language, innateness and the brain ling 200 spring 2006 prof. sharon hargus
TRANSCRIPT
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)– = 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.
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)
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
Some innate human behaviors
innate not innate
walking skating, playing football
speaking or signing a language
reading or writing a language
Some characteristics of innate behaviors
innate behavior language as an innate behavior
Emerges before needed. Speed of learning L1 (age 5)
Not the result of a conscious decision.
All needed for L1: immersion in lgc environ.
Not triggered by (extraordinary) external events.
‘Poverty of stimulus’: Children exposed to motherese, adult performance
• 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
Results of chimp studies
Neurolinguistics
Brain hemispheres
right hemisphere
left hemisphere
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:
Right hemisphere specialties
• Holistic, spatial processing– pattern-matching (e.g. recognizing faces) – spatial relations – emotional reactions – music (processing by musically naive
individuals)
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
• Aphasia
• Dichotic listening experiments
• Split-brain patients
Language processing as a left hemisphere task
Aphasia
• Brain injury locations resulting in speech deficits are almost always in left hemisphere
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.
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
Split-brain patients • Severe cases of epilepsy treated by severing
corpus callosum
corpus callosum (connects hemispheres)
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
Effects on lateralization
• Lesser left hemisphere specialization for language if:– left-handed– female– illiterate– multilingual
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
• 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
Lateralization and handedness
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
Lateralization and literacy
• Language more symmetrically located in illiterate speakers
• Aphasia just as likely with right-hemisphere injury
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
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
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
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
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
Localization for language
• I.e. localization within hemisphere
• Hypothesis: specific parts of brain control specific parts of body or bodily functions, including language
Some language centers (left hemisphere)
Broca’s
Wernicke’s
Arcuate fasciculus
• 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.
Broca’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?’
Wernicke’s area
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
• Lesions at angular gyrus – Anomia
• difficulty finding words, especially names
– Reading difficulties
Angular gyrus
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
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
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)
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
Next time
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