23-11-2011 1Herhaling titel van presentatie

Neurolinguistics of Bilingualism: Neuroimaging Multilinguals

Esli Struys

Linguistics & Neurosciences, Class 6

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Non-clinical neurolinguistics

-Large body of neuroimaging studies

-Neural networks underlying different domains language processing

-Has led to new discoveries

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Clinical approach to multilingualism

-claim of different L2 localization–Scoresby-Jackson (1861)

–Dominant for over a century

–Now challenged by neuroimaging studies

– Distinction between language representation andlanguage control

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Acquisition and processing of L2 grammar

-L1 grammar generally acquiredimplicitly, L2 grammar acquiredexplicitly (Paradis, 2004)

-Declarative/procedural model–Monolinguals: words >< grammatical rules

–Bilinguals: words >< grammatical rules

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Different localization

-Procedural system–Fronto-striatal network (Broca’s area and the basal ganglia)

-Declarative system–Left temporal areas

–Cf. regular vs. Irregular verbs

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Implications for L2 processing

Will Broca’s area, along with the basal ganglia, be responsible only for L1 processing or will it also underlie processing of L2 grammar?

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Regular verbs in English

-regular verbs–Most affected by Parkinson’s disease

-irregular verbs–Most affected by Huntington’s disease

(Both are striatal dysfunctions)

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But …

-damage to basal ganglia has impact on cortical regions

-no association found by (Longworth et al., 2005) for English & by (Penke et al., 2005) for German

-neocortical classical language regions more important

-inhibition of competing alternatives

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Basal ganglia

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Basal ganglia

-higher-order motor control

-control of voluntary movement

-highly involved in learning and memory–Feedback processing

-language control

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Neuroimaging to the rescue

To what extent is there functional neuroimaging evidence of the involvement of these brain structures in the acquisition of a second language?

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Two models

-L2 grammar acquisition in adulthood does not rely on same brain structures as L1 (fronto-striatal network) (Ullman, 2001)

-neural differences between L1 & L2 speakers may disappear as proficiency increases (Green, 2003)

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Artificial grammar learning

-increasing proficiency leads toincreased recruitment of Broca’s area

-L2 acquisition through existing L1 syntax network (Opitz & Friederici, 2004)

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Wartenburger et al., 2003

-research design that enablescomparison between high and low proficient late bilinguals

-AoA more important than Proficiency for localization L2 grammar processing

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Lexico-semantic processing

-L2-related differences found in low proficient and/or less exposed bilinguals (Perani et al., 2003; Pallier et al., 2003)

-greater engagement of LIFG & selective engagement PFC– Single word production paradigms– Lexical decision & semantic judgment– Story comprehension

– Involvement of temporal lobes in L2 vs activity in PFC

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Why neural differences?

-Fact I: Broca’s area and temporal lobes less involved in L2 processing (for low-proficient and/or late learners)

-Fact II: PFC involvement higher in L2 processing (for …)

-Distinction between linguistic representation & language control

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Prefrontal effect

-competition between lemmas in L1 & L2

– Inhibiting any active, non-target language

-interference from a prepotent concept name

-less effort lexical retrieval– From controlled to automatic processing

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Explaining recovery patterns

Why should an L2 that is mastered with a low degree of proficiency be represented more extensively at the brain level?

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Explaining recovery patterns

-Again, paramount is the distinction between

language specific neural representations & processing-specific demands

-Analogy with monolingual case–Cognitive effort reduced in a well-mastered task

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Crucial role of prefrontal cortex

-strategic position & interconnectivity with a multitude

neocortical and subcortical areas (Abutalebi & Green, 2007)

-top/down control inhibitory mechanism vs.

more local and bottom-up inhibitory mechanism

-dedicated network of brain areas for language control

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Mechanism of language control

-inhibition of a current task (speaking in language A) in favour of a new task (speaking in language B)– Application: language switching, translation, …

-withholding a potential prepotent response– Application: language selection, …

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Language control network

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Language control networks

-No single level of control–For example competition between lemmas, …

-Multiple neural levels of control involved–Also devoted to motor or cognitive control, …

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Link between language and cognition

-what is the effect of using these cognitive control networks on non-verbal control tasks?– Less interference in a Simon task– Highly controversial topic– Does bilingualism improve selective attention?– Or similar to switching between registers?

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