BU CAS LX 400 - Week 11a. Neurolinguistics and bilingualism: Aphasia CAS LX 400

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1Week 11a. Neurolinguistics andbilingualism: AphasiaCAS LX 400Second Language AcquisitionLanguage and the brain• How is language represented in the brain?• What are the differences between thelanguage representations found inmonolingual speakers and in bilingualspeakers (of varying degrees of L2proficiency)?Localization• Brain = mass of interconnected neurons.• Divided into two halves, left and right hemisphere.– The hemispheres are quite separate but for the corpuscallosum which connects the two.– The connection to the outside world is generallycontralateral—right hemisphere has control of left side motorcontrol, receives left visual and aural input, etc.• Certain areas of the brain have specific functions(visual cortex; auditory cortex; motor cortex) despitehigh levels of interconnectivity.• Does language specifically have its own area?Localization• Early evidence for localization came from aphasicpatients—patients with specific linguistic deficits dueto brain lesions, which could be correlated withlocation in an autopsy.• Broca, French surgeon, 1861.– Saw patient who lost had his ability to speak (could onlyutter the monosyllable tan except if agitated—reputedlyoften—when he could swear).– Intelligence, comprehension spared– Gradual paralysis of right side of the body.– In autopsy, a lesion was discovered in what became knownas “Broca’s area”—left hemisphere, frontal lobe.Broca’s area• After several more patients were studiedpostmortem, the pattern emerged—lesionsin the left hemisphere in this region seemedto correlate with this language deficit.• >95% of right-handed people have primarylanguage functions lateralized to the lefthemisphere (and over 90% of people areright-handed).Broca’s area2Spinning brain• This came from here:http://brainmuseum.org/Specimens/primates/human/qtvrbrains.htmAphasias• Broca’s aphasia.Spontaneous speecheffortful, closed-classwords omitted, verbalcomprehension ofsimple sentences isgood, repetition abilitylimited. Frequentlyaccompanied by right-side paralysis.Awareness of deficit.Aphasias• Wernicke’s aphasia.Fluent speech but withmany non-words.Verbal comprehension,naming, repetitionimpaired. Oftenaccompanied byblindness in right visualfield. Lack ofawareness of deficit.Function areas• We can make someguesses as to what thefunctions of the areas ofthe brain are, based onwhat happens inaphasic patients.ConceptsVerbal motor memoryAcoustic word memoryFunction areas• Anywhere betweenBroca’s area andRolandic fissure resultsin non-fluent speech.ConceptsVerbal motor memoryAcoustic word memory3Function areas• Anywhere betweenBroca’s area andRolandic fissure resultsin non-fluent speech.• Anywhere betweenWernicke’s area andRolandic fissure resultsin poor comprehension.ConceptsVerbal motor memoryAcoustic word memoryFunction areas• Anywhere betweenBroca’s area andRolandic fissure resultsin non-fluent speech.• Anywhere betweenWernicke’s area andRolandic fissure resultsin poor comprehension.• Anywhere betweenBroca’s are andWernicke’s area resultsin poor repetition.ConceptsVerbal motor memoryAcoustic word memoryAphasiastranscorticalmotornonfluentcompr okrep oktranscorticalsensorynonfluentcompr poorrep pooranomicfluentcompr okrep okconductionfluentcompr okrep poorWernicke’sfluentcompr poorrep poorBroca’snonfluentcompr okrep poorLateralization• The two hemispheres of the brain also seem tohave somewhat different functions.• Left hemisphere generally controls the majority oflanguage function.• Right hemisphere appears to be involved inmaintaining focus of attention, and also possiblyprosody.– Right hemisphere lesions have been known to severelyaffect ability to analyze metaphors, summarize complextexts, as well as disrupt prosody in otherwise normallanguageDichotic listening• Consider three kinds of audio stimuli (verbal,environmental noise, music).• Present two different kinds of stimuli to each earof a subject simultaneously, have them write downwhat they heard.• Turns the right ear (processed by the lefthemisphere) is superior for the purposes ofidentifying verbal stimuli, left ear (processed bythe right hemisphere) superior for the others.Verbal-manual interference• A similar task: Get subject to tap a key asrapidly as possible with left hand, then withright hand. Record control condition result.• Then, have them perform a verbal task (recitedays, count, etc.), and test the tapping.• Right-hand (left hemisphere) interference willbe greater—right-hand tapping will slow downmore than left-hand tapping will.4Memory• A primary concern of neuroscience hasbeen the mechanisms of memory, whichcomes in various forms with variousproperties.• Many studies carried out to determine whathappens to the brain of an animal havinglearned a task.Neural connections• Individual neurons are connected to one another viaexcitatory and inhibitory connections, and has a certainlevel of activation. When a neuron’s level of activationreaches a critical threshold, the neuron fires, spreadingpositive activation to other neurons that it isexcitatorily connected to and negative activation toneurons that it is inhibitorily connected to.• Neurons that fire together wire together. Connectionsare developed or strengthened between neurons whosefirings temporally coincide. Function has changed.Memory. It becomes likely now that if one fires theother will too. Long-term memory?A neuron synapseImpulsePresynaptic neuronVesicleTransmittersSynaptic cleftReceptorsPostsynapticneuronPostsynaptic activityWorking vs. long term memory• Working memory is short term, used for immediatememorization/repetition tasks, remembering what wasjust said.• Working memory and long term memory appear to bedoubly dissociable:– H.M. (Milner et al.): Long term memory storage mechanismimpaired as result of brain surgery to relieve severe epilepsy.Working memory, intelligence, linguistic competenceunimpaired; old memories retained; no new memories could bestored (didn’t recognize therapist, couldn’t remember newaddress).– K.F. (Warrington & Shallice 1969): Very limited short termmemory, but normal (long term) learning capacity.Long term memory types• Long term memory comes in different kinds aswell.• Explicit memory: Conscious, learned, able to berecalled and expressed. Both semantic(knowledge of world) and episodic. (Krashen’s“learning”)• Implicit memory: unconscious, skill


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