about Development

6-12 Months: What Changes?

Structure Changing

Patricia KuhlU. of Washington

Structure Adding

• Evidence for Structure Adding(i) Some discrimination retained when sounds presented close together (e.g. Hindi d-D contrast)(ii) Discrimination abilities better when people hear sounds as non-speech(iii) Adults do better than 1-year olds on some sound contrasts

• Evidence for Structure Changing(i) No evidence of preserved non-native category boundaries in vowel perception

Sources of Evidence

• Structure-changing: mostly from vowels

• Structure-adding: mostly from consonants

• Conjecture: structure-adding is correct in domains where there are natural articulatory (or acoustic) boundaries

So how do infants learn…?

• Surface phonetic patterns

So how do infants learn…?

• Phoneme categories and alternations

– Perhaps more like a phonologist than like a LING101 student - look directly for systematic relations among phones

– Gradual articulation of contrastive information encoded in lexical entries

– Much remains to be understood

Learning Sound Patterns

• Phonological learning problem– 1 year olds know distribution of surface categories– They behave as if they know conditioned allophones because the

critical tests involve phonotactic violations– The challenge is to learn relations among surface patterns - implies

some notion of phonological similarity, e.g. t-th are related, or evidence of morphophonological alternations

– Challenge: similarity space is not straightforward, e.g., flap is an allophone of /d,t/ in English, but of /r-l/ in Korean.

– Surface patterns can be learned without knowing meanings, i.e. without a lexicon; meanings shouldn’t be necessary even for learning conditioned allophony

• So what is the connection between lexical learning and phonological encoding?

Learning the Lexicon

• Developmental change in lexical encoding– Prior to ‘vocabulary spurt’ (~50 words), lexical encoding is slow and labored -

fine detail only evident in highly familiar words

– Later, detailed lexical encoding can be handled much more efficiently

• Is this related to the learning of a phonological system?– Early difficulties in encoding could be attributed to the lack of an appropriate

phonological ‘alphabet’ for the native language

– But how can this be reconciled with the surface knowledge of sound patterns in 12-month olds?

• Do children gradually develop more efficient lexical representations as they accrue knowledge of what is predictable?