Main components

Virtual reality comprises two main elements: the user's environment and the virtual environment. As the user interacts with the virtual reality system, the two environments communicate and exchange information through a barrier called an interface. The interface can be considered as a translator between the user and the virtual reality system. When the user applies input actions (e.g. movement, force generation, voice, etc.), the interface translates these actions into digital signals, which can be processed and interpreted by the system. On the other hand, the calculated reactions of the system are also translated by the interface into physical quantities, which the user can perceive through the use of different display and actuator technologies (e.g., images, sounds, smells, etc.). Finally, the user interprets this information and reacts to the system accordingly.[10]​.

Importance of multimodality

In virtual reality applications, the exchange of different physical quantities between the user and the virtual environment occurs through different channels or modalities. Such modalities can be sound, vision or touch. Communication with multiple modalities is called multimodal interaction. Multimodal interaction allows several types of modalities to be exchanged simultaneously between the user and the virtual environment. The goal of applying multimodal interaction is to provide a complete and realistic picture of the situation, to provide redundant information, for example, for security reasons, and to increase the quality of presence[10].

Virtual reality can be of two types: immersive or non-immersive and semi-immersive.[11] Immersive virtual reality methods are often linked to a three-dimensional environment created by a computer, which is manipulated through helmets, gloves or other devices that capture the position and rotation of different parts of the human body. Non-immersive virtual reality also uses the computer and uses media such as the one currently offered by the Internet, in which you can interact in real time with different people in spaces and environments that do not actually exist without the need for additional devices to the computer. This case is close to navigation, through which the subject is offered the possibility of experiencing (moving, moving, feeling) certain spaces, worlds, places, as if he were in them.

Non-immersive virtual reality offers a new world through a desktop window. This non-immersive approach has several advantages over the immersive approach such as low cost as well as easy and rapid user acceptance. Immersive devices are high cost and generally the user prefers to manipulate the virtual environment through familiar devices such as the keyboard and mouse rather than through heavy helmets or gloves.

The high price of immersive devices has widespread the use of virtual environments that are easy to manipulate through simpler devices, as is the example of the important business of video game consoles or games in which numerous users interact through the Internet. It is through the Internet that VRML was born, which is a standard for the creation of these non-immersive virtual worlds, which provides a set of primitives for three-dimensional modeling and allows giving behavior to objects and assigning different animations that can be activated by users.

Semi-immersive virtual reality is very similar to immersive reality, with the difference that there are four cube-shaped screens that organize the user, requiring glasses and movement tracking devices and allowing contact with real-world resources, one of the most representative examples being the Cave Automatic Virtual Environment.

Finally, we must highlight some improvements that virtual reality systems facilitate, with regard to the treatment of diseases related to mobility problems.

Virtual reality can be carried out through different methods such as: a simulator or an avatar "Avatar (Internet)"), the projection of real images, using a computer or immersion in a virtual environment.

• - Simulators: The first type is through a virtual reality simulator. Vehicle driving simulators, for example, give on-board users the impression that they are driving a real vehicle, since it predicts the movement of the vehicle by giving a command and receiving the corresponding visual and auditory response (we press the accelerator and see on the screen how the car moves faster and we hear how the vehicle's revolutions rise). Simulators have been being used effectively to develop systems, to improve safety and to study human factors. Likewise, there are surgery simulators that provide dynamic and accessible practices.[12]​.

• - Avatars: With avatars, users can join the virtual environment in two ways: 1) Choosing a pre-designed avatar with computer graphics. 2) Making a recording of yourself through a video device. In the case of recording via a webcam, the background of the image is removed to contribute to a greater sense of reality. Virtual reality through avatars improves the interaction between the person themselves and the computer, since this form is more effective than the conventional desktop computer system. An example is Facebook VR avatars where the user can create their character based on their photos found in their user profile.[13]​.

• - Projection of real images: In the projection of real images applied in virtual reality, the graphic design of real environments plays a vital role in some applications such as: Autonomous navigation and construction of the graphic design of flight simulators. This type of VR is gaining popularity especially in computer-designed graphics, since it improves realism using photo-realistic images and the modeling process is much simpler. When generating realistic models, it is essential to accurately record data in three dimensions (3D). Cameras are normally used to design small objects at close range.[14]​.

• - By computer: This type of virtual reality involves showing a three-dimensional world on an ordinary computer without using any type of specific motion sensor. Many current computer games use resources such as characters and other devices that can be interacted with, to make the user feel part of the virtual world. A common criticism of this type of immersion is that there is no sense of peripheral vision, since the user's knowledge of what is happening around them is limited to their closest environment.

• - Immersion in virtual environments: The best option to experience VR is through a brain-machine interface, which allows direct communication between the brain and an external device. An intermediate step would be to produce a “virtual space” using a virtual reality headset where the images that appear on the headset are controlled through a computer. The only limits are the capacity of the computer that serves the experience, the quality of the VR glasses and the content available on the virtual reality platform.[15]​.

La realidad virtual se aplica a diversas áreas, incluyendo industria para adultos"),[16]​ arte, educación,[17]​ entretenimiento y videojuegos así como narrativas interactivas, milicia, educación, y medicina. Debido al crecimiento latente es predecible que llegue a cubrir otras industrias.[1][18]​[19]​.

Education

It was in 1993, when the first practical use of an application of virtual reality in education was carried out and was developed through a prototype of an applied physics laboratory.[20]​ It is advancing in leaps and bounds in the field of education, although there is still much to do. The possibilities of virtual reality and education are endless and bring many advantages to students of all ages. Currently there are few initiatives that create content for education, since all the attention and advances are being made in the entertainment industry, although many assume that it is what is coming in the future and will be a key piece in education.[21]​ In university studies this is already used for practice purposes and to generate experience such as to design architecture models (engineering) or see some systems of the human body (medicine). With the same objectives, a pilot test was carried out at the Hunters Lane Institute (Tennessee, USA) in 2017.[22]​.

Psychotherapy

In psychotherapy, the use of virtual reality has been quite novel, since it ensures that the subject is no longer in a passive position, allowing the subject to move around the environment and interact with it in different ways, making the interaction more intimate and thereby gaining ergonomics. Virtual reality can be used as a form of diagnostic and therapeutic intervention.[23]​ The main applications that have been developed so far have to do with exposure techniques commonly used for the treatment of phobias. Max M. North, Sarah M. North and Joseph K. Coble, these scientists treated aerophobia, social phobia, agoraphobia, but progress has also been made in other fields such as eating disorders.[24]​ Also, there are numerous applications of virtual reality for psychological rehabilitation and psychomotor.[25]​.

In the case of aerophobia or fear of flying, virtual reality offers many advantages for the treatment of mental illnesses or disorders. Firstly, the control over what happens in the virtual world is total, which is why the patient can be guaranteed that whatever they want to happen in that virtual world will happen. In this way, the therapy environment will be characterized as a protected environment where the patient can explore without obtaining direct consequences and, subsequently, can apply the acquired skills in the natural environment.[26]​.

With regard to psychotherapy research, several advantages offered by virtual reality are being used and can be summarized as: greater control over the introduction of stimuli; greater variety in response options; introduction of stimuli in three dimensions; creation of complex scenarios; generation of varied sensory stimuli, potentially including audio, touch, smell and movement, that are perceived simultaneously with the graphically generated environment; precise and independent manipulation of the geometric and photometric relationship between objects; possibility of examining sophisticated and complex behaviors of participants such as avoidance; and the study of situations that in real life may be impractical, dangerous or ethically questionable. However, despite the enormous potential of virtual reality, researchers must be aware of certain limitations, among which the variable "presence" stands out, since virtual immersion is not necessarily sufficient to give the participant the sensation that the objects are "really there" and to react genuinely.[27][28]​.

Medicine

Recent years have brought about a drastic change in patient awareness and sense of adverse effects in healthcare. Combining this process with an increasing focus on patient safety has challenged traditional educational paradigms in the medical field. Especially in the surgical field, the time-honored concept of theoretical education followed by supervised clinical practice, often referred to as "see, do, teach", is becoming less acceptable, so innovative and complementary methods of teaching medical knowledge are sought. Other concerns are based on the high cost of teaching in a clinical setting. The level of costs, complexity, risks and temporal exposure of the training process increases with the fidelity of the objects.[29]​.

The application of virtual reality (VR) technology in medicine, for example for learning anatomy and especially in the clinical area: especially for surgical training of residents in training, and for patients in pain management, physical rehabilitation and therapeutic treatment of mental illnesses.[30]​.

Compared to animal models, videos and e-learning, virtual reality simulations are more realistic because the anatomical structures displayed in 3D graphics are more intuitive. Students can interact with all anatomical structures, such as skin, muscles, bones, nerves, and blood vessels. The changes that occur after each surgical step are very similar to those in reality. The entire performance can be recorded, compared and analyzed, making the data permanently available to trainees.[31]​ From a different perspective, supervisory supervision and patient participation are no longer necessary during the period of training and acquisition of basic skills, as virtual reality simulations can provide a controlled virtual environment necessary to satisfy these requirements outside the operating room.[32]​.

Multiple aspects of a learner's psychomotor performance skills can be directly measured through the objective performance assessment that is offered by simulations. The training effect of VR simulations is usually evaluated by standard parameters, including time taken to complete the task, route length, number of collisions, injuries, number of anatomical landmarks identified, number of loose bodies found, satisfaction, etc.[30]​.

The idea of ​​using VR-based surgical simulators to train potential surgeons has been a topic of research for more than a decade. However, surgical simulation is still far from being integrated into the medical curriculum. There are a number of questions still open, for example, the level of simulation realism that is needed for effective learning, the identification of the components of surgical skills that must be trained, as well as the validation of the training effect. Current research strives to address these issues with a new generation of highly realistic simulators. A key element of realism is the fidelity and variability of the training scene, which reflects differences in individual patients.[33]​.

Entertainment

Throughout the decade, media have been incorporated whose purpose is to entertain the user, opening a new level of exponential communication channel. The most notable examples are the short films made by Google Spotlight Stories, highlighted for their quality of storytelling for virtual reality. Its approval is given by the accessibility of using it from a mobile phone to a PC with tracking sensors. On the other hand, the inclusion of 360-degree cameras such as GoPro, VIRB, Samsung, Insta 360 ONE"), Nikon KeyMission 360, Insta 360 Air, among others,[34]​ have allowed the use of mobile devices to reproduce content in 360 degrees for later editing.

