Biomedical Engineering Reference
In-Depth Information
or contracting optic flow fields [
3
,
70
]. Comparing different motion directions shows
vection facilitation for up-down (elevator) vection, presumably because visual motion
does not suggest a change in the gravito-inertial vector as compared to front-back or
left-right motion [
30
,
112
].
In recent times, VR technology has been successfully introduced to perceptual
research as a highly flexible research tool (see recent reviews by Hettinger [
34
]
and Riecke [
86
]). It has been shown that both linear and circular vection can be reli-
ably induced using modern VR technology, and the fact that this technology allows
for precise experimental stimulus control under natural or close-to-natural stimulus
conditions is much appreciated by researchers.
2.3 Self-Motion Sensation from Walking
Although walking on a linear treadmill cannot itself reliably induce vection, walking
in a circular pattern on a rotating disc (“circular treadmill”, see Fig.
2.1
c) can induce
compelling curvilinear or circular vection [
13
,
14
]. That is, stepping along a circular
treadmill in darkness or with eyes blindfolded can induce strong sensations of self-
rotation in the direction opposite to the floor motion (i.e., congruent with the walking
motion), irrespective of step size and without any net body motion [
13
,
14
]. Several
names have been used to refer to this phenomenon, including “
apparent stepping
around
” by Bles and colleagues [
13
,
14
], “
podokinetic vection
” by Becker et al.
[
8
], or “
biomechanical vection
” by Bruggeman et al. [
18
] and Riecke et al. [
92
].
Note that the mere act of moving one's leg as if walking but without floor contact
does not induce any vection. While the above-mentioned studies reported reliable
and consistent biomechanical vection for circular treadmill walking without net body
motion, Becker and colleagues observed biomechanical vection only in rare cases:
only 25 % of participants occasionally reported biomechanical vection, suggesting
that their procedure did not reliably induce vection [
7
]. As suggested by Becker et al.
[
18
], this unusually low rate of biomechanical circular vection occurrences might be
related to the specific instructions used by Becker et al., in that they asked participants
to “track angular self-displacement relative to the platform” (p. 461), not relative the
surrounding stationary room.
In addition to biomechanically-induced self-motion illusions, Bles and colleagues
also reported nystagmus and Coriolis-like effects when participants performed active
head tilts, corroborating the strength of vection that can be induced by biomechan-
ical cues [
13
,
14
]. Biomechanical vection from stepping-around occurs similarly in
labyrinth-defective patients, although their somatosensory nystagmus was stronger
[
12
]. While actual rotation results in self-rotation illusion after-effects in the direction
opposite
to the prior motion, circular vection induced by blindfolded stepping along
a rotating disc results in illusory self-rotation after-effects in the
same
direction as
the prior perceived self-motion [
44
].
Apart from walking on a circular treadmill, passive arm or foot movement can
induce similar circular vection [
15
]: Participants sat stationary in complete darkness
inside a slowly rotating optokinetic drum (10
◦
/s). When they touched the rotating