Ability of imagination is one of the profound traits of the human psyche which distinguishes us from other organisms. Our interminable efforts to reimagine the real world should be considered as an instinctive behavioral aspect. How often do we end up indulging ourselves in the virtual realms of daydreams or a fictitious world triggered by literature or similar stimulus? Our mind, the most intuitive Virtual Reality device, seamlessly simulates these explorations which are influenced by the traces of memories developed by virtue of the constant interactions with the real world.
The term Virtual Reality (VR) is a conjunction of two antonymous words ‘virtual’ and ‘reality’, describing the nature of experience which it caters to. VR can be defined as the experience of actually being present in a virtual world with the help of a system which makes us believe that we are in a real world.
Components of VR
• Virtual World:
Virtual World is an alternative realm which is simulated for the user to experience, by a VR system. The components of the virtual world depend on the purpose for which the world is designed. This imaginative space progresses through the ideas of the creator, which is simulated using computer programs. The degree of immersion achieved by a VR experience often depends on the ability of the virtual world to respond to the user’s interactions by constantly updating itself.
The believability of any virtual space to be real depends upon its ability to respond to the user’s interactions. When a virtual world is presented to us by a system with immense possibilities of interaction, we tend to react intuitively to the objects, characters and the space itself. The interactions can be in the form of sensory inputs or physical movements with respect to the imaginary space. The computer system which acts as a mediator gathers these inputs, analyses them and updates the virtual world accordingly.
The hardware comprises of the physical equipment which aids the user to involve in a VR experience. The head mounted display, cameras, and sensors for position tracking are some of the typical examples of hardware components. The information regarding the user interactions, often in the form of sensory cues are assessed by the hardware and passed on to the computer system (software) which updates the virtual world.
Software includes the computational components which are used to render and manipulate the virtual world according to the user’s interactions with the system. The effectiveness of a virtual world depends on the computational power of a Graphical Processing Unit which is responsible for rendering the visual representations and adding possibilities of interactions. Another parameter decided by the software is called ‘motion to photon latency’ which is the time required for the virtual world to update according to the head movement (perspective shift) or other sensory interactions. A higher value of this latency can cause adverse effects like motion sickness and nausea.
Fig 1. An overview of a VR System
The definitions and explanations of VR and its derivatives are always prone to iterations because of the evolving nature of the domain. In 1994, Paul Milgram and Fumio Kishino define a spectral representation of experiences related to VR called Reality-Virtuality Continuum . The spectrum exists between the ideal extremes of a completely virtual world and real world keeping the augmented versions of these in between.
Fig 2. Adopted from Reality-Virtuality Continuum 
• Mixed Reality:
The conventional definition of a VR experience refers to when the user is immersed in a completely synthetic world with the help of a system. As the technology progressed to cater different applications, a subclass of experiences related to VR came into existence which required combinations of real and virtual world possibilities. Mixed Reality can be considered as a range of experiences existing between the completely virtual or real extremes of the spectrum. The derivatives of Mixed reality can be augmented forms of the real world by virtual elements (Augmented Reality) or augmented forms of the virtual world by real elements (Augmented Virtuality).
• Augmented Reality:
Augmented Reality can be defined as the experience of actually being present in a real world which is enriched by the virtual entities which are augmented on it with the help of a system. On contrary to the VR experience, here, the reality itself is modified by integrating desired virtual elements into it which opens up various possibilities of interaction.