Biomedical Engineering Reference
In-Depth Information
feedback, the only statistically reliable effect of the visual manipulation was a reduc-
tion of the vertical movements of the head at the highest walking speeds during
overground walking as compared to stationary walking. When visual feedback was
not available, this produced some trends in the gait parameters (increases in step
frequency and decreases in step length and walk ratio), although these were not
statistically significant.
6.2.3 Potential Implications for CyberWalk
One specific finding that impacted the design specifications of the CyberWalk plat-
form was that it took at least 2 s to accelerate the treadmill to the very slow speed
of 0.5m/s. As we will see in the following section, providing vestibular inputs by
allowing movement through space is an important part of simulating natural loco-
motion. Thus, from this perspective it meant that the CyberWalk platform needed
to ideally be big enough to accommodate such start up accelerations. The finding
that stationary walking does not change the main walking parameters of step length
and step frequency is encouraging as it means that the walking data on the treadmill
should be representative of normal gait. This also affected the design of the platform,
albeit in a more indirect fashion. We surmised that the platform should ideally have a
surface that is as stiff as possible since the most typically studied walking surfaces are
very stiff (e.g., sidewalks). Head movements, on the other hand, did change during
stationary walking in that they were less pronounced than during overground walk-
ing. This might seem advantageous in light of the fact that on the CyberWalk, head
mounted displays (HMDs) are the primary means of visually immersing the user
in VR and therefore having less head bounce would reduce visual motion artifacts
and potential tracking lags for rapid movements. However, it does raise the possi-
bility that the normal head stabilization function during walking (e.g., [
80
]) may be
different during treadmill walking, which may affect the role of the proprioceptive
receptors in the neck and also the role of coincident vestibular inputs.
6.3 Multisensory Self-Motion Perception
A veridical sense of self-motion during walking is a crucial component for obtaining
ecological validity in VR. Of particular interest to us is the multisensory nature of
self-motion perception. Information about the extent, speed, and direction of ego-
centric motion is available through most of our sensory systems (e.g. visual, audi-
tory, proprioceptive, vestibular), making self-motion perception during locomotion
a particularly interesting problem with respect to multisensory processing. During
self-motion perception there are important roles for the visual system (e.g. optic
flow), the vestibular system (the inner ear organs including the otoliths and semi-
circular canals), the proprioceptive system (the muscles and joints), and efference
