Dealing with the Emotions of Non Player Characters

Usually in games, the interaction between player and NPCs are very limited and does not allow the spontaneous creation of long-term relationships. The NPCs are cold, direct and faithfully follow his instructions while keeping a well-defined pattern of behavior. The present paper proposes a model to ease the way NPCs act and react, based on human psychology and simulation of emotions. Therefore, the emotions are used to modify the mental state of the NPC, enabling decisions for different reactions and the same event. Each NPC has a personality described using the OCEAN model that is commonly used by psychologists to determine an individual personality. The personality description of a NPC determines how the emotional stimuli are interpreted differently and its current emotions are calculated based on the influential emotion generated by an event and its personality. Finally, state machines are used taking into account human emotions and the individual personality of each NPC, allowing the player to be friend or foe of NPCs depending on their actions with each NPC. This model has been used to develop an experimental game has shown excellent results. In this game, the player plays the role of an adventurer who explores exotic lands and meet creatures (NPCs) that at first may not react to their presence. If the player decides to attack the NPCs, will react by attacking, evading, or becoming friends depending on their personality modeled through a Big Five test.