Embodiment of a functionally altered virtual arm in adults and children

Why can we learn to feel ownership over some non-human body parts, but not others? One potentially critical yet underexplored factor is the functionality of the given body part. This study addressed the contribution of body function to embodiment by examining how participants embodied a dynamic virtual arm with altered function. To understand the full extent of how flexible embodiment might be, participants included children as well as adults. Participants used a virtual arm to feed animals within an immersive environment. Reach functionality was systematically manipulated by adjusting the arm's final reaching length from a normal condition to be slightly reduced; slightly increased; or markedly increased. Only extreme functionality alterations significantly reduced subjective ratings of limb ownership, particularly in adults. Motor adaptations, for example in arm velocity, largely reflected a smooth integration of the virtual arm's perceived capabilities with the participants' own physical limitations. Children responded to the altered embodiment with more cautious, less refined movement strategies than adults. Across ages, exposure to functionally enhanced virtual arms led to increased subjective estimates of reaching affordances, highlighting significant plasticity within this domain. Collectively, these results demonstrate that embodiment is largely flexible with respect to body function, with some constraining effects on the sense of body ownership and the properties of sensorimotor control. Moreover, for children function constrains motor control more than ownership. These findings reveal flexibility regarding body function, and age-dependent changes in how it shapes the boundaries of embodiment.