Simultaneous Presence Continuum: Portal Overlays for Overlapping Worlds in Virtual Reality

This paper introduces the Simultaneous Presence (SP) Continuum, a novel concept designed to enhance the use of portals in virtual reality (VR) by understanding users' experiences across multiple environments. Portals traditionally provide access to secondary worlds, but their limited field of view (FoV) can hinder full engagement with these environments. To overcome this, we introduce portal overlays, which expand the portal's FoV by superimposing the secondary world over the user's view of the primary world. We explore several overlay techniques-Contours, Blended (Opacity and Stencil), and Absolute-to adjust user experience across the SP Continuum. The Contours overlay, renders only the edges of objects, offering a minimalistic view and immersion of the secondary world. The Blended overlay allows for adjustable immersion between worlds through opacity or the distribution of pixels. The Absolute overlay virtually immerses users completely in the secondary world. Importantly, these overlays are context-activated instead of always on, to suit situational needs. Our study revealed high SP was possible in both worlds, and overlays significantly impacted users' experiences on the SP Continuum. The Blended overlay provided balanced SP, while Contours had the highest primary presence but lower secondary presence. In contrast, the Absolute overlay, alternating full immersion between worlds, had the highest secondary presence but resulted in reduced primary presence, slower navigation and selection times, higher effort and frustration, and lower usability.