Virtual Reality

"Virtual Reality," or VR (also known as "artificial reality" (AR) or "cyberspace"), is the creation of an interactive computer-generated spatial environment. This simulated environment can represent what one might encounter in everyday experience, represent pure fantasy, or be a combination of both.

Early "first-generation" computer interfaces handled only simple onedimensional (1D) streams of text. The second generation, developed in the late 1970s and early 1980s for two-dimensional (2D) environments, started to use a computer screen's windows, icons, menus, and pointers (WIMP), including sliders, clicking to select, dragging to move, and so on. The third generation of interfaces is characterized by three-dimensional (3D) models and expressiveness.

VR uses various computer techniques, including realtime 3D computer graphics and animation, position tracking , and multimodal input/output (I/O) , especially stereographics and spatial sound . Fully developed VR will use all the senses: vision (seeing), audition (hearing), haptics (feeling, including pressure, position, temperature, texture, vibration), and eventually olfaction (smell) and gustation (taste).

Humans have the capacity to absorb a great deal of data, but traditional two-dimensional computer interfaces rarely generate more than a few hundred bits per second worth of data. Traditional computer interfaces force a user to interact graphically, in the plane of the screen. Virtual reality, however, opens up this interaction between user and computer by creating an 3D-environment in which the user can manipulate volumetric objects and navigate through spaces.

Virtual Reality and Immersive Hypermedia

If simple, linear (1D) text, such as a story, is augmented with extra media— such as sound, graphics, images, animation, video, and so on—it becomes multimedia. If this same story is extended with nonlinear attributes—such as annotations, cross-references, footnotes, marginalia, bibliographic citations, and hyperlinks—it becomes hypertext. The combination of multimedia and hyper text is called "hypermedia."

VR is interactive hypermedia because it gives users a sense of immersion or presence in a virtual space, including a flexible perspective or point of view, with the ability to move about.

"Classic" VR uses a head-worn display (HWD), also known as a head-mounted display (HMD), that presents a synthetic environment via stereophonic audio and miniature displays in front of the eyes. Such a helmet, or "brain bucket," often uses a position tracker to determine the orientation of the wearer and adjust the displays accordingly. Users may also wear "Data-Gloves," sets of finger and hand sensors that can be used to virtually grasp, manipulate, and move virtual objects. Full-body VR-suits are manufactured and sold, but they are less common because they are still expensive and cumbersome.

Mixed Reality

Reality and virtuality are not opposites, but rather two ends of a spectrum. What is usually thought of as "reality" is actually filled with sources of virtual information (such as telephones, televisions, and computers), and virtuality has many artifacts of the real world, such as gravity.

Along the reality-virtuality spectrum are techniques called "mixed reality," also variously known as or associated with augmented, enhanced, hybrid, mediated, or virtualized reality/virtuality. In a mixed reality system, sampled data (from the "real world") and synthesized data (generated by computer) are combined. An example of a mixed reality is a computer graphic scene that includes images captured by a camera.

Head-mounted displays (HMDs) are important for mixed reality systems. A typical mixed reality system adds simulation to reality by either overlaying computer graphics on a transparent display ("optical see-through," which uses half-silvered mirrors) or mixing computer graphics with a video signal captured by a camera mounted in front of the face, presenting the result via an opaque display ("video see-through"). Similarly, computer generated spatial sound can be added to the user's environment to provide navigation cues. Mixed reality systems encourage "synesthesia," or cross sensory experiences. For example, infrared heat sensor data could be shifted into the visible spectrum.

Liquid Presence

A rich multimedia environment, like that enabled by (but unfortunately not always provided by) VR, carries the danger of overwhelming a user with too much information. Control mechanisms are needed to limit the media streams and help the user focus attention. For example, "radio buttons," like those used in a car to select a station, automatically cancel any previous selection (since only one station is listened to at once). On an audio mixing console, controls are associated with every channel, so they may be selectively disabled with "mute" and exclusively heard with "solo" (in the spirit of "anything not mandatory is forbidden"). Predicate calculus provides a mathematical notation for describing logical relations. For these mixing console functions, the relation can be written:

active(source_x) = ¬ mute(source_x) ∧ (∃y solo(source_y) ⇒ solo(source_x)), where means "not," ∧ means "and," ∃ means "there exists," and ⇒ means "implies."

