Biomedical Engineering Reference
In-Depth Information
Sound
source
Optokinetic drum
painted with
striped pattern
circular
treadmill
(a)
(c)
(b)
Visual vection
Auditory vection
Biomechanical vection
Fig. 2.1 Top-down sketch of different circular vection conditions. a Visual vection induced by
an optokinetic drum rotating around the stationary observer. b Auditory vection induced by sound
sources rotating around blindfolded listeners. c Biomechanical or “apparent stepping around” vec-
tion induced by blindfolded participants stepping along a rotating floor (“circular treadmill”)
stimulus velocity
(e.g. optic flow or treadmill rotation)
60
40
20
0
Time
Fig. 2.2
Schematic depiction of typical stimulus motion and resulting vection time course
can lead to paradoxical sensations of continuous illusory self-rotation despite perceiv-
ing only limited overall body tilt of generally no more than 20 [ 1 , 32 , 133 ]. Com-
plete head-over-heals tumbling sensations can, however, be induced when the conflict
between rotating visual cues and gravitational cues (from otoliths and somatosensory
system) is reduced, e.g., in bilateral vestibular loss patients [ 22 ] or in micro-gravity
conditions [ 21 , 134 ]. Alternatively, even under normal gravitational conditions, 360
head-over-heals tumbling sensations can be induced in most observers when a fully
furnished naturalistic room is rotated around a stationary observer [ 1 , 40 , 43 , 71 ].
2.2.2 Linear Vection
In a similar manner, linear vection can be induced by presenting optic flow patterns
that simulate translational motion. The traditional method used to induce linear vec-
tion in the laboratory is to use two monitors or screens facing each other, with the
participant's head centered between the two monitors and aligned parallel to the
screens, such that they cover a large part of the peripheral visual field [ 10 , 47 , 58 ].
Optic flow presented in this peripheral field induces strong linear vection. For exam-
ple, Johansson showed that observers perceive an “elevator illusion”, i.e., upward
linear vection, when downward optic flow is shown [ 47 ]. More recent studies often
use a monitor or projection screen in the front of the participant to show expanding
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