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to the movements of a virtual object, operated by a six-degrees-of-freedom sensor, to
help the user obtain the desired motoricity (the object's supporting surface will be
parallel to the table surface when they are close to each other) (Maman, 1998). All
these interface using aids are grouped under the generic term “Behavioural Software
Aids'' (BSAs). Some of them will focus on a sensorimotor aid (SMSA) while the rest
will focus on a cognitive aid (CogSA). We will explain different categories of aids
in paragraph 2.4.3. Therefore, it is necessary to design and program the coupling
between the interface and the programmed virtual world, hence the terms programmed
motoricity and perception are used in the figure 2.7.
Effective perception, which is imposed on the user, is a sensory perception which
is ideally made easy but has the inconvenience of almost always being partial and more
or less coherent. For example, the perception of movement in the real world is based
on vision, force sensitivity, vestibular apparatus (semicircular canals and otoliths) and
touch. Depending on the behavioural interface selected, certain types of sensory recep-
tors will not be stimulated while others will be stimulated with characteristics different
from those detectable by man in a real environment. All effective stimulations together
can create discrepancies that the brain will have to manage at the risk of failure. The
problem is similar in the case of effective motoricity. These difficulties caused by dis-
crepancies are inherent to the techniques of virtual reality and will always be complex
to solve in many cases. Will the brain be able to adapt to them or will it refuse them?
The experiments and knowledge of the specialists of cognitive sciences can help us to
validate or refute our conceptions. We will discuss this question in paragraph 2.3.3.
2.3.2 Behavioural interfaces, schema and metaphors
2.3.2.1 Concept of schema
In principle, we would like to offer the user a relatively natural 2 interaction and immer-
sion so as to make them effective with respect to the application. In this case, we will
talk about a pseudo-natural immersion (and also the interaction). What does this con-
cept cover? First of all, we can confirm that whatever is done naturally in the real
world is done unconsciously and without a great mental effort. We can, in principle,
think that it will be the same in case of a virtual environment if the interaction and
immersion are relatively similar to the human behaviour in the real world. Let's take
an example: In a virtual shop, the consumer wants to go about the aisles. A real trolley
is offered to him as a behavioural interface which he will push and take through the
aisles, facing the screen. In this case, the consumer will unconsciously and naturally
use some of the automatic reflexes he has acquired while shopping in real shops in
this virtual shop with a few sensorimotor differences. That is why we use the prefix
“pseudo'' to refer to this type of immersion and interaction.
The user thus uses a schema that he has adopted in the real world in his sensori-
motor activity. The concept of schema is proposed by psychologist Piaget (Piaget &
Chomsky, 1979). On analysing the origin of intelligence in an infant, mainly in its sen-
sorimotor dimension, he states that the subject uses the schemas as the means to adapt
to situations and objects he comes across. We would like to draw a parallel between
2 i.e. close to human behaviour in the real world.
 
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