Biofeedback interaction offers interesting opportunities for video games since it allows player physiological information to be used in novel interaction techniques. Despite several contributions in the area, biofeedback interaction faces a set of challenges relating to its design and implementation. First, it has mainly been used as a method to replace more traditional interaction devices, such as gamepads, mice or keyboards. Also, few of the previous interaction techniques have made an essential use of physiological data: exploring possibilities that could only be developed by involving physiological inputs.

This dissertation explores how different physiological methods, such as electroencephalography, eye tracking, electrocardiography, electrodermal activity, or electromyography, could be used in the design and development of natural user interaction techniques that might be applied to entertainment video games, highlighting technical details for the appropriate use of physiological signals. The research also discusses interaction design principles from a human-computer interaction perspective, evaluates several novel biofeedback interaction techniques with a set of user studies, and proposes ethical considerations for the appropriate exposure to virtual reality and physiological sensor technology.

Results show that the use of biofeedback inputs in novel interaction techniques, vary in complexity and functionality depending on the type of measurements used. They also showed that biofeedback interaction can positively affect player experience since it allows games and virtual reality applications to synchronize with player physiology, making of playing games a personalized experience. Results highlighted that biofeedback interaction can significantly affect player performance, being influenced by the interaction complexity and the reliability of the sensor technology used.

Psychophysiological interaction offers the opportunity of delivering unique and innovative experiences that synergize with human physiological and psychological nature. Even though several publications have explored the use of psychophysiological interaction in video games in the past, there is still a set of challenges associated with its suitability for commercial entertainment games, and with the assessment of its relationship with the perceived player experience.

This dissertation explores psychophysiological interaction and its implementation within entertainment video games. It presents a review of multiple physiological methods, such as eye tracking, electrodermal activity, or electroencephalography, and discusses the possibilities and challenges that these methodologies offer for the design and implementation of natural user interaction techniques. The dissertation presents a set of user studies that evaluated the efficiency of psychophysiological interaction in desktop and virtual reality video games, and statistically assessed how the variations of player physiological data may relate to their respective changes in the perceived player experience. The dissertation also offers a set of ethical and methodological guidelines for the appropriate design of novel interaction techniques, and for the safe exposure of physiological sensors and virtual reality technologies to the general public.

The results obtained from this research show that the implementation of psychophysiological interaction in entertainment video games tends to positively affect player experience. However, this benefit comes as a tradeoff to player performance and their perceived sense of control. Additionally, the variations in electrodermal activity data, specifically in the skin conductance level, showed a tendency to correlate with negative player experience variables. Finally, psychophysiological interaction should be consistent with the natural behavior and reactions from players, and should be complementary to more traditional game interaction technologies.