Oman York Conference (2001 in press)11/2/01 determined by the interaction of environmental frame F and polarity P cues, and the idiotropic ctor M. Depending on the relative weighting the Sv is captured by the visual vertical v or the resultant of the idiotropic vector M and the gravireceptor bias vector B. Unlike the near-upright 1-G case, the sv never lies in an intermediate direction between V and(M+). It is al ways captured by one or the other. In Figure 6, the observer is depicted has canted overhead racks. The structured environment provides a strong set of symmetry cues F Here. the observer's feet are oriented toward the canted ceiling, and the footward idiotropic bias overcomes subjective relatively weak polarity cues available from the visual scene The perceptual visual vertical and the sv point toward the true ceiling, which the perceives as a subjective floor The observer experiences a visual reorientation illusion SV It is important to understand that frame and polarity cues are not physical properties of the entire igure 7. Model for VRi when working close to a canted visual environment. Both depend Upper rack in Spacelab on the observer's viewpoint and gaze direction. For example, Figure 7 shows a crewmember working on equipment mounted in the upper Spacelab racks Working close to the upper racks, the dominant frame cue in the scene is aligned Twue F oor Subjective Floar with the upper rather than lower racks Written labels on rack mounted equipment enhance the strength of downward polarity cues. As a result, V is parallel to the plane of the upper rack, which is perceived as a subjective wall. Unless the subject has a strong idiotropic bias M, the Sv is also in the plane of the upper rack. If the observ momentarily looks"down"at the lower rack he is surprised that it seems to tilt outward at the bottom Figure 8. Model for 0-G Inversion IllusionOman York Conference (2001 in press) 11/2/01 Page 9 determined by the interaction of environmental frame F and polarity P cues, and the idiotropic vector M. Depending on the relative weighting the SV is captured by the visual vertical V or the resultant of the idiotropic vector M and the gravireceptor bias vector B. Unlike the near-upright 1-G case, the SV never lies in an intermediate direction between V and (M+B). It is always captured by one or the other. In Figure 6, the observer is depicted inside a Spacelab module, which has canted overhead racks. The structured environment provides a strong set of symmetry cues F. Here, the observer’s feet are oriented toward the canted ceiling, and the footward idiotropic bias overcomes relatively weak polarity cues available from the visual scene. The perceptual visual vertical and the SV point toward the true ceiling, which the observer perceives as a subjective floor. The observer experiences a visual reorientation illusion. It is important to understand that frame and polarity cues are not physical properties of the entire Figure 7. Model for VRI when working close to a canted visual environment. Both depend Upper rack in Spacelab. on the observer’s viewpoint and gaze direction . For example, Figure 7 shows a crewmember working on equipment mounted in the upper Spacelab racks. Working close to the upper racks, the dominant frame cue in the scene is aligned with the upper rather than lower racks. Written labels on rack mounted equipment enhance the strength of downward polarity cues. As a result, V is parallel to the plane of the upper rack, which is perceived as a subjective wall. Unless the subject has a strong idiotropic bias M, the SV is also in the plane of the upper rack. If the observer momentarily looks “down” at the lower rack, he is surprised that it seems to tilt outward at the bottom. Figure 8. Model for 0-G Inversion Illusion