Neurolinguistics

1. Neurolinguistics LING 200 Spring 2003 Reading: File 9.1

2. Neurolinguistics • Neurolinguists investigate • How the brain processes language • Where the brain processes language • Who neurolinguists study • Normal subjects • Abnormal subjects • patients with brain injury (e.g. stroke) • patients who have had brain surgery

3. Aphasia • Language disorder associated with trauma to the brain • ‘aphasic’ individuals

4. Why neurolinguistics of interest • Brain exhibits specialization for language • lateralization • localization • Language as an innate, species-specific property

5. Brain hemispheres right hemisphere left hemisphere

6. 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:

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

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

9. Language processing as a left hemisphere task • Evidence from dichotic listening experiments • stimulus presented to different ears • linguistic sounds: right ear (left brain) advantage • environmental sounds: left ear (right brain) advantage

10. Language processing as a left hemisphere task • Evidence from dichotic listening experiments • Thai tonal contrasts • [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

11. Language processing as a left hemisphere task • Evidence from aphasia • Brain injury locations resulting in speech deficits are almost always in left hemisphere

12. Language processing as a left hemisphere task • Evidence from split-brain patients • Severe cases of epilepsy treated by severing corpus callosum • 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

13. corpus callosum (connects hemispheres)

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

15. 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

16. Lateralization and handedness • Lateralization in left-handed individuals • 65-70% have left hemisphere specialization for language • 30-35% have right hemisphere specialization or apparently bilateral • Aphasia in left handed individuals • tends to be less severe, shorter in duration • 8x more likely to get aphasia if right hemisphere is damaged than right handed individual

17. 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

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

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

20. 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

21. 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 with brain damage • 3 left brain damage, 3 right brain damage

22. If left hemisphere was damaged • Sign language aphasia resulted • GD: ‘halting and effortful signing,’ reduced to single sign utterances without syntactic and morphological marking • KL: ‘selection errors’ in phonological structure of ASL signs, ‘sign comprehension loss’ • PD: fluent signing but grammatical/syntactic impairment

23. If right hemisphere was damaged • Non-aphasic problems resulted (e.g. avoidance of left signing space) • 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

24. Modality and lateralization • No effect of language modality on lateralization for language • Left hemisphere specialization for language even for signed languages

25. Localization for language • Hypothesis: specific parts of brain control specific parts of body or bodily functions, including language

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

27. Evidence for localization: aphasia • Broca's area lesions 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.

28. Evidence for localization: aphasia • Wernicke’s area lesions • 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?’

29. Evidence for localization: aphasia • Lesions at arcuate fasciculus (subcortex nerve fibers connecting Broca’s, Wernicke’s areas) • Conductive/conduction aphasia • Characteristics • usually good comprehension, fluent speech but • difficulty repeating • difficulty reading out loud • difficulty writing

30. Evidence for localization: aphasia • Lesions at angular gyrus • Anomia • difficulty finding words, especially names • Reading difficulties

31. Angular gyrus

32. 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 or some kind of vocalization

33. Evidence for localization • Spoken vs. written language may be separately localized • 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

34. 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)

35. 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