Figure 2. Examples of round and associated ranking proposed to the participant during phase 1.

A) Example of one round of the game during phase 1. In this game, the participant was asked to decide which side of the screen contained the largest amount of dots. B) Example of three-level ranking presented to the participant after each round of the game. Participant's face was the only photograph displayed in color during this phase. All the subjects of the photographs used here have given written informed consent, as outlined in the PLOS consent form, to publication of their photograph.