Biomedical Engineering Reference
In-Depth Information
116
], as well as for more complex online tasks such as spatial updating. However, the
accuracy and precision of vestibularly-acquired spatial information is typically rather
low, and degrades rapidly as the knowledge derived from it becomes more complex.
For example, Sholl [
94
] pushed blindfolded participants in a wheelchair over paths of
varying complexity. Most participants were able to track simple two-segment paths
with well-better than chance accuracy (see also [
38
]); however, participants were
generally unable to keep track of complex trajectories (i.e., those involving more
than three turns). With respect to the creation of relatively complex and enduring
spatial knowledge, the sufficiency of vestibular information is largely unexplored
in the literature, although Sholl's results would suggest that it is difficult to acquire
complex route or survey knowledge on the basis of vestibular information alone.
Among healthy adults, vestibular information may also be necessary for successful
interaction with the environment, as sudden loss or disruption of it through pathol-
ogy [
20
,
32
,
75
,
76
] or experimental manipulation [
101
] can significantly impair
performance on basic spatial tasks such as turn and distance estimation. However,
people can generally adapt to a gradual progressive degradation of the vestibular sys-
tem [
57
], and thus its full functioning is not always necessary for acquiring spatial
knowledge. The role of the vestibular system as well as its relation to other idiothetic
senses is reviewed in [
57
].
Although the terms proprioceptive and kinesthetic are often used interchangeably
in the literature, we use the former to refer to information about a relatively static posi-
tion or attitude of the musculature; whereas the latter refers to information about the
movement of one's limbs or effectors. By this distinction, knowledge of the location
of one's unseen hand, for example, may come from a proprioceptive sense; whereas
the ability to brush one's teeth without a mirror would require kinesthetic informa-
tion. A relatively small research literature has found that kinesthetic information is
generally sufficient for acquiring knowledge of distances [
67
,
102
] and orientation
changes [
8
,
13
,
52
]. Indeed, compared to the vestibular and somatosensory compo-
nents of idiothetic information, the proprioceptive component may enable relatively
more accurate performance in a variety of online tasks, such as heading estimation
[
73
,
103
], turn estimation [
53
], distance estimation [
67
], and spatial updating [
94
].
As with vestibular information, the sufficiency of kinesthetic information for acquir-
ing relatively sophisticated knowledge about spatial layout is under-researched. But
the ability to acquire accurate spatial information about traveled distances [
28
], turns
[
83
], routes [
114
], and spatial layout [
86
] from purely visual sources demonstrate
that kinesthetic (and other sources of) information is not strictly necessary for the
acquisition of spatial knowledge.
1.3 Efferent Sources of Information
Finally, we consider the contributions to spatial knowledge of four other internal
sources of spatial information—efference copy, attention allocation, cognitive deci-
sion making, and mental transformations. Of course it is incorrect to consider these
