Game Development Reference
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that “metrics can be defined to describe a system''. Immersion is thus defined as what
technology allows, from an objective point of view. Slater thus disagrees with Witmer
and Singer (1998), who define immersion as a psychological state characterised by
the fact of perceiving oneself “in'' an environment (virtual) that provides a continuous
flow of information.
Here, in the following part, we will follow Slater's definition, which is more
workable.
It helps to distinguish between what falls in the field of technology and what falls
in the field of behaviour. From this, presence is described as the subjective response to
immersion, the feeling of being in the virtual world, as opposed to that of being in the
real world (also see Held &Durlach, 1992; Heeter, 1992; Sheridan, 1992; Lombard &
Ditton, 1997; Biocca, 1997). To illustrate the dichotomy, Slater (1999) observes that
the colour of an object can be described in terms of wavelength, which will be the
equivalent of immersion as an objective description of a device. The perception of this
colour (even the emotion that it arouses) will be the equivalent of presence.
However, it is evident that this “objective'' definition of immersion is valid within
the boundaries of our knowledge about the functioning of the human subject. It makes
no sense to describe a colour that is invisible to the human being. It is thus necessary to
somewhat put the “objective'' character of immersion into perspective. The definition
of the immersive character of a device depends on the activity it is meant for. Please also
note that here we are describing immersion as identical to the I 2 concept (Immersion
and Interaction). We consider this to be a rational approach, attempting to objectify
everything that concerns technology in the virtual environment (before introduction of
the human operator). The three levels described in the introduction (I 2 sensorimotor,
I 2 cognitive and I 2 functional) will thus correspond to the different aspects of the
behaviour of the operator interacting with the virtual environment. We will call this
aspect presence.
5.2 IMMERSION
Steuer (1992) suggested a classification of the virtual reality devices along two lines:
sensory richness (vividness for Steuer) and interaction. A high score on these two
lines corresponds to an “optimally'' immersive device. In this sense, a book is not
very interactive and provides poor sensory stimulation. Sensorama (Rheingold, 1993;
Burdea & Coiffet, 1994) is rich from the sensory point of view, but not interactive.
The telephone is interactive, but uses only one sensory channel. A virtual reality device
is interactive and provides good sensory stimulation.
5.2.1 Sensory richness
The objective of an immersive device is to sensorily isolate the user from the real world
and substitute the sensory stimulations coming from the real world with computer-
generated sensory stimulations. At present, the visual and acoustic domains are
relatively the most advanced, particularly from the point of view of spatial coher-
ence and the panoramic aspect of stimulation, or even its quality, in terms of temporal
refresh rate of data, compatible with the perception of a continuous movement and
in terms of spatial resolution. There remains a lot of theoretical, experimental and
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