Stereoscopic displays create the illusion of depth by presenting to each eye an image of the same scene from a slightly different perspective.
The closer an object is, the greater the difference in the image each eye receives, and that difference allows our brains to determine how far away the object is.
While these screens create a sense of depth, they are still an external display within the viewer's environment.
Virtual reality, on the other hand, replaces everything we see with a virtual environment. This is commonly achieved with a head-mounted display equipped with a range of sensors and trackers that determine the orientation (and sometimes position) of the user's head.
The headset then renders a view of the virtual environment from the user's perspective on to its screen.
Presence delivers a powerful experience
Presence is the word used to describe the experience of feeling you actually exist within a virtual environment.
This sense of presence is behind many of the extreme reactions users display during VR demonstrations.
People can subconsciously lean in an effort to maintain their balance on a virtual rollercoaster or flinch in order to avoid a virtual threat.
This is why VR delivers such a powerful experience, but it also presents a problem: users tend to forget their existence in the real world. Their reactions to virtual stimuli can cause damage to the equipment or, worse, injury to themselves or others.
If it is implemented safely, a strong sense of presence can provide a high level of engagement and help developers immerse a user in their application.
For games developers it provides an opportunity to create a more entertaining and immersive game that transports the player to another reality where they no longer just control a character, but start to become the character.
VR moves out of gaming
This level of immersion opens up other applications for VR technology, including education and training.
Educational projects already unveiled include the British Museum's use of VR to take visitors back to the Bronze Age or an experience that allows visitors to London's Natural History Museum to explore the Earth's prehistoric oceans, with commentary by David Attenborough.
Training for jobs where mistakes may be costly or dangerous is another possibility.
Giving users a sense of presence means they not only learn to deal with the task at hand, but also their own subconscious reactions and fears. The use of VR in therapeutic applications could allow users to address their fears in controllable doses and environments.
Is the human body ready for VR?
But are our bodies ready for this new technology? There are a number of factors that contribute to presence, or detract from it and the technology has some challenges to overcome.
The display frame rate (number of images the device can display per second), resolution (number of pixels) and latency (the delay between the user performing an action and that action being reflected by the virtual environment) have a direct effect on the quality of the experience.
Low resolution or frame rate or high latency reduce the sense of presence and are thought to contribute to virtual reality sickness (or cyber-sickness) - the symptoms of which are similar to motion sickness.
While issues around these factors have largely been addressed, we are still waiting for developers to create new techniques for representing the user's virtual body in the virtual environment.
This can be tricky, with many applications currently displaying nothing and giving users a sense of being a disembodied head floating through the world.
The other key challenge is to overcome the user's awareness of movement. There is a disconnect because their eyes tell them they are moving through a virtual environment, but their other senses tell them they are sitting or standing still.
This difference between the sense of motion in the real and virtual worlds is another contributor to cyber-sickness.
As a result, VR headsets currently come with warnings about nausea, eyestrain and headaches. It's only when these issues can be resolved that the mainstream take-up of VR can really take off.
- Dr Daniel Playne is a lecturer at Massey University's Institute of Natural and Mathematical Sciences.
