When most people think of "virtual reality", they probably imagine someone
with a bulky helmet on, flailing her arms wildly at nonexistent objects. She might
also be wearing tactile gloves. This is the type of virtual reality that was
popular at shopping mall arcades in the early 1990s. When one of these machines
showed up in the mall of my childhood hometown, it was considerably more expensive
than any other video game, and yet the line (consisting mainly of teenagers) snaked
throughout the mall. I never tried one of these machines (the line was too long
and besides, I didn't have the pocket money) but I remember standing there watching
the ceiling-mounted CRT screens that showed onlookers what the helmeted players
were seeing. There were two "games": one was some sort of motorcycle simulation,
and the other seemed to simply be a rather blank-looking "world" in which a person
could walk around and view various 3D objects generated by the computer. The
graphics were fairly primitive, consisting of simple shapes and perspective planes.
Yet the idea that you could be walking while standing still, and looking at objects
that didn't really exist, was quite exhilirating for those accustomed to the
white-bread tranquility of deepest suburbia.
The history of virtual reality interweaves with the history of the
computer itself. The 1950s and 60s saw computers employed as vast data-crunching
engines; few imagined that the future held computers to be something of a practice
arena for real life. A critical, but seemingly obvious necessity in the development
of virtual reality was the idea of the interface -- a means for humans to interact
in real-time with the electronics within the computer. Virtual reality represents
the ultimate abstraction layer between man and machine; the very presence of the
machine is muted by the interface. Our minds "know" that what we are experiencing
is not real, yet our senses react in the same manner as they would to an actual
event or situation. This concept explains why one of the first applications
of VR-like technology was that of the flight simulator. If a pilot can learn
how to control and maneuver an aircraft while s/he is safely on the ground, liability
is reduced and the pilot has the opportunity to acquire real-life skills. Flight
simulators give pilots the luxury of learning from their mistakes, mistakes that
might be fatal in an actual airplane.
From the beginning, the difference between looking at a screen and interacting with
a virtual environment has been a matter of immersion. Virtual reality systems
started out as bulky head-mounted displays (HMDs), such as the 1968 monstrosity
known as Ivan Sutherland's Sword of Damocles (which sounds like a good name for a
heavy metal band). It was constructed by a Harvard student and incorporated a large
mechanical sensing arm. Simulation hardware and software, then, have been in existence for
quite some time. The term Virtual Reality was not coined until 1989, by computer scientist
Jaron Lanier. Lanier used "virtual reality" to describe any interactive three-dimensional
environment generated by a computer. Nowadays, most virtual reality systems are
still mounted on helmets or headbands, but they are much smaller and lighter than
their predecessors. LCD screens have been put to good use in virtual reality
technology, owing to their lightness and relatively low power requirements.
In order to successfully create the illusion of a three-dimensional world-within-
a-machine, it is important to understand the way human vision works. When we examine
an object, our eyes move over its surface. A three-dimensional object can have one
shape when viewed in a particular plane, and an entirely different shape when viewed
in another. Virtual reality needs to "know" what the user's eyes are doing, and
react accordingly. The process of gathering and responding to information about
the position of a person's eyes and head is called tracking.
The most basic method of tracking involves simply determining the position of the
head. The virtual reality effect garnered from this method, however, can be somewhat
distorted because people aren't necessarily looking exactly where their head is pointing.
A more realistic effect results when the more accurate (but more expensive) method of
eye tracking is used.
There are two main types of eye tracking: limbus tracking and video tracking. Limbus
tracking employs an infrared LED whose beam is bounced off the surface of the eye.
The reflections from the LED are picked up by a photodetector, and the eye's position
can be determined by the intensity of the reflected light. Video tracking, on the other
hand, acquires images of the eye and uses these images to determine the center of the
pupil. Once again, however, an LED is reflected off the eye, resulting in a highlight.
The computer uses the vector between the pupil and the corneal reflection to determine
the angle of the eye at a given moment.
In addition to tracking a user's head and eye movements, it is also important for a
VR system to provide adequate field of view and frame rate. In a sophisticated
simulation, one might also want to consider auditory and tactile as well as visual effects.
By using the same position tracking technology, a computer can determine how to make
sounds seem to emanate from objects in the virtual environment, and how to make ambient
sound seem realistic. Specialized virtual reality gear might also include gloves,
boots or other clothing that applies force feedback to create the illusion of actually
touching objects or experiencing vibrations. I'm sure the Internet porn empire is
simply drooling, waiting for the full-body VR suits to make their debut.
A recent intriguing, if unanticipated, application of virtual reality
technology has been in the world of psychiatry. Patients with severe phobias
can now be exposed to their worst fear...be it of heights or of snakes...
in a safe and less threatening manner. Aversion therapy has been around for
years, but only recently have computers been called upon to create the stimuli.
Another, perhaps even more innovative use of VR in the psychiatric world is
that of using it to "teach" schizophrenics the difference between fantasy and
reality. Common hallucinations, such as shadowy figures or "hearing voices"
can be simulated; the patient then has to figure out whether this stimuli is
being internally or externally generated.
In the world of entertainment, virtual reality is everywhere. From the
literary works of William Gibson and Neal Stephenson to the much-hyped
film The Matrix, the idea of a computer-generated universe has captured the
collective imagination. In many science-fiction examples of virtual reality,
technologies such as direct neural interface are used heavily. We don't
yet have the ability to put a chip in a person's head that will create a
perfectly realistic virtual environment, but I am almost certain someday we will.