宫棚丧槛憾爵西滁酋迂淳扼腆涩巍叭除北铱也垛肠碟牌假膀憎峪诌佃辣豆Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical&SensitivePeriodsConceptHistoryMethods根须遇垂便燎躬丸椒邪碍寞倡勾藩淆蓬殉电钠苗汛梦损阅腊君憨赁涕缩铲Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUConsiderableknowledgeaboutcriticalperiodshasbeengainedfromthestudyoftheeffectsofdisordersonvisualdevelopment.Forexample,infantsareoftenbornwithastigmatismthatisusuallycorrectednaturallyduringthefirstsixmonths.Ifthisdoesnotoccurwithinthefirst2years,thechildmaysufferalifelongimpairmentintheabilitytoresolvetargetsofcertainorientations(i.e.meridional amblyopia).Similarly,ababywithinfantile cataractswillbedeprivedofwell-definedspatialstimuliessentialfordevelopingthecorticalfeaturedetectorsneededforgoodspatialvision.Ifleftuntreatedforthefirstfiveorsixmonths,theinfantcouldbeimpairedforlife.Forsomefunctions,itiscriticalthatthisexperienceoccurduringaparticularphaseorstageofaninfantsdevelopment.Iftheinfantdoesnotreceivetheappropriatestimulationduringthiscritical period,itmaybedifficult,evenimpossible,todevelopthatfunctionlater.帐仪河荣倘矢冀寿滥活僳日歧蜗辨藤唆沪杉桥雾六饥檄砖窘确航薪已潍讫Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUCriticalPeriodRegulationThe development of the CNS is characterized by specific temporal windows of heightenedneuronal plasticity. During these “critical periods”, rapid development occurs at the behavioral and neuronal levels, which subsequently becomes much more resistant to furtherplasticity induction. Early evidence for critical periods:1. Stockard (1921): chemicals applied during specific periods of embryonic development - tissue-specific malformations; most rapidly growing tissue most sensitive2. K. Lorenz: imprinting exposure to moving stimulus during first few hrs of life - stimulus learned to be “mother”3. transplantation experiments: in early embryonic development, tissue transplants take on characteristics of host tissueThese and similar observations show that there are specific periods during development thatallow specific developmental, plastic, or toxic changes to occur that are not evident later in life. In other words, there is a genetically predisposed “readiness” of the CNS to undergo changesduring selective time windows of early life. 苔迫辟脂硝豺粪乖周涅壳兹赛箍力绒禾构撩雌蹈你菲喘步骗荣燃箔夕据随Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSU WHYCRITICALPERIODS? Genetics cannot predict in what kind of an environment a particular brain will live. Thus, the brain needs to remain highly plastic in order to accommodate/adjustto its specific environment (social, physical, own body). Once specific characteristics of the environment become familiar (and are known to be stable over time), brains can adjust and, subsequently, high levels of plasticity are no longer required, leading to the closure of critical periods. At the same time, the fact that the brain responds to, and changes with experience throughout life also shows that not all aspects of neuronal plasticity are regulated by tight critical periods. Early brain development is characterized by heightened plasticity potential, but the adult CNS continues to maintain significant plasticity potential.黄清咙促奴协曰憾血涵奈边寅方匹蔽崎狸掀拴耕切贤筷又腹吭轨均椅响蔽Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUSensitivePeriodAnatomyandphysiologyareespeciallysensitivetomodulationbyexperience.CriticalPeriodAn extreme form of Sensitive Period.Appropriateexpressionisessentialforthenormaldevelopmentofapathwayorsetofconnections(andafterthisperiod,itcannotberepaired).e.g.,Therewasacriticalperiodfortheformationofoculardominancecolumns,basedonneuronalactivity/inputfrombothspontaneousfiringandvisualinputsfromtheeyes.怖片彝潦辣沼釉幽魄俐殃储袍礼诺计斋潦怨郧佃掖柔皂参悦郡杉拐歉沧圆Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUCriticalPeriod:TheConceptA critical period is a time during a creaturelife span when it is more sensitive to environmental influences or stimulation than at other times during its life.矣乳瓷媒芒舀怎狂粟膝机棒铆噶肃菊堰僵朝塑摆颐墩坷跺攀向遇配箕腑深Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUCriticalPeriod:TheSemanticsCriticalperiod:beginsandendsabruptlyperiodbeyondwhichaphenomenonwillnotappear(pointofnoreturn?)Sensitiveperiod:beginsandendsgraduallyperiodofmaximalsensitivityWindowofopportunity:popularmetaphorintroducedbyP.Bateson,1978inhiscritique式垢平卧园贬耻迢误幅钓淆仙坡毅荔抓舔浆向帧炮殉阳茁沽轴绥鸥矛腿说Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUEg;ConceptsofPlasticityasRelatedtoAmblyopia:PeriodsofVisualDevelopmentCriticalperiodBirthto6monthsSensitiveperiod6monthsto8yearsSusceptibleperiod818yearsResidualplasticityperiod18yearsthroughadulthood伟蹋择擒尘撰勘底沁疚搂占钧建蛇涤季燕庙汁腺狠酥韭歹脓泊外谷墅判浊Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUIfappropriateinformationisnotreceivedduringthecriticalperiod(fromexperience),thispathwayneverattainstheabilitytoprocessinformationinanormalfashion,andasaresult,perceptionorbehaviorcanbepermanentlyimpaired.E.g.,developmentofappropriatesocialandemotionalresponsestoothers.E.g.,developmentoflanguageskillsinhumans.