This expression means that a particular source channel x is active unless it has been explicitly excluded (turned off) or another channel y has been included (focused upon) when the original source x is ignored. Symmetrically, the opposite of an information or media source is a sink. In an articulated sound system, equivalents of mute and solo are deafen and attend:

active(sink_x) = deafen(sink_x) ∧ (∃y attend(sink_y) ⇒ attend(sink_x)).

In general, a user might want to listen to multiple audio channels simultaneously. For example, one might want to have a private conversation with a small number of people while simultaneously monitoring an ongoing conference as well as a nursery intercom, installing pairs of virtual ears in each interesting space. Such an omnipresence capability is equally useful for other sensory modalities. For instance, a guard might generally have access to many video channels from security cameras but may sometimes want to focus on some subset of them or disable some of them (for privacy).

Virtual environments allow users to control the quality and quantity of their presence. For example, some interfaces allow a user to cut/paste a representative icon between windows symbolizing rooms, using the pasteboard as a science-fiction teleporter. Coupling such capability with a metaphorical replicator, a user can copy/paste their icon, allowing them to clone their avatar and distribute their presence. A general predicate calculus expression modeling multimedia attributes and such liquid presence is:

active(x) = exclude(x) ∧ (∃ y include(y) ⇒ include(x)).

Related Technology and Approaches

Important core technologies for VR include computer graphics and animation, multimedia, hypermedia, spatial sound, and force-feedback displays. Trackers (including magnetic, inertial, ultrasonic, and optical), along with global positioning systems (GPSs), are needed to sense users' positions and, in the case of mixed reality systems, align the displays with the real world. VR systems are often integrated with other advanced interface technology, like speech understanding and synthesis. Virtual Reality is also encouraged by Internet technology, including Java (and Java3D), XML (eXtensible Markup Language), MPEG-4 (for low bit rate videoconferencing and videophony), and QTVR (QuickTime for Virtual Reality, enabling panoramic image-based rendering), as well as the VRML (Virtual Reality Modeling Language) and its successor X3D.

Expressive figures are increasingly important in virtual environments, and virtual humans, also known as "vactors" (virtual actors), integrate natural body motion (sometimes using "mocap," or motion capture, along with kinematics and physics), facial expressions, skin, muscles, hair, and clothes. As such technology matures, its realtime performance will approach in realism the prerendered special effects of Hollywood movies. A related idea is "A-life" (for "artificial life"), the programming of organic or natural-seeming processes, including genetic algorithms, cellular automata, and artificial intelligence.

Applications

Applications of virtual reality and mixed reality are unlimited, but are currently focused on allowing users to explore and design spaces before they are built; "infoviz," or information visualization (of financial or scientific data, for example); simulations (of vehicles, factories, etc.); entertainment and games (like m assively m ultiplayer o nline r ole p laying g ames [MMORPG], modern equivalents of the classic Dungeons and Dragons games); conferencing (chatspaces and collaborative systems); and, especially for mixed reality, medicine.

In the Future

Future goals of virtual reality include a whole-body user interface paradigm and ultimately a system that allows people to enjoy completely virtual worlds without any restrictions, like the Holodeck on the television show Star Trek:

Next Generation. Current VR systems are more like 3D extensions to 2D interfaces, in which the world has become a mouse pad and the user has become a mouse. For example, the Vivid Mandala system (www.vivid.com) uses "mirror VR," in which users watch a chromakey reflection of themselves placed in computer graphics and photographic context, gesturing through fantasy scenarios.

On the horizon are full-immersion photorealistic and sonorealistic interfaces in shared virtual environments via high-bandwidth wireless Internet connections, perhaps using visual display technology that writes images directly to the retina from one's eyewear, or head-mounted projective systems that reflect images back to each wearer via retroreflective surfaces in a room. Virtual reality will be extended by mixed reality and complemented by pervasive or ubiquitous computing (also known as "ubicomp")—that exploits an environment saturated with networked computers and transparent interfaces, including information furniture and appliances sensitive to human intentions—and wearable computers.

see also Computer Animation; Computers, Future.

