Virtual reality (VR) is a simulated experience that can be similar to or completely different from the real world. Applications of virtual reality include entertainment (particularly video games), education (such as medical or military training) and business (such as virtual meetings). Other distinct types of VR-style technology include augmented reality and mixed reality, sometimes referred to as extended reality or XR. 
Currently, standard virtual reality systems use either virtual reality headsets or multi-projected environments to generate realistic images, sounds and other sensations that simulate a user's physical presence in a virtual environment. A person using virtual reality equipment is able to look around the artificial world, move around in it, and interact with virtual features or items. The effect is commonly created by VR headsets consisting of a head-mounted display with a small screen in front of the eyes, but can also be created through specially designed rooms with multiple large screens. Virtual reality typically incorporates auditory and video feedback, but may also allow other types of sensory and force feedback through haptic technology.
" Virtual" has had the meaning of "being something in essence or effect, though not actually or in fact" since the mid-1400s.  The term "virtual" has been used in the computer sense of "not physically existing but made to appear by software" since 1959. 
In 1938, French avant-garde playwright Antonin Artaud described the illusory nature of characters and objects in the theatre as "la réalité virtuelle" in a collection of essays, Le Théâtre et son double. The English translation of this book, published in 1958 as The Theater and its Double,  is the earliest published use of the term "virtual reality". The term " artificial reality", coined by Myron Krueger, has been in use since the 1970s. The term "virtual reality" was first used in a science fiction context in The Judas Mandala, a 1982 novel by Damien Broderick.
Widespread adaption of the term "virtual reality" in the popular media is attributed to Jaron Lanier, who in the late 1980s designed some of the first business-grade virtual reality hardware under his firm VPL Research, and the 1992 film Lawnmower Man, which features use of virtual reality systems. 
One method by which virtual reality can be realized is simulation-based virtual reality. Driving simulators, for example, give the driver on board the impression of actually driving an actual vehicle by predicting vehicular motion caused by driver input and feeding back corresponding visual, motion and audio cues to the driver.
With avatar image-based virtual reality, people can join the virtual environment in the form of real video as well as an avatar. One can participate in the 3D distributed virtual environment as form of either a conventional avatar or a real video. Users can select their own type of participation based on the system capability.
In projector-based virtual reality, modeling of the real environment plays a vital role in various virtual reality applications, such as robot navigation, construction modeling, and airplane simulation. Image-based virtual reality systems have been gaining popularity in computer graphics and computer vision communities. In generating realistic models, it is essential to accurately register acquired 3D data; usually, a camera is used for modeling small objects at a short distance.
Desktop-based virtual reality involves displaying a 3D virtual world on a regular desktop display without use of any specialized VR positional tracking equipment. Many modern first-person video games can be used as an example, using various triggers, responsive characters, and other such interactive devices to make the user feel as though they are in a virtual world. A common criticism of this form of immersion is that there is no sense of peripheral vision, limiting the user's ability to know what is happening around them.
A head-mounted display (HMD) more fully immerses the user in a virtual world. A virtual reality headset typically includes two small high resolution OLED or LCD monitors which provide separate images for each eye for stereoscopic graphics rendering a 3D virtual world, a binaural audio system, positional and rotational real-time head tracking for six degrees of movement. Options include motion controls with haptic feedback for physically interacting within the virtual world in an intuitive way with little to no abstraction and an omnidirectional treadmill for more freedom of physical movement allowing the user to perform locomotive motion in any direction.
Augmented reality (AR) is a type of virtual reality technology that blends what the user sees in their real surroundings with digital content generated by computer software. The additional software-generated images with the virtual scene typically enhance how the real surroundings look in some way. AR systems layer virtual information over a camera live feed into a headset or smartglasses or through a mobile device giving the user the ability to view three-dimensional images.
Mixed reality (MR) is the merging of the real world and virtual worlds to produce new environments and visualizations where physical and digital objects co-exist and interact in real time.
