Definition and delimitation
On the scale of the reality-virtuality continuum  (see also Augmented Reality), complete virtual reality (VR) is at the other end from complete real reality. In contrast to augmented reality (AR) systems, in which the physical environment is enriched with holographic elements, VR is the computer-generated simulation of a three-dimensional image or environment with which users can interact in an apparently real or physical way in real time with the aid of special electronic equipment, such as data glasses or data gloves.
“Immersion” and “presence” are regarded as central key concepts here .
The level of immersion, or “technological immersion”, refers to the degree of physical stimulation acting on the sensory systems and the sensitivity of the system to motor input. The degree of immersion is considered objective and measurable – one system may have a higher degree of immersion than another and depends on various technological factors, such as the rendering software or the display technology of the system (e.g. the size of the field of view).
The psychological product of technological immersion is presence – the psychological feeling of being in the virtual environment rather than the physical environment and interacting with media. Presence is often described as the feeling of “being there” in the virtual space. The degree of presence is often measured by self-report and increasingly by physiological indicators (i.e. physical reactions during a VR experience such as increased heart rate and skin conductance or decreased skin temperature) of a user.
VR systems vary by viewing medium, interaction method, technological requirements and gaming options, and are widely applied using everything from highly immersive technologies to popular commercially available interactive video game consoles. Highly immersive VR systems require special hardware for display, often special data glasses (head-mounted displays, HMDs) or virtual rooms (so-called CAVEs). Virtual rooms use screens or projections. Well-known VR headsets are Facebook’s Oculus Rift and the HTC Vive. The device is worn on the head, with a screen directly in front of the eyes that displays two images from different perspectives, allowing three-dimensional capture. These must be updated in real time, with at least 25 to 60 images per second.
Interactions with the virtual world are possible via external input devices (3-D mouse, digital gloves, joysticks, special treadmills) as well as gestures. Motion capture technology is used to translate and transmit movements, e.g. of the body or hand, directly into the virtual world. Depending on the input device, algorithms are necessary that calculate the position of the fingers, for example.
To fill the VR world with content, there are various possibilities, e.g. 360-degree cameras or the creation of 3-D content by means of 3-D modelling or 3-D reconstruction.
In the beginning, no distinction was made between augmented reality and virtual reality, and the first concepts were already idealised before 1960 (see also information on the history of augmented reality). VR is characterised by ambitious ideas and concepts, which in their early development phases mostly failed due to their complexity in technical implementation. Sir Charles Wheatstone created the first stereoscope in 1838, with which a 3-D scene is represented spatially by two offset images. Morton Heilig, VR pioneer and filmmaker, wanted to revolutionise the movie theatre in 1956 and presented a prototype of “Sensorama” – a special cinema experience including wind simulation and smells – but it was not commercially successful. Sutherland presented “Ultimate Display” in 1965, which lets users interact with virtual objects. A little later, he presented “Sword of Damocles” in his publication “A Head-Mounted-Three Dimensional Display” . These later contributed significantly to the development of modern head-mounted displays. in 1929, flight simulations, the first highly immersive VR applications, were available for pilot training. CAVEs were not developed until 1992 at the University of Illinois. Headlines were made in 2012 by Oculus with the release of VR goggles, which was bought by Facebook 2 years later for $2 billion.
Application and examples
Well-known manufacturers of VR devices are the following:
The possibilities of VR applications are manifold  and can be found in the following areas, among others:
- Entertainment, e.g. video games, virtual exhibitions in museums, virtual showrooms and shopping, virtual events (such as the broadcasting of concerts or league games)
- Education and training, e.g. pilot training in flight simulators, visualisation, surgical training, military training
- Medicine and health, e.g. treatment of phobias, pain, post-traumatic stress disorder or body image disorders
- Fitness and physical/cognitive/mental rehabilitation, e.g. active video games or VR-based fitness equipment
- Visualisation in various sectors such as tourism, industry (e.g. virtual prototypes), architecture, chemistry, energy, spatial planning, advertising and real estate industries
Criticism and problems
VR sickness (simulation/cyber/motion sickness)
So-called VR sickness is caused by conflicts between the visual and vestibular systems, usually develops during the VR experience and disappears within a few hours. Typically, sufferers express symptoms such as nausea, malaise, dizziness, headaches, vomiting, stumbling and motion instability.
In general, digitisation facilitates easy access to sensitive data, but this can lead to data protection and security concerns. These issues are also raised in connection with VR or augmented reality applications due to the processing of sometimes sensitive sensor data, e.g. in eye tracking technologies.
The PhD project ‘Mixed Reality’ as a new rehabilitative approach to disorders of everyday actions after chronic neurological disease” deals with the question of how mixed reality approaches can be used as a meaningful intervention for neurorehabilitation, for example after a stroke or in the case of dementia.
Further links and literature
The following publication provides information on possible factors influencing motor learning in virtual environments:
- Rohrbach, N. et al. (2019). What is the impact of user affect on motor learning in virtual environments after stroke? A scoping review. Journal of neuroengineering and rehabilitation, 16(1), 1-14.
 Milgram, P., & Kishino, F. (1994). A taxonomy of mixed reality visual displays. IEICE TRANSACTIONS on Information and Systems, 77(12), 1321-1329.
 Liberatore, M. J., & Wagner, W. P. (2021). Virtual, mixed, and augmented reality: a systematic review for immersive systems research. Virtual Reality, 1-27.
 Ivan E. Sutherland. 1968. A head-mounted three dimensional display. In Proceedings of the December 9-11, 1968, fall joint computer conference, part I (AFIPS ’68 (Fall, part I)). Association for Computing Machinery, New York, NY, USA, 757-764.