Biomedical Engineering Reference
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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
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