The exact origins of virtual reality are disputed, partly because of how difficult it has been to formulate a definition for the concept of an alternative existence.  The development of perspective in Renaissance Europe created convincing depictions of spaces that did not exist, in what has been referred to as the "multiplying of artificial worlds".  Other elements of virtual reality appeared as early as the 1860s. Antonin Artaud took the view that illusion was not distinct from reality, advocating that spectators at a play should suspend disbelief and regard the drama on stage as reality.  The first references to the more modern concept of virtual reality came from science fiction.
Morton Heilig wrote in the 1950s of an "Experience Theatre" that could encompass all the senses in an effective manner, thus drawing the viewer into the onscreen activity. He built a prototype of his vision dubbed the Sensorama in 1962, along with five short films to be displayed in it while engaging multiple senses (sight, sound, smell, and touch). Predating digital computing, the Sensorama was a mechanical device. Heilig also developed what he referred to as the "Telesphere Mask" (patented in 1960). The patent application described the device as "a telescopic television apparatus for individual use...The spectator is given a complete sensation of reality, i.e. moving three dimensional images which may be in colour, with 100% peripheral vision, binaural sound, scents and air breezes." 
The virtual reality industry mainly provided VR devices for medical, flight simulation, automobile industry design, and military training purposes from 1970 to 1990. 
David Em became the first artist to produce navigable virtual worlds at NASA's Jet Propulsion Laboratory (JPL) from 1977 to 1984.  The Aspen Movie Map, a crude virtual tour in which users could wander the streets of Aspen in one of the three modes (summer, winter, and polygons), was created at MIT in 1978.
In 1979, Eric Howlett developed the Large Expanse, Extra Perspective (LEEP) optical system. The combined system created a stereoscopic image with a field of view wide enough to create a convincing sense of space. The users of the system have been impressed by the sensation of depth ( field of view) in the scene and the corresponding realism. The original LEEP system was redesigned for NASA's Ames Research Center in 1985 for their first virtual reality installation, the VIEW (Virtual Interactive Environment Workstation)  by Scott Fisher. The LEEP system provides the basis for most of the modern virtual reality headsets. 
By the late 1980s, the term "virtual reality" was popularized by Jaron Lanier, one of the modern pioneers of the field. Lanier had founded the company VPL Research in 1985. VPL Research has developed several VR devices like the DataGlove, the EyePhone, and the AudioSphere. VPL licensed the DataGlove technology to Mattel, which used it to make the Power Glove, an early affordable VR device.
Atari, Inc. founded a research lab for virtual reality in 1982, but the lab was closed after two years due to the Atari Shock ( video game crash of 1983). However, its hired employees, such as Tom Zimmerman, Scott Fisher, Jaron Lanier, Michael Naimark, and Brenda Laurel, kept their research and development on VR-related technologies.
In 1988, the Cyberspace Project at Autodesk was the first to implement VR on a low-cost personal computer   . The project leader Eric Gullichsen left in 1990 to found Sense8 Corporation and develop the WorldToolKit virtual reality SDK,  which offered the first real time graphics with Texture mapping on a PC, and was widely used throughout industry and academia.  
In 1991, Sega announced the Sega VR headset for the Mega Drive home console. It used LCD screens in the visor, stereo headphones, and inertial sensors that allowed the system to track and react to the movements of the user's head.  In the same year, Virtuality launched and went on to become the first mass-produced, networked, multiplayer VR entertainment system that was released in many countries, including a dedicated VR arcade at Embarcadero Center. Costing up to $73,000 per multi-pod Virtuality system, they featured headsets and exoskeleton gloves that gave one of the first "immersive" VR experiences. 
That same year, Carolina Cruz-Neira, Daniel J. Sandin and Thomas A. DeFanti from the Electronic Visualization Laboratory created the first cubic immersive room, the Cave automatic virtual environment (CAVE). Developed as Cruz-Neira's PhD thesis, it involved a multi-projected environment, similar to the holodeck, allowing people to see their own bodies in relation to others in the room.   Antonio Medina, a MIT graduate and NASA scientist, designed a virtual reality system to "drive" Mars rovers from Earth in apparent real time despite the substantial delay of Mars-Earth-Mars signals. 
