Evidence For Cortical Specialization And Cortical

Plasticity In Early Human Language Development

Professor Dan Levitin’s Class, April 3, 2001

Laura Ann Petitto McGill University Department of Psychology &

McDonnell-Pew Cognitive Neuroscience Centre

McConnell Brain Imaging Centre

Montreal Neurological Institute

FUNDING: NSERC, MRC, SSHRC, McDonnell-Pew Foundation

Guggenheim Foundation, Spencer Foundation

BEHAVIORAL LEVELWHAT WE KNOW

Birth 12 MonthsBirth 12 Months

NEURAL LEVELWHAT WE KNOW

BEHAVIORAL & NEURAL WHAT’S THE LINK?

What brain mechanisms underlie the infant’s ability to acquire language?

What components of the environment are most critical?

What is the neural basis for Language...

Sound vs Patterns?

PREVAILING ASSUMPTIONSpeech or Sound is

Critical to

Language

Acquisition

& its’

Cerebral organization

PREVAILING ASSUMPTION

Speech modality set before birthSpeech modality set before birth

TESTING SPEECH-BASED THEORIES

NEW ANSWERS FROM STUDY OF SIGNED LANGUAGES

Brain is set for specific patterns found in

Natural Language

NOT speech

Modality is set after birth

NOT before birth

Mechanism is an interaction of

Perceptual, Neural Substrates dedicated to aspects of Natural Language patterning & Motor

Very early brain development involves

neural pathways linking and

differentiating these properties

THREE TYPES OF DISCOVERIES

1. Similar timing milestonesin sign & speech

2. Structural homologuesin sign & speech

manual babbling &

its physical parameters

3. Similar brain activation (PET)in sign & speech

SIGN & SPEECH IDENTICAL TIME COURSE

10 BABBLING(Petitto, 1984, 1985a, 1987a, 1988;

Petitto & Marentette, 1991)

12 FIRST WORDS-FIRST SIGNS(Petitto, 1983, 1984, 1985a, 1988; Petitto & Marentette, 1990)

18 FIRST 2 WORDS-FIRST 2 SIGNS(Petitto, 1987a, 1988, 1992)

24 MORPHOLOGICAL & SYNTACTIC(Petitto, 1984; Petitto & Bellugi, 1989)

SEMANTIC (Petitto & Charron, 1988; Charron & Petitto, 1991)

PRAGMATICS & DISCOURSE (Petitto, 1984; Charron & Petitto, 1991; Wilbur & Petitto, 1981, 1983)

NORMS FOR FIRST WORD MILESTONE - HEARING

BILINGUALSHearing

Signed & Spoken

Hearing Controls2 Spoken

TIME OF ONSET OF FIRST SIGNS & WORDS- BILINGUALS

0

1

2

3

4

5

6

7

8

9

10

11

Marie June Albert Brian

SignWord

101099

1111 1111

RARE POPULATIONHEARING infants exposed exclusively to signed languages, no systematic spoken language input in early life

MONOLINGUALASL or LSQ, NO speech

BILINGUALASL and LSQ, NO speech

HEARING NO SPEECHMONOLINGUAL SIGN INPUT

AGE AT

FIRST SIGN

0123456789

101112

ASLLSQ

0123456789

101112

ASLLSQ

11.811.8

1010

HEARING NO SPEECHBILINGUAL SIGN INPUT

01

23

45

67

89

1011

12

Sharon Rebecca

ASLLSQ

10101111

TIMING MILESTONES SPEECH & SIGN

TIME OF FIRST

WORD AND

FIRST SIGN

SAME

DISCOVERY OF STRUCTURAL HOMOLOGUES

PROPERTIES

WHY IMPORTANT?Shows Neuroanatomical neurophysiological developments of the motor control of speech production NOT necessary for babbling

HEARING DEAFReduced subset of possiblephonetic units

YES

Syllabic organization YESUsed without reference YES

WHY IMPORTANT?OLD HYPOTHESIS “...a rhythmic alternation between an open and closed

configuration of the vocal tract accompanied by phonation.”

“...oscillations of the mandible...” (MacNeilage & Davis, 1990; Studdert-Kennedy, 1991)

YES rhythmic alternation

NO oscillations of mandible

NEW HYPOTHESIS

Same mechanism underlies Vocal & Manual babbling

Mechanism=Rhythmic Oscillator

HOW TO STUDY?

