The virtuality continuum represents the full spectrum of technological possibilities between the entirely physical world or real environment and the fully digital world or virtual environment. It includes all current technologies that alter reality with computer-generated graphics as well as those yet to be developed.
© Laia Tremosa and the Interaction Design Foundation
In a continuum, adjacent parts are almost indistinguishable, but the extremes are very different. Therefore, the exact limits of the various terms are not a hundred percent clear. The term mixed reality covers any environment where the real and virtual objects are combined within a single display. According to this framework, mixed reality covers most of the continuum except for the endpoints. The researchers Paul Milgram and Fumio Kishino first introduced the virtuality continuum or reality-virtuality continuum concept in 1994.
The virtuality continuum, as initially proposed by Milgram and Kishino in 1994, considered only visual displays. Therefore, the different sections within the continuum only take into account the visual aspect of the blending between the physical and digital worlds. This continuum does not take into account sound, smell, haptics or taste.
The virtuality continuum is broken down into four categories:
Real environment: consists solely of real or physical objects. The real environment represents the left end of the virtuality continuum.
Augmented reality: the real world is augmented with digital elements.
Augmented virtuality: the virtual world is augmented by the inclusion of real or physical objects.
Virtual environment: consists solely of digital objects. The virtual environment represents the right end of the virtuality continuum.
It is important not to confuse the virtuality continuum components with the different extended reality (XR) technologies. The virtuality continuum is a theoretical framework. The different sections of the continuum define how many real elements vs. digital elements are displayed, starting from the left end—the real environment—where 100% of what is displayed are real or physical objects and 0% are digital elements versus the right end—the virtual environment—where 100% of the objects displayed are digital and 0% are physical objects.
Some researchers have stated that the virtual environment, which is considered the right end of this continuum, should be included within the mixed reality definition. They argue that a fully immersive digital environment is unreachable only considering the visual display. Even if the user only sees a digital environment, they would still have the real-world environment physical constraints; for instance, the user won’t be able to move freely if there is a physical wall in front of them, even if there is no wall in the virtual world they are immersed in. Also, they would be able to taste food or smell a flower.
Many revised versions of Milgram and Kishino’s virtuality continuum have been developed to include the notion of a user and to include all senses. However, there is no new universally accepted standard yet.
Learn how to design your own XR experiences with our course: How to Design for Augmented and Virtual Reality.
Watch the How To Influence Behavior Through Virtual Reality Narratives on-demand Master Class by VR pioneer Mel Slater.
To see new revisions of the virtuality continuum, read this paper: Skarbez, R., Smith, M., & Whitton, M. (2021). Revisiting Milgram and Kishino's Reality-Virtuality Continuum. Frontiers In Virtual Reality, 2. doi: 10.3389/frvir.2021.647997
Here’s the entire UX literature on Virtuality Continuum by the Interaction Design Foundation, collated in one place:
