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
Results of chimp studies
• 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
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
Language processing as a left
hemisphere task
• Aphasia
• Dichotic listening experiments
• Split-brain patients
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’
[nā:] ‘field’
(high)
(mid)
[nâ:] ‘face’ (falling)
[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 and handedness
• 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 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
Broca’s area
• 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.
Wernicke’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?’
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
Angular gyrus
• Lesions at
angular gyrus
– Anomia
• difficulty
finding words,
especially
names
– Reading
difficulties
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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