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1Psych 56L/ Ling 51:Acquisition of LanguageLecture 4Biological Bases of Language IILanguage LocalizationWhy the left hemisphere?Left hemisphere may process information more analytically.Trained musicians process music in the left hemisphere.Normal (untrained) people process it on the right.Left hemisphere may be better at executing well-practicedroutines, while right is better at responding to novelstimuli.Language, for adults, is a well-practiced routine.Where is language located?Not-just-left hemisphere evidenceSometimes, aphasia doesn’t result when there is lefthemisphere damage.Sometimes, aphasia results when there is right hemispheredamage.In some people (usuallyleft-handed people),language is controlledby the right hemisphere.2Where is language located?Not-just-left hemisphere evidenceRight hemisphere contributions to language: tone contour,emotional tone, jokes, sarcasm, figurative languageinterpretation, following indirect requests(much of this falls under pragmatics)Evidence: right hemisphere lesion patientsRight hemisphere activated by semantic processing, whileleft hemisphere activated primarily by syntacticprocessingEvidence: ERP studiesEvidence: late language learners who aren’t as proficientwith syntax, and have language located primarily in righthemisphereHow does a left hemispherespecialization for language develop?Equipotentiality hypothesis: left and right hemispheres have equalpotential at birth Prediction: dichotic listening and brain injury in children showless specialization for language than adultsInvariance hypothesis: left hemisphere specialization available atbirthPrediction: dichotic listening and brain injury data from childrenshould look like the corresponding data from adultsHow does a left hemispherespecialization for language develop?fMRI studies: newborns and 3-month-old infants show greater left-hemisphere than right-hemisphere activation in response tospeech stimuli (as do adults)- But also greater left-hemisphere activity in response to non-speech sounds, suggesting general bias to process sounds inleft hemisphere (older children [10-month-olds] and adultsprocess non-speech sounds with right hemisphere)How does a left hemispherespecialization for language develop?Dichotic listening tasks: Right-ear advantage for verbal stimuli in2-year-oldsSpeech vs. non-speech?Best (1988): right-ear advantage forconsonants but not for vowels.Consonants have rapidly changingacoustic properties compared withvowels. Could tie in to left-hemispherespecialization for serial processing.3How does a left hemispherespecialization for language develop?Summary from experimental studies: Language processing appears to be specialized to the lefthemisphere as early as researchers can test it. But the infant brain is not the same as the adult brain -specialization/lateralization continues to increase as the brainmatures.How does a left hemispherespecialization for language develop?Childhood aphasia: Aphasia nearly always results from lefthemisphere damage and rarely from right hemisphere damage(Woods & Teuber 1978)However, immature brain is not organized the same way asthe mature brain.- children more likely to suffer Broca’s aphasia (non-fluentaphasia) than Wernicke’s- children tend to recover better from brain damage, withyounger children recovering better than older childrenNeural plasticity in childrenPlasticity: the ability of parts of the brain to take over functionsthey ordinarily would not serve - ex: right hemisphere takingover language functions if left hemisphere is damaged.However, plasticity isn’t the perfect solution - ex: subtlesyntactic impairments in these cases suggest that the righthemisphere isn’t as good at parts of language as the lefthemisphere is.Neural plasticity in childrenHow plasticity works:The child’s brain has much redundancy (extra synapticconnections.)Maturation = pruning unnecessary connectionsWhat’s necessary: what gets used (where child’s brain activityis).Once connections are pruned, redundancy is lost and particularfunctions become localized.4Neural plasticity in childrenBut wait - young children use their right hemisphere (somewhat)for language. Since there’s language activity, why does theright hemisphere lose its language functionality?Maturation hypothesis: adult language brain structures develop inthe left hemisphere and take over (specialization is geneticallydetermined)Process change hypothesis: children change the way theyprocess language, and the new way is more in line with the lefthemisphere natural capacities. (specialization is by-product ofprocess change)The Critical Period HypothesisCritical & sensitive periods“critical period for language” = biologically determined periodduring which language acquisition must occur in order forlanguage to be learned fully and correctlyOther biologically determined deadlines:- imprinting: chicks & ducklings follow first thing they seeforever (it’s likely their mommy)- visual cells in humans: if cells for both eyes don’t receivevisual input during the first year or so of life, they lose the abilityto respond to visual input“sensitive period”: biologically determined period during whichlearning must occur for development to most likely happencorrectlyCritical & sensitive periodsHow do we test for a critical period for language acquisition?5Critical & sensitive periodsHow do we test for a critical period for language acquisition?Ideal experiment: deprive children of all linguisticinput during the purported critical period and seehow language development occurs.Problem: ideal experiment isn’t so ideal ethically or logistically(just ask the Egyptians)Critical & sensitive periodsHow do we test for a critical period for language acquisition?Some historical cases that have unintentionallyprovided lack of linguistic input to children:“wild children”: like Victor of AveyronProblem: the lack of language maybe due to other reasonsCritical & sensitive periodsHow do we test for a critical period for language acquisition?Some historical cases that have unintentionallyprovided lack of linguistic input to children:Lenneberg (1967): “the only safe conclusions to be drawnfrom the multitude of reports is life in dark closets, wolves’dens, forests, or sadistic parents’ backyards is not conduciveto good health or normal development”Critical & sensitive periodsHow do we test for a critical period for language acquisition?One success story for lack of linguistic


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UCI PSYCH 56L - Biological Bases of Language II

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