Biomedical Engineering Reference
In-Depth Information
might potentially (at least in some cases)
decrease
instead of increase the sensation
of self-motion and thus potentially decrease the overall effectiveness of the motion
simulation. Thus, caution should be taken when adding walking interfaces, and each
situation should be carefully tested and evaluated as one apparently cannot assume
that walking will always improve the user experience and simulation effectiveness.
2.5 Further Cross-Modal Effects on Self-Motion
Perception in VR
Helmholtz suggested already in 1866 that vibrations and jerks that naturally accom-
pany self-motions play an important role for self-motion illusions, in that we expect
to experience at least some vibrations or jitter [
33
]. Vibrations can nowadays easily
be included in VR simulations and are frequently used in many applications. Adding
subtle vibrations to the floor or seat in VR simulations has indeed been shown to
enhance both visually-induced vection [
94
,
100
] and auditory vection [
85
,
88
], espe-
cially if accompanied by a matching simulated engine sound [
119
,
120
].
Vection can also be substantially enhanced when the vection onset is accompanied
by a small physical motion (such as a simple jerk of a few centimeters or degrees)
in the direction of visually-simulated self-motion. This has been shown for both
passive movements of the observer [
9
,
93
,
100
,
126
] and for active, self-initiated
motion cueing using a modified manual wheelchair [
84
] or a modified Gyroxus
gaming chair where participants controlled the virtual locomotion by leaning into
the intended motion direction [
87
]. For passive motions, combining vibrations and
small physical movements (jerks) together was more effective in enhancing vection
than either vibrations or jerks alone ([
100
], exp. 6).
These findings are promising for VR applications, as both vibrations and minimal
motion cueing can be added to existing VR simulations with relatively little effort
and cost. Moreover, these simple means of providing vibrations or jerks were shown
to be effective despite being physically incorrect—while jerks normally need to be in
the right direction to be effective and be synchronized with the visual motion onset,
their magnitude seems to be of lesser importance. Indeed, for many applications
there seems to be a surprisingly large coherence zone in which visuo-vestibular cue
conflicts are either not noticed or at the least seem to have little detrimental effect
[
115
]. Surprisingly, physical motion cues can enhance visually-induced vection even
when they do not match the direction or phase of the visually-displayed motion [
128
]:
When participants watched sinusoidal linear horizontal (left-right) oscillations on a
head-mounted display, they reported more compelling vection and larger motion
amplitudes when they were synchronously moved (oscillated) in the vertical (up-
down) and thus orthogonal direction. Similar enhancement of perceived vection and
motion amplitude was observed when both the visual and physical motions were
in the vertical direction, even though visual and physical motions were always in
opposite
directions and thus out of phase by 180
◦
(e.g., the highest visually depicted
