Biomedical Engineering Reference
In-Depth Information
ular, the nature of natural unconstrained walking and the effects of treadmill walking
on characteristics of gait. The second part of this chapter describes the multisensory
nature of walking, with a focus on the integration of vestibular and proprioceptive
information during walking. The third part of this chapter describes research on
large-scale human navigation and identifies possible causes for the human tendency
to veer from a straight path, and even walk in circles when no external references are
made available. The chapter concludes with a summary description of the features
of the CyberWalk platform that were informed by this collection of research findings
and briefly highlights the current and future scientific potential for this platform.
6.1 Introduction
By far the most natural way to move through our environment is through locomotion.
However, the seemingly effortless act of walking is an extremely complex process
and a comprehensive understanding of this process involves scientific and clini-
cal studies at different levels of analysis. Locomotion requires preparing the body
posture before initiating locomotion, initiating and terminating locomotion, coordi-
nating the rhythmic activation patterns of the muscles, of the limbs and of the trunk,
and maintaining dynamic stability of the moving body [
77
]. There is also a need to
modulate the speed of locomotion, to avoid obstacles, to select appropriate, stable
foot placement, to accommodate different terrains, change the direction of locomo-
tion, and guide locomotion towards endpoints that are not visible from the start. To
this end, locomotion engages many different sensory systems, such as the visual,
proprioceptive, auditory and vestibular systems, making it a particularly interesting
multisensory problem. Importantly, these are also factors that must be considered
when developing a realistic walking interface to be used with Virtual Reality (VR).
Although many of these aspects of locomotion have received extensive scientific
attention, much of the earlier laboratory-based research, though highly valuable,
has lacked ecological validity. Ultimately, scientific research should, when possi-
ble, evaluate human behaviors as they occur under natural, cue-rich, ecologically
valid conditions. To this end, VR technology has been providing researchers with
the opportunity to provide natural, yet tightly controlled, stimulus conditions, while
also maintaining the capacity to create unique experimental scenarios that would
(or could) not occur in the real world [
16
,
24
,
68
,
105
]. An integral part of VR
is to also allow participants to move through the Virtual Environments (VE) as
naturally as possible. Until recently a very common way of having observers nav-
igate through VEs was to have them manipulate unnatural control devices such
as joysticks, computer mice, and keyboards. Despite having some advantages over
mere visual stimulation, such rudimentary motion control devices are severely lim-
ited. While using such devices, the physical actions which drive self-motion are
very different from the action of natural locomotion which they are intended to
replace (e.g. clicking a mouse button to move forward versus stepping). Moreover,
the sensory input is mainly visual and other important sensory information is lacking,
