Artificial intelligence researchers attempting to create engaging, apparently living creatures may find important insight in the work of artists who have explored the idea of believable character. In particular, appropriately timed and clearly expressed emotion is a central requirement for believable characters. We discuss these ideas and suggest how they may apply to believable interactive characters, which we call "believable agents." This work was supported in part by Fujitsu Laboratories and Mitsubishi Electric Research Laboratories. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of any other parties.

The concept of an agent has recently become important in Artificial Intelligence (AI), and its relatively youthful subfield, Distributed AI (DAI). Our aim in this paper is to point the reader at what we perceive to be the most important theoretical and practical issues associated with the design and construction of intelligent agents. For convenience, we divide the area into three themes (though as the reader will see, these divisions are at times somewhat arbitrary). Agent theory is concerned with the question of what an agent is, and the use of mathematical formalisms for representing and reasoning about the properties of agents. Agent architectures can be thought of as software engineering models of agents; researchers in this area are primarily concerned with the problem of constructing software or hardware systems that will satisfy the properties specified by agent theorists. Finally, agent languages are software systems for programming and experimenting with agents; these languages typically embody principles proposed by theorists. The paper is not intended to serve as a tutorial introduction to all the issues mentioned; we hope instead simply to identify the key issues, and point to work that elaborates on them. The paper closes with a detailed bibliography, and some bibliographical remarks. 1

this article, we further motivate our proposal of using interactive computer games for AI research, review previous research on AI and games, and present the different game genres and the roles that human-level AI could play within these genres. We then describe the research issues and AI techniques that are relevant to each of these roles. Our conclusion is that interactive computer games provide a rich environment for incremental research on human-level AI

this paper we discuss our research and development towards creating an architecture, and a story design using this architecture, that integrates a broad and shallow approach to natural language processing, a novel character authoring language and a novel drama manager, in order to build an interactive drama about human relationships. Faade: an experiment in interactive drama In Faade, you, the player, using your own name and gender, play the character of a longtime friend of Grace and Trip, an attractive and materially successful couple in their early thirties. During an evening gettogether at their apartment that quickly turns ugly, you become entangled in the high-conflict dissolution of Grace and Trips marriage. No one is safe as the accusations fly, sides are taken and irreversible decisions are forced to be made. By the end of this intense oneact play you will have changed the course of Grace and Trips lives motivating you to replay the drama to find out how your interaction could make things turn out differently the next time. Figure 1. Real-time rendered characters Grace and Trip in Faade, with player-typed text and hand cursor. Faade is an attempt to create a real-time 3D animated experience akin to being on stage with two live actors who are motivated to make a dramatic situation happen. Instead of providing the player with 40 to 60 hours of episodic action and exploration in a huge world, we want to design an experience that provides the player with 20 minutes of emotionally intense, unified, dramatic action. The player's actions should have a significant influence on what events occur, which are left out, and how the drama ends. The experience should be varied enough that it supports replayability; only af...

This paper provides a brief description of the project goals and design requirements, discusses the problem of autonomy in the context of story-based believable agents, and finally describes an architecture that uses the dramatic beat as a structural principle to integrate plot and character

The Oz project is developing technology for high quality interactive fiction and virtual realities. An important aspect of this research is the development of intelligent, emotional agents to occupy these micro-worlds. We present here some preliminary work on Em, a implemented model of emotion for use in these agents. Em is based on the theoretical, cognition-based emotion model of Ortony, Collins, and Clore and has shown promise of being a flexible model of emotion.

We are studying how to create believable agents that perform actions and use natural language in interactive, animated, real-time worlds. Believable agents are autonomous agents that have specific, rich personalities like characters in movies and animation. We have extended Hap, the behavior-based architecture used by the Oz group to construct non-linguistic believable agents, to support natural language text generation. These extensions allow us to tightly integrate text generation with other aspects of the agent, including action, perception, inference and emotion. We describe our approach, and show how it leads to agents with properties we believe important for believability, such as: using language and action together to accomplish communication goals; using perception to help make linguistic choices; varying generated text according to emotional state; varying generated text to express the specific personality; and issuing the text in real-time with pauses, restarts and other brea...

Researchers studying autonomous agents are increasingly examining the problem of integrating multiple capabilities into single agents. The Oz project is developing technology for dramatic, interactive, simulated worlds. One requirement of such worlds is the presence of broad, though perhaps shallow, agents. To support our needs, we are developing an agent architecture, called Tok, that displays reactivity, goal-directed behavior, and emotion, along with other capabilities. Integrating the components of Tok into a coherent whole raises issues of how the parts interact, and seems to place constraints on the nature of each component. Here we describe briefly the integration issues we have encountered in building a particular Tok agent (Lyotard the cat), note their impact on the architecture, and suggest that modeling emotion, in particular, may constrain the design of integrated agent architectures.

Emotional reasoning can be an important contribution to auto- mated tutoring and training systems. This paper describes mile, a model of emotional reasoning that builds upon existing approaches and significantly generalizes and extends their capabilities. The main contribution is to show how an explicit planning model allows a more general treatment of several stages of the reasoning process. The model supports educational applications by allowing agents to appraise the emotional significance of events as they relate to students' (or their own) plans and goals, model and predict the emotional state of others, and alter behavior accordingly.

This research was funded in part through fellowships from the Litton and Intel Corporations. Any opinions, findings and conclusions or recommendations expressed in this publication are those of the author and do not necessarily reflect those of the sponsors.