Avatars can serve as virtual representations of a user's body, replicating their movements in real time within an immersive environment. When these movements are closely synchronized with those of the user, a sense of embodiment over the avatar is often experienced. Recent research shows that introducing spatial offsets between a user's real movements and those of their avatar can alter motor behavior, with users aligning with the distorted avatar. While previous studies have typically focused on upper-limb movements toward visual targets, it remains unclear how users respond to distortions without such targets, particularly during lower-limb tasks where postural demands may impose constraints. This study examined whether users adjust their movements to follow their distorted avatar during upper- and lower-limb reaching without visual targets. Twenty-four participants performed reaching tasks while their avatar's movements were spatially offset. Results revealed that participants counteracted the avatar's distortion by moving in the opposite direction in both limb tasks. These findings suggest that, in the absence of explicit visual targets, participants treat spatial distortions as execution errors and prioritize internal movement goals over minimizing sensory conflict. This suggests that adaptation depends not only on a strong embodiment but also on whether the task performance permits reducing the mismatch between the user's and the avatar's movements.

Several studies have shown that users of immersive virtual reality can feel high levels of embodiment in self-avatars that have different morphological proportions than those of their actual bodies. Deformed and unrealistic morphological modifications are accepted by embodied users, underlying the adaptability of one's mental map of their body (body schema) in response to incoming sensory feedback. Before initiating a motor action, the brain uses the body schema to plan and sequence the necessary movements. Therefore, embodiment in a self-avatar with a different morphology, such as one with deformed proportions, could lead to changes in motor planning and execution. In this study, we aimed to measure the effects on movement planning and execution of embodying a self-avatar with an enlarged lower leg on one side. Thirty participants embodied an avatar without any deformations, and with an enlarged dominant or non-dominant leg, in randomized order. Two different levels of embodiment were induced, using synchronous or asynchronous visuotactile stimuli. In each condition, participants performed a gait initiation task. Their center of mass and center of pressure were measured, and the margin of stability (MoS) was computed from these values. Their perceived level of embodiment was also measured, using a validated questionnaire. Results show no significant changes on the biomechenical variables related to dynamic stability. Embodiment scores decreased with asynchronous stimuli, without impacting the measures related to stability. The body schema may not have been impacted by the larger virtual leg. However, deforming the self-avatar's morphology could have important implications when addressing individuals with impaired physical mobility by subtly influencing action execution during a rehabilitation protocol.

It has recently been shown that inducing the ownership illusion and then manipulating the movements of one's self-avatar can lead to compensatory motor control strategies in gait rehabilitation. In order to maximize this effect, there is a need for a method that measures, and monitors embodiment levels of participants immersed in VR to induce and maintain a strong ownership illusion. The objective of this study was to propose a novel approach to measuring embodiment by presenting visual feedback that conflicts with motor control to embodied subjects. Twenty healthy participants were recruited. During experimentations, participants wore an EEG cap and motion capture markers, with an avatar displayed in a HMD from a first-person perspective. They were cued to either perform, watch or imagine a single step forward or to initiate walking on the treadmill. For some of the trials, the avatar took a step with the contralateral limb or stopped walking before the participant stopped (modified feedback). Results show that subjective levels of embodiment correlate strongly with the difference in μ - ERS power over the motor and pre-motor cortex between the modified and non-modified feedback trials.

The emerging use of self-avatars for physical and motor rehabilitation leads to specific requirements for their real-time animation that combine properties from the fields of computer graphics and of biomechanics. We present a method for animating a self-avatar in real-time that allows for high-fidelity representation of whole-body kinematics using anatomical and reproducible bone-segment definition. The method requires little setup time and has low motion-to-photon latency.