This research shows that in an experimental game it is the perception of an actual relationship, of an interaction with the other person more than the nature of the game which creates a climate in which cooperative responses can be established. Cooperative sets can be induced through the Representation of the partner: a reactive partner promoting cooperation, and a rigid one promoting competition. In addition it is noted that in order to understand the reactions induced by the partner's behavior, the behavior in itself it not sufficient. Indeed it is interpreted and understood in terms of the initial representation. The analysis of a person's behavior when in relation with another, should be based on a joint study of the existing representations and of the actual behavior observed.