Language, innateness and the brain

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) [na:] ‘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

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