Michael Cohen

Bibliography

Barfield, Woodrow, and Thomas A. Furness III, eds. Virtual Environments and Advanced Interface Design. New York: Oxford University Press, 1995.

Begault, Durand R. 3-D Sound for Virtual Reality and Multimedia. Academic Press, 1994.

Durlach, Nathaniel I., and Anne S. Mavor, eds. Virtual Reality—Science and Technological Challenges. Washington, D.C.: National Research Council, National Academy Press, 1995.

Krueger, Myron W. Artificial Reality II. Reading, MA: Addison-Wesley, 1991.

Kunii, Tosiyasu L., and Annie Luciani, eds. Cyberworlds. Tokyo: Springer-Verlag, 1998.

McAllister, David F. Stereo Computer Graphics and Other True 3D Technologies. Princeton, NJ: Princeton University Press, 1993.

Nelson, Theodor H. Computer Lib/Dream Machines, 1974. Redmond, WA: Tempus Books of Microsoft Press, 1998.

Thalman, Nadia Magnenat and Daniel Thalman, eds. Artificial Life and Virtual Reality. New York: John Wiley & Sons, 1994.

Wolfram, Stephen. A New Kind of Science. Champaign, IL: Wolfram Science, 2001.

Internet Resources

IEEE-VR: IEEE Virtual Reality Conference. <http://www.ieee-vr.org>. Sponsored by the IEEE Computer Society. <http://www.computer.org>.

Java3D: 3D framework for Java. <http://java.sun.com/products/java-media/3D/>.

MPEG Home Page. <http://www.cselt.it/mpeg>.

Presence: Teleoperators and Virtual Environments. <http://mitpress.mit.edu/journal-home.tcl?issn 10547460>.

QuickTime for Virtual Reality. <http://www.apple.com/quicktime/qtvr/>.

SIGGRAPH: Special Interest Group on Computer Graphics. <http://www.siggraph.org>.

Web 3D Consortium. <http://www.web3d.org>.

XML: eXtensible Markup Language. <http://www.w3.org/XML/>.

Virtual Reality

The terms virtual reality (VR) and virtual environment (VE) refer to an artificial reality created by computer technology that provides the user with a first-person, interactive view into the virtual world that has been created. It is this interactive capability that distinguishes VR from other systems based on computer graphics such as the extremely realistic computer animations that are increasingly being used by the filmmaking industry. Actors do not actually interact with the computer animations that will ultimately appear in a film. Instead, they interact with an "imaginary" scene or animation that is then added later to provide realism for the moviegoer. This provides the audience with a third-person view of a virtual world. Such a view is in sharp contrast to VR, in which the environment is centered around the perspective of the user who will also typically have the ability to interact dynamically with it.

Although its origins date back to the 1950s, the phrase "virtual reality" first became widely known in the mid-1980s, when mainstream computer technology finally become powerful enough to perform the calculations necessary to create a minimally realistic virtual environment. However, in spite of earlier technological limitations, VR ideas were envisioned long before the 1980s. In 1957 Mort Heilig filed a patent for a head-mounted "stereoscopic television apparatus for personal use." Thus, the head-mounted display (HMD) was born, though at the time, applying this technology to view a virtual world created by a computer was not considered or envisioned.

In 1965 Ivan Sutherland published an article called "The Ultimate Display," which described how a computer could someday be used to provide a window into virtual worlds. Then in 1968, Sutherland combined these ideas together with head tracking and built a head-mounted display providing a stereoscopic view into a simple 3D world that remained stationary despite viewer head movements! Virtual reality was born.

Today VR consists of much more than just head-mounted displays. Gloves containing strain gauges or fiber optics can be used to allow a user to interact with a virtual world through hand gestures. Force feedback information, such as the weight of a virtual object, can be provided via haptic devices, and a virtual reality modeling language, called VRML, has even been developed to allow Internet browsers to interact with 3D environments.

