Biomedical Engineering Reference
In-Depth Information
(a)
(b)
10
10
5
5
0
*
0
−5
−5
−10
−10
−10
−5
0
5
10
−10
−5
0
5
10
Test velocity (
o
/s)
Test velocity (
o
/s)
Fig. 6.5
Self-motion perception during walking with extreme conflicts between proprioceptive and
vestibular signals.
a
The perceived self-motion for eleven participants after averaging across the six
replications of each condition. The
solid black line
represents the fit of the MLE model to the group
means. The
asterisk
indicates a significant difference between test velocity and mean pointing rate.
b
Data categorized according to whether motion was perceived as backward (
open black circles
)
or forward (
filled black circles
). The sizes of the
circles
reflect the relative proportion of trials that
contributed to the represented mean value. Clearly there were a substantial number of cases in which
direction was confused. Pointing rates were virtual mirror images for the forward and backward
perceived trials. To illustrate this, the
grey circles
show the backward perceived motion but with
the sign inversed. The solid lines represent fits of the adapted MLE model to the group means. The
annotations show the estimates for the proprioceptive weights that correspond to the fitted model
from the fact that the proprioceptive input is directionally unambiguous. Two subse-
quent experiments, in which we manipulated either the walking speed or the walking
direction, clearly showed that there is an effect of the proprioceptive input on the
distribution of the number of trials that are perceived as forward or backward motion.
For instance, the proportion of trials perceived as forward was, as before, close to
50%when mechanically walking forward in place, but dropped to around 25%when
mechanically walking backwards. In other words, stepping backwards also made the
participant feel like they were moving backwards most of the time, but not always.
The contribution of the proprioceptive input to the perceived direction is therefore
only partial. It remains an open question as to what all of the determining factors are
for perceived direction.
6.3.4 Potential Implications for CyberWalk
Taken together, these studies reveal the clear importance of vestibular inputs for self-
motion perception during walking. The vestibular sense registers primarily acceler-
ations and will gradually stop responding once a constant speed has been reached.
However, this cessation of sensory stimulation does not mean that there is lack of
motion information. After all, if no change in velocity occurs, this would indicate that
