Hierarchical Parallel Markov Models for Interactive Social Agents
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NORTHWESTERN UNIVERSITY HIERARCHICAL PARALLEL MARKOV MODELS FOR INTERACTIVE SOCIAL AGENTS A DISSERTATION SUBMITTED TO THE GRADUATE SCHOOL IN PARTIAL FULFILLMENT OF THE REQUIREMENTS for the degree DOCTOR OF PHILOSOPHY Field of Computer Science by ROBERT ZUBEK EVANSTON, ILLINOIS June 2005 © Copyright by Robert Zubek 2005 All Rights Reserved ii Abstract Hierarchical Parallel Markov Models for Interactive Social Agents Robert Zubek In this report I present hierarchical parallel Markov models for the creation of interactive social agents for video games and entertainment. The approach extends existing, popular character technologies for social, communicative interaction. First, adding the knowledge of temporal interaction structure enables natural language interaction on a time scale much longer than current chatterbot technologies. Second, adding support for hierarchical interaction decomposition, where an interaction is represented as a collection of smaller, simpler elements, simplifies the authoring of complex engagement. Third, adding support for the concurrent engagement of these elements enables engagement in interleaved, naturalistic communication. The resulting decomposition supports redundancy of representation, graceful performance degradation through the simultaneous engagement of behaviors on different levels of abstraction, and the stochastic approximation mechanism increases robustness in the face of noise and ambiguity. iii In this report, I present the details of hierarchical parallel Markov models, I examine two entertainment agents that use this technique, and explain the implementational details of how such an approach can be used in the development of future systems. iv Rodzicom, Katarzynie i Henrykowi. Przez nich wszystko się stało Co się stało. v Acknowledgements Albowiem nie szukamy tego co doskonałe, szukamy tego, co zostaje z nieustannego dążenia. / Pamiętając, ile znaczy traf szczęśliwy, zbieg słów i okoliczności, ranek z obłokami, który później wyda się nieuchronny. For we do not seek perfection, we seek that, which remains from endless pursuit. / Remembering how important is the stroke of luck, the coincidence of words and events, the morning with puffy clouds, that will later seem inevitable. — Czesław Miłosz, Do Alana Ginsberga. I have been lucky to be surrounded by great people. It is thanks to you that I first noticed what only later became significant, and first started working on what would eventually consume my passions. Who I am, I owe to you. First, I would like to thank my research group, a spectacular set of people whose company I will miss greatly: Ian Horswill, my advisor, a source of great inspiration over the decade I’ve known him, and whose support for my unorthodox research I will always appreciate; Robin Hunicke, who taught me all I know about game design; Aaron Khoo, an astute partner in research as well as gaming; Magy Seif El-Nasr, whose passion vi for interactive characters fueled my own; and Dac Le, Cuong Pham, and other students with whom I worked on robots and entertainment technologies. Many thanks go the members of the computer science department, especially Ken Forbus, who provided endless support and advice not only in my research work, but also in my undergraduate education, and Andrew Ortony, whose work on emotion was a great motivation, and who got me started on interactive characters in the first place. My friends inside and outside of the department made the entire experience immensely enjoyable, and I appreciate their advice, camaraderie, and indulging me in frequent shop talk about various items of geeky interest: Praveen Paritosh, whose thirst for knowledge was completely contagious; David Ayman Shamma, the rare exemplar of a scientist with artistic abilities, and an artist with scientific insight; Jason Skicewicz, who never sweats the small stuff; and Pinku Surana, who inspired me to see the world as full of solutions just waiting to be discovered. Special thanks go to Anna Szuber, for sharing her linguistic insight, which I will never be able to match; and former housemates Mark DePristo and Matt Hubenschmidt, who made grad school experience so enjoyable. Finally the greatest thanks go to my parents, for their unending support, and to my partner Matt, for his inspiration and encouragement, for keeping me sane and, really, for putting up with me for so many years. You were right—I miss it all already. vii Table of Contents Abstract ........................................................................................................................................ iii Acknowledgements .....................................................................................................................vi Table of Contents ...................................................................................................................... viii Table of Figures......................................................................................................................... xiii Table of Tables.............................................................................................................................xv Chapter 1. Introduction. ..............................................................................................................1 1.1. Motivation and Overview.................................................................................................2 1.2. Domain Constraints...........................................................................................................6 1.2.1. Authoring ....................................................................................................................7 1.2.2. Believability ................................................................................................................9 1.2.3. Efficiency ...................................................................................................................11 1.2.4. Constraints Reconsidered .......................................................................................13 1.3. Hierarchy and Parallelism..............................................................................................14 1.3.1. Hierarchy and Parallelism in Interaction.............................................................14 1.3.2. The Hierarchy Requirement...................................................................................16 1.3.3. The Parallelism Requirement.................................................................................18 1.3.4. The Hierarchical-Parallel Problem........................................................................23 1.4. Hierarchical Parallel Markov Models...........................................................................23 1.5. Contributions ...................................................................................................................25 viii 1.6. Dissertation Outline ........................................................................................................26 Chapter 2. Perspectives on Interaction. ..................................................................................28 2.1. Simple Techniques ..........................................................................................................29 2.1.1. Command Interfaces................................................................................................29 2.1.2. Nonstructural Techniques......................................................................................31 2.1.3. Menus and Conversation Trees..............................................................................36 2.2. Finite-State Dialog...........................................................................................................38 2.2.1. Finite-State Approach .............................................................................................39 2.2.2. Language Abstraction..............................................................................................40 2.2.3. Stochastic Dialogs.....................................................................................................41 2.2.4. Stochastic Model Decomposition and Coupling..................................................43 2.3. Plan-based Dialog ............................................................................................................48 2.3.1. Dialog as Activity......................................................................................................49 2.3.2. Mixed Approaches....................................................................................................52 2.4. Perspectives from the Social Sciences .........................................................................54 2.4.1. Situated Action .........................................................................................................54 2.4.2. Conceptual Structures.............................................................................................58 2.5. Personal Perspective: Towards a New Model..............................................................60 2.5.1. Structure in Interaction ..........................................................................................61 2.5.2. Interactions Tend Towards Structure...................................................................63 2.5.3. Virtual World Simplifies Ontology ........................................................................65 2.5.4. Proceduralizing Émigrés.........................................................................................67