If you’re following VR, you’re probably hearing a lot about presence. But what is it?
The definition is elusive. Presence in virtual environments has been described, measured, and theorized in all kinds of ways. Whether they have dedicated decades of their lives to the subject or they are part of today’s new generation with a fresh take on VR, researchers are still struggling to come up with a unified conception of presence.
As a huge new wave of presence-inducing technologies hits the market this year, for the first time many people will experience presence and broken presence in virtual environments, so understanding what works and doesn’t is important.
A “sense of being in an environment” 
As these technologies become ubiquitous in our lives the concept of presence becomes more important than ever to understand. Yet, terms like presence, immersion, and engagement are often wrongly interchanged, and VR theorists are trying to delineate the differences and grasp a full and unified understanding of presence.
Immersion is what technology offers, such an untethered, cord-free experience, a room-full of monitors with amazing graphics, or faster refresh rates. Immersion, on the other hand, is a measure of the technology itself from an objective point of view , while engagement represents the measure of attention or cognitive resources a user delegates to certain stimuli.
Presence includes engagement but there is much more to it. Put simply, presence is a subjective experience, a user’s response to an environment or stimuli in an environment whether that environment is physical reality or virtual.
The “perceptual illusion of non-mediation,”  But presence goes beyond these simple definitions. Measures of presence, for starters, is one area of the field that researchers are having a hard time with. For decades, the definitive measure of presence was by self-reporting, like the presence questionnaire developed by Witmer & Singer–you fill out a Q&A immediately after an experience in a virtual space. However, this doesn’t allow room for presence to be considered a transient experience in which the level of presence changes throughout the experience, as some researchers have noticed.
Behavioral measures, on the other hand, look at whether someone responds in VR as they would in real-life. But does displaying behavior similar to that in real-life really mean the person felt present? And does not displaying that behavior mean they are not present?
Or, consider that you are in a VR environment walking a path and suddenly find yourself walking over a gorge – does your heart rate increase? This kind of physiological measure of presence can be fun, but just because your heart starts to race, does that really mean presence?
Other, neurological measures can be helpful in determining if a person is present, but wearing an EEG in addition to a head-mounted display can be cumbersome and sitting in an fMRI restricts movement.
Considering the advantages and disadvantages of each type of measure, the opinion of the research community seems to suggest that converging lines of evidence — using multiple modes of measurement— is best.
Part of the struggle
We know that in reality, everything we understand about our individual lives is actually a subjective perceptual interpretation based off our memories, ease of accessing them, our established schemas about the way the world works, and our past experiences. In this way, perception mediates our impression of the world, and the world is constantly mediated for us by those memories, schemas, and experiences. There is not a single reality. Do these rules about physical reality transfer to our experience in the virtual?
To determine why presence occurs, researchers have pulled from evolutionary psychology. From this perspective, presence can be seen as an adaptive mechanism allowing the brain to automatically make a determination about what is real and what is not, allowing us and our ancestors to not fear shadows or imagined objects.
This cognitive mechanism makes us behave as if things were real when we know they are not and vice-versa. For instance, you can view a photograph, understand that it is a copy of reality, but not feel present in it, while getting lost in your favorite movie may elicit a higher degree of presence than a photograph.
A “psychological focus on perceptual processing” 
Is presence a structural component of consciousness? Researchers have looked at how a stimulus is followed by emotions that interpret the bodily reaction before you make cognitive designations such as real or unreal. So if response and emotion come before understanding, then couldn’t VR designers cut right through the real/un-real cognitive task and head straight for emotional responses?
What about the objects in the virtual world? If you are in a VR space and the physics of the space – how things move, respond to interaction, the weight and size influencing the behavior of objects in the space –don’t make sense, and it’s not explained within the space why those relationships might be altered , this disconnect can cause a major break in presence. The narrative content of a virtual experience helps with this problem, and designers use the story behind the experience to explain changes to the physics of the virtual world they offer. Surprisingly, the story’s logic plays a powerful role in what users will accept as real and therefore presence-inducing. This also applies to things like latency or lag in the image you see compared to the movement of your eyes, the movement of an object in the space, or a task you are trying to perform in the space.
Some researchers have said that presence is a “willful suspension of disbelief” [6,7,8]– giving our minds permission to believe the virtual space is real and therefore inviting ourselves to feel present in that space. Other researchers have described presence as simply not noticing the mediation—forgetting you’re wearing a virtual device and becoming lost in the story you are experiencing. Reality judgment is psychometrically measurable, but there are still questions remaining.
An experience of feeling real versus tricking the mind to be real.
A major challenge is that the degree of presence will be different for each person. This is why some of the measures of presence struggle to establish a base-line “normal” with which to compare the presence state, because each individual’s “normal” will be different. Further, each person’s perception of the world – whether the real world or the virtual one – depends on their memories, ease of access of those memories, past experiences, and previous interactions with virtual experiences.
The “subjective veridicality of perceptual processing” 
Is presence a state that you either are or are not? Or is it instead a transient experience with different degrees of presence or levels of presence? Does presence lie on a continuum?
Milgram’s virtual reality continuum, for example, places fully-immersive virtual reality on one end of a spectrum and physical reality (real life) on the other end of the spectrum, with all kinds of mixed reality devices spread out across the continuum depending on the level of immersion provided by the technology. Immersion is defined as the degree to which the technology blocks out reality, replacing physical sensorial information with corresponding virtual stimuli. So a high-immersion device would be a fully-virtual environment, while a low immersion device would include only a bit of the virtual mixed into the real.
Researchers like Jeremy Bailenson & Jim Blascovich note that making changes in virtual environments that affect social presence is a useful tool for studying the psychology of social interactions. Presence has fed into other psychological research, too. Virtual therapy is one area in which presence is especially effective for treatment, perhaps because people are more willing to suspend their disbelief if they believe it will offer relief or help them recover.
Presence is a new frontier for understanding what the change to a more and more virtual world will mean for the humans who experience the world virtually. The more of our lives we spend in VR, the more we will need to understand presence and how it affects us, how it is made possible, and how we can design VR experiences from a standpoint that takes psychological processes into account.
-Max Parola & Amelia Jaycen
 M. Slater, “A note on presence terminology,” Presence Connect, vol. 3, no. 3, pp. 1–5, 2003.
 J. Steuer, F. Biocca, M. R. Levy, and others, “Defining virtual reality: Dimensions determining telepresence,” Commun. Age Virtual Real., pp. 33–56, 1995.
 M. Lombard and T. Ditton, “At the Heart of It All: The Concept of Presence,” J. Comput.-Mediat. Commun., vol. 3, no. 2, pp. 0–0,1997.
 E. L. Waterworth and J. A. Waterworth, “Focus, locus, and sensus: The three dimensions of virtual experience,” Cyberpsychol. Behav., vol. 4, no. 2, pp. 203–213, 2001.
 A. K. Seth, K. Suzuki, and H. D. Critchley, “An Interoceptive Predictive Coding Model of Conscious Presence,” Front. Psychol.,vol. 2, 2012.
 C. Coelho, J. G. Tichon, T. J. Hine, G. M. Wallis, and G. Riva, “Media presence and inner presence: the sense of presence in virtual reality technologies,” Commun. Presence Cogn. Emot. Cult. Ultim. Commun. Exp., pp. 25–45, 2006.
 B. Reeves and C. Nass, How people treat computers, television, and new media like real people and places. CSLI Publications and Cambridge university press, 1996.
 N. N. Holland, “The willing suspension of disbelief: A neuro-psychoanalytic view.,” PsyART, 2003.