Due to the significant EEG fluctuation of one participant in the formal experiment, he was excluded, and finally, the data of 30 participants (15 with HOC and 15 with LOC) were analyzed in the EEG analysis part. SPSS17.0 was used for statistical analysis of the EEG data. Based on past research and the whole brain activity, the position of the electrode to be analyzed was determined. The cue-related and stimulus-related ERP components were extracted under different ex-perimental conditions and the difference ANOVA was used to determine the differences in neural activity between the high and low groups under different cue conditions.
According to the purpose of this study and the total average map, combined with the basis of previous studies [32–33] and the analysis of the brain topographic map, we selected the data of 15 electrode points in the centre line (Fz et al.), bilateral electrodes (F3\4, C3\4, P3\4) and occipital lobe electrodes (PO3, PO4, PO7, PO8) for statistical analysis. At which electrodes the individuals showed significant differences in cue correlation and stimulus correlation were measured respectively.
3.1 Cue-related ERP
Through the analysis and comparison of the relevant components of each electrode point, we found that in the cue stage, when faced with the three probability cues (80%, 50%, 20%), individuals with LOC and HOC showed significant differences in the activation of EEG components at the midline electrode point. Among them, Fz, Cz and FCz were particularly obvious at three electrode points (as shown in Fig. 2 and Fig. 3). It can be found that P2 (150–250) and N2 (300-450ms) and P3 (450–600) components can be observed at the midline electrode points of the frontal-parietal lobe (Fz et al.). Through repeated measurement ANOVA for the total mean amplitude of each electrode point at the midline by groups (HOC, LOC) * cue probability conditions (80%, 50%, 20%), we found that:
In the P2 component, the main group effect is not significant. The main effect of cue probability condition is significant with F(2,36) = 4.43, p = .02, η²=.20,1-β = .73. The interaction effect of clues probability conditions and group is significant with F (2,56) = 4.14, p = .02,η²=.19,1-β = .70 (as shown in Fig. 4). A further simple analysis showed no significant differences in the amplitude under the three cueing probability conditions in the high group. However, in individuals with LOC, there were significant differences in the amplitude under the three cue probability conditions with F(2,28) = 6.79, p = .006,η²=.38,1-β = .87 (Fig. 3).There are significant differences in the average amplitude under 50%. The results indicate that there are significant differences between the two groups under 80% (F (1,28) = 5.12,p = .04,η²=.22,1-β = .57) and 50% (F(1,28) = 5.75, p = .03,η²=.24,1-β = .62) probability conditions (Fig. 2). The amplitude of individuals with LOC was significantly higher than that of individuals with HOC. However, under the 20% probability condition, the difference between the two groups is insignificant.
In N2 and P3, the main effects of group and cue probability conditions were not significant, and the interaction effect was not significant either. The results showed that there were significant differences among individuals in both groups in N2 (F(1,28) = 6.48, p = .02,η²=.27,1-β = .67) and P3 (F(1,28) = 5.46, p = .03,η²=.23,1-β = .60) components under the 80% cue probability condition and the amplitude of the low-propensity individuals was significantly higher than that of the high-propensity individuals. In contrast, there were no significant differences among individuals in both groups in N2 and P3 components under 50% and 20% probability conditions.
3.2 Stimulus-related ERP
(1) Comparison of EEG differences between the two groups under three kinds of cue probability cues
In the stimulation stage, through the analysis and comparison of the relevant components of each electrode point, we found that the EEG response of individuals from the high and low groups under the three kinds of cue probability prompts would activate different EEG components at different stages, and the EEG differences under different conditions were particularly significant in different electrode points. By observing the average ERP waveform of the high and low groups under three kinds of cue conditions, it was found that there were prominent P2 (100–200), N3 (250–300), P3 (300–450) components in the frontal-parietal region, and obvious N2 (100–200), N3 (250–300) and P3 (300–450) components in the temporal occipital region. Through repeated measurement ANOVA for the total mean of the amplitude of each component at each brain region by groups (HOC, LOC) *cue probability conditions (80%, 50%, 20%), we found that:
In the N2 component of the posterior occipital region (PO7, PO8, POZ) (Fig. 5, taking PO8 as an example), the main group effect was insignificant, and the main cue effect was insignificant. The interaction effect of clues and group was effect with F(2,56) = 2.76, p = .07,η²=.13, 1-β = .51( Fig. 6). Further simple analysis showed that the amplitudes of the three kinds of cues were not significantly different in the high-propensity individuals. However, the amplitudes under the three cue probability conditions were significantly different among individuals with HOC with F(2,28) = 4.34, p = .03,η²=.33, 1-β = .68, and the amplitudes under 80% probability conditions were significantly higher than those under 20% probability conditions. The results showed no significant differences among individuals in both groups under the three cue probability prompts.
