Biomedical Engineering Reference
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sive movement. This VR study further showed that although both proprioceptive
and vestibular cues contributed to travelled distance estimates, a higher weighting
of vestibular inputs were observed. These results were effectively described using a
basic linear weighting model.
6.3.2 Integration of Vestibular and Proprioceptive Information
in Human Locomotion
Consider walking through an environment that is covered in fog or walking in the
pitch dark. While these scenarios render visual information less reliable, evidence
shows that humans are still very competent in various locomotion tasks even in the
complete absence of vision (e.g., [
22
,
34
,
67
,
73
,
83
,
103
,
109
]). Past research often
reports that when either walking without vision or when passively moved through
space, body-based cues are often sufficient for estimating travelled distance [
7
,
21
,
24
,
51
,
58
,
67
,
73
,
92
,
102
,
103
] and to some extent self-velocity [
7
,
22
,
58
,
92
].
A series of studies have also looked specifically at the interactions between the
two main sources of body based cues; the proprioceptive system and the vestibular
system. Studies that have investigated the role of vestibular and/or proprioceptive
information in self-motion perception have done so by systematically isolating or
limiting each cue independently. Typical manipulations include having participants
walk on a treadmill (mainly proprioceptive information), or passively transporting
them through space in a vehicle (mainly vestibular information specifying transla-
tions through space). The logic is that walking in place (WIP) on a treadmill pro-
duces proprioceptive but no vestibular inputs associated with self-motion through
space, while during passive movement (PM), there are vestibular inputs but no rele-
vant proprioceptive information from the legs specifying movement through space.
These conditions can then be compared to normal walking through space (WTS),
which combines the proprioceptive and vestibular inputs of the unisensory WIP and
PM condition. For instance, Mittelstaedt and Mittelstaedt [
73
] reported that partici-
pants could accurately estimate the length of a travelled path when walking in place
(proprioception), or when being passively transported (vestibular). In their study,
even though both cues appeared sufficient in isolation, when both were available at
the same time (i.e., when walking through space) proprioceptive information was
reported to dominate vestibular information. But what this study could not specify
was by how much it dominates or, more generally, what the relative weights of the
individual cues are.
There is, however, a fundamental problem that makes it very difficult to make
assessments of cue weighting and studying the multisensory nature of self-motion
in general. The problem is that there is a very tight coupling between vestibular and
proprioceptive information during normal walking. The two signals are confounded
in the sense that under normal circumstances there can be no proprioceptive activ-
ity (consistent with walking) without experiencing concurrent vestibular excitation.
