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But his vision is directed to the screen, not to his hands, and the object is held without
actually closing the hands. In spite of these alterations, the user unconsciously uses the
same schema.
Piaget concludes that sensorimotor intelligence manages to solve a set of problems
of actions (reaching an object, etc.) by constructing a complex system of assimilation
schemas and to organise the real world as per a set of time-space and causal rules.
Hence our fundamental postulate of virtual reality:
In an interactive virtual environment, a person uses the same approach that he
uses in the real world to organise the virtual world as per the set of time-space
and causal rules.
2.3.2.2 Use of schemas, metaphors or sensorimotor substitutions
In case of technical, economic or theoretical difficulties that obstruct the use of
an Imported Behavioural Schema, we can get around these difficulties by using a
“metaphor'' . Instead of using a sensorimotor behaviour and the person's knowledge,
we offer him a symbolic image of the action or of the desired perception visually in
most cases. For example, in a virtual shop, we can give the consumer the opportunity
to confirm the purchase of a product simply by clicking on its image and then on an
icon representing a cash box. This action becomes symbolic and no longer represents
the sensorimotor action in a real shop. Here, the immersion and interaction are less
pseudo-natural.
Using a metaphor may require more cognitive efforts if the metaphoric symbols
are not known to the users. They need to make an effort to understand and assimilate
the symbol, so that it gradually becomes a schema of use. But an Imported Behavioural
Schema (IBS) itself can require certain efforts, as it must be adapted to a virtual world
with a certain artefact and under the constraint of sensorimotor discrepancies. We use
either a metaphor or an IBS depending on the psychological, technical and economic
difficulties and the planned application. In practice, we can have a combined use of
metaphors and IBS, as per the type of activities required.
In case of difficulties in using an IBS or a metaphor using the same motor senses
and responses as in the real world, a metaphor with sensory substitution or a metaphor
with motor substitution can also be used. For example, it is often difficult to transfer
the force to the user in a force feedback interface. We can by-pass this difficulty by
substituting the sense of perceiving the force by a sense of hearing. A sound is heard
when the object handled by the user faces an obstacle. This sensory substitution is
effective in this case if the user does not need to be warned about the obstacle. On the
other hand, if the perception of intensity and the directions of forces are necessary for
the application (for example, assembling parts), substituting would not be appropri-
ate. The substitution can also be motor and not sensory: Instead of getting about by
walking, the user can orally give commands to move virtually (I want to move forward,
move back, turn left, turn right, etc.) with a voice-command interface and in front of
a dynamic point of view of the virtual world. Here, it is a case of a metaphor with
motor substitution.
Metaphors with sensory or motor substitutions separate the virtual action from
the real action. But do not assume that immersion and interaction will automatically
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