It remains to be noted that the film industry has focused on channeling advertising in 360 degrees, as in Isle of Dogs "Isle of Dogs (film)") where you experience the scenery of the stop-motion film alluding to a behind-the-scenes in virtual reality, drawing attention on social networks.[35]​.

Finally, the animated short film Pearl directed by Patrick Osborne") in 2007 and winner of the Emmy Award-Winner expresses the narrative potential that can be evoked from the use of new technologies, allowing psychological knowledge of the characters, making the user maintain attention to their entire environment to better understand the story.[36]​.

As Matthew Schnipper" mentions in the report "The State of Virtual Reality")[37]​ for the portal The Verge: “The promise of virtual reality has been overestimated. Wear glasses, position yourself here and you will be transported there. It is the same escapism promised by drugs, alcohol, sex or art – shedding worldly shackles through metaphysical transportation to altered states.”[38]​[39]​.

Video games

Video games have evolved considerably. The graphic quality has reached the point of equaling that of consoles such as those already seen Doom VR and Fallout 4 VR, making virtual movement through teleportation within the map. The mix between virtual reality experience and VR video game culminates in a hybrid of experiences as can be seen in Rick and Morty:Virtual Rick-ality") or Job Simulator, allowing the user to act easily in the environment without having to travel by means of teleportation in order to avoid visual fatigue.[40]​.

As a precedent for incorporating a VR monitor into consoles, we find the PlayStation VR that incorporates controls with motion sensors that delimit a location in space and the work engine falls on the console, in order to excuse the purchase of a demanding PC, gradually introducing the community to new technologies to implement exponential developments.[41]​ However, consoles like the Xbox One have not announced any type of competition in that field, casting doubt on whether the future of entertainment is reality. virtual.

As virtual reality technologies advance, the strong influence of video games on culture affects non-fiction storytelling and also journalism as they seek to impact current trends.[42]​.

Virtual reality rooms with immersive games have been inaugurated in Spain and Argentina;[43]​[44]​ these are spaces designed to offer entertainment and simulation experiences through virtual reality technology. In addition to visors, they can also be equipped with haptic gloves, motion sensors, and motion platforms. These additional devices allow you to interact naturally with a virtual environment and, in the case of motion platforms, simulate physical movements, thus increasing the feeling of immersion.[45]​.

Software

Currently, after the incorporation of HDM compatible with Steam VR, they have allowed this technology to be incorporated into design software, providing a new perspective and manipulation of the environment for the creation of digital content. Software such as Autodesk Maya, Maxon Cinema 4D, Sidefx") Houdini 16"), Adobe After Effects, Adobe PremierPro, Blackmagic Fusion 9"), among others, have integrated the editing option using virtual reality devices either to reproduce or create content for the same platform. interactive creating entertainment, augmented reality or virtual reality experience.[49]​ If the content is cinematic, it can be exported to be played on 360-degree video platforms such as YouTube or Steam applications.[50]​.

360-degree videos or VR allow the user to be at the center of the action regardless of the purpose sought by the user.[51]​.

On the other hand, within the field of web design we can find what is known as the immersive web[52]​ which refers to the inclusion of virtual, augmented and mixed reality experiences that are very useful in areas such as training, news and retail. For this area, frameworks such as A-Frame, React 360 or Amazon Sumerian have been developed that facilitate the inclusion of this technology for web developers and designers.

Finally, programs such as Adobe Audition[51]​ or Final Cut Pro

The origin of virtual reality dates back to World War II. The United States Navy contacts MIT (Massachusetts Institute of Technology) for the possible creation of a flight simulator suitable for training bomber pilots. The project was called Whirlwind and its construction ended a few years later in 1951. It was not until 8 years later when the USAF (United States Air Force) took up the project under the name "Claude Project") and a civilian use of 3D technology appeared.[55]​.

Various virtual reality systems have been created throughout the century. In 1962, Morton Heilig built the Sensorama, a machine that displayed wide-angle three-dimensional stereoscopic images, with stereo sound, wind and aroma effects, and a moving seat. In 1968, Ivan Sutherland built The Sword of Damocles, a virtual reality headset that displayed stereoscopic images with wireframe models.[57]

In 1978, an MIT team led by Andrew Lippman created the Aspen Movie Map, a program that allowed the user to explore the streets of the city of Aspen, using real footage of the place, and interact with certain buildings, allowing the user to see their interior and historical data.[58]​.

In 1984, the Baltimore headquarters of the Six Flags amusement park chain debuted The Sensorium, a 4D movie theater that combined a movie with stereoscopic projection, vibrating seats, and aromatic effects.[59]

In 1987, Nintendo released the Famicom 3D System and Sega released the Master System, both virtual reality headsets with shutter lenses.[60][61]​.

In 1991, Sega announced the release of the Sega VR, a virtual reality headset with an LCD screen and stereo headset for arcade machines and video game consoles. The device was introduced to the public in 1993, and was announced to cost $200, but was never marketed.

In 1994, it launched the Sega VR-1, a motion simulator that incorporated a headset with three-dimensional polygonal graphics and head movement tracking.

In 1995, Nintendo released the Virtual Boy, a virtual reality headset with a monochrome parallax display.[62] That same year, Forte released the VFX1, a virtual reality headset with stereoscopic imaging, head movement tracking, and stereo headsets.[63]​.

In 2012, Palmer Luckey presented the first prototype of the Oculus Rift virtual reality headset.[64]​ The customer version began shipping in 2015. In 2016, Sony launched the PlayStation VR,[65]​ while HTC and Valve launched the HTC Vive.[66]​.

Diversas empresas están trabajando actualmente sobre productos de realidad virtual. Algunos están en fase de desarrollo, otros disponibles comercialmente:.

Helmets or glasses

Also known as HMD (head-mounted display), there are basically two types: those with a built-in screen and those that are essentially a casing for the user to insert a smartphone.

As for the display, LCD technology used to be used, although some are beginning to appear, such as the Razer OSVR HDK 2, the PlayStation VR itself, or the new Oculus with OLED screens. While some HMDs use two LCD displays (one for each eye), others opt for a single display with a division in the center. Some have lenses placed between the eyes and the display, and can be adjusted to the distance of the eyes. The lenses modify the image for each eye, changing the angle of the 2D image of each display to create a 3D effect, simulating the differences with which things are seen with one eye compared to the other.[67]​.

Another important aspect of HMDs is the field of view. Human beings have a horizontal field of vision of about 180° to 220°, sometimes more, although it varies from person to person. This vision is monocular, that is, it is only perceived by one of the two eyes. The field of vision perceived by both eyes (and therefore seen in 3D) is about 114°. For this reason, a 360° field of view would be unnecessary. Most HMDs operate with a field of view between 110° and 120°.[67]​[68]​.

Finally, two points must be highlighted: frames per second (FPS) and latency. A minimum of 60 FPS is essential so that the eye perceives the images naturally and does not cause dizziness. All major HMDs exceed this minimum. The other point is the latency, which must be less than 20 ms so that the user does not experience a feeling of delay between what they do and what they see.[67]​.

• - Rift: virtual reality device for both recreational and professional uses, developed by the company Oculus VR (acquired by Facebook for almost 2 billion euros in 2014[69]​). It is in the development phase but you can buy its experimental model. It works connected to a computer, where the software runs, allowing you to take advantage of all the power of that computer for your recreation of the virtual world.

• - PlayStation VR: also known as Morpheus, is a virtual reality headset currently under development by Sony. It is designed to be fully functional with the Playstation 4 and Playstation 4 Pro console. Released on October 13, 2016.

• - Vive: joint project of Valve Corporation and HTC, currently in development, of an HMD with an announced resolution of 1080x1200 for each eye, refresh rate of 90 Hz, and more than 70 position and orientation sensors. It is part of Valve's SteamVR project, its viewing range is 100°.

• - VivePro: Launched in early 2018, they stand out for their superior image clarity than their predecessor, consecutively integrating two cameras that allow better user tracking for a better experience. On the other hand, they offer better comfort as they are lighter and for the first time the headphones are included, standing out from the previous model by not having to purchase an extra accessory. Separately, they offer the company's first transmitter working at 60 Hz, excusing the TPcast Archived May 10, 2020 at the Wayback Machine.

• - StarVR"): developed by Starbreeze Studios and compatible with the SteamVR open system. They stand out for their wide field of vision (210º) by using two 2560 x 1440 screens, one for each eye.

• - FOVE VR"): They have the peculiarity of incorporating eye tracking, which allows things like focusing the image according to where you are looking, or new forms of visual interaction.

• - Pimax 4k"): they have two 2k monitors culminating in 4k vision. Unlike the competition, the glasses have a gyroscope sensor instead of the already known motion tracking.

• - Pimax 8k"): compatible with SteamVR "Steamroller (microarchitecture)"), these glasses incorporate two 4k monitors and have tracking points for compatibility with scanning sensors. Their first instance was thanks to Kickstarter where the Pimax company innovated with the prototype with 200° of vision, surpassing the competition. Finally, they have eye tracking and compatibility with HTC Vive.

• - Gear VR: virtual reality device developed by Samsung in collaboration with Oculus VR. Unlike the Oculus Rift, it does not include a screen, but is mostly a case with some buttons and an advanced motion sensor, designed to place advanced phones from Samsung itself that will act as a screen and computer processor.

• - Cardboard: cardboard casing developed by Google and intended to be able to cheaply experience virtual reality at home by placing a smartphone of any brand in it.[70]​[71]​ Launched in 2014 and discontinued in 2021.

• - Daydream View: viewer of the Daydream virtual reality platform developed by Google. Launched in 2016 and discontinued in 2019, it was compatible with a few certified mobile devices and was accompanied by a controller with orientation sensors. The first services presented were Google Street View or a cinema experience.[72]​.

• - Virtual Boy: console launched by Nintendo in 1995 that included monochrome glasses that reproduced a 3D environment, therefore a precursor to virtual reality. Its commercial failure caused it to disappear from the market the year after its launch.

