Affective Decision Making in Artificial Intelligence : Making Virtual Characters With High Believability

Sammanfattning: Artificial intelligence is often used when creating believable virtual characters in games or in other types of virtual environments. The intelligent behavior these characters show to the player is often flawed, leading to a worse gameplay experience. In particular, there is often little or no emotional impact on the decision making of the characters. This thesis focuses on extending decision-making and pathfinding mechanisms for virtual characters, with a particular focus on the use of emotions. The thesis is divided into three parts.The first part is an introductory study concerning the requirements designing a believable virtual character places on the architecture used. Gameplay design patterns are used as a tool to analyze the proposed agent architecture and discussions are presented regarding the necessary properties of such an architecture with respect to gameplay.The second part extends two action selection mechanisms to include emotional impact. In particular, behavior networks are extended to take complex emotional impact into account, including emotional parameters, emotional goals, and emotional influences.Moreover, time-discounting is introduced into behavior networks as a factor in the decision making. The time-discounting is also under emotional influence. The second action selection mechanism extended to use emotional impact is behavior trees. Since behavior trees are widely used by game designers, allowing full control over the characters’ behaviors, the work in this thesis proposes a new type of emotional selector which only affects a part ofthe behavior tree, leaving the control in the hands of the designer.The third part focuses on more complex pathfinding where more factors than finding the shortest collisionfree path through an environment are considered. A new type of visibility map is introduced. Using the knowledge of the virtual character about previous enemy positions, a more accurate visibility map is created. The visibility map is used for covert pathfinding, where the character tries to find a path through an environment while trying to minimize the risk of being seen by the enemy. Finally, a new kind of pathfinding, emotional pathfinding, is introduced, based on the use of emotion maps. Humans often have emotional attachment to geographical locations because they have previously felt emotions at those locations. This approach takes advantage of this knowledge and enables a virtual character to find a path through an environment that is as emotionally pleasant as possible.