Biomedical Engineering Reference
In-Depth Information
surroundings. Thus, it seems to make sense that we should be able to walk through
virtual environments in a similar manner, in the hope that walking will enable us to
more easily remain oriented and reach our destination with little effort or cognitive
load, just like in the real world. As several chapters in this topic discuss in detail,
however, enabling humans to use this most intuitive mode of transportation in VR
bears many challenges, both from technical and perceptual points of view (see also
[
37
] for a review). Allowing VR users to walk naturally requires them to carry the
visual display with them, typically using position-tracked head-mounted displays
(HMDs). Although technology is advancing, there are still major technical limita-
tions (e.g., pixel resolution, limited (FOV) of view, and tracking/display latencies) as
well as perceptual challenges including spatial misperception such as underestima-
tion of distance [
59
] or motion sickness [
31
,
66
]. Moreover, allowing for actual and
unencumbered walking requires huge tracked free-space walking areas, especially
if virtual environments larger than room-sized are intended.
A variety of techniques have been proposed to address these fundamental issues,
including virtual walking interfaces, walking-in-place metaphors, or redirected walk-
ing. While many of these approaches are promising and discussed in detail in other
chapters of this topic, they include non-trivial technical challenges, and often either
restrict the walking motions or possible trajectories as in the case for re-directed
walking (e.g., [
111
], and Chap.
10
of this topic), change the biomechanics of walk-
ing fundamentally (as in the case for walking-in-place interfaces, see Chap.
11
of this
topic) and/or require considerable technical, financial, and safety efforts to imple-
ment (as in the case for larger or omni-directional treadmills, where additional safety
measures like harnesses are needed). Many of these issues are actively researched,
and we are hopeful that most of these issues might be solved eventually.
Treadmills are probably the most promising and most widely used and researched
approaches to allow for walking in VEs, as they are commercially available for
relatively affordable prices and allow for fairly natural biomechanical cues from
walking, especially when augmented with a force-feedback harnesses for linear or
omni-directional locomotion ([
37
], and Chap.
6
of this topic). Somewhat counter-
intuitively, though, despite allowing for fairly natural walking motions, even the
most advanced treadmills do not seem to provide the user with an actual compelling
sensation of self-motion unless accompanied with wide-FOV visual motion cues.
That is, while actual walking is naturally accompanied with an embodied sensation
of self-motion through the environment, even in the absence of visual or auditory
cues, walking on a linear treadmill is typically not. Walking can, however, sometimes
affect our visual perception: for example, Yabe and Taga [
131
] showed that walking
on a linear treadmill can affect the perception of ambiguous visual motion, similar to
motion or action capture phenomena. This “treadmill capture” effect seems to disap-
pear, however, for extended experience of treadmill locomotion in regular treadmill
runners [
132
].
There is little published research on the perception or illusion of self-motion
(“vection”) on linear treadmills. Durgin et al. [
26
] observed, for example, that “during
treadmill locomotion, there is rarely any illusion that one is actually moving forward”
(p. 401) and continues to state that “people do not have the illusion that they are
