Multisensory integration of visual cues from first- to third-person perspective avatars in the perception of self-motion.

In the perception of self-motion, visual cues originating from an embodied humanoid avatar seen from a first-person perspective (1st-PP) are processed in the same way as those originating from a person's own body. Here, we sought to determine whether the user's and avatar's bodies in virtual reality have to be colocalized for this visual integration. In Experiment 1, participants saw a whole-body avatar in a virtual mirror facing them. The mirror perspective could be supplemented with a fully visible 1st-PP avatar or a suggested one (with the arms hidden by a virtual board). In Experiment 2, the avatar was viewed from the mirror perspective or a third-person perspective (3rd-PP) rotated 90° left or right. During an initial embodiment phase in both experiments, the avatar's forearms faithfully reproduced the participant's real movements. Next, kinaesthetic illusions were induced on the static right arm from the vision of passive displacements of the avatar's arms enhanced by passive displacement of the participant's left arm. Results showed that this manipulation elicited kinaesthetic illusions regardless of the avatar's perspective in Experiments 1 and 2. However, illusions were more likely to occur when the mirror perspective was supplemented with the view of the 1st-PP avatar's body than with the mirror perspective only (Experiment 1), just as they are more likely to occur in the latter condition than with the 3rd-PP (Experiment 2). Our results show that colocalization of the user's and avatar's bodies is an important, but not essential, factor in visual integration for self-motion perception.