Neurolinguistics

1. Neurolinguistics LING 400 Winter 2010

2. Overview • Vocal tract specialization for language • Brain specialization for language • Innateness Hypothesis for further learning: LING/PSYCH 347 (Psychology of Language I), or SPHSC 425 or 445 please turn off your cell phone

3. Human language seems unique among animal communication systems • Chimps can learn some aspects of human language • Show some spontaneity, creativity • Skills comparable to 1-2 year old child • …but • Don’t get better than 1-2 year old child • Limited syntax

4. Human vocal tract shows specialization for speech • Adult human vocal tract • Chimp vocal tract

5. Human brain also shows specialization for language • Some brain areas seem to be “dedicated” to language processing

6. The Localization Hypothesis • Different brain areas are responsible for different functions • Most people have same basic “wiring scheme” • Damage to a brain area impairs functions handled by that area • Direct electrical stimulation of different brain areas  distinct responses (twitches, numbness, hallucinations, transient impairments) • Stimulation of “language areas” can cause vocalizations or difficulty speaking

7. TOP VIEW Basic Brain Anatomy • Left and right hemispheres divided by longitudinal fissure • Corpus callosum (not shown) • bundle of nerve fibers that allows information to pass between hemispheres

8. SIDE VIEW Basic Division of Cortical Functions • Outer cortex divided into lobes separated by fissures (sulci [|sʌlsaɪ], singular sulcus [|sʌlkəs]) • Temporal lobe: primary auditory processing, long-term memory • Occipital lobe: primary visual processing • Parietal lobe: high-level visual processing, sensory integration & synthesis (spatial awareness) • Frontal lobe: primary motor control, planning, decision-making

9. Primary LanguageProcessing Areas • Broca’s Area • primarily involved in language production • adjacent to motor cortex • Wernicke’s Area • primarily involved with language comprehension • adjacent to primary auditory cortex (pink and bigger) • Arcuate fasiculus (not shown) • nerve fibers that connect Wernicke’s & Broca’s areas • Angular Gyrus • plays a role in understanding metaphor

10. Language Deficits: Broca’s Aphasia • non-fluent, telegraphic speech • basic meaning usually clear, good comprehension • some pronunciation errors • A Broca’s aphasic tells the story of Cinderella • Cinderella... poor... um ’dopted her... scrubbed floor, um, tidy... poor, um...’dopted... si-sisters and mother... ball. Ball, prince um... shoe. • http://www.youtube.com/watch?v=f2IiMEbMnPM

11. Language Deficits: Wernicke’s Aphasia • fluent production, but nonsensical • poor comprehension • A Wernicke’s aphasic describes a knife • 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? • http://www.youtube.com/watch?v=aVhYN7NTIKU

12. Lateralization • = Difference in Function Between Hemispheres • Right Hemisphere: “holistic” processing • pattern-matching (e.g., recognizing faces), spatial relations, emotional reactions, music (in musically naïve individuals) • Left hemisphere: “analytical” processing • mathematics, logical reasoning, temporal relations, rhythm, music (in musically sophisticated individuals) • Language processed by left hemisphere for most people

13. Contra-Lateral Control • In general, rightside of brain processes information and controls movement for left side of body, and vice versa • Some exceptions, including • speech sounds processed by left auditory cortex (Wernicke’s area) (including sound from left ear); non-speech sounds usually processed by right auditory cortex

14. Evidence for Left-Lateralization of Language Processing • Aphasia • Most aphasias result from left hemisphere damage • ‘Split brain’ patients • Corpus callosum severed (e.g. to control severe seizure disorders like epilepsy) • Marked performance difference on language tasks involving left vs. right sides • E.g. naming object • left eye open (right brain), right eye covered much harder than (or impossible) • right eye open (left brain), left eye covered

15. Evidence for Left-Lateralization of Language Processing • Dichotic listening tasks • If speech sounds heard by only one ear, processed faster and more accurately when heard by right ear (left brain) • Non-speech sounds processed faster and more accurately through left ear • Tone (pitch) • Speakers of tonal languages (e.g., Thai) process linguistic tone in left hemisphere • Speakers of non-tonal languages (e.g. English) process tone in right hemisphere

16. What About Signed Languages? • Signers, like speakers, tend towards left-lateralization • Aphasias are similar • Wernicke’s: difficulty recognizing single signs, following commands, and understanding sentences; sign selection errors • Broca’s: sign production impairment (“halting and effortful”), but comprehension OK

17. Right Hemisphere Damage in Native Signers • Non-aphasic problems such as left hemispatial neglect • When describing furniture in a room: “furniture piled in helter-skelter fashion on the right, and the entire left side of the signing space left bare...” • Describing the Cookie Theft Picture: girl ignored

18. Summary • Human brain shows some specialization for language • Caveats re localization and lateralization

19. Against Localization • For complex cognitive tasks, processing more diffuse than specific areas • Functions lost due to permanent injury can be recovered (to a certain extent) by “recruiting” new areas to perform function of damaged area • Non-localized neurological decay (e.g. Alzheimer’s disease) can also cause language deficits (among other problems) • Functions of areas not entirely specialized • Localized damage to “language areas” sometimes causes motor control problems and cognitive/perceptual deficits

20. Against Left-Lateralization of Language • Right-hemisphere damage can cause language deficits, even in people who appear to be “left-lateralized,” affecting • prosody (emotion, tone of voice) • discourse (jokes and puns; reference to things said in previous sentences) • pragmatics

21. Lateralization Statistics: Handedness • Likelihood of left-lateralization increases if: • adult / male / right-handed / literate / monolingual • ≈ 90% of humans right-hand dominant • ≈ 90% of these left-lateralized for language • the rest almost all right-lateralized • ≈ 10% of humans left-hand dominant or ambidextrous • ≈ 65% of these left-lateralized for language • the rest either right-lateralized or bilateral

22. Lateralization Statistics: Gender and literacy • Left-lateralization seems to be less strong in women • Left hemisphere damage in women less likely to result in aphasia • Aphasia from left hemisphere damage tends to be milder • Dichotic listening tests don’t show right ear advantage as often • Illiterate speakers • Language processing tends to be more bilateral • Aphasias can result from damage to either hemisphere

23. The Innateness Hypothesis • Humans “genetically programmed” for language ...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... — Noam Chomsky

24. Universal Grammar (UG) • There are universal properties of human languages. • UG determines possible forms of human language • Why would UG exist? • Maybe UG is innate knowledge hard wired into brain • Or maybe UG a consequence of structural properties that are common to all (normal) human brains