• - Forte VFX1"): was an HMD launched on the market in 1995. It connected to a PC and offered a stereoscopic image with three-axis head tracking and a resolution of 263 x 230 pixels per eye.

• - eMagin Z800 3DVisor"): HMD manufactured since 2005, with two 800x600 pixel OLED screens, which was mainly intended for viewing 3D images or for use as a portable monitor, although it also incorporated motion sensors that made it possible to use them with first-person shooter video games.[73]​.

Position sensors

The most advanced HMDs are sold accompanied by devices known as position sensors that, placed in the room, allow the system to determine the location of the HMD and other peripherals that the user may carry, thus giving the user the possibility of moving freely in the virtual space to scale.

Among the best known are the Lighthouse used by the HTC Vive glasses, or the Constellation used by the Oculus Rift. [74]

Drivers

Virtual reality systems usually incorporate control devices that allow interaction with the displayed environment, and which normally consist of controls with buttons that are held with the hands and that have absolute positional tracking. This is the case of the Oculus Touch or the HTC Vive controllers or the Sony PSVR. There are also gloves, or position sensors capable of detecting the position of the body or parts of it.

• - Leap Motion"): accessory consisting of a sensor that remotely perceives the movements of the hand, thus converting it into an input device (a controller).

• - STEM System"): system for wireless detection of body movements, developed by the company Sixense. It represents an extension on the Razer Hydra controller, from the same manufacturer (Sixense).

• - PrioVR"): similar in functionality to the previous one, it is responsible for transferring the user's body movements to the virtual environment.

• - Gloveone"): virtual reality haptic device developed by NeuroDigital Technologies. It is a glove that allows receiving haptic sensations through ten actuators strategically arranged on the fingertips and palm of the hand in order to give the user the sensation of having or feeling an object in their own hand. Gloveone also provides hand and finger tracking by itself, although it is 100% compatible with Leap Motion and RealSense. It allows you to interact with objects displayed on the screen. from a computer or on an HMD such as the Rift, Gear VR, Vive or OSVR.[75]​.

• - PowerClaw"): interface that stimulates the skin, developing the sense of touch. The device has the functionality of generating the sensation of heat, cold, vibration and roughness. This system has direct integration with the Oculus Rift, virtual reality helmet and Leap Motion"), which is a gesture control system.

• - HTC Vive Virtual Reality System Tracker: External sensor to the viewers that integrates information to the positioning sensors to incorporate everyday objects into virtual reality by emitting information about their positioning.[76]​.

• - VR Gun: Device that incorporates the HTC VIVE Virtual Reality System Tracker") to an external control in the form of a weapon in order to make the virtual reality experience more enjoyable and integrate into shooting games.[77]​.

• - Pimax Controller"): Controller similar to the predecessors, however, they have a pad similar to that of the Oculust Rift but incorporating a ribbon that makes it possible to hold the controller without having to use fingers, giving the user the sensation of grabbing and releasing objects within the visual environment when connecting in virtual reality. The built-in triggers allude to the predecessor designs to comply with compatibility in Steam and flight simulators.[78]​ They are also compatible with the positioning sensors of HTC Vive.[79]​[80]​.

Other peripherals

• - Virtuix Omni: peripheral accessory for the Rift, consisting of an omnidirectional platform on which the user can walk without leaving the site.

• - Cyberith Virtualizer"): another omnidirectional platform, similar to the previous one, developed by an Austrian company.

• - TPcast Archived May 10, 2020 at the Wayback Machine: complementary accessory for Oculus and HTC Vive that allows wireless transmission, however, external batteries and a Wifi signal repeater are required.

Other systems

• -

CAVE system at the University of Illinois at Chicago

CAVE System (Cave Automatic Virtual Environment): is a technology that creates a virtual reality environment in a cube-shaped room, on whose walls images are projected. The user, located in the center of the cube, observes the images around him with 3D glasses to have a sense of depth. The sound is generated with speakers located at different points in the room. These systems have existed since the 1990s.

Software and content

Along with the hardware products just mentioned, various companies are developing software and content, with the tools available for this, to be enjoyed through virtual reality devices. Some that can be highlighted are:

• - Demos (environments to explore): Tuscany Dive, Riftcoaster, Evil Dead Project, Cmoar Roller Coaster VR, Ready Player One: OASIS beta"), among others.[81]​.

• - Video games: Elite: Dangerous, Alien Isolation, EVE Valkyrie, Hardcode VR, Herobound, Lamper VR, Anshar Wars 2, Land's End, House of Terror VR, and others; as well as mods of classic games adapted to VR such as Team Fortress 2, Half-Life 2, Richard Burns Rally, Quake VR, The Elder Scroll V SKYRIM VR, Doom VR, Fallout 3 VR and others.[82]​.

• - Video: 360 videos of different genres (documentary, fiction, recreation, musical, among others) and applications to view them (Youtube, Within, Cineveo, CineVR, etc.).[83]​.

• - Education: Space Engine, Expeditions, Unimersiv, Apollo 11 VR, Hindenburg VR, Oneiric Masterpieces - Paris, Douarnenez VR, Great Pyramid VR, 7VR Wonders, 3D Organon VR Anatomy, The Body VR: Journey Inside a Cell, InCell VR, InMind VR.[84]​.

• - Virtual tourism: VR Cities, Sites in VR, Visoplaces.

• - Plastic arts: Inception VR.

• - Communication: AltspaceVR.

• - Medicine: ER VR, 3D Organon VR Anatomy, The Body VR: Journey Inside a Cell.[85]​.

• - Utilities: MINT VR, Supermedium- VR Browser, Pluto, LIV client, NVR Player, Hub Culture VR, HELI, Windows Mixed Reality for SteamVR, VoxVR, VRMakingSense, Virtual Sapce, among others.[86]​.

• - Solidarity: Empowered Reality.[87]​.

Problems identified by consumers

Forbes identifies four problems to avoid in upcoming VR products:[88]​.

• - Need to connect the glasses to a PC (the introduction of a mobile phone is important).

• - Price too high for most people.

• - Lack of content that justifies the purchase.

• - Very heavy helmets, which allows them to be worn only for a limited time.

• - Only one user can occupy the device at a time.[89]​.

Other aspects that are sometimes criticized are:

• - High demands on PC graphics cards.

• - Some helmets do not include headphones, making the experience uncomfortable.

• - You need ample space to scale the motion sensors.

• - Eye fatigue after long exposure.

• - Ability to hit objects in the room while using the headset.

• - The use of prescription lenses does not favor the VR experience due to the use of the helmet.

• - Difficulty sharing the experience (the viewer is for individual use).

• - Reduced field of vision with deformation on the sides.

• - Use of cables that hinder movement.[90]​.

• - Heavy controls without flexibility.

• - Not suitable for epileptic users.

• - Problems in positioning sensors.[91]​.

• - Requirements of large empty spaces for a correct arrangement of positioning sensors.[92]​.

Para proporcionar a los usuarios la sensación de realismo al utilizar los dispositivos de realidad virtual, se requieren una serie de técnicas como el seguimiento de cabeza, de movimiento y ocular. De igual forma los mandos forman parte importante de la experiencia pues, al contar con vibración conectan al usuario con las acciones que realiza en la pantalla.[93]​.

head tracking

Head tracking allows an application to recognize the user's head movements, and pan the image when the user moves their head in any direction. To carry out this monitoring, accelerometers, gyroscopes and magnetometers incorporated into the HMDs are used. In addition, each company uses its own technique to determine the position of the head.[67]​.

The Oculus Rift uses its own positioning system called Constellation. It consists of a set of twenty infrared LEDs placed around the helmet forming a recognizable pattern and a sensor. The sensor captures frames and analyzes the position of all the LEDs, thus allowing tracking.[67]​.

Something similar is what PlayStation VR uses, except there are only nine LEDs. The disadvantage of PSVR is that it has to be adjusted with the camera every time a person of a different height (for example) uses it. In addition, the PlayStation Camera, necessary to be able to use it, must be close enough to the user to work well. In fact, Sony recommends that you use the PSVR sitting down, approximately 1.5 meters from the camera and with enough room to make some light movements. In fact, from this distance the performance decreases, and Sony does not guarantee that the camera correctly detects movement from 9.8 feet (about 3 meters).[94]​[95]​.

The method used by the Vive is much more innovative. This is a tracking system called Lighthouse, developed by HTC and Valve. It does not require any camera, and the HMD does not emit light. The system consists of two boxes that are placed on the wall at a 90° angle. These boxes contain LEDs and two laser emitters, one horizontal and one vertical. On the other hand, the HMD and the two controls (two are necessary to determine the position of both hands and arms) have sensors that capture the light and lasers emitted by the boxes that are located on the walls of the room. The LEDs light up and the receiving devices start counting. One of the two lasers emits a sweep throughout the room. The devices detect which sensors have been hit by the sweep and how much time has passed since the LEDs flashed and use this information to calculate their position with respect to the boxes. When you get too close to a wall, a translucent grid appears warning you that you are close to a real wall. All this with a jitter (the imprecision of measurements when the object is stationary) of only 0.3 mm.[96]​[97]​.

Motion tracking

Motion tracking or tracking is an extension of head tracking, but allowing other types of movements to be recognized, such as that of the extremities. This field is not as advanced as the previous one, although large companies are focusing their interest on it.[67]​.

Apart from the promising and already mentioned Lighthouse from Valve, there are other options, for example the Leap Motion Orion. This is an extremely accurate hand tracking system. It detects all finger and joint movements even in diffuse environments and with varying levels of light, although it has some disadvantages, such as the fact that you have to be looking at your hands for the system to detect them. Another problem, not unique to Orion, is the lack of something tangible in the hands. In real life, when you come into contact with something, your sense of touch is activated and you feel that something. In virtual reality, however, your hands are empty and therefore you have no way of knowing if you are holding the object the way you want, or the force that is being applied to it. Developers are trying to make up for this lack of tactile response through auditory signals that indicate when and how to come into contact with an object, but the sensation is not the same.[98]​[99]​.

