Does attachment to money affect reciprocity behaviour?

In this study, we test experimentally how a player who must decide how much money to transfer back in a trust game is affected by the experiment's monetary incentive. We find that positive reciprocity or altruism in a trust game is affected by the player's attachment to the money he received. We also argue that in a trust game played with virtual money, the players are affected by their willingness to punish the other player, consistent with the 'altruistic punishment' hypothesis.