Re: Why do we perceive virtual reality as if it were real?

Dear Melissa,

In everyday life, what you consider as reality mainly comes from your 
senses. Your eyes are stimulated by specific patterns of light that allow 
you to see objects; you can also touch these objects and stimulate 
receptors inside the skin which send specific messages to your brain which 
in turn recognises the form of objects and so on. The idea of virtual 
reality would be to recreate a given environment by stimulating your 
senses in the same way as they would be in a real environment. 

So far, some interesting technological devices, such as flight simulators, 
have been created to simulate the reality encountered in some 
circumstances.  Since these are probably one of the most advanced 
technological devices, they are often referred to as some kind of virtual 
reality. The problem is that some other kind of virtual reality that you 
can imagine does not actually exist yet. Vision plays a key role in so-
called virtual reality and can be exploited to influence the sense of 
balance, for example. I think your question is about the three-dimensional 
illusion produced by material such as 3D movies. If that is right, the 
answer is that this technique exploits the fact that the two eyes are 
separated horizontally from each other and therefore receive slightly 
different images on each retina. Try the following experiment : look at a 
fixed point with one eye then switch to the other. You will notice that 
the image is slightly « disparate » from the one seen with the other eye. 
Horizontal disparity is a strong depth cue for the brain and is exploited 
by 3D movies. The special goggles that you wear when watching a 3D movie 
send a slightly different image to each eye : two movies are actually 
presented on a flat screen but they are slightly disparate from each other 
(you can see this if you take off your goggles) but each eye can only see 
one of the two images projected. In some systems, goggles have special 
shutters that are synchronised with the movie projectors in such a way 
that at a given moment, one eye sees a movie and a very short moment 
after, it is the other eye that sees the other movie. Since the shutters 
alternate very quickly, you are not aware of this but the brain 
nonetheless receives a particular input.  While making the movies, the two 
cameras were horizontally spaced like your two eyes would be in reality. 
When you watch the movie, each eye receives what it would in a real scene. 
That shows how binocular disparity strongly influences our appreciation of 
depth. On the other hand, binocular cues (involving the two eyes) are not 
the only cues that allow the perception of depth. There are also other 
binocular cues but also strong monocular cues (involving only one eye). 
Monocularly blind people can easily perceive depth in everyday life: what 
they see does not look like a flat screen... For example, you can easily 
say, using one eye only, that object A is behind object B because part of 
object B is masking object A.   Finally, the motor system or other senses 
such as the sense of touch are difficult to exploit in the same manner as 
vision can be.  Some technological improvements remain to be done in that 
domain.

Hope that helps,
Eric