Lateralization and the critical period

Lateralizationandthecriticalperiod邵红梅Lateralization(大脑偏侧化)Thehumanbrainisacomplicatedcontaineroftenbillionneuronswhichareresponsibleforperception,memorization,information-processing,thinking,communicationandsoon.Themostimportantpartisthecerebralcortex(大脑皮层),handlingmuchofthecognitionandreasoningandspeaking.Lateralization(大脑偏侧化)Theentirebraincanberoughlydividedintotwoparts:theleftandtherighthemisphere.Itisbelievedthatallmentalfacultiesarelocalizedinthetwohemispheres.Thislocalizationofdifferentfacultiesiscalledlateralization（大脑偏侧化）.Lateralization(大脑偏侧化)Tounderstandwhatislateralization,wecanredirectourattentiontocerebraldominance(大脑半球优势),thatisthenormaltendencyforonehalfofthebraintoexercisemorecontrolovercertainfaculties.Lateralization(大脑偏侧化)Thelefthemispherecontrolslanguage,analyticreasoning,temporalordering,readingandwriting,calculation,associativethinking,etc.Therighthemispheretacklesvisualandspatialskills,holisticreasoning,recognitionofpatterns,perceptionofnonverbalsignalslikemusicalmelodiesandsoon.Thelocalizationoffacultiesiscalledlateralization.Lateralization(大脑偏侧化)Inthelefthemisphere,therearethreelinguisticareas:Broca'sarea（布洛卡区）——responsibleforspeechproductionandsyntax,Wernicke'sarea（韦尼克区）——controllingspeechcomprehensionandsemantics,angulargyrus（角形脑回）——capableofturningvisualstimuliintoauditoryformsandviceversa.Lateralization(大脑偏侧化)Whensomeoneistalkingtous,wehearandunderstandthesignalsbytheWernicke'sarea,andthenwetransferthemtotheBroca'sareainordertospeakforaresponse.Whenhementionsanameofanobject,thesignalwillgofromtheauditorycortexofourstotheWernickeareaforinterpretation,wherethemessageistransportedtotheangulargyrusfortheimage-conversation.CriticalPeriodThecriticalperiodisamaturationalstageduringwhichthenervoussystemisespeciallysensitivetocertainenvironmentalstimuli.If,forsomereason,theorganismdoesnotreceivetheappropriatestimulusduringthiscriticalperiodtolearnagivenskillortrait,itmaybedifficult,ultimatelylesssuccessful,orevenimpossible,todevelopsomefunctionslaterinlife.CriticalPeriodCriticalPeriodTheCriticalPeriodHypothesis(CPH)statesthatthefirstfewyearsoflifeconstitutethetimeduringwhichlanguagedevelopsreadilyandafterwhich(sometimebetweenage5andpuberty)languageacquisitionismuchmoredifficultandultimatelylesssuccessful.Tip:CriticalPeriodHypothesis(CPH)wasfirstproposedbyLenneberginhisbookBiologicalFoundationsofLanguageCriticalPeriodThecriticalperiodhypothesisholdsthatfirstlanguageacquisitionmustoccurbeforecerebrallateralizationiscomplete,atabouttheageofpuberty.Onepredictionofthishypothesisisthatsecondlanguageacquisitionwillberelativelyfast,successful,andqualitativelysimilartofirstlanguageonlyifitoccursbeforetheageofpuberty.lateralization&thecriticalperiodCriticalperiodhypothesis(CPH)wasfirstproposedbyLenneberginhisbookBiologicalFoundationsofLanguage.AccordingtoCPH,thereisafixedspanofyears(between2andpuberty（青春期）—around12or13yearsofage,oraround15asotherpeopleargue).lateralization&thecriticalperiodFixedspanofyears:2—puberty(fromtheperspectiveoflateralizationconcerninglanguage)Itisuniversallybelievedthatbeforetheageof2,mentalfacultiesarenotdivided,andbetweentheageof3and5,thelateralizationofhumanbraintakesplacethusfinallyformsrespectivecerebraldominancebeforetheendofpuberty,hencethelefthemispherecontrolinglanguage.lateralization&thecriticalperiodFixedspanofyears:2—puberty(fromtheperspectiveofthecriticalperiodconcerninglanguage)Duringthisperiod,languagelearningcantakeplacenaturallyandeffortlessly,andafterwhichitisnotpossibletobecompletelysucessful,forthebrainlackstheabilityforadaptation.ThankYou！