In the N3 component of the midline region (FZ, CZ, FCz) (Fig. 7, taking Cz as an example), the main group effect was not significant, and the main cue effect was not significant either. The interaction effect of clues and group was significant with F (2,56) = 4.92, p = .01,η²=.22,1-β = .77 (Fig. 8). Further simple analysis showed no significant differences among individuals with HOC under the three cue probability conditions. However, the differences among the individuals with LOC were significant with F(2,28) = 4.07, p = .04,η²=.31, 1-β = .65. The amplitude under the 80% probability condition was significantly higher than that under the 20% probability condition. The results showed no significant differences among individuals in both groups under the three cue probability prompts.
The analysis of P3 components showed that there were differences in multiple brain regions, and the differences were mainly reflected in the differences between groups, especially the electrodes in the left brain region (F3, C3, P3) and the occipital lobe (PO3, PO4, POz) (Fig. 9, C3 and PO3 as examples). ANOVA for the total mean of the amplitude of P3 components in these two brain regions showed that there were no significant differences in the main effect of cues and interaction in the occipital region, while the main group effect was significant with F(1,28) = 4.57, p = .046,η²=.20, 1-β = .53. Further analysis showed that under 80% (t = 2.19,p = 0.04) and 50% (t = 2.32,p = 0.03) probability conditions, the differences among individuals in both groups were significant. The amplitude of individuals with LOC was significantly more extensive than that of individuals with HOC, but the differences were insignificant under the 20% probability condition. In the left brain region, the main effect of cue and interaction was not significant, but the main effect of the group was significant with F(1,28) = 9.01, p = .01,η²=.33,1-β = .81. Further analysis showed that under the three probability conditions (80%: t = 2.88,p = 0.01; 50%: t = 3.11,p = 0.01; 20%:t = 2.57,p = 0.02),there were significant differences among individuals in both groups and the amplitude of individuals with LOC was significantly greater than that of individuals with HOC.
(2) Comparison of EEG differences between the two groups under cue validity
By observing the average ERP waveform of the two groups under both effective and ineffective cues, it was found that there were prominent P2 (120–200), N3 (230–300) and P3 (300–450) components in the frontal-parietal region. N2 (120–200), N3 (250–300), P3 (300–450) were found in the temporal occipital region. The analysis of these EEG components in both groups under the effective and ineffective cues showed that there were no significant differences in P2, N3 and P3 components, but there was a difference in N2, which was mainly reflected in the electrode points in the temporal occipital region (PO3, PO4, PO7 and PO8) (see Fig. 10). Through repeated measurement ANOVA for the total mean amplitude of N2 in this region by groups (HOC, LOC) * cue validity (valid cue, invalid cue), it was found that:
The main effect of the group was not significant, and the interaction effect of cue validity and group was not significant. However, the main effect of cue validity was significant with F(1,28) = 13.83, p = .002,η²=.43,1-β = .94. Further simple analysis showed that there were no significant differences in the amplitude of N2 components induced by effective cues and ineffective cues among individuals with HOC. However, there were significant differences among individuals with LOC in the amplitude of N2 induced by effective cues and ineffective cues with F(1,14) = 40.84, p < .001,η²=.82,1-β = 1.00, and the amplitude of N2 induced by effective cues was more significant than that induced by ineffective cues. The two groups had no significant differences under both effective and ineffective cues.