In 1992, Nicole Stenger created Angels, the first real-time interactive immersive movie where the interaction was facilitated with a dataglove and high-resolution goggles. That same year, Louis Rosenberg created the virtual fixtures system at the U.S. Air Force's Armstrong Labs using a full upper-body exoskeleton, enabling a physically realistic mixed reality in 3D. The system enabled the overlay of physically real 3D virtual objects registered with a user's direct view of the real world, producing the first true augmented reality experience enabling sight, sound, and touch.  
By July 1994, Sega had released the VR-1 motion simulator ride attraction in Joypolis indoor theme parks,  as well as the Dennou Senki Net Merc arcade game. Both used an advanced head-mounted display dubbed the "Mega Visor Display" developed in conjunction with Virtuality;   it was able to track head movement in a 360-degree stereoscopic 3D environment, and in its Net Merc incarnation was powered by the Sega Model 1 arcade system board.  Apple released QuickTime VR, which, despite using the term "VR", was unable to represent virtual reality, and instead displayed 360-degree interactive panoramas.
Nintendo's Virtual Boy console was released in 1995.  A group in Seattle created public demonstrations of a "CAVE-like" 270 degree immersive projection room called the Virtual Environment Theater, produced by entrepreneurs Chet Dagit and Bob Jacobson.  Forte released the VFX1, a PC-powered virtual reality headset that same year.
In 1999, entrepreneur Philip Rosedale formed Linden Lab with an initial focus on the development of VR hardware. In its earliest form, the company struggled to produce a commercial version of "The Rig", which was realized in prototype form as a clunky steel contraption with several computer monitors that users could wear on their shoulders. The concept was later adapted into the personal computer-based, 3D virtual world program Second Life. 
The 2000s were a period of relative public and investment indifference to commercially available VR technologies.
In 2001, SAS Cube (SAS3) became the first PC-based cubic room, developed by Z-A Production ( Maurice Benayoun, David Nahon), Barco, and Clarté. It was installed in Laval, France. The SAS library gave birth to Virtools VRPack. In 2007, Google introduced Street View, a service that shows panoramic views of an increasing number of worldwide positions such as roads, indoor buildings and rural areas. It also features a stereoscopic 3D mode, introduced in 2010. 
In 2010, Palmer Luckey designed the first prototype of the Oculus Rift. This prototype, built on a shell of another virtual reality headset, was only capable of rotational tracking. However, it boasted a 90-degree field of vision that was previously unseen in the consumer market at the time. Distortion issues arising from the lens used to create the field of vision were corrected for by software written by John Carmack for a version of Doom 3. This initial design would later serve as a basis from which the later designs came.  In 2012, the Rift is presented for the first time at the E3 video game trade show by Carmack.   In 2014, Facebook purchased Oculus VR for what at the time was stated as $2 billion  but later revealed that the more accurate figure was $3 billion.  This purchase occurred after the first development kits ordered through Oculus' 2012 Kickstarter had shipped in 2013 but before the shipping of their second development kits in 2014.  ZeniMax, Carmack's former employer, sued Oculus and Facebook for taking company secrets to Facebook;  the verdict was in favour of ZeniMax, settled out of court later. 
In 2013, Valve discovered and freely shared the breakthrough of low-persistence displays which make lag-free and smear-free display of VR content possible.  This was adopted by Oculus and was used in all their future headsets. In early 2014, Valve showed off their SteamSight prototype, the precursor to both consumer headsets released in 2016. It shared major features with the consumer headsets including separate 1K displays per eye, low persistence, positional tracking over a large area, and fresnel lenses.   HTC and Valve announced the virtual reality headset HTC Vive and controllers in 2015. The set included tracking technology called Lighthouse, which utilized wall-mounted "base stations" for positional tracking using infrared light.   
In 2014, Sony announced Project Morpheus (its code name for the PlayStation VR), a virtual reality headset for the PlayStation 4 video game console.  In 2015, Google announced Cardboard, a do-it-yourself stereoscopic viewer: the user places their smartphone in the cardboard holder, which they wear on their head. Michael Naimark was appointed Google's first-ever 'resident artist' in their new VR division. The Kickstarter campaign for Gloveone, a pair of gloves providing motion tracking and haptic feedback, was successfully funded, with over $150,000 in contributions.  Also in 2015, Razer unveiled its open source project OSVR.
