Biomedical Engineering Reference
In-Depth Information
Fig. 6.2
The circular treadmill (CTM) at the Max Planck Institute for Biological Cybernetics. It
consists of a large motorized wooden disc (Ø = 3.6m) covered with a slip resistant rubber surface
and a motorized handlebar. The disc and handlebar can be actuated independently from each other.
The disc's maximum angular velocity is 73
◦
/s, and the handlebar can reach a maximum velocity of
150
◦
/s. Walking on the CTM is natural and intuitive and does not require any explicit training (see
also [
42
]). For the overground versus treadmill study (Sect.
6.2.2
) the setup was equipped with a
TrackIR: Pro 4 (NaturalPoint) optical tracking device for tracking the position and orientation of the
head. It was fixed on top of the depicted laptop monitor that was mounted in front of the participant.
Thedevicehasa46
◦
field of view and provides 6 DOF tracking with mm and sub-degree precision
for position and orientations, respectively. For the experiments described in Sects.
6.3.2
and
6.2.3
,
a custom-built pointing device was mounted on the handlebar within comfortable reaching distance
of the right hand (at a radius of 0.93 m from the center of the disk). The pointing device consisted of a
USB mechanical rotary encoder (Phidgets, Inc.) with a pointing rod attached and encased in plastic
(see also [
42
]). Note that the CTM has since moved to the department of Cognitive Neurosciences
at Bielefeld University. (Photograph courtesy of Axel Griesch)
step length than sighted individuals and that sighted participants who were blind-
folded also showed similar changes in gait (see also [
74
]). Further, in the absence of
vision, normally sighted participants walked slower and had lower step frequencies
when blindfolded compared to when full vision was available, which was hypothe-
sized to reflect a more cautious walking strategy when visual information was absent.
However, it is not known whether walking is differentially affected by the presence
and absence of congruent visual feedback.
Humans have a strong tendency to stabilize the head during walking (and various
other locomotor tasks) in the sense that they minimize the dispersion of the angular
displacement of the head [
13
]. Interestingly, visual feedback does not appear to be
important for this stabilization [
80
]. However, the walking conditions under which
this has been studied have been very limited. Participants were asked to walk at their
own preferred speed or to step in place [
80
]. Very little is known about the generality of
this lack of an effect of vision and whether there are differences between overground
and treadmill walking.