The Oculus alternative is Touch, a control system that consists of two gripped controls and a wrist strap, which makes the user feel that they are using their own hands. Each of these two controls is shaped like a crescent and has two buttons, an analog stick and an analog trigger, as well as a mechanism called a hand trigger, which replicates the sensation of firing a gun. Touch also makes use of the Constellation positioning system and unlike Leap Motion's Orion, it does have tactile feedback. The controls also have sensors that allow them to detect a series of hand gestures, such as making a fist, pointing with the index finger or raising the thumb. The disadvantage of Touch compared to Orion is that, despite being very advanced, it is still a command and therefore far from the freedom of movement that the latter offers.[100]​[101]​.

It is also worth highlighting the contribution of the Spanish company NeuroDigital Technologies with its GloveOne"). It is a glove that aims to give the user that much-desired tactile feedback. It currently does not have a tracking system, so it uses a Leap Motion for this, but it allows the user to perceive the weight, shape, volume and texture of the objects with which it interacts. To do this, it uses sensors located near the thumb, index and central fingers, in addition to the palm of the hand. In addition, it contains 10 actuators distributed between the palm and the tips of the fingers. Each of them vibrates individually, with different frequencies and intensities, precisely reproducing the sensations of touch.[102]​[103]​.

There are other motion tracking systems, such as suits, voice controls or even treadmills such as Virtuix Omni, which allow the user to explore long distances by walking (or running).[67]​.

Eye tracking

This is a technology that the main companies have not yet incorporated, but it is present in the FOVE VR HMD. This virtual reality helmet incorporates interior infrared sensors that capture eye movements. This allows a range of options that range from replicating your eye movements in your virtual avatar, to provoking reactions from other characters depending on the way you look at them. What's more impressive is the realism that eye tracking offers.

In real life, the eyes have a central focus point, while the rest is out of focus. This is very difficult to replicate, leading to an over-focus on other companies' systems, which reduces the feeling of immersion. Eye tracking solves this problem, allowing you to focus only on what the user is looking at. Furthermore, it could lead to hypothetical optimizations: the application could use its resources to render high-quality objects that are in the user's field of view, applying few resources to everything that is out of focus at that moment. This technology however requires high resolution screens, since the point focused on by the user should be as realistic as possible. Overfocusing the other systems can cause motion sickness, something that eye tracking could also prevent.[67][104]​.

physical problems

One of the biggest difficulties of virtual reality is making the user feel a sensation of immersion without feeling nausea, dizziness, etc. Experiencing these symptoms when using virtual reality is known as cybersickness or virtual reality sickness and is similar to classic motion sickness, or the motion sickness that pilots experience in simulators. The perception of these symptoms also depends on the person. For some, vomiting appears within a few minutes, while others can enjoy virtual reality for hours without any consequences.

The problem lies in a mismatch between the vestibular system (the liquids and fluids in the cavities inside the ear, which send information to the brain about direction, angles, etc.) and the visual system.[105]​.

These side effects of virtual reality have different causes. Developers try to perfect their systems to avoid or combat them in the best possible way, these being latency, image duplication and persistence among others.

Latency is the delay between the action performed by the user and its representation on the screen, producing imbalances between the vestibular and visual systems, in turn causing nausea and dizziness.[105]​.

The common latency in video games is the time interval between the user pressing a button and the pixels updating, generally being a minimum of 50 ms. It is important not to confuse this delay with the time between when a user presses a button and the action is carried out, being insufficient for virtual reality, which requires a latency of at least 20 ms so that the user does not experience a delay. In fact, most experts believe that the limit is even lower, at 15 or even 7 ms. Oculus Rift has a delay under optimal conditions of between 30 and 40 ms.

This is because the process of rendering the image requires the tracking system to determine the exact position and orientation of the HMD, the application rendering the scene, so that the hardware transfers the rendered scene to the HMD screen and it begins to emit photons for each pixel.

The first step, tracking takes between 10 and 15 ms when it comes to optical tracking, which in itself is too long. Accelerometer tracking is much faster with a latency of 1 ms or less, but it is imprecise and drifts a lot. One of the main problems is that 60 Hz screens, for example, already introduce a delay of about 15 or 16 ms in rendering. This value is dependent on the CPU and GPU, but is usually in that range except for older applications that require primitive rendering.

Finally, the hardware transfers the rendered scene to the HMD screen. For most frequency scanning based systems, this means a delay of about 16 ms in the worst case (assuming 60 Hz displays are used). If the image is transmitted immediately, that is, the photons begin to appear instantly upon arrival, the sum of the latencies mentioned above is much higher than 20 ms and is an abysmal distance from the desired 7 ms.

Another major drawback is image judder or duplication. It is a combination of two phenomena, image blurring and stroboscopy. Blurring or smearing is a motion blur present in virtual reality. Strobing or stroboscopy, on the other hand, consists of the perception of multiple copies of an image at the same time, making it appear that there is no movement between them. The union of these two phenomena constitute image duplications.

Judder normally produces dizziness and all related symptoms, so you should try to avoid it. One cause of judder is the fact that pixels move across the retina while they are on (causing smearing). The obvious solution to image duplication is an increase in frame rate. The problem is that to avoid it completely, a frame rate of between 300 and 1000 FPS would be necessary, something too far from reality. Therefore, although the solution is obvious, it is also totally impossible due to technological limitations.

The other solution has to do with persistence. Most displays have full persistence, so the pixels always stay on. The level of blur does not depend on what fraction of a frame the pixels are on, but on the total time that they are on. This is why a frame rate of around 1000 FPS would be ideal with full persistence, as the time would be just 1 ms.

Since this frame rate is currently unattainable, low persistence must be used to achieve the same result. With zero (or almost zero) persistence, the movement of lit pixels across the retina is eliminated, since they remain lit for a very short time. Thus, the blur component in image duplication is eliminated. However, low persistence also has disadvantages, as it can increase stroboscopy. In fact, the smearing itself obscures the stroboscopy quite a bit. By reducing the first using low persistence screens, the second is manifested more clearly. However, this problem is not that serious. The reason is that in the image that the eye is focusing on, stroboscopy will not occur, since the eye itself will avoid it by following it, because the same pixels will go to the same point on the retina in each frame. Although this effect will occur in the rest of the image, it will not be as noticeable since it will be out of focus.[106]​[107]​[108]​.

Privacy and data protection

As new technologies advance, concerns about data protection grow considerably. It is not only important who has access to our data, but also the great unknown of the purposes for which these data will be used.[109]​ This therefore generates an ethical debate that must be addressed.

It is important to consider that virtual reality not only makes use of our personal data, but also goes beyond the traditional limits of social networks. This means that these types of technologies go one step further and involve new categories of individual recognition with greater granularity and precision. Examples include the glasses used, which extract information from the variations of the iris, or the controls, which act as an interface with the virtual world and analyze postural changes to immediately analyze the emotional response.

The analysis of the relative position of the avatars in said world, the times and the way of reaction, generate a biomechanical study of the individual. If neural interfaces are also added, the result is knowledge of the individual at levels that were never intended to be reached with social networks.[110]​.

Thus, virtual reality generates a new paradigm in terms of data protection, covering not only the privacy and security of the individual's information, but also their physical and neural integrity.

Physical and psychological conditions

Virtual reality can have a significant impact on the physical and psychological well-being of users. This impact can be both positive and negative, given that on the one hand, it is used as a tool to treat various mental health conditions, such as phobias, post-traumatic stress disorder (PTSD) and depression, but at the same time it can generate unwanted effects such as addiction or desensitization.

Given these possibilities, monitoring and protecting the well-being of users is very necessary. We can achieve a safe environment by carrying out sufficient testing on applications and devices to ensure proper quality and security, or by promoting a healthy balance between using virtual reality and carrying out real-life activities, such as socializing or exercising.[111]​.

Other problems

In addition to these technological impediments, virtual reality faces other problems. Firstly, although the short-term effects do not go beyond dizziness and vomiting, no one knows for sure how continued use of virtual reality can affect a person, either physically or mentally.

On the other hand, the costs of the necessary equipment are still too high for the average user. A high-quality virtual reality headset is around €600, and you must also take into account the price of a device (computer or console) capable of running the applications satisfactorily.

Finally, virtual reality needs to generate profits to be viable. Currently, most of the interested public are gamers, but it is necessary to attract more sectors in a broader way to survive economically.[112]​[113]​.

Muchos libros y películas de ciencia ficción han imaginado personajes atrapados o entrando en una realidad virtual.

Cinema

Virtual reality has been a relevant topic for some films in the film sector, which have dealt with or been based on it for their films.

• - The Matrix (1999): Neo, a skilled hacker, will discover that his world is a lie, that he, along with the rest of the humans, is connected to a digital simulation, the Matrix, created by machines, who use them to continue functioning. Now knowing the truth, Neo must face the Agents, programs that trap those who have discovered and resist remaining in The Matrix, in order to save themselves.[114]​.

• - Ready Player One (2018): Teenager Wade Watts, like everyone else, spends his hours in a virtual universe, OASIS, where anything is possible. But soon his life will take a turn when he deciphers one of the tests of a competition held within said universe, whose winner will gain absolute control of the OASIS. However, he will not be the only one who goes after the prize.[115]​.

• - Inception (2010): Dom Cobb is a thief of ideas: he infiltrates people's subconscious during their dreams and extracts the ideas that his clients want to obtain. However, this job ends up costing him his freedom and his family. Willing to do whatever it takes to recover his past life, he agrees to an extraordinary job: he must implant an external idea in the mind of another person. If you succeed, you will get forgiveness. Although he will have to face an enemy he did not count on.[116]​.

• - Ender's Game (2013): After Earth is attacked by an alien race known as Formics, Ender Wiggin will be selected and prepared as commander of the team responsible for protecting what remains of Earth and humanity from the threat of the Formics, who are about to return to finish the job.[117]​.

• - Jumanji: Welcome to the Jungle (2017) and Jumanji: The Next Level (2019): Four teenagers are trapped inside a strange video game that they discover by chance. In order to return home, they must overcome all the "levels", all the challenges that this virtual world imposes on them, without dying more than three times, or else... Game Over.[118]​[119]​.

• - Hyperreality.

• - Cyberculture.

• - Holographic universe.

• - Virtual reality applications.

• - Metaverse.

