multilingual brain

Multilingual Brain

By :Prakhar Asthana

Entry No.-2011CS1027Indian Institute of Technology Ropar, India

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What is Multilingualism

There is no one definition.• People who speak or have been spoken in two

or more languages since birth.Or

• People who have been speaking one language since birth and later learned other languages.

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Types of Bilinguals

• Compound Bilinguals: Has one semantic system but two linguistic codes. Usually refers to someone whose two languages are learnt at same time, often in same context.

• Coordinate Bilinguals: Has two semantic systems and two linguistic codes. Usually refers to someone whose two languages are learnt in two languages are learnt in distinctively separate contexts

• Subordinate bilingual: The weaker language is represented to the stronger language.

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Mental lexicon of bilinguals

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Hemispherical Lateralization of Language

• Involvement of one hemisphere of brain to a particular activity makes it dominant

• Language is believed to be heavily lateralized function, with left hemisphere dominating the right one in handling language related tasks

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• Left hemisphere controls lexical and syntactic language, writing and speech, phonetics and semantics.

• It does not mean that right hemisphere serves no purpose.

• Patients which get their right hemisphere surgically removed show no aphasia, but do show deficiencies in verbal selection and metaphor understanding.

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How multilinguals switch between languages

• Researchers have used brain imaging techniques like functional magnetic resonance imaging (fMRI) to investigate which brain regions are active when bilingual people perform tasks in which they are forced to alternate between their two languages.

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• When bilinguals have to switch between naming pictures in Spanish and naming them in English, they show increased activation in the :– dorsolateral prefrontal cortex (DLPFC )– anterior cingulate cortex (ACC)– bilateral supermarginal gyri– left inferior frontal gyrus (left-IFG)

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• Patients with damage or lesion in these parts of brain undergo involuntary change in language while speaking

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How multilingual’s brain is different?

• Are areas associated with L1 and L2 same or different?

• Is Multilingual’s brain structurally different?• What about brain activation?

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• A major hypothesis: Different languages, different brain regions.

• Studies conducted on bilingual aphasiac patients show that in most of the cases only one of the mastered language is affected.

• This gives an indirect proof to the above mentioned hypothesis.

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• Eye tracking studies show that at early stages of language acquisition both the languages are parallely activated and have shared cortical structures.

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• fMRI scans show that for the late acquitted languages, language sensitive regions in the frontal lobe of brain (Broca’s Area) are spatially separated from that of language sensitive regions of native language

• But when second language is acquired early, native and second language sensitive areas tend to overlap.

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• But in both late and early bilingual subjects, the temporal-lobe language-sensitive regions (Wernicke's area) also show effectively little or no separation of activity based on the age of language acquisition.

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• fMRI scans show that there are also language specific zones in brain with L2-specific sites located exclusively in the posterior temporal and parietal lobes.

• Bilinguals possessed seven perisylvian language zones, which are L2 restricted.

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Structural Changes in Bilingual’s Brain

• Learning a second language increases the density of grey matter in the left anterior parietal cortex

• Age of second language acquisition and proficiency in that language affects its extent.

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Structural Changes in Bilingual’s Brain

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More brain activation in bilingual brain

• Cerebral Blood Flow(CBF) measuring techniques show that in word repeating tasks, there is more blood flow in left putamen of brain for second language

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• Word generation has also led to larger foci of brain activation for the second language within multilinguals.

• Activation is principally found in the left prefrontal cortex (inferior frontal, middle frontal, and precentral gyri).

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Effect of Age of Acquisition

• The subcortical organization of languages in bilingual brain can change according to the age of acquisition of second language.

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• Studies done on trilinguals show that more neural substrates of Broca’s Area are engaged in performing same language tasks for later acquired languages.

• Language Activation follows order L3>L2>L1.• Later acquired languages require more

activation.

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Effect of Proficiency in Language

• Researches show that very early bilinguals display no difference in brain activation for L1 and L2 — which is assumed to be due to high proficiency in both languages.

• Larger cerebral activation is measured when a language is spoken less fluently than when languages are spoken more fluently .

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Effect of Proficiency in Language

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Proficiency V Age of acquisition

• Generally these go parallelly.• But what happens in contradictory case e.g.

late proficient bilinguals.

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Proficiency V Age of acquisition

• Researches show that proficiency outweighs age of acquisition.

• Cerebral representation is going to be same for two languages if one is equally proficient in both of them. It doesn’t matter when they were acquired.

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Bimodal Individuals

• Bimodal individuals are those who are fluent in both sign language and oral language.

• PET scans show that there is separate region in the brain related to sign language production and use.

• Bimodal individuals use different areas of the right hemisphere depending on whether if they are speaking using verbal language or sign-language .

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• fMRI scans show that bimodal bilinguals show greater signal intensity in Wernicke’s area while using both languages in rapid alternation as compared to the oral and sign language monolinguals.

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Advantages of being Multilingual

• Bilinguals are more adept than monolinguals at solving certain kinds of mental puzzles.

• Bilingual people are better than monolingual people at switching between two tasks.

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• For e.g. when bilinguals have to switch from categorizing objects by color (red or green) to categorizing them by shape (circle or triangle), they do so more rapidly than monolingual people.

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Bilingualism also help adults

• Bilingualism’s effects also extend into the twilight years.

• Bilingual adults show delay in onset on alzeihmer’s disease by 4 years.

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If brain is an engine, bilingualism improves its mileage

• Actually brains of the bilingual people appeared to be in worse physical condition.

• This suggest that despite of more brain damage, bilinguals were able to resist more.

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Bilingualism- always a boon?

• Researches gives evidence that bilingual children have less vocabulary in one language as compared to monolinguals.

• They take longer time and make more errors in naming tasks.

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Questions Still Unanswered

• Which proficiency level to be declared as bilingual/multilingual?

• What is the best age at which one should start learning second language?

• Whether the two languages should be similar or different to get more advantage?

• Whether there is a limit to no. of languages upto which a person will always be in gain?

• Whether there are any “better” languages that should be learnt?

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Reference:• Fabbro, Franco. The neurolinguistics of bilingualism: An introduction. Psychology

Pr, 1999. • Paradis, Michel. A neurolinguistic theory of bilingualism. Vol. 18. John Benjamins

Publishing Company, 2004. • PERANI, D. (2001). The bilingual brain as revealed by functional

neuroimaging.Bilingualism: Language and cognition, 4(2), 179-190 .• Tierney, Michael C., et al. "PET evaluation of bilingual language compensation

following early childhood brain damage." Neuropsychologia 39.2 (2001): 114-121.

• Kim, K. H., Relkin, N. R., Lee, K. -M., & Hirsch, J. (1997). Distinct cortical areas associated with native and second languages. Nature,388, 171–174.

• Bialystok, E., Craik, F. I., & Luk, G. (2012). Bilingualism: Consequences for mind and brain. Trends in Cognitive Sciences, 16(4), 240–250

• Rönnberg, Jerker, Mary Rudner, and Martin Ingvar. "Neural correlates of working memory for sign language." Cognitive Brain Research 20.2 (2004): 165-182.

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