The Theory Behind VR

Philosophically speaking, the objective of VR is to create an environment that is believable to the user, but which does not exist in the physical world. The understanding of our world, our reality, is ultimately derived from our senses. Humans have five major senses: sight, hearing, touch, smell, and taste. These senses provide our brains with information that enables us to understand the world around us—our "reality." The most important sense for understanding the physical world is sight, followed by sound and touch.

At the present time, computer technology has enabled the development of sophisticated means to stimulate our senses of sight and hearing. To a lesser degree, the technology for stimulating touch has also been developed. A virtual environment which the brain can easily interpret as being real is created when these technologies are integrated into a system where the sensory data that are produced are consistent with (i.e., conforms to) what we have observed in the physical world.

Anyone who has experienced "motion sickness" while sitting perfectly still and watching a plane fly in a 360-degree theater will attest to the fact that the brain can be decisively tricked through visual stimulus alone. Recognizing that a large part of our understanding of reality is based on visual stimulus has led significant effort in VR research to be devoted to visual-based stimulus such as image generation and animation.

Concepts such as perspective, reflection of light, texturing, and rotation of 3D images form the basis of constructing stationary images and provide us with a way to navigate through such images. These concepts are well understood and have been precisely defined by mathematical equations. Manipulating these mathematical equations has allowed computers to generate images that are exceedingly real. However, generating such ultra-realistic images involves tremendous mathematical calculations and even the fastest computers yet made cannot support real-time animation of such images. This is why the computer animations used in movies are so much more realistic than present-day VR systems.

The next piece of the visual puzzle is animation, that is, making objects in the virtual world move. Animation is based on kinetics and kinematics . These fields of study are essentially concerned with how things move and react to forces. Although the advances in this area have been significant, there is much work that remains to be done in order for computers to be able to generate animations that are truly consistent with our understanding of the physical world. For example, we all know how people and animals walk or run, and we are very good at distinguishing "natural" motion from the motion that computer animations are presently capable of generating. We have never actually seen a dinosaur run, but when we see it in a movie, we know that its motion is close, but not quite right.

A complementary technique that can be used to amplify the realism of a virtual word is called immersion. A user can be immersed in a virtual world by removing the conflicting stimulus associated with the physical world. In other words, it is easier for someone to imagine she is in a virtual world if she is only allowed to see that virtual world and nothing else. Immersion is what makes 360-degree theaters so realistic.

Applications

As with all technologies, the use of virtual reality is often limited only by the imagination of the user. In movies like The Lawnmower Man and The Matrix, Hollywood shows a more sinister look at how VR might someday be abused. However, the ability to create realistic virtual environments has the potential to benefit society significantly. This stems from the fact that a virtual environment is a model of reality. Models typically do not contain every aspect of the thing they are modeling. What this means in the context of VR is that in a virtual environment, the rules of the physical world can be broken or bent!

For example, a pilot can learn to fly a commercial airliner in a virtual environment, without having to worry about experiencing the consequences associated with an actual crash. Fly-by-wire systems or new airplane designs can be tested without the cost or worry of crashing an aircraft. Surgeons can master complex operations without having to worry about accidentally killing a patient. The effects of a nuclear reactor meltdown can be studied without any risk to the environment. New designs for supertankers that minimize oil spillage in the event of a collision can be studied without the cost associated with physically testing. The list of interesting and useful applications of VR is long and growing rapidly.

see also Interactive Systems; Optical Technology; Simulation; Simulators; Virtual Reality in Education.

Victor Winter

Bibliography

Hollands, Robin. The Virtual Reality Homebrewer's Handbook. New York: John Wiley & Sons, 1996.

Vince, John. Essential Virtual Reality Fast: How to Understand the Techniques and Potential of Virtual Reality. New York: Springer-Verlag, 1998.

virtual reality (VR) is a technology that allows people to enter and interact with three-dimensional computer graphics worlds. Another term for these worlds is virtual environments. When a person uses a virtual world the sensory information that is present in the real world is replaced by computer-generated information, which may be of sufficient fidelity to allow the person effectively to believe that they are in the virtual world.

