Biomedical Engineering Reference
In-Depth Information
(b)
(a)
60
W
v
= 1
Vestibular only
1
W
v
= 0.75
0.8
50
W
v
= 0.50
W
v
= 0.25
0.6
Proprioception
40
W
v
= 0
0.4
30
0.2
0
20
Proprioception only
20
30
40
50
−20
−10
0
10
Vestibular input (
o
/s)
Vestibular input − proprioceptive
o
/s)
input (
Fig. 6.4
Relative weighting of vestibular information. The relative weighting of the vestibular
and proprioceptive inputs were investigated by fixing the proprioceptive input to a single value
and varying the vestibular input (note that in [
42
] the proprioceptive inputs were varied). Eight
participants were tested with a 2-IFC paradigm with four standards that all had the same walking
speed but had different vestibular inputs, as explained below. The conflicts we tested differed in size
and in direction. In the first condition there was no conflict and both the vestibular and proprioceptive
inputs were the same (i.e., both at 40
◦
/s). In the second condition, the vestibular input was slower
(20 or 30
◦
/s) than the proprioceptive input, and in the third condition, the vestibular input was
larger (50
◦
/s) than the proprioceptive inputs. To illustrate how this last condition was achieved, the
handlebar was moved at 50
◦
/s to establish the vestibular input. However since this by itself would
also give a proprioceptive input of 50
◦
/s and not the desired 40
◦
/s, the difference was created by
moving the disc at 10
◦
/s in the same direction as the handlebar.
a
The group means for the PSEs
(and SEMs) for the main experiment (
black markers
) and the control experiment (
grey markers
,
see text for details). The
dotted diagonal lines
illustrate hypothetical vestibular weighting schemes.
b
The estimated vestibular weights extracted from the results in panel (
a
). The horizontal
dotted
lines
on the
top
and
bottom
of the
panel
represent hypothetical instances in which the perceived
walking speed is entirely determined by the vestibular (
top
) or proprioceptive input (
bottom
)
This alternative interpretation is unlikely given the results of a control experiment
in which two new participants were tested in the exact same experiment but with
explicit instructions to judge how fast they were moving through space and to ignore
how fast they were walking. The results are clearly different from those of the main
experiment (Fig.
6.4
a, grey markers). The PSEs are now close to the theoretical line
for complete vestibular dominance. However, the PSEs are not exactly on the line
but show an influence of the proprioceptive input, which is what we would expect
under the mandatory integration hypothesis (i.e. even though participants were told
to ignore their speed of proprioception, these proprioceptive cues still influenced
their responses).