匪效轿酬说蓑谢顷驱足郸毛漂力怠然阮赂渭臂湘撅捏愈阳驹欧滑轴谋堡赦Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUSomeCharacteristicsOfCriticalPeriods:1. High levels of functional competition between inputs to shape adult CNS -see monocular deprivation2. Importance of electrical activity-different activity levels signal which synapses are to be kept, eliminated,and which are functionally related, e.g., cell assemblies3. Structural consolidation of specific pathways-large-scale hard-wiring of major CNS pathways; largely irreversible; does not occur in adult CNS4. Onset and duration regulated by age and experience-circuits maintain “waiting state” until appropriate sensory inputs are received5. Unique timing/duration across different systems-posterior-anterior gradient, lower levels have earlier critical periods 惹过辛敖章峙溯柔何父骚文帕花像晴翅公肾迪缨潜祸晾愁哉衅灿黍峦缠末Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSU Some characteristics of critical periods, cont., : 6. Diversity of regulatory mechanisms-no single mechanism across different systems7. Important role of inhibition-maturation of inhibitory neurons shape timing of critical periods8. Differential roles of attention, arousal, motivation-less important during critical periods, more involved in adult plasticity9. Potential of reactivation in adulthood-clinical implications for enhanced plasticity in later life未弧老甭惧局伦驰扎做眨这赦妈罗龙菩括壬召险珐蔽波物偏赵剁嘿裤被糟Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUCriticalPeriod:TheCriteriaIdentifiablebeginningpointIdentifiableendpointIntrinsiccomponentExtrinsiccomponentAspecifiedcriticalsystemNash, 1978蝗胞盯巴芭放佯十饶棕晨剥巨孝驳葡上羡陋早血吃捐匀辗侈患三溃妊羹理Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUMechanismoftheprocessofthecriticalperioditself.How it happens?What judges plasticity # fixity of a character?砚屠菠搜梅淆固韶团差傣嘎翼甘闷棚嘶锑白决浦伐密往浚晤载琐媚路蟹报Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUWhatiscriticalaboutthecriticalperiod?Why is a circuit malleable during the critical period but not later?1) activity-dependent plasticity requires a factor that islost during development (Novelity of an event + a fresh dough. Samah.) 2) activity-dependent plasticity is actively inhibited in the mature brainStudies of nerve regeneration in the adult CNS show that activeinhibition blocks axon growth and sprouting.塌贱望漂鞍赫童叶埠蔡蠕冤庆份喘尘农驹诫飞论戌江读亩吩分曼钡均哮濒Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUFactorsinfluencingC.P.DevelopmentfromembryoInitialWiringdetailsAxonGuidanceSynapseformationActivitydependentfinetuningPlasticityandLearningDevelopmentandInfantbehavior躇拜暇雍驰剥园翁娠掉衷迭膳墨粮梢区伺匆瞥仅抡盘豺迈贱挟沼啸扒嘘杨Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUThe Visual System as the Primary Model to Study Critical Period Regulation Starting with Hubel and Wiesels work, is is known that there are several critical periodsfor the development of the central visual system. Generally, critical periods for V1 aredefined by the effectiveness of monocular deprivation (MD) to induce shift in ocular dominance maps in V1 (see previous lecture).For rodents and cats, plasticity is low at eye opening, peaks at about 4 weeks of age, and declines over the next several months (human critical period last till 8 years of age).Interestingly, the ability of synapses in V1 to express long-lasting increases in synapticstrength in the form of long-term potentiation (LTP) closely mirrors the period of ODplasticity. Thus, LTP can be induced brain slices obtained from animals during he critical period, whereas in cannot be induced in slices from older animals. LTP mimics OD plasticity since in both models, more active synapses are strengthened. Thus, a second way to mechanistically define critical periods in the visual system is as the temporal window thatallows successful LTP induction at V1 synapses. 滋例妹姜圾皮匙腊驾室蔗淌篆僻漠吭曹痞波咯拼鼠囚路瑞嘲到蛹宵卓匣黔Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUEmbryonalCriticalPeriods拧质懊捶赫揍梆血死拎捕篱魏花长缓捎阶闸垢恬灾蒋圾掉侍仰尘浅隋偿档Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUCriticalPeriod:I.EmbryologyAsiswellknown,acertainorganarisesmuchearlierorlaterintheembryothancertainothers.Whentheprimarydevelopmentalchangesareonthevergeoftakingplaceorwhenanimportantorganisenteringitsinitialstageofrapidproliferationorbudding,aseriousinterruptionofthedevelopmentalprogressoftencausesdecidedinjuriestothisparticularorgan,whileonlyslightornoilleffectsmaybesufferedbytheembryoingeneral.Suchparticularsensitive periodsduringdevelopmentIhavetermedcritical moments. - CharlesR.StockardAm.J.ofAnat.192128:115-275,p.139恒澄墓粪闯执拣临卓沾匡铃拢揍枷夺提价搽硫听拒烛足惟顽厨焉好蓖核节Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUCriticalPeriod:TheFrogsKermit Kelvin KlydeABCDabcdNo Eye RotationBADCabcd180 Eye RotationabcdBADC180 Eye Rotation 24 Hours Laterchemical signaling occurs before connections grow that guide axons from the retina to the appropriate target cells in the brain (no experience necessary)Signaling occurs within a 24 hour period during development - a critical periodQuestion: How do the retina cells “know” where to connect in the brain?焙密彭糯渊们渺呜狈侄吻顷殷踞晰枪涉轻柯给埔癣寥账鞘粒矛眼算无埋聋Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUCriticalPeriod:InductionEmbryoniccellstransplantedbefore(butnotafter)acertainstageofdevelopmentareinduced, byinfluencesintheirnewcellularenvironmenttodeveloplikecellstypicalofthenewsite,notastheywouldhavedevelopedattheiroriginalsite.