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will then use a gesture or a pointer to separately indicate an object, but the syntactical
or rather semantic coherence of these mono-modal interactions generally will not be
2.4.1 VR reference model
The considerations on the cognitive processes related to behavioural interfacing given
earlier are not enough to establish a method to design a virtual reality device. For this
purpose, we would like to offer a general model for virtual reality that defines three
levels of immersion and interaction with their own characteristics. As explained earlier,
as far as the physical level is concerned, we talk about sensorimotor immersion and
interaction as the computer is physically connected to the person through his senses
and motor responses. This level of immersion and interaction can be quantified with
respect to the characteristics of the senses andmotor responses used. As explained in the
triadic diagram (Figure 2.7), the user must be mentally immersed in the virtual world,
the “lower'' level of immersion and sensorimotor interaction in front of him must be
mentally invisible (transparent). In this case, we talk about cognitive immersion and
interaction. The cognitive processes of interfacing (schemas, metaphors, substitutions)
are located at this level. At the third level, the objective is to attempt to immerse the
person in a given task (or a functionality) and not a mere mental immersion in that
virtual world. In this case, we talk about functional immersion and interaction 4 .We
can compare this three-level division to a similar representation by M. Fréjus: sensory
model (instead of sensorimotor model), cognitive model and operative model (Fréjus &
Drouin, 1996). This division helps us to better clarify different problems faced in
immersion and interaction of a subject. They are closely related and not opposite. To
better understand their connection, imagine that you are grasping an object. We can
use the schema of gripping (cognitive I 2 ) using a six-degrees-of-freedom tracker and
a screen displaying the object (sensorimotor I 2 ). But if the sensorimotor I 2 are not of
good quality (long response time between action with the tracker and the feeling of
movement on the screen), the schema of gripping cannot be used. On the other hand,
if the interfaces do not use the schema of gripping, the cognitive I 2 will fail even with
the interfaces functioning accurately.
The foundation of our approach is based on this hierarchical 3-level model and
also on a diagonal division between the subject and the virtual world: Parallel to
various levels of sensorimotor and cognitive I 2 for the person, we have two levels of
software functioning for the virtual world. The computer should manage the software
part in real time (real-time hub and drivers for hardware interfaces) symmetrically to
the sensorimotor I 2 ,to physically create the virtual world . This includes simulation
based on physical laws (mechanical, optical, biomechanical, etc.) acting on the objects
and living things.
4 Hereinafter, we will use the abbreviation I 2 for immersion and interaction.
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