Computational techniques for reasoning about and shaping player experiences in interactive narratives
Roberts, David L.
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Interactive narratives are marked by two characteristics: 1) a space of player interactions, some subset of which are specified as aesthetic goals for the system; and 2) the affordance for players to express self-agency and have meaningful interactions. As a result, players are (often unknowing) participants in the creation of the experience. They cannot be assumed to be cooperative, nor adversarial. Thus, we must provide paradigms to designers that enable them to work with players to co-create experiences without transferring the system's goals (specified by authors) to players and without systems having a model of players' behaviors. This dissertation formalizes compact representations and efficient algorithms that enable computer systems to represent, reason about, and shape player experiences in interactive narratives. Early work on interactive narratives relied heavily on "script-and-trigger" systems, requiring sizable engineering efforts from designers to provide concrete instructions for when and how systems can modify an environment to provide a narrative experience for players. While there have been advances in techniques for representing and reasoning about narratives at an abstract level that automate the trigger side of script-and-trigger systems, few techniques have reduced the need for scripting system adaptations or reconfigurations---one of the contributions of this dissertation. We first describe a decomposition of the design process for interactive narrative into three technical problems: goal selection, action/plan selection/generation, and action/plan refinement. This decomposition allows techniques to be developed for reasoning about the complete implementation of an interactive narrative. We then describe representational and algorithmic solutions to these problems: a Markov Decision Process-based formalism for goal selection, a schema-based planning architecture using theories of influence from social psychology for action/plan selection/generation, and a natural language-based template system for action/plan refinement. To evaluate these techniques, we conduct simulation experiments and human subjects experiments in an interactive story. Using these techniques realizes the following three goals: 1) efficient algorithmic support for authoring interactive narratives; 2) design a paradigm for AI systems to reason and act to shape player experiences based on author-specified aesthetic goals; and 3) accomplish (1) and (2) with players feeling more engaged and without perceiving a decrease in self-agency.