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

10. 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 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 Lateralization and handedness

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. 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. Evidence for localization: aphasia

28. 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?’ Evidence for localization: aphasia

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

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