GLaDOS: Integrating Emotion-Based Behaviours into Non-Player Characters in Computer Role-Playing Games

Abstract

Non-Player Character (NPC) believability is a game aspect that can be exploited to increase a game's replayability, but little research has been conducted on the topic. One method for enhancing a NPC's believability is to integrate human-like behaviours into their design, so that they react to players in a realistic and interesting way. A large part of human behaviour can be explained by their emotions; therefore it was selected as the inspiration for the GLaDOS system.

Two psychological theories of emotion, Lazarus's cognitive appraisal and Plutchik's psycho-evolutionary synthesis, guided the design of the GLaDOS system, although several components are not unique to these theories. An implementation of the design was created as a "mod" for the popular CRPG "The Elder Scrolls V: Skyrim" to test its feasibility within the context of a commercial game. This task required an additional psychological model, PAD space, to map appraisal values to emotion codes and intensities. Feasibility testing was done via a user study to determine if the GLaDOS system increases player engagement when compared to the original game. While the objective analysis found that there were no significant differences between the two versions, subjective participant responses expressed a strong affinity for the GLaDOS system. Since player engagement is inherently subjective, it is encouraging to see positive responses from participants. This indicates that the GLaDOS system, and NPC believability in general, is one aspect of video games that has the potential to increase a game's replayability and should be investigated further.