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2 The scope of the term 'Virtual Reality'

Virtual Reality is a term whose usage has become very widespread. In conducting this survey we have chosen not to limit its meaning, so that respondents are free to use it as they wish. As will be clear from the results presented later, it is a term which is used very loosely. However, in analysing the results we have felt it useful to distinguish at least the following two broad categories:

Desktop VR and Virtual Environments.

These usually refer to the use of a conventional computer monitor as the output device onto which the 3D environment is rendered. In some cases, stereoscopic displays are used - for example, stereo shutter glasses - but at the low-end of the market this is generally not the case. Interaction is often by means of a 2D mouse, although 3D devices - such as a dataglove, or 3D mouse - may be used. Useful work developing underlying software can be carried out in this way.

Immersive VR.

Here, some kind of immersive display and tracking equipment is employed in order to create the psychological illusion of being inside the computer-generated environment, rather than viewing it from the outside through a screen. When appropriate means of input are provided, inter action with the environment can also be directly experienced, greatly enhancing the psychological effect. There are two main ways in which this effect can be achieved: by using a head-mounted display (HMD); or by using a large-screen system, such as a video projector, which creates the illusion of immersion by filling the field of view of the user. This is similar to the effect achieved in an IMAX or Omnimax cinema.

It is important to realise that a desktop environment is different - both in terms of the user's psychological responses and the system's HCI requirements - from an immersive one. There is nothing which fundamentally distinguishes desktop VR from conventional 3D graphics. It is the ability to perceive the environment from within and to interact directly with it (direct manipulation in 3D space), which is the significant new feature that immersive VR brings to human-computer interaction, and which distinguishes it from traditional 3D graphics, and thus from a desktop environment.

In the published literature the term VR is usually synonymous with immersive VR as defined here. For example, if one looks at papers by academic researchers and industrial developers, it is the novel aspects of interaction within a world which are seen as the fundamentally new feature of VR interfaces, as distinct from more traditional graphical user interfaces. The engagement of human perceptual skills, and other aspects of psychology form an important part of this.

Nonetheless, an informal observation is that the community is divided into two camps: those who view the immersive interface as the significant innovation in VR; and those who regard the use of a 3D environment to be the significant innovation to which an immersive interface can be tacked on fairly easily.

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