Each block started with a new pair of symbols and consisted of 16 trials/choices. This way participants learned which symbol to choose to maximize the rewards in the long run. In addition, when participants were observed, a red frame was shown on their computer’s screen and the displays of the participants’ computers were transmitted onto the observers‘ laptop screens. The observers were seated at a desk with a laptop and had an equal view of all the participants. In the observed condition, two female observers, introduced as NGO association representatives entered the room and watched participants perform the task. In the private condition, participants were informed that their performance is completely anonymous and no one (including the experimenter) would know how much money they would earn for themselves and the charitable organization. After data collection was complete, saliva samples were analyzed by liquid chromatography-tandem mass spectrometry.
