Neurolinguistics
LING 200
Spring 2003Reading: File 9.1
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
Aphasia
• Language disorder associated with trauma to the brain
• ‘aphasic’ individuals
Why neurolinguistics of interest
• Brain exhibits specialization for language
• lateralization– localization
• Language as an innate, species-specific property
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 (processed by musically sophisticated
individuals)– mathematics – intellectual reasoning – language, speech sounds
• especially so for adult, male, right-handed, literate, monolingual subjects
• 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
Language processing as a left hemisphere task
• 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
Language processing as a left hemisphere task
• Evidence from aphasia – Brain injury locations resulting in speech
deficits are almost always in left hemisphere
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
corpus callosum (connects hemispheres)
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 – 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
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
• Recovery from aphasia – 50% recover both languages to same extent– 25% do not regain 1 or more languages
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 with brain damage– 3 left brain damage, 3 right brain damage
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
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
Modality and lateralization
• No effect of language modality on lateralization for language
• Left hemisphere specialization for language even for signed languages
Localization for language
• 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 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
• 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
Evidence for localization: aphasia
• 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
• Lesions at angular gyrus – Anomia
• difficulty finding words, especially names
– Reading difficulties
Evidence for localization: aphasia
Angular gyrus
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
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
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