Figure 1

Overview of how game type, fairness, social preferences, and responder actions vary with biophysical responses to offers. Panels (A–C) show a step-by-step breakdown of the three-way interaction of offer (fair/unfair), game (UG/IG) and social preference (prosocial/individualistic) on the MFN. Presented are event-related waveforms (P2 and MFN on the 10/20 EEG locations FC1, Fz, and Cz) in response to the offers showing the statistically relevant effects, and current source density (CSD) maps to visualize an estimation of the location of the underlying source in the brain. Panel (A) Waveforms across both games: The MFN is stronger in response to unfair compared to fair offers. Panel (B) Waveforms for UG and IG offers separately: Only in the UG is the MFN stronger in response to unfair compared to fair offers. Panel (C) Waveforms separately for prosocial and individualistic responders to UG offers: Only in prosocial responders are the P2 and MFN stronger in response to unfair compared to fair UG offers. Panel (D) CSD map illustrating the amplification and left-frontal shift of the MFN in prosocial responders after receiving unfair UG offers that are accepted versus those that are rejected. Panel (E) Estimated marginal means with standard errors of the averaged EMG-activity (2 s) of the ‘frown’ (corrugator supercilii) and ‘smile’ (zygomaticus major) muscles in response to fair and unfair offers in the IG and UG for individualistic (Ind) and prosocial (Pro) responders. Only for prosocial responders in the IG do we see that unfair offers evoke more frowning. Significance levels come from two-level regression models with asterisks indicating the significance of the relevant comparisons: *p < 0.05, **p < 0.01, ***p < 0.001 (see Tables S2.6–S2.11). All CSD maps are based on the average signal between 260 and 300 ms after the offers, which is also the interval used for the analyses of the MFN, indicated with yellow areas in the waveform graphs.