VR is currently used in applications such as aircraft pilot training, medical rehabilitation, training for surgical procedures, engineering and scientific visualization, manufacturing design, the control of remote (tele-operated) vehicles, and computer games. Some of the worlds used for these applications are designed to be virtual equivalents of real-world (i.e. physical) environments. Other virtual worlds exist only in their virtual form and for these worlds the term virtual ‘reality’ is something of a misnomer.

The variety and fidelity of sensory information provided by VR applications varies widely and is typically limited by a trade-off between cost and benefit. A person's sense of presence is one nebulous, subjective measure of the degree to which they feel that they are actually inside a virtual world, and this quantity is influenced by factors that include the size of the visual field of view, the inclusion of auditory information, and the use of head-tracking, where the person's physical movements control their direction of view. Although an increase in presence does not necessarily produce a corresponding increase in the accuracy or speed with which tasks are performed, it does provide a general measure of the degree to which real-world sensory information is replaced by information contained in the virtual world.

Three-dimensional computer graphics allow the shape and form of objects to be perceived, and the use of photo-realistic textures for colour provides detailed visual information. The patterns contained in textures help to increase optic flow and this increases a person's perception of movement as they travel through a virtual world. Technical and cost limitations often restrict a person's field of view to an angle as small as 50 degrees (compared with the 200 degrees or more of normal vision). This effectively means that the person looks at the virtual world using blinkers. The lack of peripheral vision seems to inhibit people's ability to develop mental ‘models’ of the layout of virtual worlds and frequently causes people to miss events that occur just outside the field of view, but which they would detect in the real world.

Some virtual worlds provide auditory and haptic information. Simple sounds such as a ‘bump’ can be added to indicate that a person has collided with a ‘solid’ object. More realistic, spatial sounds can be provided using binaural, stereophonic technology. Force feedback is particularly useful in virtual worlds that are used for pharmaceutical drug research, where it may be used to simulate the powerful forces that are present between different atoms in molecules.

When a person initially navigates a virtual world they tend to become very disoriented but, if they are given sufficient time, they can develop knowledge of the virtual world's layout which is as accurate as the knowledge they develop of the real world environments in which they live and work. The amount of visual detail which is present in a virtual world has an effect on the rate at which a person learns spatial knowledge, because these details are frequently used as landmarks that aid the learning of routes. Other devices such as a compass or a map can also provide effective navigational aids.

In some virtual worlds no interaction is allowed apart from a person's movement (the world is visualized but little else). In more complex worlds each object can have its own behaviour. Thus, doors may be opened, a phone can be used to have a conversation with another person, or a virtual computer can be used to send real electronic mail. Virtual worlds that contain complex object behaviours are time-consuming to develop but are becoming more commonplace. Of course, there is nothing to stop a virtual world redefining the laws of physical reality so that objects can, for instance, ‘fall’ upwards when they are dropped!

Finally, a significant proportion of people who view virtual worlds using helmet-mounted displays (HMDs) suffer from the side-effects of VR sickness, common symptoms of which include eye-strain, nausea, and a loss of balance. VR sickness seems to be related to motion sickness and has many contributory causes. One is the vestibular conflicts which are caused by the (small) time delays that occur between a person's actual bodily movements and the HMD being updated to reflect those movements. Another is the optical quality of the displays themselves. The magnitude of the problems caused by VR sickness is likely to reduced gradually as improvements take place in display and sensor technology, and a better understanding is reached of the factors which contribute toward the sickness.

Roy A. Ruddle, and Robert J. Snowden

Bibliography

Rheingold, H. (1992). Virtual reality. Mandarin, London.

Virtual Reality

Virtual reality is that part of human experience that does not happen in a physical space. Reading a book creates virtual reality, as does participating in an online chat or a telephone conference. These experiences are called "virtual" because the people involved are not actually in the story of the book or in a conference room with other people but physically separated; nonetheless, they participate in the community through thought and imagination and, in some cases, through their eyes, via the monitors, and fingers, via the keyboards.