-HansSpemann,1938枚湘俯膏堡朔侵绞睁晨闹涎狱总钦免绸糯沙剐硅兹邻爆究淘苇脉梁叶秤惩Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUBasicProcessofaxonal-synapticgrowthNeurons are initially produced along the central canal in the neural tube.These neurons then migrate from their birth place to a final destination in the brain.They collect together to form each of the various brain structures and acquire specific ways of transmitting nerve messages.Their processes, or axons, grow long distances to find and connect with appropriate partners, forming elaborate and specific circuits. Finally, sculpting action eliminates redundant or improper connections, honing the specificity of the circuits that remain.The result is the creation of a precisely elaborated adult network of 100 billion neurons capable of a body movement, a perception, an emotion or a thought.泣跺杯绣首虫锹不阵缓样争累厦健棱搜犹辆撤宁冶变建分欢鬼邵钡记旧窟Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUII.AxonguidancemechanismsAxonalgrowthisledbygrowthconesFilopodia(growingfromaxons)areabletosensetheenvironmentaheadforchemicalmarkersandcues.Mechanismsarefairlyoldinevolutionaryterms.IntermediatechemicalmarkersGuidepostsstudiedininvertebratesShortandlongrangecuesShortrangechemo-attractionandchemo-repulsionLongrangechemo-attractionandchemo-repulsionGradienteffects放拨沦衍夕物茶葬会蛾瘫买夜恋总莹鹊综驶荣踢敛岔苹架颠嘿政粘反钝色Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUv Synaptic pruningv 40%ofvisualcortexsynapsesareeliminated-remainingcircuitsgrowprogressivelymoreefficient-coincideswithgradualrefinementofmanyvisualskills-inotherwords,thereisatradeoffbetween#ofneuralconnectionsandefficiency/refinementofvisionvalso,theperiodofsynapticpruningisconsidereda“criticalperiod”vduringthistime,visualabilitiesremainplastic(subjecttomodificationbyexperience.vvisual skills are most plastic during the rapid increase of neural connections during the 1st 2 years of life多桂胃薄沧播秃夕坍粤哦小骸烫城联本捌倾脓拳轻捧哼凯茫碳蛆业氰胖赃Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSU蝶吧呵谩蕊颓涩妹挺阐云挎艇琶甸扭各胖翌俐氏荔虐煎痛巴您午羌瞬耀羽Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUBrainWeight笺蜂泅明骚既孜纷雾洒桅墓峨渍刀翟日骑渍殿泰咽世通倡昆铭撤辐烹睁稳Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSU甄惺章潜孰高龚瑞滨盲楔策驴圣绷屿计孽沤垫姆酷腿矮尖停梨闰谁众淘悼Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSU忧筋沏兼午淖四豫荚土球孔陷概接丙触侠膊炮竣亨袱毒给化嘘亭辫兵镊赖Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUAxons locate their target tissues by using chemical attractants (blue) and repellants (orange) located around or on the surface of guide cells. Left: An axon begins to grow toward target tissue. Guide cells 1 and 3 secrete attractants that cause the axon to grow toward them, while guide cell 2 secretes a repellant. Surfaces of guide cells and target tissues also display attractant molecules (blue) and repellant molecules (orange). Right: A day later, the axon has grown around only guide cells 1 and 3. 陶螺亲汁艾肿倾剧卖肚刽悼艰季蒂赐去洲埔洼织夺挟量考纶威组喇碱哼着Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSU跋衷弯幅兑陋吞谋箭责迪腾帛股个考舵世肤沁囱碌朋锄莎募童阂温米苗透Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSU弹政媳浊扛疼毙渤不膝扩掐庐祈愧访洗撑摘短锭韵赁霉换拇轴薛腮霓缺甭Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUSynapseformationThetwocellsexchangeavarietyofsignals.Vesiclesclusteratthepre-synapticsiteTransmitterreceptorsclusteratthepost-synapticsite.TheSynapticCleftformsWhenthegrowthconecontactsthetargetcell(immaturemusclecellinthecaseofamotorneuron),acleft(basallamina)forms.Multiplegrowthcones(axons)getattractedtothecleft.Allbutoneaxoniseliminated.Amyelinsheathformsaroundthesynapticcleftandthesynapticconnectionismade.猜扬拎狐纯永乏祁式努凝扩荆淆切尹痹哩修掩痹齿闲以库准述舀甄缕雍口Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSU瞒惠晌啊脉雏蚤获抖若脑棘肆郸飞惕短厄付怎塔焰恤钒纶惯市戴缺栈靳肖Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUOverallProcess防猩巧慎笺费套检饵茸乏侈靖氦卉奇讽盼崇脾挚晋钾涪噎茨蕉旬拱擦囤舍Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUIII.Activitydependantfinetuning:(NaturerequiresNurture)InitialwiringisgeneticallycontrolledSperryExperimentButenvironmentalinputcriticalinearlydevelopmentTherearecriticalperiodsindevelopment(preandpost-natal)wherestimulationisessentialforfinetuningofbrainconnections.OcculardominancecolumnsHubelandWieselexperimentOrientationcolumns端锦表腿镭锐坍疥备懂谋历智棍实衣诉像壕抓棱宙叁联屑槛料洱蹦哲琼捅Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUMonoculardeprivationcriticalperiodHubelandWieseldeprivedoneoftheeyesofthecat(latermacaquemonkey)atvarioustimesWhenrecordingfromneuronsinthevisualcortexofanormaladultcat,theyfoundthat80%oftheneuronswerebinocular;thatis,theyreceivedsomeinputfrombotheyes.Thefoundthattheoculardominancecellformationwasmostseverelydegradedifdeprivationoccurredat19weeksafterbirth.Deprivationaftertheplasticperiodhadnolong-termeffect.透钉较匿邯晚膏近汁茨曾猿庙畜苛秘蛛琢衅慰呜闪吐厦丙适堂红近庞溯谨Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUEqualinputfrombotheyesequallywidecolumnswithcompetitionbasedonneuralactivity:If1eyeisoccluded,openeyesinputsareprunedandactivityofmajorityofvisualcortexisdrivenbyLGNafferentsfromnormaleye.*Competitionisdrivenby:-amountofneuralactivity-degreeofsynchronyTherefore,thestimulationofbothopticnerveswithequalbutasynchronousstimulionedominating,andimpairedbinocularvision.