Does Random Movements mean Random Results? Why Asynchrony in Experiments on Body Ownership does not Work as Intended

Effects of embodying virtual avatars are routinely validated experimentally by comparing synchronous and asynchronous movements between virtual and real bodies. This experimental paradigm, however, lacks justification, validation, and standardization. Asynchrony is implemented in numerous ways, such as through delayed, dislocated, or prerecorded movements, and these may impact embodiment and user experience distinctively. An online study ($N = 202$) revealed that variations of asynchrony cause disparate responses to embodiment and user experience, with prerecorded movements distorting embodiment the most. A think-aloud study ($N = 16$) revealed that asynchronous conditions lead to peculiar and oftentimes negative experiences. Furthermore, asynchronous conditions in some cases maintain, rather than break the body ownership illusion, as participants imitate the virtual body. Our results show that asynchrony in experiments on embodiment entails profound validity issues and should therefore be used with caution.