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

• Announcements