Vection and Motion Thresholds as a Function of Contrast

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Vection and Motion Thresholds as a Function of Contrast

Frederick Patterson; Yancy York


NAMRL-09-32

Background/Introduction. Vection can be defined as a sensory-spatial illusion t hat creates false sensations of self motion, in either linear or angular directi ons. Although false perceptions of self motion are common, visual characteristi cs linked to this type of illusion are not fully understood. Vection can be strongly influenced by various physical aspects, such as optical velocity
of the visual stimulus, spatial frequency, and field of view. Although previous research documents how perceived motion can be influenced by several variables associated with visual contrast, they do not provide insight into the relationship between color variation and onset of vection illusion. Since very little is known about the relationship between visual contrast thresholds and susceptibility to vection, and even less is known about the impact of color variations on self motion illusions; it was deemed beneficial to further evaluate this topic from a qualitative perspective. Method. This study was conducted on 20 aviator candidates awaiting flight training. A Visual Vestibular Sphere Device (VVSD) was used to elicit the illusion of self-motion (vection) while subjects viewed the moving VVSD surround through a window that allowed visual contrast to be varied; this method led to the determination of contrast thresholds for the detection of surround motion and the onset of vection. The objective was to determine the effect of color saturation altered visual contrast on detection of surround motion and vection.
Results. The threshold for detection of vection was 2.5% contrast. A similar contrast threshold was obtained for detection of surround motion; however, surround motion was reported sooner than vection at a given contrast. Above threshold, lower contrast stimuli were associated with longer latencies to onset of vection and lower ratings of vection strength (realism of the
illusion) at the time of onset of vection. Conclusions. Vection was triggered readily at very low levels of visual contrast. It appeared that as long as the observers could detect any surround motion, they reported vection. Nevertheless, the vection illusion was stronger and was elicited faster under conditions of high contrast.