Successfully Defended My Dissertation

Today, I successfully defended my dissertation, titled Behavioral Biometrics in Extended Reality: Implicit User Authentication Through Artificial Intelligence, at the University of Duisburg-Essen. I am delighted and deeply grateful that the dissertation was awarded summa cum laude.

As extended reality (XR) systems become more widely used, protecting them from unauthorized access becomes increasingly important. Conventional authentication methods such as passwords and PINs can be cumbersome in virtual environments and may be exposed to observers. My dissertation therefore explores a different approach: identifying users implicitly and continuously through their characteristic body movements and interactions in augmented and virtual reality.

Across six empirical studies, the dissertation investigates which aspects of human behavior can serve as reliable biometric signals and which factors influence recognition performance. These include movement components, physiological characteristics, colocated interactions, changes over time, gaze and head behavior, and fine-grained hand and finger movements. The results show that behavioral biometrics can enable reliable user identification in XR, while also highlighting the importance of study design, temporal stability, fair evaluation, and the ethical handling of sensitive biometric data.

This dissertation brings together research conducted between 2019 and 2025. I am sincerely grateful to everyone who contributed to this journey through collaboration, discussion, technical support, study participation, and encouragement.

My deepest thanks go to my supervisor and first reviewer, Prof. Dr. Stefan Schneegaß, for giving me the opportunity to pursue this doctorate and for his guidance, ideas, and continuous support throughout the years. I would also like to thank my reviewers, Prof. Dr. Florian Alt and Prof. Dr. Antonio Krüger, for their time, thoughtful assessment, and valuable feedback. I am equally grateful to Prof. Dr. Gregor Schiele and Prof. Dr. Volker Gruhn for serving on and chairing the examination committee.

The dissertation is available open access through DuEPublico and can also be downloaded directly as a PDF.