Psych 56L/ Ling 51: Acquisition of LanguageLanguage LocalizationWhy the left hemisphere?Where is language located? Not-just-left hemisphere evidenceSlide 5How does a left hemisphere specialization for language develop?Slide 7Slide 8Slide 9Slide 10Neural plasticity in childrenSlide 12Slide 13The Critical Period HypothesisCritical & sensitive periodsSlide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29PowerPoint PresentationCritical vs. sensitive, revisitedSlide 32So why are younger children better?Slide 34Genetic Basis of Language DevelopmentHeritability of individual differencesSlide 37Genetics of language impairmentSlide 39In summary…Questions?Psych 56L/ Ling 51:Acquisition of LanguageLecture 4Biological Bases of Language IILanguage LocalizationQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.QuickTime™ and a decompressorare needed to see this picture.Why 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-practiced routines, while right is better at responding to novel stimuli.Language, for adults, is a well-practiced routine.QuickTime™ and a decompressorare needed to see this picture.Where is language located? Not-just-left hemisphere evidenceSometimes, aphasia doesn’t result when there is left hemisphere damage. Sometimes, aphasia results when there is right hemisphere damage.In some people (usually left-handed people), language is controlled by the right hemisphere.QuickTime™ and a decompressorare needed to see this picture.Where is language located? Not-just-left hemisphere evidenceRight hemisphere contributions to language: tone contour, emotional tone, jokes, sarcasm, figurative language interpretation, following indirect requests(much of this falls under pragmatics)Evidence: right hemisphere lesion patientsRight hemisphere activated by semantic processing, while left hemisphere activated primarily by syntactic processingEvidence: ERP studiesEvidence: late language learners who aren’t as proficient with syntax, and have language located primarily in right hemisphereHow does a left hemisphere specialization for language develop?Equipotentiality hypothesis: left and right hemispheres have equal potential at birth Prediction: dichotic listening and brain injury in children show less specialization for language than adultsInvariance hypothesis: left hemisphere specialization available at birthPrediction: dichotic listening and brain injury data from children should look like the corresponding data from adultsHow does a left hemisphere specialization for language develop?fMRI studies: newborns and 3-month-old infants show greater left-hemisphere than right-hemisphere activation in response to speech stimuli (as do adults)- But also greater left-hemisphere activity in response to non-speech sounds, suggesting general bias to process sounds in left hemisphere (older children [10-month-olds] and adults process non-speech sounds with right hemisphere)QuickTime™ and a decompressorare needed to see this picture.How does a left hemisphere specialization for language develop?Dichotic listening tasks: Right-ear advantage for verbal stimuli in 2-year-oldsQuickTime™ and a decompressorare needed to see this picture.Speech vs. non-speech?Best (1988): right-ear advantage for consonants but not for vowels. Consonants have rapidly changing acoustic properties compared with vowels. Could tie in to left-hemisphere specialization for serial processing.How does a left hemisphere specialization for language develop?Summary from experimental studies: Language processing appears to be specialized to the left hemisphere 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 brain matures.How does a left hemisphere specialization for language develop?Childhood aphasia: Aphasia nearly always results from left hemisphere damage and rarely from right hemisphere damage (Woods & Teuber 1978)However, immature brain is not organized the same way as the mature brain.- children more likely to suffer Broca’s aphasia (non-fluent aphasia) than Wernicke’s- children tend to recover better from brain damage, with younger children recovering better than older childrenNeural plasticity in childrenPlasticity: the ability of parts of the brain to take over functions they ordinarily would not serve - ex: right hemisphere taking over language functions if left hemisphere is damaged.However, plasticity isn’t the perfect solution - ex: subtle syntactic impairments in these cases suggest that the right hemisphere isn’t as good at parts of language as the left hemisphere is.QuickTime™ and a decompressorare needed to see this picture.Neural plasticity in childrenHow plasticity works:The child’s brain has much redundancy (extra synaptic connections.)Maturation = pruning unnecessary connectionsWhat’s necessary: what gets used (where child’s brain activity is).Once connections are pruned, redundancy is lost and particular functions become localized.QuickTime™ and a decompressorare needed to see this picture.Neural plasticity in childrenBut wait - young children use their right hemisphere (somewhat) for language. Since there’s language activity, why does the right hemisphere lose its language functionality?Maturation hypothesis: adult language brain structures develop in the left hemisphere and take over (specialization is genetically determined)Process change hypothesis: children change the way they process language, and the new way is more in line with the left hemisphere natural capacities. (specialization is by-product of process change)The Critical Period HypothesisQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.QuickTime™ and a decompressorare needed to see this picture.Critical & sensitive periods“critical period for language” = biologically determined period during which language acquisition must occur in order for language to be learned fully and correctlyOther biologically determined deadlines:- imprinting: chicks & ducklings follow first thing they see forever (it’s likely their mommy)- visual cells in humans: if cells for both eyes don’t receive visual input during the