Avatars, Should We Look at Them Directly or Through a Mirror?: Effects of Avatar Display Method on Sense of Embodiment and Gaze.

In the real world, the body typically remains within the downward field of view (FOV) irrespective of whether it is consciously or unconsciously observed. However, with head-mounted displays (HMDs) that have restricted viewing angles, users are unable to see their own avatars directly unless they tilt their heads significantly downward. To overcome this, virtual mirrors are commonly employed in virtual environments (VEs) to provide users with a full-body view of their avatars, which ultimately enhances the viewer's sense of embodiment (SoE). However, positioning users directly in front of a virtual mirror may restrict their movement and reduce their sense of presence. To overcome this limitation, we developed an HMD with an extended downward field of view (FOV) integrated with eye-tracking. We compared the impact of using virtual mirrors alone versus the extended downward FOV in terms of several parameters, including the head pitch angle, perceived SoE, presence, and task difficulty during a reaching task that involves both hand and foot movements. The results demonstrated that the extended downward FOV offered by the proposed HMD improved the users' sense of agency toward their avatars and enhanced their sense of presence compared to when only virtual mirrors are used. In addition, the participants tended to use the virtual mirror for hand movements and relied on the extended downward FOV for foot movements, often maintaining a stable head angle. Both the virtual mirror and extended downward FOV facilitated easier and faster completion of a reaching task while encouraging an upward head angle. However, the combined use of virtual mirrors and extended downward FOV did not have a significant impact on the SoE or presence. Notably, the extended downward FOV alone, without the integration of the virtual mirror, was more effective in increasing both SoE and presence.