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technological work to be done on this point before going on to a device close to the
capabilities of the human perceptual system.
As regards the haptic or proprioceptive stimulations, the various available tech-
nologies can still be considered to be at a primitive stage. Please also note that, at
present, there are efforts towards olfactive stimulations. Naimark (1990) speaks about
realism, about the sensory characteristics of virtual environments. This “term'' does
not seem very appropriate from two points of view.
First, realism relates back to the question of the purpose of the application of virtual
reality, and it is neither desirable nor feasible to create a virtual environment that is
a “copy'' of reality. Second, virtual environments may incorporate places or creatures
without an equivalent in the real world. From this point of view, cinema has long been
investing in immersion, as much in screen format as in the sound (“surround'') and
panoramic image coupling, and even in the extremely developed avatars, be it their
“texture'' or their expressions (progress related to the movement capture systems). In
this regard, we will find a review of the parallel evolution of media and virtual reality,
mainly in relation with the quest for perceptual realism (Ijsselsteijn, 2003) and “total
cinema'' (Bazin, 1967; Meusy, 2003).
5.2.2 Interaction
We have until now described the sensory aspects of virtual environments. However, it
is obvious that as soon as we speak about perception, we must admit that it is active.
This characteristic of immersion brings us closer to Gibson's theses (1979), for whom
the individual, by his behaviour, creates visual movement (and on a more general level,
sensory information) using which he takes the information in the environment (also see
Mestre, 1992; Warren, 1998). In this regard, Sheridan (1992) observes that the con-
cept of interaction with the virtual environment is multi-dimensional. He particularly
suggests distinguishing between two types of interactions.
First, there are the opportunities that the observer has to modify the sensory infor-
mation from the environment, according to his position in the environment. This is
done, for example, by systems capturing the position of the observer's head, which
make it possible to modify the image of (or more generally the sensory data from)
the environment according to the position occupied by the subject there. This aspect
of interaction thus concerns navigation. Ensuring perceptual coherence of the virtual
world when the user changes his view point can be considered to be the main problem.
Second, there are the possibilities that the observer has to effectively modify the envi-
ronment. For example, a dataglove, measuring the position of the hand and fingers
and providing haptic feedback, helps the subject to handle objects in the virtual world.
One of the problems that arise in this regard is ensuring continuity between the body
of the subject and the objects of the virtual world. This is taken care of by generating a
representation of the part of the subject's body that will be in contact with the objects
of the virtual world. Please also note that, beyond handling of objects, there is also the
interaction of the user with the autonomous entities of the virtual environment.
5.2.3 Structural factors of immersion
Until now, we have mentioned a few examples that aimed at describing the main
types of stimuli and interactions involved in an immersive environment. Beyond this
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