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Language, innateness and the brain

Language, innateness and the brain. LING 200 Spring 2006 Prof. Sharon Hargus. Organization. Innateness hypothesis Neurolinguistics Lateralization Localization. Innateness hypothesis. Humans are genetically programmed for language. Humans are equipped with Universal Grammar (UG)

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Language, innateness and the brain

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  1. Language, innateness and the brain LING 200 Spring 2006 Prof. Sharon Hargus

  2. Organization • Innateness hypothesis • Neurolinguistics • Lateralization • Localization

  3. Innateness hypothesis • Humans are genetically programmed for language. • Humans are equipped with Universal Grammar (UG) • = universal properties of language; structure or phenomena found in all languages • UG severely constrains the possible form that a human language may take. • The actual form of language is determined by environment/language experience.

  4. Noam Chomsky • ...language appears to be a true species property, unique to the human species in its essentials and a common part of our shared biological endowment, with little variation among humans apart from rather serious pathology. (p. 2)

  5. Evidence for innateness hypothesis • lg has characteristics of innate behavior • no other species has a communication system like human lg • brain (and vocal tract) show evidence of specialization for lg

  6. Some innate human behaviors

  7. Some characteristics of innate behaviors

  8. Results of chimp studies • Chimps are capable of learning some aspects of human language • Show some spontaneity, creativity • Skills comparable to 1-2 year old child • But chimps lack latent capacity for human language • don't get past 2-3 word stage • limited syntax

  9. Neurolinguistics

  10. Brain hemispheres right hemisphere left hemisphere

  11. Lateralization • Contra-lateral control • a given hemisphere controls opposite side of body • Left hemisphere controls right side of body • Right hemisphere controls left side of body • Other hemispheric specializations:

  12. Right hemisphere specialties • Holistic, spatial processing • pattern-matching (e.g. recognizing faces) • spatial relations • emotional reactions • music (processing by musically naive individuals)

  13. Left hemisphere specialties • Sequential processing • rhythm • temporal relations • analytical thinking • music (as processed by musically sophisticated individuals) • mathematics • intellectual reasoning • language, speech sounds • especially so for adult, male, right-handed, literate, monolingual subjects

  14. Language processing as a left hemisphere task • Aphasia • Dichotic listening experiments • Split-brain patients

  15. Aphasia • Brain injury locations resulting in speech deficits are almost always in left hemisphere

  16. Dichotic listening experiments • I.e. stimuli presented to different ears • linguistic sounds: right ear (left brain) advantage • environmental sounds: left ear (right brain) advantage • advantage = correctly identified more often, identified more quickly, etc.

  17. Tone in dichotic listening experiments • Tonal contrasts in Thai • [ná:] ‘aunt’ (high) [nâ:] ‘face’ (falling) [nā:] ‘field’ (mid) [nǎ:] ‘thick’ (rising) [nà:] (nickname) (low) • Thai speakers process tone with left hemisphere • English speakers presented with tonal contrasts process tone with right hemisphere

  18. Split-brain patients • Severe cases of epilepsy treated by severing corpus callosum corpus callosum (connects hemispheres)

  19. Split-brain patients • Task of naming object held in left hand (right brain) • left eye open (right brain), right eye covered much harder than • right eye open (left brain), left eye covered

  20. Effects on lateralization • Lesser left hemisphere specialization for language if: • left-handed • female • illiterate • multilingual

  21. Lateralization and handedness • General population • 90% predominantly right-handed • 10% strongly left-handed or ambidextrous • Lateralization in right-handed individuals • 90% left hemisphere specialization for language • 10% right hemisphere specialization

  22. Lateralization and handedness • Lateralization in left-handed individuals • most (65-70%) have left hemisphere specialization for language, like right-handed • a larger percentage (30-35%) have right hemisphere specialization or apparently bilateral • Aphasia in left handed individuals • 8x more likely to get aphasia if right hemisphere is damaged than right handed individual

  23. Lateralization and gender • In women, language may be bilateral more often • if left hemisphere damage, milder aphasia or less likely to result in aphasia • dichotic listening tests don't show right ear advantage as often as for men

  24. Lateralization and literacy • Language more symmetrically located in illiterate speakers • Aphasia just as likely with right-hemisphere injury

