1.1 What Is Virtual Reality?

Virtual reality (VR) technology is evolving rapidly, making it undesirable to define VR in terms of specific devices that may fall out of favor in a year or two. In this book, we are concerned with fundamental principles that are less sensitive to particular technologies and therefore survive the test of time. Our first challenge is to consider what VR actually means, in a way that captures the most crucial aspects in spite of rapidly changing technology. The concept must also be general enough to encompass what VR is considered today and what we envision for its future.

Figure 1.1: In the Birdly experience from the Zurich University of the Arts, the user, wearing a VR headset, flaps his wings while flying over virtual San Francisco. A motion platform and fan provide additional sensory stimulation. The figure on the right shows the stimulus presented to each eye.

Figure 1.2: (a) An experimental setup used by neurobiologists at LMU Munich to present visual stimuli to a gerbil while it runs on a spherical ball that acts as a treadmill (Figure from [329]). (b) A picture of a similar experiment, performed at Princeton University.

We start with two thought-provoking examples: 1) A human having an experience of flying over virtual San Francisco by flapping his own wings (Figure 1.1); 2) a gerbil running on a freely rotating ball while exploring a virtual maze that appears on a projection screen around the mouse (Figure 1.2). We want our definition of VR to be broad enough to include these examples and many more, which are coming in Section 1.2. This motivates the following.

Definition of VR: Inducing targeted behavior in an organism by using artificial sensory stimulation, while the organism has little or no awareness of the interference.

Four key components appear in the definition:

1. Targeted behavior: The organism is having an ``experience'' that was designed by the creator. Examples include flying, walking, exploring, watching a movie, and socializing with other organisms.
2. Organism: This could be you, someone else, or even another life form such as a fruit fly, cockroach, fish, rodent, or monkey (scientists have used VR technology on all of these!).
3. Artificial sensory stimulation: Through the power of engineering, one or more senses of the organism become co-opted, at least partly, and their ordinary inputs are replaced or enhanced by artificial stimulation.
4. Awareness: While having the experience, the organism seems unaware of the interference, thereby being ``fooled'' into feeling present in a virtual world. This unawareness leads to a sense of presence in an altered or alternative world. It is accepted as being natural.

You have probably seen optical illusions before. A VR system causes a perceptual illusion to be maintained for the organism. For this reason, human physiology and perception represent a large part of this book.