http://arstechnica.com/gaming/2013/05/u ... f-legends/
They even experimented on changing how players think:
Riot Games decided to experiment with priming players by introducing game tips that would be shown to players on loading screens, during gameplay, or both. The tips were divided into five categories, including commentary on positive behavior (“If you cooperate with your teammates you’ll actually win more games.”), negative behavior (“If you engage in toxic behaviors you’ll be punished by our Tribunal system.”), and self-reflection (“Who will be the most sportsmanlike player in this particular game?”). These priming messages could also be displayed in red, blue, or white, a decision spurred by other priming experiments that showed font color could affect test performance in different ways in different cultures.