Main components

Virtual reality comprises two main elements: the user's environment and the virtual environment. As the user interacts with the virtual reality system, the two environments communicate and exchange information through a barrier called an interface. The interface can be considered as a translator between the user and the virtual reality system. When the user applies input actions (e.g. movement, force generation, voice, etc.), the interface translates these actions into digital signals, which can be processed and interpreted by the system. On the other hand, the calculated reactions of the system are also translated by the interface into physical quantities, which the user can perceive through the use of different display and actuator technologies (e.g., images, sounds, smells, etc.). Finally, the user interprets this information and reacts to the system accordingly.[10]​.

Importance of multimodality

In virtual reality applications, the exchange of different physical quantities between the user and the virtual environment occurs through different channels or modalities. Such modalities can be sound, vision or touch. Communication with multiple modalities is called multimodal interaction. Multimodal interaction allows several types of modalities to be exchanged simultaneously between the user and the virtual environment. The goal of applying multimodal interaction is to provide a complete and realistic picture of the situation, to provide redundant information, for example, for security reasons, and to increase the quality of presence[10].

Virtual reality can be of two types: immersive or non-immersive and semi-immersive.[11] Immersive virtual reality methods are often linked to a three-dimensional environment created by a computer, which is manipulated through helmets, gloves or other devices that capture the position and rotation of different parts of the human body. Non-immersive virtual reality also uses the computer and uses media such as the one currently offered by the Internet, in which you can interact in real time with different people in spaces and environments that do not actually exist without the need for additional devices to the computer. This case is close to navigation, through which the subject is offered the possibility of experiencing (moving, moving, feeling) certain spaces, worlds, places, as if he were in them.

Non-immersive virtual reality offers a new world through a desktop window. This non-immersive approach has several advantages over the immersive approach such as low cost as well as easy and rapid user acceptance. Immersive devices are high cost and generally the user prefers to manipulate the virtual environment through familiar devices such as the keyboard and mouse rather than through heavy helmets or gloves.

The high price of immersive devices has widespread the use of virtual environments that are easy to manipulate through simpler devices, as is the example of the important business of video game consoles or games in which numerous users interact through the Internet. It is through the Internet that VRML was born, which is a standard for the creation of these non-immersive virtual worlds, which provides a set of primitives for three-dimensional modeling and allows giving behavior to objects and assigning different animations that can be activated by users.

Semi-immersive virtual reality is very similar to immersive reality, with the difference that there are four cube-shaped screens that organize the user, requiring glasses and movement tracking devices and allowing contact with real-world resources, one of the most representative examples being the Cave Automatic Virtual Environment.

Finally, we must highlight some improvements that virtual reality systems facilitate, with regard to the treatment of diseases related to mobility problems.

Virtual reality can be carried out through different methods such as: a simulator or an avatar "Avatar (Internet)"), the projection of real images, using a computer or immersion in a virtual environment.

• - Simulators: The first type is through a virtual reality simulator. Vehicle driving simulators, for example, give on-board users the impression that they are driving a real vehicle, since it predicts the movement of the vehicle by giving a command and receiving the corresponding visual and auditory response (we press the accelerator and see on the screen how the car moves faster and we hear how the vehicle's revolutions rise). Simulators have been being used effectively to develop systems, to improve safety and to study human factors. Likewise, there are surgery simulators that provide dynamic and accessible practices.[12]​.

• - Avatars: With avatars, users can join the virtual environment in two ways: 1) Choosing a pre-designed avatar with computer graphics. 2) Making a recording of yourself through a video device. In the case of recording via a webcam, the background of the image is removed to contribute to a greater sense of reality. Virtual reality through avatars improves the interaction between the person themselves and the computer, since this form is more effective than the conventional desktop computer system. An example is Facebook VR avatars where the user can create their character based on their photos found in their user profile.[13]​.

• - Projection of real images: In the projection of real images applied in virtual reality, the graphic design of real environments plays a vital role in some applications such as: Autonomous navigation and construction of the graphic design of flight simulators. This type of VR is gaining popularity especially in computer-designed graphics, since it improves realism using photo-realistic images and the modeling process is much simpler. When generating realistic models, it is essential to accurately record data in three dimensions (3D). Cameras are normally used to design small objects at close range.[14]​.

• - By computer: This type of virtual reality involves showing a three-dimensional world on an ordinary computer without using any type of specific motion sensor. Many current computer games use resources such as characters and other devices that can be interacted with, to make the user feel part of the virtual world. A common criticism of this type of immersion is that there is no sense of peripheral vision, since the user's knowledge of what is happening around them is limited to their closest environment.

• - Immersion in virtual environments: The best option to experience VR is through a brain-machine interface, which allows direct communication between the brain and an external device. An intermediate step would be to produce a “virtual space” using a virtual reality headset where the images that appear on the headset are controlled through a computer. The only limits are the capacity of the computer that serves the experience, the quality of the VR glasses and the content available on the virtual reality platform.[15]​.

La realidad virtual se aplica a diversas áreas, incluyendo industria para adultos"),[16]​ arte, educación,[17]​ entretenimiento y videojuegos así como narrativas interactivas, milicia, educación, y medicina. Debido al crecimiento latente es predecible que llegue a cubrir otras industrias.[1][18]​[19]​.

Education

It was in 1993, when the first practical use of an application of virtual reality in education was carried out and was developed through a prototype of an applied physics laboratory.[20]​ It is advancing in leaps and bounds in the field of education, although there is still much to do. The possibilities of virtual reality and education are endless and bring many advantages to students of all ages. Currently there are few initiatives that create content for education, since all the attention and advances are being made in the entertainment industry, although many assume that it is what is coming in the future and will be a key piece in education.[21]​ In university studies this is already used for practice purposes and to generate experience such as to design architecture models (engineering) or see some systems of the human body (medicine). With the same objectives, a pilot test was carried out at the Hunters Lane Institute (Tennessee, USA) in 2017.[22]​.

Psychotherapy

In psychotherapy, the use of virtual reality has been quite novel, since it ensures that the subject is no longer in a passive position, allowing the subject to move around the environment and interact with it in different ways, making the interaction more intimate and thereby gaining ergonomics. Virtual reality can be used as a form of diagnostic and therapeutic intervention.[23]​ The main applications that have been developed so far have to do with exposure techniques commonly used for the treatment of phobias. Max M. North, Sarah M. North and Joseph K. Coble, these scientists treated aerophobia, social phobia, agoraphobia, but progress has also been made in other fields such as eating disorders.[24]​ Also, there are numerous applications of virtual reality for psychological rehabilitation and psychomotor.[25]​.

In the case of aerophobia or fear of flying, virtual reality offers many advantages for the treatment of mental illnesses or disorders. Firstly, the control over what happens in the virtual world is total, which is why the patient can be guaranteed that whatever they want to happen in that virtual world will happen. In this way, the therapy environment will be characterized as a protected environment where the patient can explore without obtaining direct consequences and, subsequently, can apply the acquired skills in the natural environment.[26]​.

With regard to psychotherapy research, several advantages offered by virtual reality are being used and can be summarized as: greater control over the introduction of stimuli; greater variety in response options; introduction of stimuli in three dimensions; creation of complex scenarios; generation of varied sensory stimuli, potentially including audio, touch, smell and movement, that are perceived simultaneously with the graphically generated environment; precise and independent manipulation of the geometric and photometric relationship between objects; possibility of examining sophisticated and complex behaviors of participants such as avoidance; and the study of situations that in real life may be impractical, dangerous or ethically questionable. However, despite the enormous potential of virtual reality, researchers must be aware of certain limitations, among which the variable "presence" stands out, since virtual immersion is not necessarily sufficient to give the participant the sensation that the objects are "really there" and to react genuinely.[27][28]​.

Medicine

Recent years have brought about a drastic change in patient awareness and sense of adverse effects in healthcare. Combining this process with an increasing focus on patient safety has challenged traditional educational paradigms in the medical field. Especially in the surgical field, the time-honored concept of theoretical education followed by supervised clinical practice, often referred to as "see, do, teach", is becoming less acceptable, so innovative and complementary methods of teaching medical knowledge are sought. Other concerns are based on the high cost of teaching in a clinical setting. The level of costs, complexity, risks and temporal exposure of the training process increases with the fidelity of the objects.[29]​.

The application of virtual reality (VR) technology in medicine, for example for learning anatomy and especially in the clinical area: especially for surgical training of residents in training, and for patients in pain management, physical rehabilitation and therapeutic treatment of mental illnesses.[30]​.

Compared to animal models, videos and e-learning, virtual reality simulations are more realistic because the anatomical structures displayed in 3D graphics are more intuitive. Students can interact with all anatomical structures, such as skin, muscles, bones, nerves, and blood vessels. The changes that occur after each surgical step are very similar to those in reality. The entire performance can be recorded, compared and analyzed, making the data permanently available to trainees.[31]​ From a different perspective, supervisory supervision and patient participation are no longer necessary during the period of training and acquisition of basic skills, as virtual reality simulations can provide a controlled virtual environment necessary to satisfy these requirements outside the operating room.[32]​.

Multiple aspects of a learner's psychomotor performance skills can be directly measured through the objective performance assessment that is offered by simulations. The training effect of VR simulations is usually evaluated by standard parameters, including time taken to complete the task, route length, number of collisions, injuries, number of anatomical landmarks identified, number of loose bodies found, satisfaction, etc.[30]​.

The idea of ​​using VR-based surgical simulators to train potential surgeons has been a topic of research for more than a decade. However, surgical simulation is still far from being integrated into the medical curriculum. There are a number of questions still open, for example, the level of simulation realism that is needed for effective learning, the identification of the components of surgical skills that must be trained, as well as the validation of the training effect. Current research strives to address these issues with a new generation of highly realistic simulators. A key element of realism is the fidelity and variability of the training scene, which reflects differences in individual patients.[33]​.

Entertainment

Throughout the decade, media have been incorporated whose purpose is to entertain the user, opening a new level of exponential communication channel. The most notable examples are the short films made by Google Spotlight Stories, highlighted for their quality of storytelling for virtual reality. Its approval is given by the accessibility of using it from a mobile phone to a PC with tracking sensors. On the other hand, the inclusion of 360-degree cameras such as GoPro, VIRB, Samsung, Insta 360 ONE"), Nikon KeyMission 360, Insta 360 Air, among others,[34]​ have allowed the use of mobile devices to reproduce content in 360 degrees for later editing.

