Biomedical Engineering Reference
In-Depth Information
environments that is drastically different from previous implementations, and dis-
cuss the challenges and future work we have identified based on feedback from
demonstrations and military personnel.
14.2 Redirected Walking
Redirected walking exploits imperfections in human perception of self-motion by
either amplifying or diminishing a component of the user's physical movements
[
14
]. For example, when the user rotates his head, the change in head orientation is
measured by the system, and a scale factor is applied to the rotation in the virtual
world. The net result is a gradual rotation of the entire virtual world around the
user's head position, which in turn alters their walk direction in the real world. These
rotation gains
are most effective when applied during head turns while the user is
standing still [
6
] or during body turns as the user is walking around [
3
]. However, the
virtual world can also be rotated as the user walks in a straight line in the virtual world,
a manipulation known as
curvature gains
. If these manipulations are applied slowly
and gradually, the user will unknowingly compensate for the rotation, resulting in a
walking path that is curved in the real world. Studies have shown that the magnitude
of path curvature that can be applied without becoming perceptible is dependent on
the user's velocity [
11
].
The illusion induced by redirected walking works perceptually because vision
tends to dominate over vestibular sensations when these two modalities are in conflict
[
1
]. In practice, redirection is useful in preventing the user from exiting the boundaries
of the physical workspace. From the user's perspective, it will appear as though they
are proceeding normally through the virtual environment, but in reality they will be
unknowingly walking in circles. Thus, when applied properly, redirected walking
can be leveraged to allow a user to physically walk through a large and expansive
virtual world using a real world tracking area that is substantially smaller in size, an
advantage that is especially useful for training environments.
Redirected walking is a promising method for enabling natural locomotion in
virtual environments; however, there is a perceptual limit for the magnitude of con-
flict between visual and vestibular sensations. Excessive manipulation can become
noticeable to the user, or at worst cause simulator sickness or disorientation. As a
result, an important focus of research has been to quantify the detection thresholds
for redirected walking techniques. Psychophysical studies have found that users can
be physically turned approximately 49 % more or 20 % less than the perceived vir-
tual rotation and can be curved along a circular arc with a radius of at least 22 m
while believing they are walking in a straight line [
21
]. Because of these limitations,
deploying redirected walking in arbitrary environment models remains a practical
challenge—if the users' motions are not easily predictable, redirection may not be
able to be applied quickly enough to prevent them from walking outside of the
boundaries of the tracked space.
