ERP:P3a(Novel p300)成分

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P3a/Novelp300概述产生:传统P300实验中,在典型的刺激构成的刺激序列中,偶然出现的新异刺激(novelty,如狗叫、色块等)也会引起显著的P300,称为P3a或NoveltyP300.潜伏期较短(200~280ms),头皮分布较为广泛,最大波幅位于额叶后部,比反映靶刺激加工过程的P3b明显靠前。心理含义:新异刺激不是一般的刺激或环境变化,而是一种未预料到的突然的刺激,它以产生朝向反应为特征。现已公认,NoveltyP300是朝向反应的主要标志。新异刺激反复呈现会使P3a的波幅减小。与注意有关干扰刺激产生P3a,靶刺激产生P3bNeuraloriginsandNeuropharmacologyofP3aandP3bP3a主要产生在额叶,P3b主要产生在颞顶叶。P3a和P3b产生起源于额叶和颞顶叶的激活。P3a和P3b在额叶和颞顶叶之间形成一个通路。海马对P3a有影响,对P3b无影响。P3a和额叶的注意和工作记忆有关,受多巴胺活动的调节。P3b和颞顶叶的活动有关,受去甲肾上腺素的调节P3a反映了刺激驱动的自下而上的前脑区注意加工机制P3b反映了任务驱动的自上而下的颞顶区注意和记忆机制P3a和NoveltyP300P3a:infrequentstimuli(tones,letters,etc)presentedwithphysicallydifferentfrequenttonesintheabsenceofatask,central/parietal波幅最大,潜伏期相对较短NoveltyP300:新异刺激(dogbarks,colorforms,etc.),frontal/central波幅最大,潜伏期相对较短已有研究表明P3a和NoveltyP300是同一电位三刺激范式:插入infrequent-nontargetstimuli.①infrequentnontargetstimuli:‘novel’stimuli(e.g.dogbarks,etc.)——noveltyP300②infrequentnontargetstimuli:‘typical’stimuli(i.e.notnovel)——nogo-P300P3aCentral/parietalInfrequentnontargetstimuliNovelty-P300frontal/centralnovelstimuliP3bTemporal/parietaltargetstimuliNogo-P300central/parietalnon-novelstimuliP3b——靶刺激P300P3a/‘novelty’P300‘no-go’P300低频非靶子刺激TheP3a,novelty,andno-goP300findingssuggestthatthetypeofnontargetdistracterandtaskdemandsdeterminecomponentamplitudeportraitureP3a、Novelty和nogo-P300是同一ERP电位的不同变体,非靶子刺激的类型和任务要求决定波幅来自典型的视觉和听觉刺激的P3a和P3bMarcoD.Comerchero,JohnPolich(April1998)实验目的:系统操纵靶刺激/标准刺激的区分难度来评估这个变量如何影响靶刺激和非靶刺激引起的P300的头皮分布,both视觉和听觉刺激。方法:三刺激范式(靶刺激、标准刺激、非靶刺激),被试(n=16)只对靶刺激反应,靶刺激和标准刺激的知觉辨认难度分为简单和困难,非靶刺激特性保持不变。2(视觉/听觉)×2(简单/困难)被试内设计实验流程:听觉和视觉两种刺激形式,EEG记录4个blocks(2听觉,2视觉),每个350个刺激,持续时间大约12min。靶刺激、非靶刺激、标准刺激的概率分别为:0.10、0.10、0.80。任务条件为靶刺激/标准刺激辨别的难度水平,简单和困难两种。所有条件下的任务都是对靶刺激做反应。刺激材料:听觉刺激材料是75db的声调,每2s通过耳机随机向被试双耳呈现。50ms平稳期10ms升降时间。视觉刺激材料是蓝色立方体形状的图形,每2s向呈现一次,持续75ms,通过电脑显示屏。DiscussionstimuluscontextfacilitatednontargetprocessingintheDifficultcomparedtoEasytask.ThenontargetstimuliintheDifficultconditionofeachmodalityelicitedafrontalP300,whichcloselyresemblestheP3afrom‘novel’stimulusparadigms。Difficultconditioninwhichtheinfrequentlyoccurringnontargetengagedfocalattentioninamannersimilartothatobservedpreviouslyfor‘novel’stimuli。allstimuliofthepresentstudywerepurposefully‘typical’instructure,theseresultsimplythatananteriorP3acomponentcanbeproducedwithoutusing‘novel’stimuli.Ifstimuluscontextisdefinedprimarilybyadifficulttarget/standarddiscrimination,attentionalredirectiontothenontargetcouldoccurbymeansofthefrontallobeactivationthatmaygovernP3a。Arelativelyeasytarget/standarddiscrimination,however,wouldmitigatethisoutcomebecausethestimuluscontextwouldnotdemandintenseattentionalfocus,therebyfacilitatingmoreautomaticnontargetprocessing。ConclusionsResults:Whentarget/standarddiscriminationwasEasy,P300amplitudewaslargerforthetargetthanthenontargetacrossallelectrodesites,andbothdemonstratedparietalmaximums.Incontrast,whentarget/standarddiscriminationwasDifficult,targetamplitude(P3b)waslargerparietallyandoccurredlaterthannontargetcomponents,whereasnontargetamplitude(P3a)waslargerandearlierthanthetargetP300overthefrontalelectrodesites.Similaroutcomesacrosstaskconditionswereobtainedforbothauditoryandvisualstimuli.Conclusions:Thefindingssuggestthattarget/standarddiscriminationdifficulty,ratherthanstimulusnovelty,determinesP3agenerationforbothauditoryandvisualstimulusmodalities.

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