Recipients often reject unfair offers at the cost of their own interests in ultimatum games (UGs), reflecting their fairness preference. Yet fairness preference is not invariable. It is affected by various factors, among which empathy plays an important role. Individuals might, for example, sacrifice own interests to help others in need. This kind of behavior not only is contrary to the pursuit of self-interest maximization but also violates fairness principles. As individuals are not only concerned about fairness but also care for others, this study focuses on managing the relationship between the two potentially conflicting goals. We explored individuals' behaviors and time dynamic processes of brain activities when fairness conflicted with empathy. It was hypothesized that empathy could modulate fairness-related decision making behaviors and ERPs. Thirty-seven college students (26 females, 21.00 +/- 2.07 years) participated in this study and completed multiple ultimatum games. EEG signals were recorded during play. In the task, the proposers were underprivileged students (empathy condition) and ordinary children (non-empathy condition). Each proposer distributed 10 yuan between themself and one recipient. The participants played as recipients who would choose to accept or reject distribution offers (fair, disadvantageous unfair, advantageous unfair) by the proposers. The proposers and recipients would get the assigned money only if participants accepted the distribution offers. They received nothing if participants rejected the offer. The behavioral results showed that the acceptance rate in the empathy condition was greater than that in the non-empathy condition for the disadvantageous unfair condition, while the opposite result occurred in the advantageous unfair condition. The EEG results showed that in the non-empathy condition, the advantageous unfair offer induced more negative anterior NI (AN1) than it did in the empathy condition, but there was no difference between the disadvantageous unfair versus fair conditions. In the advantageous unfair condition, the P2 amplitude of the empathy condition was significantly more positive than that for the non-empathy condition, while in the disadvantageous unfair condition, P2 amplitude of the non-empathy condition was slightly positive than that of the empathy condition. The disadvantageous unfair offer induced more negative medial frontal negativity (MFN) in the empathy condition, while no difference was found between fair versus unfair offers in the non-empathy condition. Additionally, the amplitude of P3 was larger in the fair versus the unfair conditions as it was not modulated by empathy. These findings suggest that experimentally-induced state empathy modulates fairness-related decision making behaviors and accompanying neural activity. Behavioral results indicate that state empathy takes priority in guiding people's behavior when it conflicts with the fairness criterion. For EEG results, empathy mainly modulates the early stage of the fairness concern and affects early attention and motivation as well as cognition and emotion. In later stages, the higher cognitive process represented by P3 is modulated only by fairness, not empathy. In conclusion, our study systematically explored and compared behavior patterns of fairness processing with temporal dynamic characteristics of brain activities by modulating empathy. The findings provide further insight into fairness-related decision making behaviors. They indicate the potential to influence individuals' behaviors and cognition by manipulating empathy.
