Spatiotemporal Analysis Of ERP In A 2-1 Mapping Flanker Task

ObjectiveAccording to the dimensional overlap theory,the classic flanker task is a paradigm of stimulus-conflict type.During this task,a subject needs to response to the central stimulus and ignore the flanker(e.g.pressing left and right key to the letters H and S respectively).A conflict effects is referred to slower and more errorous responses to conflict stimuli(such as HHSHH or SSHSS)than neutral stimuli(such as OOHOO or OOSOO);and a congruent effect is referred the faster response with fewer mistakes to the congruent stimuli(such as HHHHH or SSSSS).However,previous studies using the 2-1 mapping flanker task suggest that the flanker conflict effect can be divided into stimulus conflict and response conflict and the neural mechanism of either the conflict effect or the congruent effect remains unclear.In this study,event-related potential(ERP)was used to further clarify the above controversy and various flanker effects.MethodsWe use 2-1 mapping flanker paradiglm.Each stimulus picture consists of the central circle and the surrounding ring.Their colors are selected from red,yellow,green and blue.The task is to ignore the surrounding circular and press the left or the right buttons according to the color of the central circle,red or yellow to the left and green or blue to the right.Because of the two colors mapped to the same button,the stimulus-incongruent(SI),response-incongruent(RI)and congruent(CO)stimuli can be classified by the manipulation of stimulus-response compatibility.The surrounding ring has an extra gray without task-irrelevent information so that the neutral(NE)stimulus is formed.The behavioral performance(response time and accuracy)and 19 channels of EEG of international 10-20 system were recorded in 24 healthy young people during the experiment.The one way of four levels(CO,SI,RI,NE)ANOVA of repeated-measures were carried out for the behavioral data.The non-spherical data were corrected by Greenhouse-Geisser method and the LSD method is used for paired comparison between conditions.The 19 channels ERP were also analyzed with one way of four levels(CO,SI,RI,NE)ANOVA of repeated-measures and paired t-test for further comparison.The F-value or t-value of the 19-channel ERP is interpolated to obtain the statistical parametric mapping(SPM).The significant threshold(a)is set to 0.05.ResultsThe main effect of the reaction time was significant:F(1.686,38.789)=21.531,P=0.000.NE:516.52±58.19;CO:526.73±69.41;SI:538.13±73.66;RI:561.25±75.20(ms).Among them,the differences between CO and NE,between SI and either NE or CO and between RI and either NE or CO were significant separately.The main effect of the accruacy was not significant:F(2.311,53.160)? 1.002,P=0.383.NE:93.96±5.51,CO:93.13±7.63,SI:92.19±6.05,RI:94.17±4.46(%).There are the P2(time window:160-240 ms),N2(240-360 ms)and P3b(360-560 ms)components and their significant effects are obtained from Fz,Cz and P3 separately.Among them,significant P2 effects include(RI-SI)and(RI-CO).Significant comparisons of N2 effects included(CO-NE),(SI-NE),(SI-CO),(RI-NE)and(RI-CO).Significant comparisons of P3b effects included(NE-CO),(SI-CO),(RI-SI),(RI-NE)and(RI-CO).The reaction time and the P3b amplitude have showed significant congruent effects(CO-NE),stimulus-conflict effects(SI-NE),double-conflict effects(RI-NE or CO),and response-conflict effects(RI-SI).The N2 amplitude reflects the first three effects.The spatiotemporal pattern of SPM(t)suggests that both the congruent effect(CO-NE)and the stimulus conflict effect(SI-NE)are related to the right ventral attention network(200-240 ms).Both the stimulus conflict effect(SI-NE or SI-CO)and the reaction conflict effect(RI-NE or RI-CO)activate the conflict monitoring system and the dorsal attention network(240-460 ms).The stimulus conflict effect(SI-CO)is more involved the left hemisphere at two-stage(100-120 ms and 300-360 ms).The response conflict effect(RI-CO)is more related to the right frontral inhibition network(240-460 ms).ConclusionThe reaction time results support the flanker interference to be divided into stimulus and response conflicts.And both conflicts enhance the frontocentral N2 in stimulus evaluation stage and reduce the parietal P3b in response selection stage.However,neither the N2 nor the P3b effect is conflict-specific since both are also elicited by the comparison between the congruent and the neutral stimuli.Furthermore,statistical parametric mapping of ERP reveals that the right frontal region for interference inhibition is shared by both conflicts and the left temporal semantic region is activated by either the stimulus-incongruent stimuli or the neutral stimuli relative to the congruent stimuli separately.Overall,our findings indicate that the two types of conflict based on short-term memory association compete for the common conflict-solution mechanism and the congruent effect is actually a kind of interference effect.