The term virtual reality came into wide use during the 1990s with the increasing popularity of the Internet, and the concept of virtual reality led to many of the metaphors used to describe Internet interactions. A chat room, for example, is not a room, and it does not even have a physical location; it consists entirely of the people who are "meeting" there and interact. They do not meet, of course, but happen to be at their personal computers at the same moment in time. They also do not chat or talk but write messages that appear on others peoples' screens. Keyed graphics called smileys, such as :-) and ;-}, convey emotional content. Sometimes people wander off into separate "rooms" to be more "intimate" with a few others instead of sharing their thoughts in "public." These and many other metaphors are used for two reasons. First, humans are physical entities, and, from an evolutionary perspective, everything they did in the past happened in physical time and space. Language arising from this background is naturally physical in its description of human interaction. But once these metaphors are used they also become a selling point for virtual reality because they suggest that virtual reality allows for complete personal interactions.

Despite their obvious popularity, chat rooms and other virtual reality entities raise serious questions. One of the most obvious is the fact that among virtual reality communities there are several churches and prayer groups. The question is, can such spiritual virtual reality communities actually replace mortar and brick churches? Cybercommunities lack the physical space that bodies, together in liturgy and practice, create. Gender, race, and age have no defined roles. In virtual reality, people can lie about themselves and construct different identities. In addition, virtual reality communities give people the freedom to project all their wishes and desires about a "real" community onto the cyber-community because there is no way to know who is there and if the people are actually likeable. But is this community? And where does this wish for clean and perfect relationships come from when everyone knows that real-world relationships are flawed, stressful, full of ambiguities, yet so much fun. Because there is no physical commitment or connection in cyberspace, web communities may be ultimately indifferent and meaningless to the people involved.

The understanding of humankind in recent years has changed from a dualistic, cognition-oriented understanding toward an embodied and social one. The intelligence of humans is not the main characteristic of the species—it is much more the human capacity to connect and to survive in any given environment. Virtual reality, however, is a direct result of the assumption that embodiment and shared physical space are not important for community building because the body is not part of what turns a human into an individual. But if cognitive science theories are correct, then virtual reality spaces lack the required physicality, and relationships in them are incomplete.

See also Information Technology

Bibliography

gray, chris hables; figueroa-sarriera, heidi j.; and mentor, steven; eds. the cyborg handbook. new york: routledge, 1996.

paul, gregory, and cox, earl d. beyond humanity: cyberevolution and future minds. rockland, mass.: charles river media, 1996.

turkle, sherry. life on the screen. new york: simon &schuster, 1995.

anne foerst

VIRTUAL REALITY

VIRTUAL REALITY refers to computer-generated, three-dimensional simulations that allow a participant to experience and interact with a setting or situation. In the most intense forms of virtual reality, a participant wears a headset that incorporates high-resolution video displays and audio speakers, immersing the participant in a computer-generated experience. The participant also wears a special glove or body suit studded with sensors that monitor all movement. Data from the participant's movements are then fed into a computer, which modifies the simulation accordingly. Virtual reality systems allow a participant to experience, navigate through, and manipulate a hypothetical area filled with imaginary structures and objects. This area is often referred to as "cyberspace," a term first used by author William Gibson in his 1984 novel, Neuromancer. By the end of the twentieth century, virtual reality not only encapsulated a specific technology, but also signaled a broader set of cultural questions about the place of technology in modern life.

The growth of the Internet, along with the advent of inexpensive and increasingly powerful computers and the development of sophisticated computer graphics techniques, has led to faster and more detailed virtual reality systems, adding to the realism of the experiences they deliver. The use of virtual reality technology in the entertainment industry holds the potential to provide consumers with a choice of exotic, surreal, or breathtaking experiences without any physical risk. Virtual reality has also been employed for more serious ends. Astronauts at the National Aeronautics and Space Administration used virtual reality devices as part of their training for the 1993 space shuttle flight, during which they repaired the Hubble Space Telescope. Department of Energy experts employ a virtual reality version of a nuclear weapon in a shipping container to train emergency workers to handle trucking accidents involving such devices. Another application of virtual reality technology is telepresence, or giving the participant a sensation of being in a distant location. Telepresence systems, for example, can allow a physician in a hospital to perform emergency surgery on a soldier by remote control while the soldier is still on the battlefield, rather than wait until the soldier is transported to the hospital. Telepresence also holds the potential to be used for operating robotic rovers on the moon or on Mars for scientific purposes, or for profit-generating entertainment ventures.

