Fig 1. Task designs of two experiments.

In the ultimatum game (A), each trial started with the presentation of a total amount of money (e.g., ¥20) which would be divided by the proposer. After 5.5 s, the monetary outcomes for both the participant and for the partner were displayed. The outcomes were presented for 3 s. Then, the participant was required to choose whether to accept the offer or reject the trial within 5 s. Finally, the feedbacks were shown according to the participant’s choice. In the social comparison game (B), each trial started with the presentation of a roulette wheel; the participant was then asked to press the Q key to make the roulette wheel run. After 3.5 s, the monetary outcomes for both the participant and for the partner were displayed. The outcomes were presented for 3 s. Then, the participant was required to choose whether to save the results or repeat the trial within 5 s. Finally, the feedbacks were shown according to the participant’s choice.