Presentation on theme: "Evidence For Cortical Specialization And Cortical Plasticity In Early Human Language Development Professor Dan Levitin’s Class, April 3, 2001 Laura Ann."— Presentation transcript:
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 & 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 ASSUMPTION Speech or Sound is Critical to Language Acquisition & its’ Cerebral organization
PREVAILING ASSUMPTION Speech modality set before birth
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 milestones in sign & speech 2. Structural homologues in sign & speech manual babbling & its physical parameters 3. Similar brain activation (PET) in sign & speech
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
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 METHODS SUBJECTS 6, 10, 12 months (Hearing, Deaf, Bilinguals) METHODS 16 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 QUESTIONS MANUAL BABBLING vs RHYTHMIC HANDS Rhythmic hand movements: All Rhythmic hand movements: Deaf INPUT: SIGN PROSODY Signing Adult to Adult Signing Adult to Infant COMPARISONS WITH SPEECH
RESULTS BABBLING & RHYTHMIC HAND MOVEMENTS HAVE DIFFERENT TEMPORAL & SPATIAL PATTERNING
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
QUESTIONS CEREBRAL 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
METHODS EVERY SUBJECT PET Blood Flow during task MRI PET & MRI scans were co-registered for precise neuroanatomical identification
CONDITIONS IN 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?
SIGNIFICANCE No 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 & RESEARCH ANSWER 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 Speech determined Speech organized PET STUDIES ACQUI STUDIES Neural Subs
ANSWER BRAIN IS SET FOR PATTERNS PRESENT IN LANGUAGE NOT MODALITY
CONCLUSION Cortical 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