It remains to be noted that the film industry has focused on channeling advertising in 360 degrees, as in Isle of Dogs "Isle of Dogs (film)") where you experience the scenery of the stop-motion film alluding to a behind-the-scenes in virtual reality, drawing attention on social networks.[35]​.

Finally, the animated short film Pearl directed by Patrick Osborne") in 2007 and winner of the Emmy Award-Winner expresses the narrative potential that can be evoked from the use of new technologies, allowing psychological knowledge of the characters, making the user maintain attention to their entire environment to better understand the story.[36]​.

As Matthew Schnipper" mentions in the report "The State of Virtual Reality")[37]​ for the portal The Verge: “The promise of virtual reality has been overestimated. Wear glasses, position yourself here and you will be transported there. It is the same escapism promised by drugs, alcohol, sex or art – shedding worldly shackles through metaphysical transportation to altered states.”[38]​[39]​.

Video games

Video games have evolved considerably. The graphic quality has reached the point of equaling that of consoles such as those already seen Doom VR and Fallout 4 VR, making virtual movement through teleportation within the map. The mix between virtual reality experience and VR video game culminates in a hybrid of experiences as can be seen in Rick and Morty:Virtual Rick-ality") or Job Simulator, allowing the user to act easily in the environment without having to travel by means of teleportation in order to avoid visual fatigue.[40]​.

As a precedent for incorporating a VR monitor into consoles, we find the PlayStation VR that incorporates controls with motion sensors that delimit a location in space and the work engine falls on the console, in order to excuse the purchase of a demanding PC, gradually introducing the community to new technologies to implement exponential developments.[41]​ However, consoles like the Xbox One have not announced any type of competition in that field, casting doubt on whether the future of entertainment is reality. virtual.

As virtual reality technologies advance, the strong influence of video games on culture affects non-fiction storytelling and also journalism as they seek to impact current trends.[42]​.

Virtual reality rooms with immersive games have been inaugurated in Spain and Argentina;[43]​[44]​ these are spaces designed to offer entertainment and simulation experiences through virtual reality technology. In addition to visors, they can also be equipped with haptic gloves, motion sensors, and motion platforms. These additional devices allow you to interact naturally with a virtual environment and, in the case of motion platforms, simulate physical movements, thus increasing the feeling of immersion.[45]​.

Software

Currently, after the incorporation of HDM compatible with Steam VR, they have allowed this technology to be incorporated into design software, providing a new perspective and manipulation of the environment for the creation of digital content. Software such as Autodesk Maya, Maxon Cinema 4D, Sidefx") Houdini 16"), Adobe After Effects, Adobe PremierPro, Blackmagic Fusion 9"), among others, have integrated the editing option using virtual reality devices either to reproduce or create content for the same platform. interactive creating entertainment, augmented reality or virtual reality experience.[49]​ If the content is cinematic, it can be exported to be played on 360-degree video platforms such as YouTube or Steam applications.[50]​.

360-degree videos or VR allow the user to be at the center of the action regardless of the purpose sought by the user.[51]​.

On the other hand, within the field of web design we can find what is known as the immersive web[52]​ which refers to the inclusion of virtual, augmented and mixed reality experiences that are very useful in areas such as training, news and retail. For this area, frameworks such as A-Frame, React 360 or Amazon Sumerian have been developed that facilitate the inclusion of this technology for web developers and designers.

Finally, programs such as Adobe Audition[51]​ or Final Cut Pro

The origin of virtual reality dates back to World War II. The United States Navy contacts MIT (Massachusetts Institute of Technology) for the possible creation of a flight simulator suitable for training bomber pilots. The project was called Whirlwind and its construction ended a few years later in 1951. It was not until 8 years later when the USAF (United States Air Force) took up the project under the name "Claude Project") and a civilian use of 3D technology appeared.[55]​.

Various virtual reality systems have been created throughout the century. In 1962, Morton Heilig built the Sensorama, a machine that displayed wide-angle three-dimensional stereoscopic images, with stereo sound, wind and aroma effects, and a moving seat. In 1968, Ivan Sutherland built The Sword of Damocles, a virtual reality headset that displayed stereoscopic images with wireframe models.[57]

In 1978, an MIT team led by Andrew Lippman created the Aspen Movie Map, a program that allowed the user to explore the streets of the city of Aspen, using real footage of the place, and interact with certain buildings, allowing the user to see their interior and historical data.[58]​.

In 1984, the Baltimore headquarters of the Six Flags amusement park chain debuted The Sensorium, a 4D movie theater that combined a movie with stereoscopic projection, vibrating seats, and aromatic effects.[59]

In 1987, Nintendo released the Famicom 3D System and Sega released the Master System, both virtual reality headsets with shutter lenses.[60][61]​.

In 1991, Sega announced the release of the Sega VR, a virtual reality headset with an LCD screen and stereo headset for arcade machines and video game consoles. The device was introduced to the public in 1993, and was announced to cost $200, but was never marketed.

In 1994, it launched the Sega VR-1, a motion simulator that incorporated a headset with three-dimensional polygonal graphics and head movement tracking.

In 1995, Nintendo released the Virtual Boy, a virtual reality headset with a monochrome parallax display.[62] That same year, Forte released the VFX1, a virtual reality headset with stereoscopic imaging, head movement tracking, and stereo headsets.[63]​.

In 2012, Palmer Luckey presented the first prototype of the Oculus Rift virtual reality headset.[64]​ The customer version began shipping in 2015. In 2016, Sony launched the PlayStation VR,[65]​ while HTC and Valve launched the HTC Vive.[66]​.

Diversas empresas están trabajando actualmente sobre productos de realidad virtual. Algunos están en fase de desarrollo, otros disponibles comercialmente:.

Helmets or glasses

Also known as HMD (head-mounted display), there are basically two types: those with a built-in screen and those that are essentially a casing for the user to insert a smartphone.

As for the display, LCD technology used to be used, although some are beginning to appear, such as the Razer OSVR HDK 2, the PlayStation VR itself, or the new Oculus with OLED screens. While some HMDs use two LCD displays (one for each eye), others opt for a single display with a division in the center. Some have lenses placed between the eyes and the display, and can be adjusted to the distance of the eyes. The lenses modify the image for each eye, changing the angle of the 2D image of each display to create a 3D effect, simulating the differences with which things are seen with one eye compared to the other.[67]​.

Another important aspect of HMDs is the field of view. Human beings have a horizontal field of vision of about 180° to 220°, sometimes more, although it varies from person to person. This vision is monocular, that is, it is only perceived by one of the two eyes. The field of vision perceived by both eyes (and therefore seen in 3D) is about 114°. For this reason, a 360° field of view would be unnecessary. Most HMDs operate with a field of view between 110° and 120°.[67]​[68]​.

Finally, two points must be highlighted: frames per second (FPS) and latency. A minimum of 60 FPS is essential so that the eye perceives the images naturally and does not cause dizziness. All major HMDs exceed this minimum. The other point is the latency, which must be less than 20 ms so that the user does not experience a feeling of delay between what they do and what they see.[67]​.

• - Rift: virtual reality device for both recreational and professional uses, developed by the company Oculus VR (acquired by Facebook for almost 2 billion euros in 2014[69]​). It is in the development phase but you can buy its experimental model. It works connected to a computer, where the software runs, allowing you to take advantage of all the power of that computer for your recreation of the virtual world.

• - PlayStation VR: also known as Morpheus, is a virtual reality headset currently under development by Sony. It is designed to be fully functional with the Playstation 4 and Playstation 4 Pro console. Released on October 13, 2016.

• - Vive: joint project of Valve Corporation and HTC, currently in development, of an HMD with an announced resolution of 1080x1200 for each eye, refresh rate of 90 Hz, and more than 70 position and orientation sensors. It is part of Valve's SteamVR project, its viewing range is 100°.

• - VivePro: Launched in early 2018, they stand out for their superior image clarity than their predecessor, consecutively integrating two cameras that allow better user tracking for a better experience. On the other hand, they offer better comfort as they are lighter and for the first time the headphones are included, standing out from the previous model by not having to purchase an extra accessory. Separately, they offer the company's first transmitter working at 60 Hz, excusing the TPcast Archived May 10, 2020 at the Wayback Machine.

• - StarVR"): developed by Starbreeze Studios and compatible with the SteamVR open system. They stand out for their wide field of vision (210º) by using two 2560 x 1440 screens, one for each eye.

• - FOVE VR"): They have the peculiarity of incorporating eye tracking, which allows things like focusing the image according to where you are looking, or new forms of visual interaction.

• - Pimax 4k"): they have two 2k monitors culminating in 4k vision. Unlike the competition, the glasses have a gyroscope sensor instead of the already known motion tracking.

• - Pimax 8k"): compatible with SteamVR "Steamroller (microarchitecture)"), these glasses incorporate two 4k monitors and have tracking points for compatibility with scanning sensors. Their first instance was thanks to Kickstarter where the Pimax company innovated with the prototype with 200° of vision, surpassing the competition. Finally, they have eye tracking and compatibility with HTC Vive.

• - Gear VR: virtual reality device developed by Samsung in collaboration with Oculus VR. Unlike the Oculus Rift, it does not include a screen, but is mostly a case with some buttons and an advanced motion sensor, designed to place advanced phones from Samsung itself that will act as a screen and computer processor.

• - Cardboard: cardboard casing developed by Google and intended to be able to cheaply experience virtual reality at home by placing a smartphone of any brand in it.[70]​[71]​ Launched in 2014 and discontinued in 2021.

• - Daydream View: viewer of the Daydream virtual reality platform developed by Google. Launched in 2016 and discontinued in 2019, it was compatible with a few certified mobile devices and was accompanied by a controller with orientation sensors. The first services presented were Google Street View or a cinema experience.[72]​.

• - Virtual Boy: console launched by Nintendo in 1995 that included monochrome glasses that reproduced a 3D environment, therefore a precursor to virtual reality. Its commercial failure caused it to disappear from the market the year after its launch.

