Figure 1. Experimental stimulus materials. A. A human allocation indirect reciprocity task. B. A computer allocation indirect reciprocity task. In order to avoid infringement of portrait rights, the photos of research members are used here as examples.

Figure 2. A. the standard dictator game distribution. B. the amount of money allocated to the third party when participates received the real person’s distribution below the social mean and the distribution above the social mean. C. the amount that participates with different levels of altruism allocated to a third party when they received a human allocation that was higher (lower) than the social mean. The horizontal and dotted lines in the figure represent the average social value of 2.548 yuan for this study. D. The amount of money allocated by participates in the four experimental conditions. The error bars in the figure represent standard errors. Small circles represent data for individual participates. *p < 0.05, **p < 0.01, ***p < 0.001.

Figure 3. Waveform map, topographic map and amplitude value of N1. The waveform shows the average amplitude of the PO5, PO6, PO7, PO8, O1 and O2. The topographic map is the average amplitude in the time window of 150~200 ms. The error bar in the figure represents standard error. Small circles represent data for individual participates. *p < 0.05.

Figure 4. Waveform map, topographic map and amplitude value of FRN. The waveform shows the average amplitude of the Fz, F1, F2, F3, F4, FCz, FC1, FC2, FC3 and FC4. The topographic map is the average amplitude in the time window of 200~250 ms. In order to more directly reflect the topographic map distribution of FRN, here is the difference topographic map: “below the social mean condition” minus “above the social mean condition”. ***p < 0.001

Figure 5. Waveform map, topographic map and amplitude value of P3. The waveform shows the average amplitude of Pz, P1, P2, P3, P4, CPz, CP1, CP2 and POz. The topographic map is the average amplitude of the time window 300~600 ms. ***p < 0.001