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Notes on Presence

Immersive Virtual Environments In 1980 Marvin Minsky introduced the concept of telepresence to describe the feeling that a human operator may have while interacting via a teleoperator system 1. The human operator sees through the eyes of the remote machine, and uses his or her own limbs to manipulate its effectors. A sense of being at the distant place may develop, with the body of the machine 'becoming' the body of the human. This experience of telepresence was thought to be conducive to effective task performance of the operator in the remote environment. The concept of telepresence has more recently been applied to experiences within virtual environments. In this case the person is immersed within an environment that is realised through computer controlled display systems, and may be able to effect changes in that virtual environment. A feeling of being present may develop in the same way that Minsky noted for physical teleoperator systems. A rigorous discussion of the concept of a 'virtual environment' has been provided by Ellis 2. Ellis defines virtualisation as " the process by which a human viewer interprets a patterned sensory impression to be an extended object in an environment other than that in which it physically exists ". According to Ellis, a virtual environment, should incorporate the participant as part of the environment, so that head motions result in motion parallax from the participant's viewpoint, and a number of physiological and vestibular responses associated with focusing and object tracking are stimulated. Clearly there are many parameters that control the quality of the experience that a person may have in such a system. The visual display, for example, may have greater or lesser field-of-view – the effective horizontal and vertical angles through which the world can be seen. A head-mounted display (HMD) system typically delivers a relatively low field of view. For example 60 degrees diagonal – compared with the more than 180 degree horizontal and 120 degree vertical in normal vision. Second, the visual display may have more or less resolution – the number of pixels per unit projected visual area. The frame-rate achieved by the computer system is a critical factor in maintaining the illusion of there being 'extended objects' in an environment. The frame-rate is the number of frames a second that the computer graphics system can deliver. Although the display will always be refreshed at a constant cycle (e.g., 60Hz) the …