While virtual reality provides the possibility of creating new communities in cyberspace, critics of virtual reality—and of technology in general—warn that it might overwhelm and erode established networks of human existence. Some educators, for instance, debate the effectiveness of virtual reality to provide a "distance learning" experience that could substitute for the traditional, four-year undergraduate education. At the most extreme, however, criticism of technology has taken the form of terrorism, as in the case of the Unabomber, Theodore Kaczynski.

BIBLIOGRAPHY

Heim, Michael. The Metaphysics of Virtual Reality. New York: Oxford University Press, 1993.

———. Virtual Realism. New York: Oxford University Press, 1998.

Rheingold, Howard. Virtual Reality. New York: Summit, 1991.

VincentKiernan

Jason ScottSmith

See alsoEducational Technology ; Medicine .

virtual reality (VR) or virtual environment (VE), computer-generated environment with and within which people can interact. The advantage of VR is that it can immerse people in an environment that would normally be unavailable due to cost, safety, or perception restrictions. A successful VR environment offers users immersion, navigation, and manipulation. VR encompasses a range of interactive computer environments, from text-oriented on-line forums and multiplayer games to complex simulations that combine audio; video, animation, or three-dimensional graphics; and scent. Some of the more realistic effects are achieved using a helmetlike apparatus with tiny computer screens, one in front of each eye and each giving a slightly different view so as to mimic stereoscopic vision. Sensors attached to the participant (e.g., gloves, bodysuit, footwear) pass on his or her movements to the computer, which changes the graphics accordingly to give the participant the feeling of movement through the scene. Computer-generated physical feedback adds a "feel" to the visual illusion, and computer-controlled sounds and odors reinforce the virtual environment. Other VR systems, such as flight simulators , use larger displays and enclosed environments to create an illusion. Less-complicated systems for personal computers manipulate an image of three-dimensional space on a computer screen. In a virtual network many users can be immersed in the same simulation, each perceiving it from a personal point of view. VR is used in some electronic games , in amusement-park attractions, in military exercises, and to simulate construction designs. Experimental and envisioned uses include education, industrial design, surgical training, and art.

Bibliography: See H. Rheingold, Virtual Reality (1991); R. A. Earnshaw, Virtual Reality Systems (1993); L. C. Larijani, The Virtual Reality Primer (1994); J. Levy, Create Your Own Virtual Reality System (1995); D. N. Chorafas and H. Steinmann, Virtual Reality: Practical Applications in Business and Industry (1995).

virtual reality Use of computer graphics to simulate a three-dimensional environment that users can explore as if it were real. A virtual reality system can allow an architect to see what the inside of a building will look like before construction begins. Computer images are produced using an architect's drawings of the building. Some video games use virtual reality to simulate space-flight adventures and ball games.

virtual reality The combination of animation, sound, and graphics which simulate some physical location such as a supermarket or the inside of a passenger plane. A typical use for this technology would be for an online supermarket where the customer walks around the shelves of the supermarket by clicking a mouse. See VIRTUAL REALITY MODELLING LANGUAGE.

virtual reality (VR) The creation and experience of environments. The central objective is to place the participant in an environment that is not normally or easily experienced. Augmented reality is similar to virtual reality but the virtual image is superimposed on a real-world image often using see-through head-mounted displays.

vir·tu·al re·al·i·ty • n. Comput. the computer-generated simulation of a three-dimensional image or environment that can be interacted with in a seemingly real or physical way by a person using special electronic equipment, such as a helmet with a screen inside or gloves fitted with sensors.