Biomedical Engineering Reference
In-Depth Information
self-motion had not ceased [
92
]. Nevertheless, the most salient moments are during
the acceleration phase (i.e., start walking) and deceleration phase (stop walking).
When simulating normal walking on a treadmill, it is therefore important to retain
these inertial cues as accurately as possible. The CyberWalk effectively achieves
this. Specifically, when the user starts to walk from a standstill, he/she initially walks
on a stationary surface and accelerates through space as they would during normal,
overground walking. Only once the user starts to reach a constant walking speed
will the treadmill start to move. Gradually, the treadmill brings the user back to the
center of the platform (ideally sub-threshold), by moving them backwards through
space while they continue to walk. Similarly, when the user stops walking or changes
walking direction, the treadmill only responds gradually, allowing the normal inertial
input to the vestibular system to occur. For this scheme to work, the walking surface
has to be large enough to accommodate several steps without large changes in tread-
mill speed. In preliminary studies this system has been shown to work very well for
controlling treadmill speed on a large linear treadmill [
94
]. Through these studies,
we determined that the minimum size of the walking surface needed to accommodate
this control scheme is 6
6 m. However, financial and mechanical considerations
limited the eventual size of the CyberWalk to 4
×
×
4m.
6.4 Large Scale Navigation
One field in which the CyberWalk is expected to have a large impact is human naviga-
tion. Navigation requires estimates of perceived direction and position while moving
through our environments. In order to achieve this we can use external devices such
as maps, street signs, compasses or GPS systems, or we can use our internal repre-
sentations of space that come from multiple cognitive and sensory sources. Much
of what we know about human spatial navigation has come from studies involv-
ing spaces of relatively small scale (i.e. room size or smaller), while comparatively
fewer human studies have considered large-scale navigation. In one recent extensive
real world study by our group, we evaluated the extent to which humans are able to
maintain a straight course through a large-scale environment consisting of unknown
terrainwithout reliable directional references [
93
]. The scenarios were those inwhich
observers were transported to the Tunisian Sahara desert or to the Bienwald forest
in western Germany and were asked to walk in a completely straight trajectory. The
area used for the forest experiment was selected because it was large enough to walk
in a constant direction for several hours and has minimal changes in elevation. The
thick tree cover also made it impossible to locate distant landmarks to aid direction
estimation.
According to a belief often referred to in popular culture, humans tend to walk in
circles in the types of desert or forest scenarios described above, yet there had been
no previous empirical evidence to support this. The Souman et al. [
93
] study showed
that people do indeed walk in circles while trying to maintain a straight course,
but only when traversing in the absence of reliable external directional references.
