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Author: 劉昆麟
Keun-Lin Liu
Thesis Title: Affective Computing for Computer Games: Bots with Emotions
Affective Computing for Computer Games: Bots with Emotions
Advisor: 何正信
Cheng-Seen Ho
李漢銘
Hahn-Ming Lee
Committee: 陳錫明
Shyi-Ming Chen
李蔡彥
Tasi-Yen Li
王榮英
Jung-Ying Wang
Degree: 碩士
Master
Department: 電資學院 - 資訊工程系
Department of Computer Science and Information Engineering
Thesis Publication Year: 2008
Graduation Academic Year: 96
Language: 英文
Pages: 96
Keywords (in Chinese): 情感運算遊戲人工智慧情緒
Keywords (in other languages): Affective Computing, Game AI, Emotion, Finite State Machine
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Games are one of the the most popular applications of Artificial Intelligence (AI) techniques. From trivial games like Pac-Man to modern complex MMORPG (Massively multiplayer online role-playing game), e.g., World of Warcraft, we can see AI techniques have been widely applied in computer games or video games in the past 30 years. A non-player character (NPC) is the major target a player interacts with in a game, and we usually call an NPC a “game bot” or simply a “bot” in an FPS (First person shooter) game. The intelligence of a bot often decides the durability, difficulty, and joyfulness of an FPS game. A poor bot design makes the players feel bored, and dramatically decreases the attraction of a game, so appropriate intelligence is definitely a must for the game bots of FPS games.
Game AI has some special characteristics to differ it from Academe AI. Since the major purpose of a computer game is to entertain people, a bot must be fast, effective, robust, and efficient, which are reckoned as the four requirements in game bot design, according to the best user gaming experiences. Therefore, no matter how good the AI techniques are, it would be unacceptable if they can’t provide the users with satisfactory experience of fun. This specific and strong user demand makes game AI design more and more important. The cutting edge technology, which can offer more sophisticated computer power, at the same time, makes game AI design more and more feasible.
Most game AI designers use scripting or rules to control bot behavior. Just like traditional AI applications, game AI mainly focuses on rational inference. But in the real world, human decision making is not only involving rationality, but also sense. In this thesis, we propose an architecture for the bot designers to include affective computing in a game bot by attributing emotions to the bot. The architecture is based upon a variety of theories, including the famous OCC model. It treats Joy, Fear, Anger, Disgust, and Distress as five basic emotions. It uses three emotional variables, namely, Desirability of an event, Blameworthiness or Praiseworthiness of an action, and Appealingness of an object, to evaluate how a specific emotion is affected by the environment. In addition to an ordinary Rational Action Engine (RAE), which controls the rational behavior of a bot, we add an Emotional Action Engine (EAE) in the architecture to make the emotional behavior possible. An Action Arbitrator is equipped to decide, given a specific time and space, whether a bot should follow the rational or emotional inference. The arbitrator simulates how humans solve the conflicts between reason and emotion.
Our testing bed is Quake II enhanced by FEAR (Flexible Embodied Animat ‘Rchitecture), on which we have followed the architecture to create a rational bot, whose behavior is solely controlled by the RAE. The RAE is implemented as a rational FSM (Finite State Machine) containing four states: Exploring, Offense, Defense, and Gathering. It decides by logical inference how proper actions and knowledge are used for a bot to win the game. We have also created a second bot that includes both RAE and EAE. The EAE is implemented as an emotional FSM containing five states: Joviality, Fright, Fury, Loathing, and Chaos. Each emotional state represents a basic emotion, and decides what actions should be taken when a specific emotion is strong enough. Our evaluation shows, compared with the behavior of a rational bot, an emotional bot can exert more realistic feedback from the player’s point of view and exhibit richer behavior in a battlefield. This means an emotional bot can bring more fun to the human players in the simulation and improve the game play experience. The most important thing is that these newly add-on emotion-relevant functions won’t break the four requirements in the game bot design.


