Comparing LLM-Driven and Script-Based Non-Player Characters Under Controlled Information Boundaries: Effects on Task Performance, Immersion, and Satisfaction

This study examines NPC dialogue mechanisms as an independent design factor in task-oriented digital games. Although generative NPCs are often discussed in relation to narrative richness, conversational naturalness, and social presence, limited controlled evidence exists on whether dialogue mechanisms themselves affect player outcomes when task information is held constant. To address this gap, the study combined a formative user study with a single-factor between-subject experiment using a controlled game prototype. The LLM-NPC and Script NPC conditions shared identical task goals, scene structure, completion criteria, predefined fact set, and task-stage prompting boundaries. The experimental contrast was therefore framed as a comparison between a script-based branching dialogue interface and a boundary-controlled LLM-based adaptive dialogue interface, rather than as a comparison involving unequal task information. The results showed that, under controlled information boundaries, LLM-NPCs significantly improved task efficiency, as reflected in shorter completion time, fewer NPC inquiries, and fewer incorrect searches. For immersion, the overall multivariate effect was not statistically significant, and no confirmatory evidence of an LLM-NPC advantage in immersion was found. For satisfaction, the LLM-NPC condition showed significantly higher total satisfaction, which was specified as the primary satisfaction endpoint. Secondary affective and overall evaluative satisfaction outcomes showed consistent uncorrected differences in the same direction. These findings suggest that, under the implemented factual and procedural controls, the value of LLM-NPCs in this task-oriented setting is less likely to lie in providing more information than in reorganizing predefined task facts in a more context-sensitive and player-adaptive manner. Boundary-controlled adaptive dialogue may therefore provide a useful design perspective for future task-oriented NPC systems.