Oman York Conference(2001 in press)11/2/01 10 Figure 8 illustrates the factors which likely contribute to a O-G inversion illusion. This observer is shown floating with his feet in the general direction of the true floor. The frame, polarity and idiotropic cues F, P, and M align the visual vertical V toward the floor. Hence the true floor is perceived as a floor, and the subjects report being"visually upright "in the cabin. However, unlike the individuals depicted in previous figures, this person has an abnormally large headward gravireceptor bias, so though visually upright with respect to the cabin, he feels that he and the entire spacecraft are somehow upside down P F B Figure 9. Model for EVA Height Vertigo Figure 9 provides a plausible explanation for the onset of eva height vertigo. In the left panel the crewmember is working "visually upright" in the payload bay of the Space Shuttle. The Earth beneath his feet, rather than feeling upside down, idiotropIc M and Earth view polaris Earth is perceived as being"above". However, if the crewmember rolls inverted, and sees the cues reverse the direction of the visual and subjective verticals, as shown in the right panel Suddenly the crewmember perceives he is hanging by one hand beneath an inverted spacecraft 4.0 Related Experiments 4. 1 Gravireceptor Bias. Laboratory evidence for the existence of a gravireceptor bias comes from the experiments of Mittelstaedt(1986), who asked observers lying on a tilting bed to set themselves gravitationally horizontal in darkness. More than 40 normals and five previously flown astronauts were tested. The tilt angle of the entire group averaged almost perfectly horizontal. but there were consistent differences between individuals. As shown in Figure 10 some tended to set the bed a few degrees head down, while others set it a few degrees head upOman York Conference (2001 in press) 11/2/01 Page 10 Figure 8 illustrates the factors which likely contribute to a 0-G inversion illusion. This observer is shown floating with his feet in the general direction of the true floor. The frame, polarity and idiotropic cues F,P, and M align the visual vertical V toward the floor. Hence the true floor is perceived as a floor, and the subjects report being “visually upright” in the cabin. However, unlike the individuals depicted in previous figures, this person has an abnormally large headward gravireceptor bias, so though visually upright with respect to the cabin, he feels that he and the entire spacecraft are somehow upside down. Figure 9. Model for EVA Height Vertigo Figure 9 provides a plausible explanation for the onset of EVA height vertigo. In the left panel, the crewmember is working “visually upright” in the payload bay of the Space Shuttle. The Earth is perceived as being “above”. However, if the crewmember rolls inverted, and sees the Earth beneath his feet, rather than feeling upside down, idiotropic M and Earth view polarity cues reverse the direction of the visual and subjective verticals, as shown in the right panel. Suddenly the crewmember perceives he is hanging by one hand beneath an inverted spacecraft. 4.0 Related Experiments 4.1 Gravireceptor Bias. Laboratory evidence for the existence of a gravireceptor bias comes from the experiments of Mittelstaedt (1986), who asked observers lying on a tilting bed to set themselves gravitationally horizontal in darkness. More than 40 normals and five previously flown astronauts were tested. The tilt angle of the entire group averaged almost perfectly horizontal, but there were consistent differences between individuals. As shown in Figure 10, some tended to set the bed a few degrees head down, while others set it a few degrees head up