Games are one of the the most popular applications of Artificial Intelligence (AI) techniques. From trivial games like Pac-Man to modern complex MMORPG (Massively multiplayer online role-playing game), e.g., World of Warcraft, we can see AI techniques have been widely applied in computer games or video games in the past 30 years. A non-player character (NPC) is the major target a player interacts with in a game, and we usually call an NPC a “game bot” or simply a “bot” in an FPS (First person shooter) game. The intelligence of a bot often decides the durability, difficulty, and joyfulness of an FPS game. A poor bot design makes the players feel bored, and dramatically decreases the attraction of a game, so appropriate intelligence is definitely a must for the game bots of FPS games.
Game AI has some special characteristics to differ it from Academe AI. Since the major purpose of a computer game is to entertain people, a bot must be fast, effective, robust, and efficient, which are reckoned as the four requirements in game bot design, according to the best user gaming experiences. Therefore, no matter how good the AI techniques are, it would be unacceptable if they can’t provide the users with satisfactory experience of fun. This specific and strong user demand makes game AI design more and more important. The cutting edge technology, which can offer more sophisticated computer power, at the same time, makes game AI design more and more feasible.
Most game AI designers use scripting or rules to control bot behavior. Just like traditional AI applications, game AI mainly focuses on rational inference. But in the real world, human decision making is not only involving rationality, but also sense. In this thesis, we propose an architecture for the bot designers to include affective computing in a game bot by attributing emotions to the bot. The architecture is based upon a variety of theories, including the famous OCC model. It treats Joy, Fear, Anger, Disgust, and Distress as five basic emotions. It uses three emotional variables, namely, Desirability of an event, Blameworthiness or Praiseworthiness of an action, and Appealingness of an object, to evaluate how a specific emotion is affected by the environment. In addition to an ordinary Rational Action Engine (RAE), which controls the rational behavior of a bot, we add an Emotional Action Engine (EAE) in the architecture to make the emotional behavior possible. An Action Arbitrator is equipped to decide, given a specific time and space, whether a bot should follow the rational or emotional inference. The arbitrator simulates how humans solve the conflicts between reason and emotion.
Our testing bed is Quake II enhanced by FEAR (Flexible Embodied Animat ‘Rchitecture), on which we have followed the architecture to create a rational bot, whose behavior is solely controlled by the RAE. The RAE is implemented as a rational FSM (Finite State Machine) containing four states: Exploring, Offense, Defense, and Gathering. It decides by logical inference how proper actions and knowledge are used for a bot to win the game. We have also created a second bot that includes both RAE and EAE. The EAE is implemented as an emotional FSM containing five states: Joviality, Fright, Fury, Loathing, and Chaos. Each emotional state represents a basic emotion, and decides what actions should be taken when a specific emotion is strong enough. Our evaluation shows, compared with the behavior of a rational bot, an emotional bot can exert more realistic feedback from the player’s point of view and exhibit richer behavior in a battlefield. This means an emotional bot can bring more fun to the human players in the simulation and improve the game play experience. The most important thing is that these newly add-on emotion-relevant functions won’t break the four requirements in the game bot design.

ABSTRACT..................................................................................................................v ACKNOWLEDGEMENT...........................................................................................vii TABLES OF CONTENTS.........................................................................................viii LIST OF TABLES........................................................................................................x LIST OF FIGURES......................................................................................................xi Chapter 1 Introduction...................................................................................................1 1.1 Background..........................................................................................................1 1.2 Motivation...........................................................................................................2 1.3 Problem Specifications........................................................................................4 1.4 Proposed Solution................................................................................................4 1.5 Contribution.........................................................................................................5 1.6 Organization of the Thesis...................................................................................6 Chapter 2 Relative Research..........................................................................................7 2.1 Dissection of Emotions........................................................................................7 2.1.1 Role of Emotions..........................................................................................7 2.1.2 Generation of Emotions................................................................................8 2.1.3 Characteristics of Emotions........................................................................11 2.2 Emotion Model..................................................................................................12 2.3 Emotion in Games.............................................................................................21 Chapter 3 System Design............................................................................................25 3.1 Design Philosophy.............................................................................................26 3.1.1 Basic emotions............................................................................................26 3.1.2 Limited resources.......................................................................................28 3.1.3 Behavior-centered instant reactions...........................................................30 3.1.4 Emotional behavior....................................................................................34 3.1.5 Interactions between rational and emotional actions..................................37 3.2 Emotional State.................................................................................................38 3.2.1 Valence and intensity of emotions.............................................................38 3.3 Rule system for AI-relevant computing............................................................42 3.4 Rational Action Engine.....................................................................................44 3.5 Emotional Action Engine..................................................................................46 3.6 Arbitration between RAE and EAE..................................................................50 Chapter 4 System Implementation..............................................................................55 4.1 Development environment................................................................................55 4.1.1 The game....................................................................................................55 4.2 System implementation.....................................................................................58 4.2.1 The Design phase.......................................................................................59 4.2.2 The Programing phase................................................................................61 4.2.2.1 Berit: a born-to-kill fighter..................................................................62 4.2.2.2 Candy: a careful hunter........................................................................63 4.3 System evaluation..............................................................................................66 4.3.1 Observation on behavior from RAE...........................................................67 4.3.2 Observation on behavior from RAE + EAE...............................................68 Chapter 5 Conclusions and Discussions......................................................................72 viii 5.1 Conclusions.......................................................................................................72 5.2 Contributions.....................................................................................................74 5.3 Discussions........................................................................................................75 5.4 Future work.......................................................................................................78 Reference.....................................................................................................................80 Appendix A Rules for RAE and EAE.........................................................................82

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