Game Development Reference
Figure 1.2 The “perception, cognition, action'' loop going through the virtual world
a request to modify the environment. In compliance with this request for modification,
the calculator assesses the changes to be made to the virtual environment and the sen-
sorial reactions (images, sound, effects, etc.) to be transferred to the sensory interfaces.
This loop in interactive virtual environment is only a transposition of the “perception,
cognition, action'' loop of man's behaviour in a real world. But two major constraints,
which are inherent to the techniques, disturb the “perception, cognition, action'' loop
and consequently the subject's behaviour: latency and sensorimotor discrepancies .
Latency is the time lag between the user's action on the motor interfaces and
the perception of the consequences of this action on the virtual environment through
sensorial interfaces. The existence of latency in the loop has an influence on the quality
of any virtual reality application. This latency is an artefact inherent to interactive
Sensorimotor discrepancies are the other artefacts of virtual reality. No matter how
many sensory channels are used in an application, no matter howmany interactions are
provided to the subject, sensorimotor discrepancies with respect to the sensorimotor
behaviour of the subject in the real world almost always exist. Do these sensorimotor
discrepancies disturb the behaviour of the subject? These two issues are covered to
some extent in this topic.
1.2 BOOK OUTLINE
This topic is an extract of “Le Traité de la Réalité Virtuelle'' (Treatise on Virtual
Reality), a book originally written in French. This collective work was governed by an
editorial committee who wanted to structure it, essentially around the general issues
related to virtual reality.
In any virtual reality application, the person is immersed in and interacting with
a virtual environment. He perceives, decides and acts in this environment, a pro-
cess schematised in a standard “perception, cognition, action'' loop, which must be
achieved within the technical, physiological and cognitive constraints (Figure 1.2).