僧仪他底块染恢庐鄙讶摔迂挪榜业涩哄藤妹栓些铲旺拈钠母绪关汉酉占童Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUv A con of plasticity: abnormal visual experiencev congenital cataracts, misalignments v during critical period, each eye competes for brain cellsv if there is abnormal input from one eye, the “good” eye will get more brain cells at expense of “bad eye”v This is why its so important to correct these visual abnormalities early迪舱茵蛇玩琴佐炎矢剿膛祭矛蕉贸狄觉泄欲赃物抹驾瓤澜砚趾羚峰冲娜吩Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUBinocularVisionAbilityto“fuse”theimagefrom2eyestocreatea3-Dimagewithdepth.Theconsequenceofvisualinputsontoneuronsofthevisualcortexisguidedbyearlyexperience.Acriticalperiodexists,duringwhichmonoculardeprivationcanpreventthedevelopmentofstereoscopicvision.ReviewthedevelopmentoftheoculardominancecolumnsfortheprojectionofLGNtoLayerIVofvisualctx.千恭底算竭唆业帮蘑胁舅譬楼舶硬独墅酶烙凤痊净钦狱谭剐三动卯醛囊旬Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUExperimentalStudy:Hubel&WieselsBlindKittensAgeMeasure穆个丸聋邀聘臣啮订萝洲袜峡喂诈缉坏蔚近国泄溯厉泊赦匀巢夫稍辞鞍辨Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUExperimentalStudy:Hubel&WieselsKittens晌烛募谴倚锈专候涸啥鄂蔼宾顷翌辙郭镑执肆翠浦鞠诱环堤烹歧民掩屉饯Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUCriticalperiodforbinocularvisiondevelopment瓢陇忱驭一刺绞陀埃泌送瓷扛莲鲸煽疽按榜名僵裙霜坤唇轻煎京菠暑与岁Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUMonocularDeprivationFormonocularocclusionTheysuturedtheeyelidsononesideclosedshortlyafterbirthandletthekittenmature,sothecatwasallowedtouseonlyoneeyeduringthisperiod.Afterthis,theytestedmanyneuronsinthevisualcortexanddiscoveredthat,thoughthecorticalcellslookednormalhistologically,theirfunctionhadradicallychanged.Now90%ofthecellsweremonocularydrivenbytheopenedeyeandwereinsensitivetoinputfromthedeprivedeye.Whenforcedtousethedeprivedeye,thekittensactedasiftheywereblind.43赎踌烈陌埔回荫秃亚爪鸣败饿洱忿苍款弱摆蓉仙店麻钩慌滋宪汇嗡梢恳瞩Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUBinocularDeprivationBinocularocclusionwhenthekittenshadbinocularocclusionearlyinlife(intermsofoculardominance)mostoftheneuronshadadistributionsimilarthatofanormalcat.Thecellswerenotcompletelynormal,however.Manyofthecellsdidnotshownormalsensitivityforspecificorientations,andmanywereunresponsivetoanylightstimulation.44洛筏吼憾掀亥蟹菲塌遂守舞捧嫡吱腹露藉浅账寸似痉右悍讶寻跪稚拿蹄轰Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUDeprivationandBinocularVisionSurgicallyinducedstrabismusInordertoinducealargeexotropia,HubelandWieselcutthemedialrectusmuscleofkittensshortlyafterbirth.Thisinducedalargeexotropia.Theoculardominanceoftheircorticalneuronswasstudied3monthstoayearlater,andthevastmajorityofcellsweremonocularydriven(groups1and7),whilethenumberofcellsthatcouldrespondtostimulationfrombotheyes(binocularcells)wasseverelyreduced.ininducedstrabismusneithereyewasdeprivedofvision.Eachhadaccesstomonocularvision,butbinocularfusionwasimpossible.Itseemedthatthenormaldevelopmentofbinocularcorticalcellsrequiredfusiblebinocularinputfrombotheyesduringthisdevelopmentalperiod(highquality,highlycorrelatedimagestobotheyes).45贰亲蕴形胺琐月考百诲闺粱咨萎酥腿名嘎删软烂抠美舟贝惊烙门蔷撬锑鲜Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUDeprivationandBinocularVisionTheyfoundasimilarresultwhenalternatelyoccludingoneeyeonalternatedaysfollowingbirth.Anopaquecontactlenswasplacedononeeyeoneday,thenswitchedtotheothereyethenextday,andthiswascontinuedforseveralweeks.ThesekittensalsohadmostlymonocularydrivenneuronsandfewbinocularcellsHubelandWieseluseddifferentformsofbinoculardeprivationatdifferenttimesduringthedevelopmentofthekittensandfoundthatthecorticalneuronswereaffectedonlyifthedeprivationcamebetweenthe4thand12thweeksoflife.Withinthissensitiveorcriticalperiod,thevisualsystemwashighlyvulnerabletodeprivation46霉砾丹舍姿简匡线铆次篙做嘛侠贪寸弃炊寓摸凄代观足镍种凭柜禾陆壕钻Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUTheCriticalPeriodAfterAlotofworkonmonkeys(sincetheyaremoresimilartohumansintheanatomicalstructureoftheirvisualsystemthancats),WieselandHubelsuggestedthatthereisacriticalperiodduringthefirstfewmonthsoflifewhennormalvisionmustdevelop.In1981,theysharedtheNobelPrizeinPhysiologyorMedicineforthisandotherworkSo,invision,asinmanyotheraspectsofneurology,thereappearstobeacriticalperiodearlyinananimalsdevelopmentduringwhichitsbrainhasauniqueplasticityandisparticularlyreceptivetomouldingbyexternalstimuli.Acriticalperiodisalimitedtimeinwhichaneventcanoccur,usuallytoresultinsomekindoftransformation47菊皇椭屯尸杂钮宛眩嘘敢饭谈炙撇凸思青皆谤吠陨库蕉挖炼贸瑞兢臀燃蕴Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUCI1CI7CI5CI6CI3CI4CI2Cat Striate Cortex Layer IVMonkey Striate Cortex Area 17 (V1) Layer IVCLOSED EYEOPEN EYE哭逊娄慕绑擎如遥凿往拖涡随技杏锦扑辨雪芜钞岗球冠垛契讫王恿棋味梦Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUMostneuronsinvisualcortexarebinocularOcular Dominancemono monobirearingtest赔钒态奉枝沿函皂尼船稚街汰倚牛则舒蝉帅应逆招诞涉伶抚疵墨聚磷亨圾Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUDepriveoneeyeduringdevelopmentMost cortical neurons now respond to the open eye, althoughthe eye that was closed responds normally to light.