Game Development Reference
The vestibular system in the inner ear carries information related to accelerations,
angular velocities and forces of inertia that the head is subjected to. By stimulating this
system and vision, as in mobile booth transport simulators, a more consistent feeling
of movement is obtained. If the person physically walks on a treadmill in front of a
screen, it will be the proprioceptive sensors of the legs, tactile receptors in the soles
of the feet and vision that are stimulated and not the vestibular system, with the head
being (almost) stationary (Burkhardt et al., 1999). In all the previous cases, virtual
movement does not stimulate all the sensory receptors required during leg movement
in the real world. If we want total correspondence, it is necessary that the leg movement
is essentially done for the same distances as in the real world, which is rarely possible
for distances greater than some metres. But, in case of walking on the treadmill, the
motor responses in the virtual movement are similar to those of a real movement. This
is an interesting possibility when we want the subject to feel tired as he does in the real
world, as is the case in the SNCF training application, shown in (Lourdeaux, 2001).
Later in this chapter, we will describe the main paradigms 4 and metaphors
known for controlling movement in a virtual environment. The selection of movement
paradigms and metaphors is based on an analysis of objectives of movement tasks,
their characteristics, the context, as well as on experimental tests that permit valida-
tion of the most efficient associations. These different aspects have been approached
in the methodological section (chapter 2).
Bowman et al. (2004) distinguish three generic objectives for a movement task:
exploration, research and manoeuvre.
A movement task has many characteristics. Without expecting a comprehensive
list, the following are the principles to be considered:
the number of degrees of freedom of movement,
the precision of movement,
the distance to be covered,
the speed of movement,
the availability of different parts of the body for interaction.
The context of the task is also to be studied carefully. The main points to be
peripherals already managed by the application,
other tasks performed, whether or not in parallel, in the application,
motivation to simulate a real movement task.
There are still relatively few experimental tests; a section at the end of the chapter
will explain the best-known work.
The presentation of movement techniques is often achieved by metaphors. This
was mainly the classification adopted in the previous version of the “Traité de la
Réalité Virtuelle'' (Treatise on Virtual Reality). For this third edition of the Treatise,
4 The term “paradigm'' is used here for representing an interaction technique that is not
necessarily a metaphor.