OPTOTRAK MOTION TEMPORAL ANALYSES OF

HANDS & FEETPetitto,

Holowka,

Sergio &

Ostry

(under

Review)

OPTOTRAK METHODSSUBJECTS

6, 10, 12 months (Hearing, Deaf, Bilinguals)

METHODS16 IREDS (8 hands, 8 feet)

PROCEDURES 5 CONDITIONS

1. Parent talking/signing

2. Parent smiling

3. Object in sight & out of reach; In sight & in reach

4. Imitation: Meaningless hands;Real sign sentences

5. Infant “alone”

OPTOTRAK QUESTIONSMANUAL BABBLING vs RHYTHMIC HANDS

Rhythmic hand movements: All

Rhythmic hand movements: Deaf

INPUT: SIGN PROSODYSigning Adult to Adult

Signing Adult to Infant

COMPARISONS WITH SPEECH

RESULTSBABBLING &

RHYTHMIC HAND

MOVEMENTS

HAVE

DIFFERENT

TEMPORAL &

SPATIAL

PATTERNING

RESULTS

RESULTS

Power Analyses

Movement Frequency (cycles per second)

Common Same

Mechanism Tissue

PET

IMPLICATIONS

1. Milestones

2. Babbling

3. Temporal patterning

PET & MRI STUDIES

PETITTO

ZATORRE

GAUNA

NIKELSKI

DOSTIE &

EVANS.

PNAS,

2000

QUESTIONSCEREBRAL BLOOD FLOW (CBF) OF ADULTS

Speech & Spoken language

Left hemisphere in processing language

QUESTIONS

What neural mechanisms mediate linguistic processing at these sites?

Are these sites “speech-specific?”

Or are these sites more general neural substrates tuned to specific types of patterns encoded

in natural language?

FIRST-TIME CROSS-LINGUISTIC DESIGN

11 Profoundly Deaf People

5 native signers of ASL Independent

6 native signers of LSQ Replication

10 Hearing Controls

5 ASL Stimuli “Hearing 1”

5 LSQ Stimuli “Hearing 2”

PRE-PET BEHAVIORAL SCREENING TASKS

i. No other neurological damage in deaf people

ii. Comparable high linguistic proficiency across

deaf & hearing

SUBJECTS

METHODSEVERY SUBJECT

• PET

Blood Flow

during task

• MRI

• PET & MRI scans were co-registered for precise neuroanatomical identification

CONDITIONSIN FIVE CONDITIONS... RESPONSE

1. Visual Fixation Viewing

2. Meaningless Phonetic/Syllabic “Nonsigns” Viewing

3. Meaningful Signs Viewing

4. Meaningful Signs Imitate

5. Signed Nouns Generate a Signed Verb

HEARING Same except C5: Printed word & generate a spoken verb

STIMULI

High frequency, Single-handed Nouns

All tasks performed twice with different stimuli

SUMMARY

Left Inferior Frontal Cortex - LEXICAL

Superior Temporal Gyrus - SUBLEXICAL

FINDINGS alter our assumption about the neuroanatomy of

Language as being tied to speech

QUESTION - What about neuroantomy of tissue as being

tied to modality?

NEW MRI: MORPHOMETRY OF A1, HG, & PT- DEAF &

HEARINGCismaru, Penhune, Petitto,

Dorsaint-Pierre, Klein & Zatorre (1999)

Sagittal (x-58) Horizontal (z=8) Coronal (y=-16)

PT

H2

H1

PT

H2

H1 H1

PTPT PT

H1 H1H2

SIGNIFICANCENo differences in Grey matter volumes of HG or PT

= DEAF No cell loss

No differences in White matter volumes of HG

= DEAF No loss of neuronal input into A1

FUNCTIONALITY OF CORTEX IS MAINTAINED

IN DEAF BRAIN

HOW? WHY?

HYPOTHESIS & RESEARCHANSWER

Ongoing sign language processing

IMPLICATION

Tissue dedicated to function not modality

NEW QUESTIONS

Polymodal sites?

Reorganization?

NEW FINDINGS

Sign & Speech

same course

Sign & Speech

same sites

Adult Brain

Child Brain

WHAT IT MEANS

Speechdetermined

Speechorganized

PET STUDIES

ACQUI STUDIES

Neural Subs

ANSWERBRAIN IS SET

FOR PATTERNS

PRESENT IN

LANGUAGE

NOT MODALITY

HOW ACQUISITION BEGINS IN ONTOGENY

ARE WE “BORN TO TALK?” NO

CONCLUSIONCortical Plasticity

Speech is not critical

Modality is set after birth

Cortical Specialization Neural systems sensitive to particular

Distributional patterns relevant to

Aspects of natural language

Regardless of the modality

Early brain development consists of Dedicated neural tissue

& those that become dedicated