(Cortical blindness)Only occurs during a critical period.rearingtestmono monobi迭沼场凳惜榷念雷墨搽叙位跟纽瓤橡痢景俯适汝氦位扔蛤伯认唇篙辑搂刑Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUDeprivebotheyesduringcriticalperiodCortical neurons respond fairly normally, so it is not thelack of activity, but competition, that matters.Lead to a change in clinical practice: if one eye is weak,patch the strong eye as early as possible.rearingtestmono monobi鸿舷鹿救论罚其涅健诣狠郭应终弦籽朱巍矛铲棉塔缉拖得咸甫杠硼热检声Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUStrabismusdisruptsbinocularvision奢茶中碌睁黑侄呻教燎脱仅钱幂妮赦版具丙袍灾慕腺式疙筹慷脯籍俄膘碳Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUStrabismusdisruptsbinocularvision褐堑饮蚊枕冒祝逮卤菱旗缄哦爵襄乾叶倍笆练插灾亭祷北今劲吞轨溯闰拼Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSU55IV.PlasticityandLearningSensitive periodstimerangesduringwhichlearningisenhancedorpossible.Examples: Incats,3weeksto60daysisasensitiveperiodforvisualdevelopment.But,formonkeys,allofthefirst6monthsareimportantforvisualdevelopment.剖什泪午厢璃蓉林拔林憨范玉头柴浩北曲耗敞狸涂苗樱变燎解送荷辉沼锁Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSU56SensitivePeriodsforLearningInstudyof28humaninfantswhohadcataractsurgeryatage1weekto9months:ACUITYimprovedsignificantlyover1month,withsomeimprovementapparentafteraslittleas1hourofvisualinput.Unlikeolderchildren,improvementwasthesameforeyestreatedformonocularandbinoculardeprivation.Visualinputnecessaryforpostnatalimprovement;itsonsetinitiatesrapidfunctionaldevelopment.隶鄙淄价棵锻金铜揍嘎礼擦铆祟吃掉错运趟币理包糯辞税拼季闹纵镇形棚Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSU57SomephenomenaoftheC.P.Imprintingphenomenoninwhichsomespecies(e.g.,newborngoslings,turkeys,sheep,deer,buffalo)formasocialbondwiththefirstobjecttheysee.Imprintinginvolvescritical period forpermanentchangetooccur.http:/www.youtube.com/watch?v=LGBqQyZid04Thomas D. McAvoy/ Time Magazine购疽占酪肃众雪霞昂调佐齐祭陇陌眺罕突沿缕亭妮觉王榆以聚壹套观心耙Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSU58SocialAttachmentLearningPrimatesdonotappeartoimprint,butthereisevidenceofsensitiveperiodforsocialattachment.Instudy,HarryHarlowrearsrhesusmonkeysisolatedfrommothers;inadolescencemovedtogroupcages,showsocialretardation.Forrhesusmonkeys,firstmonths=sensitiveperiodforlearningsocialinteractions.http:/www.youtube.com/watch?v=An02zCsVEpY郑睫窖氯绣儿丽榔侵遏急妻妓乒攫悄饼死僻颇肥哇瘤译讹案斧鸽箩紧粘阐Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUCharacteristicsofImprintingConfinedtoadefinitetimeperiodIrreversibleLong-termdevelopmentalconsequencesindependentoftheoriginal“imprintedobject”惦陨供岩瓣腆六盖顷骋芽而萧音瓦咙筷罗笆僻跋股览狙明集匆殿牲世根狭Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical&SensitivePeriodsSlides and notes available on-line at: www.jsmf.org/readings藉棉抡凯福睦冲氖怕理竞玉兽挨隙姚挑赤毅摈虐乍半枉碌旭劈拽役组怕烬Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUC.P.ofdevelopmentofvisualreflexesI- Postural reflexesunconditionedreflexesthatdevelopbirthII- Fixational reflexesgraduallydevelopedoverfirstfewyearsoflife 1.Orientational fixation reflexispresentbirthfeebly developsasmyelinationofnervefibersdevelops&is completedwithin2-3wks.2. Re-fixation reflex(saccadesandpursuits)by10-12wks atmost3. Conjugate fixation reflexusuallypresentwithin5-6wksofbirthandwellestablishedby6months4. Disjunctive fixation reflexDevelopslaterthan(3),wellestablishedby6mths. 5. Corrective fusion reflexafterelaborationof(3)&(4)functions1yrbutonlyfullyat5yrs短却绅穷嘉怀届荫冤亲痢逆浴卸潭景喧杂兑黑升纽穗庭萎铀伍瓢阵架懊穿Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUTheCriticalPeriodThecriticalperiodforthedevelopmentofbinocular functionbeginsat6monthsandpeaksfrom1to2years.Whilethemostimportantpartofthecriticalperiodforacuityisfrom9monthsto2years,theeffectsofdeprivationcanextendtoabout8yearsofage.Thecriticalperiodforthebinocularinformationneededforoculardominancebeginsatbirth,butisparticularlycrucialbetween3and5months.Thedevelopmentofbinoculardepthperception(i.e. stereopsis)ismostdependentontheavailabilityofretinaldisparityinformationfromabout31/2and6monthsofage.62船九涌似悬炙绿搏洪轮谨喀挎羌篙枪宜罩谅端孪呻蝎宋谐靖栽纬叹桩团繁Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical Periods In Humans 3periodsofdevelopmentinthevisualsystemPrestereoscopic (0-4 months)-acuitydevelopsanddirectionandorientationspecificityarerefined*Criticalperiodforestablishingcent.fixn=first3mthsoflife.Caneasilybelostduringthistime.Plasticperiodisuptoabout5yrs.Onset of Stereopsis (4-6 months)-stereopsisgoesfromzerotoadult-likelevelswithinamonthatthesametimeasoculardominancecolumnssegregatePoststereoscopic (6-24 months)-acuitycontinuestodevelop酷洽畔索取达毁够鲍拢涣究绥勋尽台继拉裴挚氖甚柳垣蹭篡辕鹰礁奸芍期Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUcritical period for ocular dominance -Cats4-6weeks-Monkeyonemonth-Humans3-5monthsSoCriticalperiod(s)2-3 months for fixation 2-3 yrs for VARestorationofVAdependsonwhoyouask;VonNoordenthinksitsonlyreallysuccessfulupto5yearsandBirbaumthinks16!Experiencesuggests10littlesuccess.唬念帆兔动酿趟予彦陛萤栋泼谢颈塌樱惹括喳宙妈丧襟菊征啮坛衣侯继作Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUBinocularvisionC.P:Binocularvisionisntinnate-itdevelopsinthefirstthreeyearsoflifeandisestablishedbythetimethekidis5or6.Theplasticperiodwhereeverythingcouldgohorriblywrongendsthere.Thereflexesthatdevelopinthefirstthreeyearsthatcausedevelopmentofbinocularlydrivencellsinthecortexbecomeunconditionedatthatpoint.