By 2016, there were at least 230 companies developing VR-related products. Amazon, Apple, Facebook, Google, Microsoft, Sony and Samsung all had dedicated AR and VR groups. Dynamic binaural audio was common to most headsets released that year. However, haptic interfaces were not well developed, and most hardware packages incorporated button-operated handsets for touch-based interactivity. Visually, displays were still of a low-enough resolution and frame rate that images were still identifiable as virtual. 
In 2016, HTC shipped its first units of the HTC Vive SteamVR headset.  This marked the first major commercial release of sensor-based tracking, allowing for free movement of users within a defined space.  A patent filed by Sony in 2017 showed they were developing a similar location tracking technology to the Vive for PlayStation VR, with the potential for the development of a wireless headset. 
In 2019, Oculus released the Oculus Rift S and a standalone headset, the Oculus Quest. These headsets utilized inside-out tracking compared to external outside-in tracking seen in previous generations of headsets. 
Later in 2019, Valve released the Valve Index. Notable features include a 130° field of view, off-ear headphones for immersion and comfort, open-handed controllers which allow for individual finger tracking, front facing cameras, and a front expansion slot meant for extensibility. 
In 2020, Oculus released the Oculus Quest 2. Some new features include a sharper screen, reduced price, and increased performance. Facebook now requires user to log in with a Facebook account in order to use the new headset. 
In 2021, EASA approves the first Virtual Reality (VR) based Flight Simulation Training Device. The device, for rotorcraft pilots, enhances safety by opening up the possibility of practicing risky maneuvers in a virtual environment. This addresses a key risk area in rotorcraft  operations, where statistics show that around 20% of accidents occur during training flights.
In early 2017, a decline was starting for the public interest in Virtual Reality due to the low accessibility for general consumers and major competition with augmented reality titles that people could carry on their phones. 
Since 2017, major strides in the integration of Virtual Reality and Cognitive Behavioral Therapy have been made, focusing on how to tailor the experience to suit each individual patient. 
Over the past 5 years, the popularity of Virtual reality technologies has been on a steady increase, and is striving as a new technology. 
Modern virtual reality headset displays are based on technology developed for smartphones including: gyroscopes and motion sensors for tracking head, body, and hand positions; small HD screens for stereoscopic displays; and small, lightweight and fast computer processors. These components led to relative affordability for independent VR developers, and lead to the 2012 Oculus Rift Kickstarter offering the first independently developed VR headset. 
Independent production of VR images and video has increased alongside the development of affordable omnidirectional cameras, also known as 360-degree cameras or VR cameras, that have the ability to record 360 interactive photography, although at relatively low resolutions or in highly compressed formats for online streaming of 360 video.  In contrast, photogrammetry is increasingly used to combine several high-resolution photographs for the creation of detailed 3D objects and environments in VR applications.  
To create a feeling of immersion, special output devices are needed to display virtual worlds. Well-known formats include head-mounted displays or the CAVE. In order to convey a spatial impression, two images are generated and displayed from different perspectives (stereo projection). There are different technologies available to bring the respective image to the right eye. A distinction is made between active (e.g. shutter glasses) and passive technologies (e.g. polarizing filters or Infitec).[ citation needed]
In order to improve the feeling of immersion, wearable multi-string cables offer haptics to complex geometries in virtual reality. These strings offer fine control of each finger joint to simulate the haptics involved in touching these virtual geometries. 
Special input devices are required for interaction with the virtual world. These include the 3D mouse, the wired glove, motion controllers, and optical tracking sensors. Controllers typically use optical tracking systems (primarily infrared cameras) for location and navigation, so that the user can move freely without wiring. Some input devices provide the user with force feedback to the hands or other parts of the body, so that the human being can orientate himself in the three-dimensional world through haptics and sensor technology as a further sensory sensation and carry out realistic simulations. This allows for the viewer to have a sense of direction in the artificial landscape. Additional haptic feedback can be obtained from omnidirectional treadmills (with which walking in virtual space is controlled by real walking movements) and vibration gloves and suits.
