3.4 Feedback P300s (a positivity peaking at 424 ms corresponded to feedback-locked P300 at Pz, see Figure 6b)
Regarding feedback P300, another mixed 2 (stimulus type: probe vs. irrelevant) by 2 (feedback type: success vs. failure) by 2 (group: guilty vs. innocent) ANOVA was performed on the feedback-P300 component. Results revealed a significant main effect of stimulus type, F (1, 58) = 39.63, p < 0.001,ηp2 = 0.41, BFInclusion = 1.36 × 1010, revealing a more positive feedback-P300 following feedback regarding the probe than the irrelevant (7.30 ± 0.89 μV vs. 4.45 ± 0.73 μV). Notably, there was a significant two-way interaction between stimulus type and group,F (1, 58) = 63.77, p < 0.001,ηp2 = 0.52, BFInclusion = 1.52 × 108. Follow-up tests indicated that the probe elicited a more positive feedback-P300 than the irrelevant did in the guilty group: 10.15 ± 1.26 μV vs. 3.70 ± 1.04 μV, F (1, 58) = 101.97, p < 0.001,ηp2 = 0.64, BF10 = 5.61 × 105. However, among innocent participants, there was no difference in the feedback-P300 between the probe and the irrelevant (4.44 ± 1.26 μV vs. 5.21 ± 1.04 μV,F (1,58) = 1.43, p = 0.24, BF01 = 0.33). Other significant interactions were not found: stimulus × feedback: (F (1, 58) = 0.06, p = 0.81, BFExclusion = 4.29); feedback × group: (F (1, 58) = 1.61, p = 0.21, BFExclusion = 1.34);stimulus × feedback × group interaction : (F (1, 58) = 0.006, p = 0.94, BFExclusion = 7.04). For grand-averaged ERPs elicited by feedback stimuli, see Figure 2. For grand-averaged ERPs and their scalp distributions elicited by feedback stimuli, see Figures 5 and 7.