  25. Lateralization and multilingualism • More right hemisphere language dominance than in monolinguals • If right hemisphere damage, multilingual individuals 5x more likely to develop aphasia than monolinguals • Recovery from aphasia • 50% recover both languages to same extent • 25% do not regain 1 or more languages

  26. An aphasic French-Arabic bilingual • French-Arabic bilingual nun in Morocco became severely aphasic after moped accident • initially lost speech altogether • 4 days after accident, could speak a few words of Arabic, no French • 14 days after accident, could speak French fluently • 15 days after accident, could speak only Arabic fluently

  27. Lateralization and modality • Sign languages use visual-spatial mode of transmission • How is lateralization for language affected by modality? • Results of a study of aphasia and other problems in 6 ASL signers • 3 left brain damage, 3 right brain damage • No effect of language modality on lateralization for language; left hemisphere specialization for language even for signed languages

  28. If left hemisphere was damaged • Sign language aphasia resulted • GD: ‘halting and effortful signing,’ reduced to single sign utterances • KL: ‘selection errors’ in formation of ASL signs, ‘sign comprehension loss’ • PD: fluent signing but impairment in sentence structure

  29. If right hemisphere was damaged • Non-aphasic problems resulted • Right-hemisphere damaged signer • avoided left side of signing space • describing furniture in a room: ‘furniture piled in helter-skelter fashion on the right, and the entire left side of signing space left bare...’ • but used left side of signing space better when such uses were linguistically required

  30. Localization for language • I.e. localization within hemisphere • Hypothesis: specific parts of brain control specific parts of body or bodily functions, including language

  31. Some language centers (left hemisphere) Broca’s Wernicke’s Arcuate fasciculus

  32. Broca’s area • Lesions to Broca’s area result in Broca's aphasia (a.k.a. expressive aphasia, motor aphasia) • Characteristics of Broca’s aphasia • basic message of meaning clear, but • speech is not fluent • phrases are telegraphic (absence of function words) • incorrect production of sounds • Cinderella, as told by a Broca’s aphasic • Cinderella...poor...um ‘dopted her...scrubbed floor, um, tidy...poor, um...’dopted...si-sisters and mother...ball. Ball, prince um...shoe.

  33. Wernicke’s area • Lesions to Wernicke’s area result in Wernicke’s aphasia • Characteristics of Wernicke’s aphasia • speech is fluent, but • often nonsensical or circuitous • Description of a knife by a Wernicke’s aphasic • ‘That’s a resh. Sometimes I get one around here that I can cut a couple regs. There’s no rugs around here and nothing cut right. But that’s a rug and I had some nice rekebz. I wish I had one now. Say how Wishi idaw, uh windy, look how windy. It’s really window isn’t it?’

  34. Arcuate fasciculus • Subcortex nerve fibers connecting Broca’s, Wernicke’s areas • Lesions at this area result in: • Conductive/conduction aphasia • Characteristics • usually good comprehension, fluent speech but • difficulty repeating • difficulty reading out loud • difficulty writing

  35. Angular gyrus • Lesions at angular gyrus • Anomia • difficulty finding words, especially names • Reading difficulties

  36. Other evidence for localization • Electrical stimulation of brain • Normal reaction: numbness, twitching, movement of contralateral body part • Electrical stimulation at ‘language centers’ • Results in • difficulty talking • some kind of vocalization

  37. Further complexities in localization • Factors: spoken vs. written language, parts of speech • Johns Hopkins study of 2 female aphasics • both found it easy to read, speak and write nouns • one could speak verbs but not write them • one could write verbs but not speak them

  38. More than language centers in the brain • Broca's aphasics • damage to Broca’s area results in • language deficits • motor control problems • problems with cognitive and perceptual tasks • Alzheimer’s disease • non-localized neurological problems result in language deficits (among other problems)

  39. Neurolinguistics summary • Hemispheres of brain have different specialties, including language (most clearly for right-handed (etc.) individuals) • Lateralization is not affected by language modality • Language centers within the brain: Broca's, Wernicke's areas especially important • Neurolinguistics provides evidence for human specialization for language

  40. Next time • Announcements

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