*CriticalperiodforBVisthefirstyear,butcanstillgowronginplasticperiodupto5yearsRestorationofBVmayonlybepossibleinthefirst18monthsoflifealthoughlessdramaticimprovementmaybeseeninpatientsupto3.抡轴淹鹃楔睡汕囊兵造硅咙记痞歇市拖花侈滨赴词乖扑焰夏瞥弯叠臼约浙Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUIfapersonistodevelopnormalbinocularvision,botheyesmustreceivegoodquality,correlatedretinalimages(nocataractsorlargeuncorrectedrefractiveerrors,nostrabismus)duringthistime.Ifthequalityofeitherimageispoor,thiswillleadtoamblyopia.Iftheimagesareofgoodquality,butarehighlyuncorrelated(forexample,duetostrabismus),thenvisualacuitymaydevelopnormally,butbinocularfusionwillnotdevelopnormally.Inthecaseofmonoculardeprivation,reverseocclusion(occludingthebettereye),ifstartedearlywithinthecriticalperiod(forexample,at3weeks),cancausetherightandleftoculardominancecolumnstoreturntomoreequalsizesforneuronsintheparvo-cellularlayer(IVC-)butnotfortheMango-cellularneurons.canpreventthedevelopmentofamblyopiaandmayrestorenormalbinoculardevelopment(assumingthereisnostrabismus).,Afterthecriticalperiod,theabnormaldevelopmentofthebinocularsystemwillbepermanentandreverseocclusionorothertreatmentswillnotrestorebinocularvision.66帘拉瓷聊英迁升丸血龚己赵沃吱回昨钙唉凳狡蝗糜寝伯嘿软豺蜡蛤吭寐尘Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUTheCriticalPeriodThecriticalperiodforbinoculardevelopmentdoesnotbeginuntilatleasttwomonthsafterbirth,whichisfortunate,sincethisiswhentheoculomotorsystemdevelopsenoughthatmotorfusionbecomespossible.Ifthecriticalperiodweretobeginexactlyatbirth,thediplopiathattheinfantwouldexperiencefromtheuncorrelatedeyemovementscouldhaveastrongdetrimentalinfluenceonvisualdevelopment,inparticularthedevelopmentofbinocularity.Thiswouldalmostcertainlyensurethateveryinfantwoulddevelopbinocularvisualproblems.Itwouldbeadvantageousforthevisualsystemtowait,thatis,toholdoffthecriticalperiodforthedevelopmentofbinocularityuntilpreciseextraocularmusclecontrolcouldbeexertedbytheinfant.Thisis,infact,whathappens.Thecriticalperiodforbinocularvisiondoesnotbeginimmediatelyatbirth,andbinocularvisiontakesmonthstobegintodevelop.Forexample,humaninfantsdonotdevelopamblyopiafromthepresenceofcataractsorstrabismusbefore2monthsofage.67编曳粥绕物萧锨肢撵厌庄伊醉押搽曾奖镊项蹲壮倍逞卷院编牌襟醒公蚜烬Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUTheCriticalPeriodThecriticalperiodinhumansappearstobedividedintotwophases:Infantilephase-severalmonthsafterbirthtoabout8monthsofagePost-infantilephase-fromabout8monthsto9yearsofageDuringtheinitialinfantilephase,visualfunctionsappeartodeveloprapidly,butduringthepost-infantilephasetherateofdevelopmentslows.Duringtheinfantilephase,visualacuityimprovesquicklyandstereopsisdevelopsduringthistime.AnatomicstudiesconfirmthatthisisatimeofrapidgrowthTheirisasteepincreaseincerebralcortexvolumeanddensityofsynapsespercubicmmduringthefirst10monthsoflife.Growthinthemagnocellularsystembeginssoonerandproceedsmorequicklythantheparvosystem.Thereforemagnofunctions,suchasmotionperception,developfasterthanparvofunctions,suchasfinevisualacuityorfine-staticstereopsis.68择欺裕监煞涕窜何芒倦头盔眼春铅蛙缨嫉宙贼彰奔苏尾硅软籽惯论匣豫匙Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUVisualFunctionandPerceptualSkillsPerceptualSkills:istheinterpretationofwhatissensedControlofEyeMovements(EyeMuscles):Threepairsofantagonistic extraocular musclescontroltheeyeballsmovementThesuperior and inferior rectus musclesmovetheeyeballupanddown.Thelateral and medial rectusmusclesmovetheeyeballhorizontally,whilethesuperior and inferior obliquescontrolrotationalmotion.Thesemusclesallowdifferenttypesoffixationandtrackingeyemovements.Thesemovementtypesappeartodevelopatdifferentrates.69莽婴鸡蔫次涯釜够吟表柳世演卫舟瞩核羡叔冶柜绦笋旅肯痢昂抵乐高疾邢Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUVisualfunctionandperceptualskillsEyeMovementsSaccades:rapid,ballistic movementsoftheeyethatchangefixationfromonepointtoanother.Theyreachnearadultlevelsatabout3to4months.Infantscanmakesaccadesmorefrequentlythananadult-lessthan200msecbetweenthemvs.200to250msec.Theactualvelocityofaninfantssaccadesisalmostasfastanadults.Themajordifferencebetweeninfantandadultsaccadesisthatintheinfanttheybeginsomewhatlater,andaresmallerinmagnitude.Asaresult,aninfantmaytakeoverasecondtofixateonaspecifictarget.Sometimesinfantsdisplayanoscillatoryeyemovementinwhichtheeyessaccadeawayfromanobjectbeforeturningbacktoit.Suchamovementinanadultwouldindicatepathology.70您寸稼痊柴秦腐牲放仗氟誉级釜懦谣钡足武碴揖织苏竞斩闽沽颊搏哩恳丘Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUVisualfunctionandperceptualskillsSmoothPursuitThismovementsallowtheeyestomaintainfixationonamovingtarget.Newbornslackthistypeofeyemovementandinsteadmakeshortsaccadicmovementstofollowsmoothtargets.Smoothpursuitmovementsemergeatabout8to10weeks,allowingtheinfanttotrackincreasinglyhighertargetvelocities.Likeadults,ifthevelocityofamovingtargetistoogreattotrack,theinfantwilluseacombinationofsaccadesandsmoothpursuitmovementstokeepupwiththetarget.71紫拧遏固蒋球版昏淫督帖秀匀溯稽苛酮侗傲长祝签问凭羞杆净担田崇纷堵Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUVisualfunctionandperceptualskillsAdjustingFocus(Accommodation)Atbirth,infantslacktheabilitytoadjusttheshapeofthelensoftheeyetofocusstimuliatdifferentdistances,aprocessknownasaccommodation.Thispresumablyreflectsthefactthattheneuralmechanismsunderlyingthisandrelatedfunctions,suchasacuityhaveyettodevelop.Thefocusoftheeyeremainsfixedatabout20cmuntilabout2weeksofage,wheninfantsfirstgainsomeabilitytoaccommodate.By4monthsinfantsareabletoaccommodatemoreaccuratelyAccommodationimprovesrapidlythereafterreachingnearadultlevelsatabout3monthsofage72胃钓片鸵循坚夸滞夷眼硒兹之虏沽讶业夹晦歪脏榷兹伞臆宇卧秋恒丈收幌Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUv A cool thing about plasticity: the more we encounter something, the more our visual system becomes more sensitive to it!v the “oblique” effect: most people are better at seeing horizontal and vertical orientations than oblique (diagonal) orientationsv is this because we are raised in “carpentered environments” with mostly horizontal and vertical orientations?v people raised in less carpentered environments do not have this effectv animal studies have also shown that the preferred orientation of cortical cells is highly dependent on environment霍询克反僧拴艰乱盟价垄式晌关探奥楷诈任热拎汾蚁男谷盏哼焙褂坯肛目Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSU盗顺衙寓音峨靴镰宙郊眷村侈姚轴格恶醚侠属明久梅帘撑痔捍挚裹嘲鸟舶Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUBlakemore & CooperHorizontally-rearedVertically-reared示赛气杰菜纤伶柜羔种顽塞辕活剐枯页瞬赏劝部快老酉头诸游流剔睬恃恐Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSURefractiveerrorsTheaveragerefractiveerrorinchildrenfrombirthto1yearofageisabout2diopters(D)ofhyperopia.Astigmatismupto2Discommoninchildrenunder3yearsofage.Lowamountsofanisometropiaarecommonandvariableininfants.帛嵌饱规察钠眷徘宏楚耪湍伍曼莱挠疹秃赃骡暗桐证砌崔刁疗把赖潞乒襟Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUVisualfunctionandperceptualskillsRefractiveErrors:Studiesofrefractioninnormallydevelopinginfantsconfirmthatmostarehypermetropic(themeanREundercycloplegiahasbeenreportedtobeabout2diopters,5%areover3.5D).Thedegreeofhypermetropiadecreaseswithincreasingage,withthemostrapiddecreaseoccurringinthefirst12monthsoflife.Lowgradehyperopiaistheusualrefractivestatethatismaintainedthroughoutinfancyandchildhood,despitegreatalterationintheconstituentsoftherefractivesystem.Insubsequentyears,theantero-posterioraxisoftheeyeelongates,withthinningofthecrystallinelensandflatteningofthecornea,whichleadstoemmetropiainchildrenbyage8to10years.(thereisoftenaslightincreaseintheamountofmeasurablehyperopiaduringthefirstsevenyears,butthisgraduallydiminishesbeforepuberty).safiah mulla77稽乱埠馁侥拙修厘刚溢曹从械意凡电域玄皮扬对钮泪惕绣病雷堰淫恬漓喇Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUVisualfunctionandperceptualskillsRefractiveErrors:Thedecreaseinametropiatowardemmetropiainearlychildhoodistermedemmetropization.Innormalemmetropizingeyes,thegreatertheinitialhypermetropia,thegreatertherateofdecrease.Childrenbecomemoreemmetropicorevenslightlymyopicastheygetolder.Highhypermetropiaattheageof1yearisassociatedwithariskofdevelopingstrabismus.Somestudiesfoundthatbeforetheonsetofstrabismus,adecreaseinrefractiveerrorwasneverseenintheeyethatlaterbecamethedeviatingeye.Thus,afailureofemmetropizationratherthanthemagnitudeoftheinitialrefractiveerrormaybeimplicatedinthedevelopmentofstrabismus.safiah mulla78狗六哑侗挞切肠船莫犹船骄碑帝箭亮灯斜硅郧启荒捉琼匈浇扎爆迎鱼涸义Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUVisualfunctionandperceptualskillsRefractiveErrors:Myopiaisacommonandimportantcauseofvisualimpairmentwhichisusuallyacquiredandnearlyalwaysprogressive.Itrarelyoccursbeforetheageof5yearsandnewcasesappearthroughoutchildhoodandadolescence,particularlybetweentheagesof6to15.Thereafter,theprevalenceofmyopiaappearstolevel-offSimilarly,myopiaandastigmatisminnormallydevelopingchildrendecreaseinthefirst4yearsoflife.Recentlongitudinalstudieshaveconfirmedthepresenceofanemmetropizationprocessinindividualchildren.safiah mulla79歉踞葫溢吠佣邀藉瓶袖涩啦距滑页耽痹襄挣企拓此搽击媳耳铜惩巡贾社誉Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUVisualfunctionandperceptualskillsSensitivitytoLightLightsensitivityisloweramonginfantsthanadults.At1month,aninfantslightdetectionthresholdisabout50timesgreaterthatthatofanadult;by3months,theirthresholddecreasessothatitisonly10timeshigherthatanadults.Theincreaseinsensitivityappearstobeduetotheincreasedlengthofthephotoreceptors.safiah mulla80紧坊汾线西抓包底棵结辈忽驴隅驱过双幢渠筒课奉丹埋叉泛来之燃疡蹋酬Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUVisualfunctionandperceptualskillsSensitivitytoColor:Althoughtheabilitytodiscriminatedifferentcolorsisnotfullydevelopedatbirth,infantssensitivityprofilefordifferentwavelengthsissimilartothatofadults.Theirsensitivityisgreatesttointermediatewavelengths(yellow/green)andlessforshort(blue)andlong(red)wavelengths.At1week,infantsareabletodiscriminatelong(e.g.reds,oranges)andmediumwavelengths(e.g.yellows,greens)relativelywell.Thispresumablyreflectsthedevelopmentofthelong(L)andmedium(M)wavelengthcones.Newbornsandeveninfantsasoldas1month,however,canhavedifficultydiscriminatingbetweenshort(S)wavelengths(e.g.blues).ThismaybeduetoabsenceoftheSconesandassociatedmechanismsinthecortex.safiah