• - Forte VFX1"): was an HMD launched on the market in 1995. It connected to a PC and offered a stereoscopic image with three-axis head tracking and a resolution of 263 x 230 pixels per eye.

• - eMagin Z800 3DVisor"): HMD manufactured since 2005, with two 800x600 pixel OLED screens, which was mainly intended for viewing 3D images or for use as a portable monitor, although it also incorporated motion sensors that made it possible to use them with first-person shooter video games.[73]​.

Position sensors

The most advanced HMDs are sold accompanied by devices known as position sensors that, placed in the room, allow the system to determine the location of the HMD and other peripherals that the user may carry, thus giving the user the possibility of moving freely in the virtual space to scale.

Among the best known are the Lighthouse used by the HTC Vive glasses, or the Constellation used by the Oculus Rift. [74]

Drivers

Virtual reality systems usually incorporate control devices that allow interaction with the displayed environment, and which normally consist of controls with buttons that are held with the hands and that have absolute positional tracking. This is the case of the Oculus Touch or the HTC Vive controllers or the Sony PSVR. There are also gloves, or position sensors capable of detecting the position of the body or parts of it.

• - Leap Motion"): accessory consisting of a sensor that remotely perceives the movements of the hand, thus converting it into an input device (a controller).

• - STEM System"): system for wireless detection of body movements, developed by the company Sixense. It represents an extension on the Razer Hydra controller, from the same manufacturer (Sixense).

• - PrioVR"): similar in functionality to the previous one, it is responsible for transferring the user's body movements to the virtual environment.

• - Gloveone"): virtual reality haptic device developed by NeuroDigital Technologies. It is a glove that allows receiving haptic sensations through ten actuators strategically arranged on the fingertips and palm of the hand in order to give the user the sensation of having or feeling an object in their own hand. Gloveone also provides hand and finger tracking by itself, although it is 100% compatible with Leap Motion and RealSense. It allows you to interact with objects displayed on the screen. from a computer or on an HMD such as the Rift, Gear VR, Vive or OSVR.[75]​.

• - PowerClaw"): interface that stimulates the skin, developing the sense of touch. The device has the functionality of generating the sensation of heat, cold, vibration and roughness. This system has direct integration with the Oculus Rift, virtual reality helmet and Leap Motion"), which is a gesture control system.

• - HTC Vive Virtual Reality System Tracker: External sensor to the viewers that integrates information to the positioning sensors to incorporate everyday objects into virtual reality by emitting information about their positioning.[76]​.

• - VR Gun: Device that incorporates the HTC VIVE Virtual Reality System Tracker") to an external control in the form of a weapon in order to make the virtual reality experience more enjoyable and integrate into shooting games.[77]​.

• - Pimax Controller"): Controller similar to the predecessors, however, they have a pad similar to that of the Oculust Rift but incorporating a ribbon that makes it possible to hold the controller without having to use fingers, giving the user the sensation of grabbing and releasing objects within the visual environment when connecting in virtual reality. The built-in triggers allude to the predecessor designs to comply with compatibility in Steam and flight simulators.[78]​ They are also compatible with the positioning sensors of HTC Vive.[79]​[80]​.

Other peripherals

• - Virtuix Omni: peripheral accessory for the Rift, consisting of an omnidirectional platform on which the user can walk without leaving the site.

• - Cyberith Virtualizer"): another omnidirectional platform, similar to the previous one, developed by an Austrian company.

• - TPcast Archived May 10, 2020 at the Wayback Machine: complementary accessory for Oculus and HTC Vive that allows wireless transmission, however, external batteries and a Wifi signal repeater are required.

Other systems

• -

CAVE system at the University of Illinois at Chicago

CAVE System (Cave Automatic Virtual Environment): is a technology that creates a virtual reality environment in a cube-shaped room, on whose walls images are projected. The user, located in the center of the cube, observes the images around him with 3D glasses to have a sense of depth. The sound is generated with speakers located at different points in the room. These systems have existed since the 1990s.

Software and content

Along with the hardware products just mentioned, various companies are developing software and content, with the tools available for this, to be enjoyed through virtual reality devices. Some that can be highlighted are:

• - Demos (environments to explore): Tuscany Dive, Riftcoaster, Evil Dead Project, Cmoar Roller Coaster VR, Ready Player One: OASIS beta"), among others.[81]​.

• - Video games: Elite: Dangerous, Alien Isolation, EVE Valkyrie, Hardcode VR, Herobound, Lamper VR, Anshar Wars 2, Land's End, House of Terror VR, and others; as well as mods of classic games adapted to VR such as Team Fortress 2, Half-Life 2, Richard Burns Rally, Quake VR, The Elder Scroll V SKYRIM VR, Doom VR, Fallout 3 VR and others.[82]​.

• - Video: 360 videos of different genres (documentary, fiction, recreation, musical, among others) and applications to view them (Youtube, Within, Cineveo, CineVR, etc.).[83]​.

• - Education: Space Engine, Expeditions, Unimersiv, Apollo 11 VR, Hindenburg VR, Oneiric Masterpieces - Paris, Douarnenez VR, Great Pyramid VR, 7VR Wonders, 3D Organon VR Anatomy, The Body VR: Journey Inside a Cell, InCell VR, InMind VR.[84]​.

• - Virtual tourism: VR Cities, Sites in VR, Visoplaces.

• - Plastic arts: Inception VR.

• - Communication: AltspaceVR.

• - Medicine: ER VR, 3D Organon VR Anatomy, The Body VR: Journey Inside a Cell.[85]​.

• - Utilities: MINT VR, Supermedium- VR Browser, Pluto, LIV client, NVR Player, Hub Culture VR, HELI, Windows Mixed Reality for SteamVR, VoxVR, VRMakingSense, Virtual Sapce, among others.[86]​.

• - Solidarity: Empowered Reality.[87]​.

Problems identified by consumers

Forbes identifies four problems to avoid in upcoming VR products:[88]​.

• - Need to connect the glasses to a PC (the introduction of a mobile phone is important).

• - Price too high for most people.

• - Lack of content that justifies the purchase.

• - Very heavy helmets, which allows them to be worn only for a limited time.

• - Only one user can occupy the device at a time.[89]​.

Other aspects that are sometimes criticized are:

• - High demands on PC graphics cards.

• - Some helmets do not include headphones, making the experience uncomfortable.

• - You need ample space to scale the motion sensors.

• - Eye fatigue after long exposure.

• - Ability to hit objects in the room while using the headset.

• - The use of prescription lenses does not favor the VR experience due to the use of the helmet.

• - Difficulty sharing the experience (the viewer is for individual use).

• - Reduced field of vision with deformation on the sides.

• - Use of cables that hinder movement.[90]​.

• - Heavy controls without flexibility.

• - Not suitable for epileptic users.

• - Problems in positioning sensors.[91]​.

• - Requirements of large empty spaces for a correct arrangement of positioning sensors.[92]​.

Para proporcionar a los usuarios la sensación de realismo al utilizar los dispositivos de realidad virtual, se requieren una serie de técnicas como el seguimiento de cabeza, de movimiento y ocular. De igual forma los mandos forman parte importante de la experiencia pues, al contar con vibración conectan al usuario con las acciones que realiza en la pantalla.[93]​.

head tracking

Head tracking allows an application to recognize the user's head movements, and pan the image when the user moves their head in any direction. To carry out this monitoring, accelerometers, gyroscopes and magnetometers incorporated into the HMDs are used. In addition, each company uses its own technique to determine the position of the head.[67]​.

The Oculus Rift uses its own positioning system called Constellation. It consists of a set of twenty infrared LEDs placed around the helmet forming a recognizable pattern and a sensor. The sensor captures frames and analyzes the position of all the LEDs, thus allowing tracking.[67]​.

Something similar is what PlayStation VR uses, except there are only nine LEDs. The disadvantage of PSVR is that it has to be adjusted with the camera every time a person of a different height (for example) uses it. In addition, the PlayStation Camera, necessary to be able to use it, must be close enough to the user to work well. In fact, Sony recommends that you use the PSVR sitting down, approximately 1.5 meters from the camera and with enough room to make some light movements. In fact, from this distance the performance decreases, and Sony does not guarantee that the camera correctly detects movement from 9.8 feet (about 3 meters).[94]​[95]​.

The method used by the Vive is much more innovative. This is a tracking system called Lighthouse, developed by HTC and Valve. It does not require any camera, and the HMD does not emit light. The system consists of two boxes that are placed on the wall at a 90° angle. These boxes contain LEDs and two laser emitters, one horizontal and one vertical. On the other hand, the HMD and the two controls (two are necessary to determine the position of both hands and arms) have sensors that capture the light and lasers emitted by the boxes that are located on the walls of the room. The LEDs light up and the receiving devices start counting. One of the two lasers emits a sweep throughout the room. The devices detect which sensors have been hit by the sweep and how much time has passed since the LEDs flashed and use this information to calculate their position with respect to the boxes. When you get too close to a wall, a translucent grid appears warning you that you are close to a real wall. All this with a jitter (the imprecision of measurements when the object is stationary) of only 0.3 mm.[96]​[97]​.

Motion tracking

Motion tracking or tracking is an extension of head tracking, but allowing other types of movements to be recognized, such as that of the extremities. This field is not as advanced as the previous one, although large companies are focusing their interest on it.[67]​.

Apart from the promising and already mentioned Lighthouse from Valve, there are other options, for example the Leap Motion Orion. This is an extremely accurate hand tracking system. It detects all finger and joint movements even in diffuse environments and with varying levels of light, although it has some disadvantages, such as the fact that you have to be looking at your hands for the system to detect them. Another problem, not unique to Orion, is the lack of something tangible in the hands. In real life, when you come into contact with something, your sense of touch is activated and you feel that something. In virtual reality, however, your hands are empty and therefore you have no way of knowing if you are holding the object the way you want, or the force that is being applied to it. Developers are trying to make up for this lack of tactile response through auditory signals that indicate when and how to come into contact with an object, but the sensation is not the same.[98]​[99]​.

