Other sensory output from the VE system should adjust in real time as a user explores the environment. If the environment incorporates 3-D sound, the user must be convinced that the sound’s orientation shifts in a natural way as he maneuvers through the environment. Sensory stimulation must be consistent if a user is to feel immersed within a VE. If the VE shows a perfectly still scene, you wouldn’t expect to feel gale-force winds. Likewise, if the VE puts you in the middle of a hurricane, you wouldn’t expect to feel a gentle breeze or detect the scent of roses.
Lag time between when a user acts and when the virtual environment reflects that action is called latency. Latency usually refers to the delay between the time a user turns his head or moves his eyes and the change in the point of view, though the term can also be used for a lag in other sensory outputs. Studies with flight simulators show that humans can detect a latency of more than 50 milliseconds. When a user detects latency, it causes him to become aware of being in an artificial environment and destroys the sense of immersion.
An immersive experience suffers if a user becomes aware of the real world around him. Truly immersive experiences make the user forget his real surroundings, effectively causing the computer to become a non entity. In order to reach the goal of true immersion, developers have to come up with input methods that are more natural for users. As long as a user is aware of the interaction device, he is not truly immersed.
REAL VIRTUAL OBJECTS AND GOING FOR A SWIM : Passive haptics are one way VE developers have tried to enhance interactivity. Passive haptics are real objects in a physical space that are mapped to virtual objects in a virtual space. Users wear an HMD or similar portable display while in the physical space. When they look toward the physical object, they'll see the virtual representation of it in their display. When they approach the object and try to touch it, they encounter the real object in the physical space. Anything a user does with that object in real space appears as a reflected action upon the virtual object in virtual space.
Swimming in VR systems doesn’t refer to jumping into a pool -- it describes the effect of latency within a virtual environment. If you were to look around in a VE and notice that the change in point of view was not instantaneous, you would experience swimming. The effect is distracting and can even make you experience motion sickness, called sim sickness or cyber sickness in VR circles.
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