Biomedical Engineering Reference
In-Depth Information
systematically affected not only perceived self-motion, but also the perceived stride
length and frequency and even the perceived stepping direction. Of particular interest
in our context is condition 3 in their experiment, in which participants were station-
ary and stepped along with the rotating floor disc while the optokinetic drum did not
move. Whereas half of the participants 'correctly' perceived to be stationary while
stepping along a rotating disc, the other half experienced illusory self-motion in the
sense that they (erroneously) reported walking forward on a stationary disc while the
optokinetic drum was moving along with them. This suggests that biomechanical
cues from walking can (at least for some participants) induce self-motion illusions
even in the presence of conflicting visual cues, illustrating that visual cues do not
necessarily dominate in cross-modal cue conflict situations. This further corrobo-
rates the different vection-inducing potential of walking in circular patterns (where
biomechanical vection is strong and can even overpower conflicting visual cues) as
compared to linear walking, where biomechanical vection does not reliably occur
at all. DiZio and Lackner [
24
] reported that combining biomechanical and visual
vection by rotating the disc of a circular treadmill together with the optokinetic drum
could even yield immediate vection onset.
Although Jürgens and Becke [
49
] demonstrated that a Bayesian sensor fusion
could be successfully applied to model the rotation perception based on vestibular,
biomechanical, visual, and cognitive information, further research is needed to fully
explain and predict cross-modal and higher-level effects and contributions. The cur-
rent data predicts substantial vection benefits for consistent multi-modal stimulation,
at least for the case of self-rotation perception. Surprisingly, however, cue combina-
tion benefits are much more ambiguous for translational vection, as we will discuss
below.
2.4.2.2 Linear Vection
Whereas walking on a linear treadmill apparently cannot by itself induce a com-
pelling sensation of self-motion (linear vection), it can modulate the occurrence and
strength of visually-induced linear vection: Although one would normally assume
that perceived self-motion during visual motion simulation in VR should benefit
from additional walking cues, a recent study by Kitazaki et al. [
52
] suggests that pro-
viding biomechanical cues from walking on a linear treadmill might, in fact, impair
visually-induced vection (see also [
51
]). Participants watched expanding or contract-
ing optic flow patterns on a 2
8 m projection screen while either standing still or
walking forward on a linear treadmill with the same 4 km/h velocity as the visually
simulated self-motion. When the visual cues simulated a forward motion, vection
occurred later when participants also walked forwards as compared to standing still.
An additional study extended these findings by including backwards walking on the
linear treadmill [
69
]. Vection onset was delayed when the visually simulated self-
motion matched participants walking direction, that is, in the condition that most
closely matches real-world walking.
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