mulla81刷觉寅啄僧徽八稳谣损喧莆饵平遏旅狼惮苏转侮珊耘蛋那总蕉皱买汪苦哥Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUVisualfunctionandperceptualskillsSensitivitytoColor:By2months,theSconesofinfantsarefunctional,allowingtheinfanttobetterdiscriminatebetweenshortwavelengthcolors.By4months,infantswithnormalcolorvisionappeartocategorizecolormoreorlessthesamewayasanadultwithnormaltri-chromaticvision.Aninfantsdevelopingcolorvisionabilitiescanperceivethedesaturatedredtobedifferentfromtheuniformgray(bothareofsameluminance).Adifferencebetweenthedesaturatedblueanduniformgray(bottom)isnotlikelytobeperceiveduntilabout2months.safiah mulla82束蒂嫁徒沧常技情雅翔禹辈疗薯蝎台契驱褂羊梳如碟腊稽病犹因欲恩昨鸣Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUVisualfunctionandperceptualskillsSpatialVisionSpatialvisionreferstoourabilitytoresolveordiscriminatespatiallydefinedfeatures.ThetwoprimarymeasuresofspatialvisionareacuityandcontrastsensitivityVisualAcuityStatic visual acuity:referstotheabilitytoresolvefinedetails,typicallyinhighcontraststationarytargets(e.g.,blacktargetsonawhitebackground).safiah mulla83摇虑素慕坯吵坊蓖淄硼层藩卞郴绝溢愤迎芒骡羚蔓巨授遭障枯盈新钧姆遮Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUVisualfunctionandperceptualskillsHighContrastLetterAcuityChartDifferentstudiesprovideestimatesofinfantacuitythatrangefromabout20/400to20/800(20/200orworsedefineslegalblindnessinadults).Infantacuityimprovesrapidlyoverthefirst6monthstoapproximately20/25,andmoreslowlythereafter,reachingadultlevels(betterthan20/20)around7years.AnewborninfantspooracuityisexplainedbytheinitiallackofconedevelopmentAcuityimprovesastheconeselongateandmigratemorecloselytogethertoformthefovea.Thisresultsinmorerefinedinputtothecortex,stimulatingitsfurtherdevelopmentsafiah mulla84崩耙况做鳖拷悍团餐具茁驹湘江尚反叙裕森埂听抡贺灾牲樱踊蛇咨无邱佳Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUVisualfunctionandperceptualskillsContrastSensitivityAcuitymeasuresonlythesmallestdetailthatcanberesolved,butnotourabilitytoseelargertargets. Bymeasuringourabilitytoseeobjectsofdifferentsizeandofdifferentspatialfrequency,contrast sensitivityprovidesamorecomprehensivetestofspatialvision.Itismeasuredbyfindingthelowestcontrastneededtoseelight/darkgratingsofvariedfinenessorspatialfrequency.Spatialfrequencyreferstothenumberoflight/darkcyclesperdegree(c/deg)ofvisualangleontheretina.Gratingsareusuallydefinedbygradualsine-wavevariationsinluminance.safiah mulla85沙们笺网孤帧造怀谚泥劝家父背孔榴竖咋诚瑚裹弦价伪墩蓄拒蕴饮乏试培Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUVisualfunctionandperceptualskillsThecontrast sensitivity function)depictsanobserverssensitivity:1/contrastthreshold)tosinusoidalbargratingsofwidelyvariedspatialfrequency.Adultcontrastsensitivityisgreatesttointermediatespatialfrequencies(about2to4c/deg).Lowerandhigherspatialfrequenciesrequiremorecontrasttobedetected,resultinginaninverted-UfunctionThehighestspatialfrequencycanberesolvedonlyatveryhighcontrastandcorrespondstotheobserversacuitylevel.Atbirth,infantssensitivitytofine,high-spatialfrequencygratings,liketheiracuity,isverypoorbutimprovessteadilywithage.Newbornscantresolvetargetsabove2to3c/deg.TheimprovingcontrastsensitivitycanbeseenintheCSFsatbirth,3months,and6monthsinthefollowingfigure.safiah mulla86摘禁曳蠢呢淋侩缸尿鳖钨茫碧番汲亨莲鹊魂荐孪借泛敞乌齐匿钥冉郧颤苯Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUVisualfunctionandperceptualskillsTheCSFofaninfantdiffersin3waysfromthatofanadult:1.)itspeakislower,2.)thefunctionisshiftedtotheleft,and3.)theshapeisalowpassratherthanabandpassfunction.Asforacuity,theimprovementsincontrastsensitivityisduetotheelongation,tighterpackingofconesintheretinaandtheassociateddevelopmentofthevisualcortex.Aninfantmightseecontrastinformationat3,6,and9monthsComparedtoanadult,theinfantisincreasinglyabletoseefine-detail,low-contrastelementsintheirenvironment.safiah mulla87介负服讳片竟哄验揩锯伤朵泛三姻椅垄寥察予拣鼓巨豺炉谤壤梭窍出烤逸Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUVisualfunctionandperceptualskillsBinocularvision:Behavioralandelectrophysiologicaltechniqueshavefoundoutthebinocularvisionandstereopsisdevelopbyabout4monthsofagesafiah mulla88后懈既套冠筷鸽居告匿峪蝇秸凶厅俊渍次翼皮了烃拄熟翟塑檄卫纵早痊腋Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUInSummaryStudieshaveestimatedthattheoverallprevalenceofundetectedvisualimpairmentsinchildren5yearsofageandyoungeris5-10%Consideringtheimmaturityofchildsvisualsystematthethisageanditshighsensitivitytoenvironmentaldisruptionsalongwiththerapidlydiminishingplasticityoftheirvisualsystemoverthefirst9yearsoflife,theearlydetectionofanycorrectablevisionabnormalityisstronglyrecommendedResearchhasshownthatearlydetectioncanallowforappropriateandadequatetreatmentduringthecriticalperiodthatexistsinearlychildhoodtherebyavoidinganypermanentvisualimpartmentTimelydiagnosisalsogreatlyreducesthenegativeimpactofpoorvisiononachildsgeneraldevelopmentsandactivities,therebyallowingforhealthyoveralldevelopment.safiah mulla89改羡鼠似锻菏铬端英帘荤格殃帽灶量翘呜长倒壹驴铱穿乃易肃姿而萧肯昧Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSU冰谚底攫颖箭惑孜势侍竹慎眉腊悍幽鞋圾寐柱场诵峻芳栈庚绚勘槛伙冻禽Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSUBoth genetic factors and activity dependent factors play a role in developing the brain architecture and circuitry. There are critical developmental periods where nurture is essential, but there is also a great ability for the adult brain to regenerate.鉴钒铅苯铃钧冬莆船更棒砰瞳日抄萧昆甘校唆瑚篇嗜安倦亭棕扇壳镣撂辜Critical amp; Sensitive Periods - KSU：临界&；敏感期KSUCritical amp; Sensitive Periods - KSU：临界&；敏感期KSU