Drive-Based Behavior Modeling for Emotionally Responsive NPCs

• Luís Fernando Bicalho PUC-Rio
• Augusto Baffa PUC-Rio
• Bruno Feijó PUC-Rio

DOI: https://doi.org/10.5753/sbgames.2025.10309

Resumo

Introduction: In recent years, the development of more believable and emotionally responsive non-player characters (NPCs) has become a growing research focus. To improve immersion and behavioral realism, many models have incorporated psychological and neuroscientific theories to simulate emotion-driven decision-making. Objective: This work proposes a computational model that integrates internal needs, emotional states, and neurotransmitter simulation to create NPCs capable of dynamic, contextsensitive behavior grounded in human psychological principles. Methodology or Steps: The model draws from Hull’s drive theory, Maslow’s hierarchy of needs, and Lövheim’s Cube of Emotion. Internal variables—such as hunger, fatigue, social need, and safety—modulate neurotransmitter levels (dopamine, serotonin, noradrenaline), generating emotional states. These emotions influence behavioral transitions in an extended Finite State Machine (FSM). A prototype developed in the Godot Engine was used to simulate and evaluate the system. Results: Simulation results demonstrate that NPCs exhibit behavior consistent with psychological expectations, including appropriate emotional triggers and adaptive decision-making. The proof-of-concept highlights the potential of the model for applications in games, simulations, and narrative systems, offering a scalable foundation for emotionally intelligent agents.

Palavras-chave: Theory of needs and drives, Emotion Modeling, Lövheim Cube, Plutchik’s Wheel, Neuroscience-inspired AI, Dynamic Emotional Responses, Behavioral Simulation, Emotion-driven NPCs

Referências

Baffa, A., Sampaio, P., Feijó, B., e Lana, M. (2017). Dealing with the emotions of non-player characters. In Proceedings of the XVI Symposium on Games and Digital Entertainment (SBGames), pages 1–10, Curitiba, Brazil. SBC. Available online.

Barros, P., Carneiro, P., e Paiva, A. (2020). Modeling affect in game characters: A review of affect-driven behavior in npcs. IEEE Transactions on Affective Computing, 11(3):398–411.

Beaudoin, L. P. (1994). Goal processing in autonomous agents. In Proceedings of the AAAI Spring Symposium on Goal-Driven Behavior, pages 1–9.

Belle, S., Gittens, C., e Graham, T. N. (2022). A framework for creating non-player characters that make psychologically-driven decisions. In 2022 IEEE International Conference on Consumer Electronics (ICCE), pages 1–6. IEEE.

Bicalho, L. F., Feijó, B., e Baffa, A. (2020). A culture model for non-player characters’ behaviors in role-playing games. In 2020 19th Brazilian Symposium on Computer Games and Digital Entertainment (SBGames), pages 71–80. IEEE.

Bostan, B. (2009). Player motivations: A psychological perspective. In Proceedings of the International Conference on Online Communities and Social Computing, pages 282–289. Springer.

Bostan, B. e Kaplancali, U. (2009). Explorations in player motivations: Game mods. In Proceedings of the 2009 GAMEON-Asia Conference, pages 1–8. EUROSIS.

Bostan, B. e Sezen, D. (2022). Player needs inventory (pni): An analytical framework for analyzing player motives in video games. In Proceedings of the 23rd International Conference on Intelligent Games and Simulation (GAME-ON 2022), pages 41–47, Lisbon, Portugal. EUROSIS.

Cannon, W. B. (1932). The Wisdom of the Body. W. W. Norton & Company. Introduces the “fight-or-flight” response, describing how fear triggers physiological changes leading to escape or defensive actions.

Fernandes, P. d. T., Baffa, A., e Feijó, B. (2024). An emotion model for non-player characters inspired by neurotransmitters. In Proceedings of the 2024 Brazilian Symposium on Computer Games and Digital Entertainment (SBGames), pages 1–10. SBC.

Gratch, J. e Marsella, S. (2004). A domain-independent framework for modeling emotion. Cognitive Systems Research, 5(4):269–306.

Han, S. (2022). A study on the psychology of game design based on the hierarchical theory of needs. In Proceedings of the 2022 3rd International Conference on Mental Health, Education and Human Development (MHEHD 2022), volume 670 of Advances in Social Science, Education and Humanities Research, pages 1343–1347. Atlantis Press.

Hull, C. L. (1943). Principles of Behavior. Appleton-Century-Crofts, New York. Introduced the Drive Reduction Theory of motivation.

Laird, J. E. e van Lent, M. (2001). Human-level ai’s killer application: Interactive computer games. AI Magazine, 22(2):15–25.

Lopes, R., Zambetta, F., e Bidarra, R. (2021). Towards emotion-driven procedural generation. In Proceedings of the 2021 IEEE Conference on Games (CoG), pages 1–8. IEEE.

Lövheim, H. (2012). A new three-dimensional model for emotions and monoamine neurotransmitters. Medical Hypotheses, 78(2):341–348. Elsevier. Umeå, Sweden. [e-mail].

Maslow, A. H. (1943). A theory of human motivation. Psychological Review, 50(4):370– 396.

Murray, H. A. (1938). Explorations in Personality. Oxford University Press, New York. Introduced the theory of psychogenic needs.

Ou, H. (2025). Ai-powered npcs in virtual environments: Creating believable characters through machine learning. In Proceedings of the 3rd International Conference on Software Engineering and Machine Learning.

Park, J.-S., O’Brien, J., Cai, C. J., Morris, M. R., Liang, P., e Bernstein, M. S. (2023). Generative agents: Interactive simulacra of human behavior. In Proceedings of the 36th Annual ACM Symposium on User Interface Software and Technology, pages 1– 22, New York, NY, USA. ACM.

Patzer, B., Chaparro, B. S., e Keebler, J. R. (2020). Developing a model of video game play: Motivations, satisfactions, and continuance intentions. Simulation & Gaming, 51(3):287–309.

Plutchik, R. (1980a). Chapter 1 - a general psychoevolutionary theory of emotion. In Plutchik, R. e Kellerman, H., editors, Theories of Emotion, pages 3–33. Academic Press.

Plutchik, R. (1980b). A general psychoevolutionary theory of emotion. In Plutchik, R. e Kellerman, H., editors, Theories of Emotion, pages 3–33. Academic Press. Characterizes sadness as a low-arousal negative emotion associated with conservation-withdrawal behaviors such as rest and disengagement.

Reisenzein, R., Meyer, W.-U., e Niepel, M. (2012). Surprise. In Encyclopedia of Human Behavior. Elsevier, Amsterdam, 2nd edition. “Surprise is the mental reaction to unexpectedness. . . ”.

Wardhana, M. I. (2023). Emotion-driven behavior of game characters. In Proceedings of the International Conference on Art, Design, Education and Cultural Studies (ICADECS). KnE Social Sciences.

Yannakakis, G. N. e Hallam, J. (2009). Real-time game adaptation for optimizing player satisfaction. IEEE Transactions on Computational Intelligence and AI in Games, 1(2):121–133.