Virtual reality cameras can be used to create VR photography using 360-degree panorama videos. 360-degree camera shots can be mixed with virtual elements to merge reality and fiction through special effects.[ citation needed] VR cameras are available in various formats, with varying numbers of lenses installed in the camera. 
Minimal Angle of Resolution (MAR) refers to the minimum distance between two display pixels. At the distance, viewer can clearly distinguish the independent pixels. Often measured in arc-seconds, MAR between two pixels has to do with the viewing distance. For the general public, resolution is about 30-65 arc-seconds, which is referred to as the spatial resolution when combined with distance. Let’s look at the actual numbers. Given the viewing distance of 1m and 2m respectively, regular viewers won’t be able to perceive two pixels as separate if they are less than 0.29mm apart at 1m and less than 0.58mm apart at 2m. 
Most small-size displays have a refresh rate of 60Hz, which will add about 15ms of additional latency. The number is reduced to less than 7ms with if the refresh rate is increased to 120Hz or even 240Hz and more. Participants will feel a lot more immersive as a result although higher refresh rates require graphics processing unit (GPU) powerful enough to process more frames per second (fps).
We need to consider our field of view (FOV) in addition to quality image. Our eyes have a horizontal FOV of about 120 degrees per side and a vertical FOV of some 135 degrees. Stereopsis vision is limited to 120 degrees where the right and the left visions overlap. Generally speaking, we have a FOV of 200 degrees x 135 degrees with two eyes. However, most of it is peripheral vision,  which varies from one person to another. So we conservatively take the average, i.e. 160 degrees. Therefore, if we keep our eyes stationary, a regular participant will have at least a stereopsis of 160 degrees x 135 degrees or 1/6 of the 360-degree FOV. We can quantify the abstract concept of immersion with the immersive index by getting the ratio of display viewing area and 1/6 of the 360-degree FOV.
Virtual reality is most commonly used in entertainment applications such as video games, 3D cinema, and social virtual worlds. Consumer virtual reality headsets were first released by video game companies in the early-mid 1990s. Beginning in the 2010s, next-generation commercial tethered headsets were released by Oculus (Rift), HTC (Vive) and Sony (PlayStation VR), setting off a new wave of application development.  3D cinema has been used for sporting events, pornography, fine art, music videos and short films. Since 2015, roller coasters and theme parks have incorporated virtual reality to match visual effects with haptic feedback. 
In social sciences and psychology, virtual reality offers a cost-effective tool to study and replicate interactions in a controlled environment.  It can be used as a form of therapeutic intervention. For instance, there is the case of the virtual reality exposure therapy (VRET), a form of exposure therapy for treating anxiety disorders such as post traumatic stress disorder ( PTSD) and phobias.   
Virtual reality programs are being used in the rehabilitation processes with elderly individuals that have been diagnosed with Alzheimer's disease. This gives these elderly patients the opportunity to simulate real experiences that they would not otherwise be able to experience due to their current state. 17 recent studies with randomized controlled trials have shown that virtual reality applications are effective in treating cognitive deficits with neurological diagnoses.  Loss of mobility in elderly patients can lead to a sense of loneliness and depression. Virtual reality is able to assist in making aging in place a lifeline to an outside world that they cannot easily navigate. Virtual reality allows exposure therapy to take place in a safe environment. 
In medicine, simulated VR surgical environments were first developed in the 1990s.    Under the supervision of experts, VR can provide effective and repeatable training  at a low cost, allowing trainees to recognize and amend errors as they occur. 
Virtual reality has been used in physical rehabilitation since the 2000s. Despite numerous studies conducted, good quality evidence of its efficacy compared to other rehabilitation methods without sophisticated and expensive equipment is lacking for the treatment of Parkinson's disease.  A 2018 review on the effectiveness of mirror therapy by virtual reality and robotics for any type of pathology concluded in a similar way.  Another study was conducted that showed the potential for VR to promote mimicry and revealed the difference between neurotypical and autism spectrum disorder individuals in their response to a two-dimensional avatar.  
Immersive virtual reality technology with myoelectric and motion tracking control may represent a possible therapy option for treatment-resistant phantom limb pain. Pain scale measurements were taken into account and an interactive 3-D kitchen environment was developed bases on the principles of mirror therapy to allow for control of virtual hands while wearing a motion-tracked VR headset.  A systematic search in Pubmed and Embase was performed to determine results that were pooled in two meta-analysis. Meta-analysis showed a significant result in favor of VRT for balance. 