The Oculus alternative is Touch, a control system that consists of two gripped controls and a wrist strap, which makes the user feel that they are using their own hands. Each of these two controls is shaped like a crescent and has two buttons, an analog stick and an analog trigger, as well as a mechanism called a hand trigger, which replicates the sensation of firing a gun. Touch also makes use of the Constellation positioning system and unlike Leap Motion's Orion, it does have tactile feedback. The controls also have sensors that allow them to detect a series of hand gestures, such as making a fist, pointing with the index finger or raising the thumb. The disadvantage of Touch compared to Orion is that, despite being very advanced, it is still a command and therefore far from the freedom of movement that the latter offers.[100]​[101]​.

It is also worth highlighting the contribution of the Spanish company NeuroDigital Technologies with its GloveOne"). It is a glove that aims to give the user that much-desired tactile feedback. It currently does not have a tracking system, so it uses a Leap Motion for this, but it allows the user to perceive the weight, shape, volume and texture of the objects with which it interacts. To do this, it uses sensors located near the thumb, index and central fingers, in addition to the palm of the hand. In addition, it contains 10 actuators distributed between the palm and the tips of the fingers. Each of them vibrates individually, with different frequencies and intensities, precisely reproducing the sensations of touch.[102]​[103]​.

There are other motion tracking systems, such as suits, voice controls or even treadmills such as Virtuix Omni, which allow the user to explore long distances by walking (or running).[67]​.

Eye tracking

This is a technology that the main companies have not yet incorporated, but it is present in the FOVE VR HMD. This virtual reality helmet incorporates interior infrared sensors that capture eye movements. This allows a range of options that range from replicating your eye movements in your virtual avatar, to provoking reactions from other characters depending on the way you look at them. What's more impressive is the realism that eye tracking offers.

In real life, the eyes have a central focus point, while the rest is out of focus. This is very difficult to replicate, leading to an over-focus on other companies' systems, which reduces the feeling of immersion. Eye tracking solves this problem, allowing you to focus only on what the user is looking at. Furthermore, it could lead to hypothetical optimizations: the application could use its resources to render high-quality objects that are in the user's field of view, applying few resources to everything that is out of focus at that moment. This technology however requires high resolution screens, since the point focused on by the user should be as realistic as possible. Overfocusing the other systems can cause motion sickness, something that eye tracking could also prevent.[67][104]​.

physical problems

One of the biggest difficulties of virtual reality is making the user feel a sensation of immersion without feeling nausea, dizziness, etc. Experiencing these symptoms when using virtual reality is known as cybersickness or virtual reality sickness and is similar to classic motion sickness, or the motion sickness that pilots experience in simulators. The perception of these symptoms also depends on the person. For some, vomiting appears within a few minutes, while others can enjoy virtual reality for hours without any consequences.

The problem lies in a mismatch between the vestibular system (the liquids and fluids in the cavities inside the ear, which send information to the brain about direction, angles, etc.) and the visual system.[105]​.

These side effects of virtual reality have different causes. Developers try to perfect their systems to avoid or combat them in the best possible way, these being latency, image duplication and persistence among others.

Latency is the delay between the action performed by the user and its representation on the screen, producing imbalances between the vestibular and visual systems, in turn causing nausea and dizziness.[105]​.

The common latency in video games is the time interval between the user pressing a button and the pixels updating, generally being a minimum of 50 ms. It is important not to confuse this delay with the time between when a user presses a button and the action is carried out, being insufficient for virtual reality, which requires a latency of at least 20 ms so that the user does not experience a delay. In fact, most experts believe that the limit is even lower, at 15 or even 7 ms. Oculus Rift has a delay under optimal conditions of between 30 and 40 ms.

This is because the process of rendering the image requires the tracking system to determine the exact position and orientation of the HMD, the application rendering the scene, so that the hardware transfers the rendered scene to the HMD screen and it begins to emit photons for each pixel.

The first step, tracking takes between 10 and 15 ms when it comes to optical tracking, which in itself is too long. Accelerometer tracking is much faster with a latency of 1 ms or less, but it is imprecise and drifts a lot. One of the main problems is that 60 Hz screens, for example, already introduce a delay of about 15 or 16 ms in rendering. This value is dependent on the CPU and GPU, but is usually in that range except for older applications that require primitive rendering.

Finally, the hardware transfers the rendered scene to the HMD screen. For most frequency scanning based systems, this means a delay of about 16 ms in the worst case (assuming 60 Hz displays are used). If the image is transmitted immediately, that is, the photons begin to appear instantly upon arrival, the sum of the latencies mentioned above is much higher than 20 ms and is an abysmal distance from the desired 7 ms.

Another major drawback is image judder or duplication. It is a combination of two phenomena, image blurring and stroboscopy. Blurring or smearing is a motion blur present in virtual reality. Strobing or stroboscopy, on the other hand, consists of the perception of multiple copies of an image at the same time, making it appear that there is no movement between them. The union of these two phenomena constitute image duplications.

Judder normally produces dizziness and all related symptoms, so you should try to avoid it. One cause of judder is the fact that pixels move across the retina while they are on (causing smearing). The obvious solution to image duplication is an increase in frame rate. The problem is that to avoid it completely, a frame rate of between 300 and 1000 FPS would be necessary, something too far from reality. Therefore, although the solution is obvious, it is also totally impossible due to technological limitations.

The other solution has to do with persistence. Most displays have full persistence, so the pixels always stay on. The level of blur does not depend on what fraction of a frame the pixels are on, but on the total time that they are on. This is why a frame rate of around 1000 FPS would be ideal with full persistence, as the time would be just 1 ms.

Since this frame rate is currently unattainable, low persistence must be used to achieve the same result. With zero (or almost zero) persistence, the movement of lit pixels across the retina is eliminated, since they remain lit for a very short time. Thus, the blur component in image duplication is eliminated. However, low persistence also has disadvantages, as it can increase stroboscopy. In fact, the smearing itself obscures the stroboscopy quite a bit. By reducing the first using low persistence screens, the second is manifested more clearly. However, this problem is not that serious. The reason is that in the image that the eye is focusing on, stroboscopy will not occur, since the eye itself will avoid it by following it, because the same pixels will go to the same point on the retina in each frame. Although this effect will occur in the rest of the image, it will not be as noticeable since it will be out of focus.[106]​[107]​[108]​.

Privacy and data protection

As new technologies advance, concerns about data protection grow considerably. It is not only important who has access to our data, but also the great unknown of the purposes for which these data will be used.[109]​ This therefore generates an ethical debate that must be addressed.

It is important to consider that virtual reality not only makes use of our personal data, but also goes beyond the traditional limits of social networks. This means that these types of technologies go one step further and involve new categories of individual recognition with greater granularity and precision. Examples include the glasses used, which extract information from the variations of the iris, or the controls, which act as an interface with the virtual world and analyze postural changes to immediately analyze the emotional response.

The analysis of the relative position of the avatars in said world, the times and the way of reaction, generate a biomechanical study of the individual. If neural interfaces are also added, the result is knowledge of the individual at levels that were never intended to be reached with social networks.[110]​.

Thus, virtual reality generates a new paradigm in terms of data protection, covering not only the privacy and security of the individual's information, but also their physical and neural integrity.

Physical and psychological conditions

Virtual reality can have a significant impact on the physical and psychological well-being of users. This impact can be both positive and negative, given that on the one hand, it is used as a tool to treat various mental health conditions, such as phobias, post-traumatic stress disorder (PTSD) and depression, but at the same time it can generate unwanted effects such as addiction or desensitization.

Given these possibilities, monitoring and protecting the well-being of users is very necessary. We can achieve a safe environment by carrying out sufficient testing on applications and devices to ensure proper quality and security, or by promoting a healthy balance between using virtual reality and carrying out real-life activities, such as socializing or exercising.[111]​.

Other problems

In addition to these technological impediments, virtual reality faces other problems. Firstly, although the short-term effects do not go beyond dizziness and vomiting, no one knows for sure how continued use of virtual reality can affect a person, either physically or mentally.

On the other hand, the costs of the necessary equipment are still too high for the average user. A high-quality virtual reality headset is around €600, and you must also take into account the price of a device (computer or console) capable of running the applications satisfactorily.

Finally, virtual reality needs to generate profits to be viable. Currently, most of the interested public are gamers, but it is necessary to attract more sectors in a broader way to survive economically.[112]​[113]​.

Muchos libros y películas de ciencia ficción han imaginado personajes atrapados o entrando en una realidad virtual.

Cinema

Virtual reality has been a relevant topic for some films in the film sector, which have dealt with or been based on it for their films.

• - The Matrix (1999): Neo, a skilled hacker, will discover that his world is a lie, that he, along with the rest of the humans, is connected to a digital simulation, the Matrix, created by machines, who use them to continue functioning. Now knowing the truth, Neo must face the Agents, programs that trap those who have discovered and resist remaining in The Matrix, in order to save themselves.[114]​.

• - Ready Player One (2018): Teenager Wade Watts, like everyone else, spends his hours in a virtual universe, OASIS, where anything is possible. But soon his life will take a turn when he deciphers one of the tests of a competition held within said universe, whose winner will gain absolute control of the OASIS. However, he will not be the only one who goes after the prize.[115]​.

• - Inception (2010): Dom Cobb is a thief of ideas: he infiltrates people's subconscious during their dreams and extracts the ideas that his clients want to obtain. However, this job ends up costing him his freedom and his family. Willing to do whatever it takes to recover his past life, he agrees to an extraordinary job: he must implant an external idea in the mind of another person. If you succeed, you will get forgiveness. Although he will have to face an enemy he did not count on.[116]​.

• - Ender's Game (2013): After Earth is attacked by an alien race known as Formics, Ender Wiggin will be selected and prepared as commander of the team responsible for protecting what remains of Earth and humanity from the threat of the Formics, who are about to return to finish the job.[117]​.

• - Jumanji: Welcome to the Jungle (2017) and Jumanji: The Next Level (2019): Four teenagers are trapped inside a strange video game that they discover by chance. In order to return home, they must overcome all the "levels", all the challenges that this virtual world imposes on them, without dying more than three times, or else... Game Over.[118]​[119]​.

• - Hyperreality.

• - Cyberculture.

• - Holographic universe.

• - Virtual reality applications.

• - Metaverse.