Game Development Reference
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between the two. In fact, the boom of special interfaces for virtual reality in the 90s
made it possible to anticipate a new approach of interfacing between a human and
an artificial device. As we have already mentioned, it was not about establishing a
communication between man and a machine (machine-tool, computer, etc.), which
comes under MMI, but carrying out activities in a virtual world, by using, if possible,
human behaviour in the real world. Hence our definition:
Behavioural interface depends on a device that uses the motricity or perceptions
of man resulting from his behaviour in the real world.
Theoretically, the “ sensory interfaces '' are designed to transfer the sensory stim-
uli from computer to man while the “ motor interfaces '' are designed to transfer
motor responses from man to computer. Some sensorimotor interfaces transfer motor
responses and, in response, the sensory stimuli are sent by the computer (force feedback
interfaces).
How should the interfaces transfer sensory stimuli and motor responses? and
How to use them for an effective behavioural interfacing?
Let's first analyse the technical aspect of these questions. The hardware design of a
behavioural interfaces starts with the choice of physical phenomenon that is be used.
The quality criteria for the interface are similar to those of a measuring unit: technical
and economical feasibility, as well as efficient metrological characteristics (accuracy,
repeatability, resolution, bandwidth, response time, etc.). They are explained in detail
in the chapters covering technical devices for each category of interface. In general, the
metrological characteristics are efficient if they correspond to the nominal capacities
of human senses or motor responses. In each chapter on interfaces, we will spec-
ify whether there are correspondences between the human capacities and technical
characteristics of the interfaces. However, we can already state that the metrological
characteristics of almost all interfaces, except for the audio interfaces, are much less
than the rated human sensorimotor capacities. We can schematise the transmission of
signals from a computer to the brain and vice versa. For example, in figure 2.3 the
computer transfers stimuli to the brain via eyes (vision), via skin receptors (touch)
and receptors in the muscles (proprioception). In figure 2.4, man acts using his hand
and by moving his eyes. It is thus necessary to design such interfaces on the basis of
a suitable physical phenomenon. We can note the difference in design for the special
case of “biosensors'', interfaces recording the efferent nervous activity. These special
interfaces do not directly detect the human motor responses, but the biological signals
of orders coming from the brain and reaching the corresponding ocular or skeletal
muscles. Laboratories offer devices that measure the small differences of potential on
the skin surface. These interfaces can be used only by specialists in the medical field.
2.2.2 Transparency of an interface
An important point in the design of a behavioural interface is its transparency :Itis
the interface's capacity to become transparent (not perceived) for the user when he is
using that interface. This notion of transparency, which is important in virtual reality,
can be studied at various levels.
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