In the fast-paced and globalised business world meetings in VR are used to create an environment in which interactions with other people (e.g. colleagues, customers, partners) can feel more natural than a phone call or video chat. In the customisable meeting rooms all parties can join using the VR headset and interact as if they are in the same physical room. Presentations, videos or 3D models (of e.g. products or prototypes) can be uploaded and interacted with. 
VR can simulate real workspaces for workplace occupational safety and health purposes, educational purposes, and training purposes. It can be used to provide learners with a virtual environment where they can develop their skills without the real-world consequences of failing. It has been used and studied in primary education,  anatomy teaching,   military,   astronaut training,    flight simulators,  miner training,  medical education,  architectural design,[ citation needed] driver training  and bridge inspection.  Immersive VR engineering systems enable engineers to see virtual prototypes prior to the availability of any physical prototypes.  Supplementing training with virtual training environments has been claimed to offer avenues of realism in military  and healthcare  training while minimizing cost.  It also has been claimed to reduce military training costs by minimizing the amounts of ammunition expended during training periods.  VR can also be used for the healthcare training and education for medical practitioners.  
In the engineering field, VR has proved very useful for both engineering educators and the students. A previously expensive cost in the educational department now being much more accessible due to lowered overall costs, has proven to be a very useful tool in educating future engineers. The most significant element lies in the ability for the students to be able to interact with 3-D models that accurately respond based on real world possibilities. This added tool of education provides many the immersion needed to grasp complex topics and be able to apply them.  As noted, the future architects and engineers benefit greatly by being able to form understandings between spatial relationships and providing solutions based on real-world future applications. 
The first fine art virtual world was created in the 1970s.  As the technology developed, more artistic programs were produced throughout the 1990s, including feature films. When commercially available technology became more widespread, VR festivals began to emerge in the mid-2010s. The first uses of VR in museum settings began in the 1990s, seeing a significant increase in the mid-2010s. Additionally, museums have begun making some of their content virtual reality accessible.  
Virtual reality's growing market presents an opportunity and an alternative channel for digital marketing.  It is also seen as a new platform for e-commerce, particularly in the bid to challenge traditional "brick and mortar" retailers. However, a 2018 study revealed that the majority of goods are still purchased in physical stores. 
In the case of education, the uses of virtual reality have demonstrated being capable of promoting higher order thinking,  promoting the interest and commitment of students, the acquisition of knowledge, promoting mental habits and understanding that are generally useful within an academic context. 
A case has also been made for including virtual reality technology in the context of public libraries. This would give library users access to cutting-edge technology and unique educational experiences.  This could include giving users access to virtual, interactive copies of rare texts and artifacts and to tours of famous landmarks and archeological digs (as in the case with the Virtual Ganjali Khan Project). 
There are many health and safety considerations of virtual reality. A number of unwanted symptoms have been caused by prolonged use of virtual reality,  and these may have slowed proliferation of the technology. Most virtual reality systems come with consumer warnings, including: seizures; developmental issues in children; trip-and-fall and collision warnings; discomfort; repetitive stress injury; and interference with medical devices.  Some users may experience twitches, seizures or blackouts while using VR headsets, even if they do not have a history of epilepsy and have never had blackouts or seizures before. One in 4,000 people, or .025%, may experience these symptoms. Since these symptoms are more common among people under the age of 20, children are advised against using VR headsets. Other problems may occur in physical interactions with one's environment. While wearing VR headsets, people quickly lose awareness of their real-world surroundings and may injure themselves by tripping over, or colliding with real-world objects. 
VR headsets may regularly cause eye fatigue, as does all screened technology, because people tend to blink less when watching screens, causing their eyes to become more dried out.  There have been some concerns about VR headsets contributing to myopia, but although VR headsets sit close to the eyes, they may not necessarily contribute to nearsightedness if the focal length of the image being displayed is sufficiently far away. 
