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Evidence For Cortical Specialization And Cortical Plasticity In Early Human Language Development

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 &

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Evidence For Cortical Specialization And Cortical Plasticity In Early Human Language Development

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  1. 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

  2. BEHAVIORAL LEVELWHAT WE KNOW Birth 12 Months

  3. NEURAL LEVELWHAT WE KNOW

  4. 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?

  5. PREVAILING ASSUMPTION • Speech or Sound is • Critical to • Language • Acquisition • & its’ • Cerebral organization

  6. PREVAILING ASSUMPTION Speech modality set before birth

  7. TESTING SPEECH-BASED THEORIES

  8. 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

  9. 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

  10. 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)

  11. NORMS FOR FIRST WORD MILESTONE - HEARING

  12. BILINGUALS • Hearing • Signed & Spoken • Hearing Controls • 2 Spoken

  13. TIME OF ONSET OF FIRST SIGNS & WORDS- BILINGUALS 11 11 10 9

  14. RARE POPULATION • HEARING infants exposed exclusively to signed languages, no systematic spoken language input in early life • MONOLINGUAL • ASL or LSQ, NO speech • BILINGUAL • ASL and LSQ, NO speech

  15. HEARING NO SPEECHMONOLINGUAL SIGN INPUT • AGE AT • FIRST SIGN 11.8 10

  16. HEARING NO SPEECHBILINGUAL SIGN INPUT 11 10

  17. TIMING MILESTONES SPEECH & SIGN • TIME OF FIRST • WORD AND • FIRST SIGN • SAME

  18. DISCOVERY OF STRUCTURAL HOMOLOGUES • PROPERTIES • WHY IMPORTANT? • Shows Neuroanatomical neurophysiological developments of the motor control of speech production NOT necessary for babbling

  19. 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?

  20. OPTOTRAK MOTION TEMPORAL ANALYSES OF HANDS & FEET • Petitto, • Holowka, • Sergio & • Ostry • (under • Review)

  21. 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”

  22. 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

  23. RESULTS BABBLING & RHYTHMIC HAND MOVEMENTS HAVE DIFFERENT TEMPORAL & SPATIAL PATTERNING

  24. RESULTS

  25. RESULTS • Power Analyses • Movement Frequency (cycles per second)

  26. Common Same Mechanism Tissue PET 1. Milestones 2. Babbling 3. Temporal patterning IMPLICATIONS

  27. PET & MRI STUDIES • PETITTO • ZATORRE • GAUNA • NIKELSKI • DOSTIE & • EVANS. • PNAS, • 2000

  28. 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?

  29. SUBJECTS • 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

  30. METHODS • EVERY SUBJECT • • PET • Blood Flow • during task • • MRI • • PET & MRI scans were co-registered for precise neuroanatomical identification

  31. 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

  32. 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?

  33. H1 H1 H2 H2 H1 H1 H2 H1 PT PT PT PT PT NEW MRI: MORPHOMETRY OF A1, HG, & PT- DEAF & HEARING • Cismaru, Penhune, Petitto, • Dorsaint-Pierre, Klein & Zatorre (1999) • Sagittal (x-58) Horizontal (z=8) Coronal (y=-16)

  34. 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?

  35. HYPOTHESIS & RESEARCH • ANSWER • Ongoing sign language processing • IMPLICATION • Tissue dedicated to function not modality • NEW QUESTIONS • Polymodal sites? • Reorganization?

  36. NEW FINDINGS Adult Brain Child Brain WHAT IT MEANS Speech organized PET STUDIES Sign & Speech same sites Neural Subs Speech determined ACQUI STUDIES Sign & Speech same course

  37. ANSWER BRAIN IS SET FOR PATTERNS PRESENT IN LANGUAGE NOT MODALITY

  38. HOW ACQUISITION BEGINS IN ONTOGENY

  39. ARE WE “BORN TO TALK?” • NO

  40. 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

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