Biomedical Engineering Reference
In-Depth Information
parameters. Virtual reality meets the requirements of standardization of the situation
through the control of synthetic humanoids. All the motion editing techniques can
indeed be applied to modify only one part of the motion up to completely control the
virtual character to react differently, such as by modifying the direction of his run,
change his stances, etc. [
36
,
41
]. Moreover, it overcomes the limitations of previous
methodologies. It indeed allows three-dimensional display, viewpoint adaptations,
and modifications of the visual information provided to the immersed subject.
13.1.2 Requirements for Using Virtual Reality for Sports
13.1.2.1 A Sufficient Level of Presence
Using virtual reality for sports analysis must nevertheless be done with caution.
Some requirements must indeed be observed. The most important is to provide an
environment that generates a high level of presence, the subject then has the feeling
of being in the virtual environment [
10
]. The sense of presence is related to various
factors. Slater and Usoh [
53
] distinguish two types of factors: external factors related
to technology and internal factors related to psychological aspects. Internal factors
are the way to internalize the experience of an individual. External factors are the
types of technologies and materials used to display and interact with the virtual
environment. Evaluation of presence is thus fundamental to consider that a virtual
environment can be used to study physical activity and sports performance.
Measuring presence is very complex since it results from a set of parameters
difficult to control. Hendrix divides this measurement into objective and subjective
evaluations [
30
]. Objective evaluation depends on several categories of indicators
[
9
]. These indicators are physiological, they are function of muscle tension, eye and
cardiovascular responses to virtual events. They are also linked to the achievement
of one or more tasks in the synthetic world, the precision of movement and speed
of response [
52
]. Subjective measures correspond to a psychological evaluation,
usually conducted using questionnaires [
51
,
55
,
64
]. Given the intrinsic nature and
complexity of the presence, validate subjective measures of presence is not obvious.
As Hendrix highlighted [
30
], “Evaluation of the presence requires both the use of
subjective and objective measures. This is the most appropriate measure.”. In the
case of physical activities, it is necessary that the subject can reproduce gestures
as close as possible to reality. This requirement is in addition to other constraints
that determine the presence. To assess the degree of presence of an athlete, it seems
necessary to use an objective method in connection with the completion of the task
in a virtual environment. This achievement must be compared to that encountered in
the real world. Comparison of the kinematics of athletes between a real and a virtual
situation is then an additional quantitative assessment of presence.
This kind of objective kinematical validation of the presence has been done by
Bideau et al. [
11
]. They focused on the duel between a handball goalkeeper and a
thrower. To this end, they defined an experiment divided into two steps: a motion