Virtual reality sickness (also known as cybersickness) occurs when a person's exposure to a virtual environment causes symptoms that are similar to motion sickness symptoms.  Women are significantly more affected than men by headset-induced symptoms, at rates of around 77% and 33% respectively.   The most common symptoms are general discomfort, headache, stomach awareness, nausea, vomiting, pallor, sweating, fatigue, drowsiness, disorientation, and apathy.  For example, Nintendo's Virtual Boy received much criticism for its negative physical effects, including "dizziness, nausea, and headaches".  These motion sickness symptoms are caused by a disconnect between what is being seen and what the rest of the body perceives. When the vestibular system, the body's internal balancing system, does not experience the motion that it expects from visual input through the eyes, the user may experience VR sickness. This can also happen if the VR system does not have a high enough frame rate, or if there is a lag between the body's movement and the onscreen visual reaction to it.  Because approximately 25–40% of people experience some kind of VR sickness when using VR machines, companies are actively looking for ways to reduce VR sickness. 
The relationship between virtual reality and its underage users is controversial and unexplored. In the meantime, children are becoming increasingly aware of VR, with the number in the USA having never heard of it dropping by half from Autumn 2016 (40%) to Spring 2017 (19%). 
Valeriy Kondruk, CEO of VR travel platform Ascape, says the app downloads in March 2020 increased by 60% compared to December 2019 and doubled in comparison with January 2020. According to Kondruk, normally, the busiest month for VR companies is December, which is associated with winter holidays and people spending more time at home. 
In early 2016, virtual reality headsets became commercially available with offers from, for example, Facebook (Oculus), HTC and Valve (Vive) Microsoft (HoloLens), and Sony (Morpheus). At the time and to this day, these brands have different age instructions for users, e.g. 12+ or 14+, this indicates a completely self-regulatory policy. 
Studies show that young children, compared to adults, may respond cognitively and behaviorally to immersive VR in ways that differ from adults. VR places users directly into the media content, potentially making the experience very vivid and real for children. For example, children of 6–18 years of age reported higher levels of presence and "realness" of a virtual environment compared with adults 19–65 years of age. 
Studies on VR consumer behavior or its effect on children and a code of ethical conduct involving underage users are especially needed, given the availability of VR porn and violent content. Related research on violence in video games suggests that exposure to media violence may affect attitudes, behavior, and even self-concept. Self-concept is a key indicator of core attitudes and coping abilities, particularly in adolescents.  Early studies conducted on observing versus participating in violent VR games suggest that physiological arousal and aggressive thoughts, but not hostile feelings, are higher for participants than for observers of the virtual reality game. 
Experiencing VR by children may further involve simultaneously holding the idea of the virtual world in mind while experiencing the physical world. Excessive usage of immersive technology that has very salient sensory features may compromise children's ability to maintain the rules of the physical world, particularly when wearing a VR headset that blocks out the location of objects in the physical world. Immersive VR can provide users with multisensory experiences that replicate reality or create scenarios that are impossible or dangerous in the physical world. Observations of 10 children experiencing VR for the first time suggested that 8-12-years-old kids were more confident to explore VR content when it was in a familiar situation, e.g. the children enjoyed playing in the kitchen context of Job Simulator, and enjoyed breaking rules by engaging in activities they are not allowed to do in reality, such as setting things on fire. 
The persistent tracking required by all VR systems makes the technology particularly useful for, and vulnerable to, mass surveillance. The expansion of VR will increase the potential and reduce the costs for information gathering of personal actions, movements and responses.  Data from eye tracking sensors, which are projected to become a standard feature in virtual reality headsets,   may indirectly reveal information about a user's ethnicity, personality traits, fears, emotions, interests, skills, and physical and mental health condition. 
In addition, there are conceptual and philosophical considerations and implications associated with the use of virtual reality. What the phrase "virtual reality" means or refers to can be ambiguous. Mychilo S. Cline argued in 2005 that through virtual reality, techniques will be developed to influence human behavior, interpersonal communication, and cognition.   
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- Drummond, Katie (2014). "The Rise and Fall and Rise of Virtual Reality". The Verge. Retrieved 15 November 2014. Interviews on the history and future of virtual reality by leaders in the field.
- "Virtual reality in human-system interaction".