1、P3a/Novel p300,概述,產(chǎn)生：傳統(tǒng)P300實驗中，在典型的刺激構(gòu)成的刺激序列中，偶然出現(xiàn)的新異刺激（novelty，如狗叫、色塊等）也會引起顯著的P300,稱為P3a或Novelty P300. 潛伏期較短（200280ms），頭皮分布較為廣泛，最大波幅位于額葉后部，比反映靶刺激加工過程的P3b明顯靠前。 心理含義：新異刺激不是一般的刺激或環(huán)境變化，而是一種未預(yù)料到的突然的刺激，它以產(chǎn)生朝向反應(yīng)為特征?，F(xiàn)已公認， Novelty P300是朝向反應(yīng)的主要標志。新異刺激反復(fù)呈現(xiàn)會使P3a的波幅減小。與注意有關(guān),干擾刺激產(chǎn)生P3a,靶刺激產(chǎn)生P3b,Neural origins and

2、 Neuropharmacology of P3a and P3b,P3a 主要產(chǎn)生在額葉，P3b主要產(chǎn)生在顳頂葉。 P3a 和P3b 產(chǎn)生起源于額葉和顳頂葉的激活。 P3a 和P3b 在額葉和顳頂葉之間形成一個通路。 海馬對P3a 有影響，對P3b 無影響。 P3a和額葉的注意和工作記憶有關(guān)，受多巴胺活動的調(diào)節(jié)。 P3b和顳頂葉的活動有關(guān)，受去甲腎上腺素的調(diào)節(jié),P3a反映了刺激驅(qū)動的自下而上的前腦區(qū)注意加工機制 P3b反映了任務(wù)驅(qū)動的自上而下的顳頂區(qū)注意和記憶機制,P3a和Novelty P300,P3a：infrequent stimuli（tones, letters, etc）pres

3、ented with physically different frequent tones in the absence of a task，central / parietal波幅最大，潛伏期相對較短 Novelty P300:新異刺激（dog barks, color forms,etc.），frontal/central波幅最大，潛伏期相對較短 已有研究表明P3a 和Novelty P300是同一電位,三刺激范式：插入infrequent-nontarget stimuli. infrequent nontarget stimuli：novel stimuli (e.g. dog ba

4、rks, etc.)novelty P300 infrequent nontarget stimuli：typical stimuli (i.e. not novel)nogo-P300,P3b 靶刺激 P300 P3a/novelty P300 no-go P300 低頻非靶子刺激 The P3a, novelty, and no-go P300 findings suggest that the type of nontarget distracter and task demands determine component amplitude portraiture P3a、Novelt

5、y 和 nogo-P300是同一ERP電位的不同變體，非靶子刺激的類型和任務(wù)要求決定波幅,來自典型的視覺和聽覺刺激的P3a和P3bMarco D. Comerchero, John Polich（April 1998）,實驗?zāi)康模合到y(tǒng)操縱靶刺激/標準刺激的區(qū)分難度來評估這個變量如何影響靶刺激和非靶刺激引起的P300的頭皮分布，both 視覺和聽覺刺激。 方法：三刺激范式（靶刺激、標準刺激、非靶刺激），被試（n=16)只對靶刺激反應(yīng)，靶刺激和標準刺激的知覺辨認難度分為簡單和困難，非靶刺激特性保持不變。 2（視覺/聽覺）2（簡單/困難）被試內(nèi)設(shè)計,實驗流程：聽覺和視覺兩種刺激形式，EEG記錄4個b

6、locks(2聽覺，2視覺)，每個350個刺激，持續(xù)時間大約12min。靶刺激、非靶刺激、標準刺激的概率分別為：0.10、0.10、0.80。任務(wù)條件為靶刺激/標準刺激辨別的難度水平，簡單和困難兩種。所有條件下的任務(wù)都是對靶刺激做反應(yīng)。 刺激材料：聽覺刺激材料是75db的聲調(diào)，每2s通過耳機隨機向被試雙耳呈現(xiàn)。50ms平穩(wěn)期10ms升降時間。視覺刺激材料是藍色立方體形狀的圖形，每2s向呈現(xiàn)一次，持續(xù)75ms，通過電腦顯示屏。,Discussion,stimulus context facilitated nontarget processing in the Difficult compare

7、d to Easy task. The nontarget stimuli in the Difficult condition of each modality elicited a frontal P300, which closely resemblesthe P3a from novel stimulus paradigms。 Difficult condition in which the infrequently occurring nontarget engaged focal attention in a manner similar to that observed prev

8、iously for novel stimuli 。 all stimuli of the present study were purposefully typical in structure, these results imply that an anterior P3a component can be produced without using novel stimuli. If stimulus context is defined primarily by a difficult target/standard discrimination, attentional redi

9、rection to the nontarget could occur by means of the frontal lobe activation that may govern P3a。 A relatively easy target/standard discrimination, however, would mitigate this outcome because the stimulus context would not demand intense attentional focus, thereby facilitating more automatic nontar

10、get processing。,Conclusions,Results: When target/standard discrimination was Easy, P300 amplitude was larger for the target than the nontarget across all electrode sites, and both demonstrated parietal maximums. In contrast, when target/standard discrimination was Difficult, target amplitude (P3b) was larger parietally and occurred later than nontarget components, whereas nontarget amplitude (P3a) was larger and earlier than the target P300 over the frontal electrode sites. Similar outcomes across task conditions were obtained for both auditory and visual stimuli. Conclusions: The