Oman York Conference (2001 in press)11/2/01 tunnel connecting Spacelab with the Shuttle mid-deck sometimes feel as if they are ascending inside a vertical tube, and encountering another crewmember coming the other way can make them suddenly feel as if they are upside down, descending headfirst. Looking backwards at their own feet makes them feel upright again After these illusions were described by Skylab crewmembers( Cooper, 1976) and in more detail by the crew of Spacelab-1, we decided to name them "visual reorientation illusions"(Oman, et al, 1984 1986: Oman 1986), since they differed from o-G inversion illusions in several important respects: First, the sensation was not necessarily of being"upside down"'-rather, the subjective vertical was frequently beneath your feet. Second, whereas Inversion Illusions were difficult Figure 2. Seeing a crewmember in an inverted position can make to reverse and continued when An observer himself feel"upside down eyes were closed, VRIs were easily reversed, and typically depended on what you were looking at. Though VRis usually occurred spontaneously, they could be cognitively manipulated in much the same way one can reverse a figure/ground illusion, or the perceived orientation of a Necker cube. "I can make whichever way I want to be down become down"was the frequent comment. When one slowly rolls inside a spacecraft, the moment of interchange of the subjective identity of the walls, ceilings, and floors is a perceptually quite distinct event, just as is the reversal of the corners of a Necker cube,or a figure-ground illusion. Lastly, most crewmembers experienced VRIs, and susceptibility continued throughout even long duration Skylab and Mir missions, whereas O-G inversion illusions are rare after the first day or two in weightlessness. VRIs have also been described in parabolic flight( Graybiel and Kellogg 1967; Lackner and Graybiel, 1983) though the distinction between inversion and reorientation illusions was not made in the older literature. astronauts now sometimes refer to VRIs as"the downs". Actually, it is possible to have a VRi right here Earth, as when you leave an underground subway station labyrinth, and familiar visual landmark, realize that e.g. you are facing east, not west. On Earth, gravity constrains our body orientation, and provides an omnipresent down"cue, so we normally only experience VRIs about a vertical axis. However, VRIs can be easily created about the gravitational horizontal in a 1-G laboratory using real or virtual tumbling rooms( Howard and Childerson, 1994: Oman and Skwersky, 1997) 2.3 Inversion Illusions. VRIs and Space Sickness. There is relatively strong circumstantial and scientific evidence(reviewed by Oman and Shubentsov, 1992)that head movements made abouOman York Conference (2001 in press) 11/2/01 Page 4 tunnel connecting Spacelab with the Shuttle mid-deck sometimes feel as if they are ascending inside a vertical tube, and encountering another crewmember coming the other way can make them suddenly feel as if they are upside down, descending headfirst. Looking backwards at their own feet makes them feel upright again. After these illusions were described by Skylab crewmembers (Cooper, 1976) and in more detail by the crew of Spacelab-1, we decided to name them “visual reorientation illusions” (Oman, et al, 1984, 1986; Oman 1986), since they differed from 0-G inversion illusions in several important respects: First, the sensation was not necessarily of being “upside down” – rather, the subjective vertical was frequently beneath your feet. Second, whereas Inversion Illusions were difficult Figure 2. Seeing a crewmember in an inverted position can make to reverse and continued when An observer himself feel “upside down”. eyes were closed, VRIs were easily reversed, and typically depended on what you were looking at. Though VRIs usually occurred spontaneously, they could be cognitively manipulated in much the same way one can reverse a figure/ground illusion, or the perceived orientation of a Necker cube. “I can make whichever way I want to be down become down” was the frequent comment. When one slowly rolls inside a spacecraft, the moment of interchange of the subjective identity of the walls, ceilings, and floors is a perceptually quite distinct event, just as is the reversal of the corners of a Necker cube, or a figure-ground illusion. Lastly, most crewmembers experienced VRIs, and susceptibility continued throughout even long duration Skylab and Mir missions, whereas 0-G inversion illusions are rare after the first day or two in weightlessness. VRIs have also been described in parabolic flight (Graybiel and Kellogg 1967; Lackner and Graybiel, 1983) though the distinction between inversion and reorientation illusions was not made in the older literature. Astronauts now sometimes refer to VRIs as “the downs”. Actually, it is possible to have a VRI right here on Earth, as when you leave an underground subway station labyrinth, and upon seeing a familiar visual landmark, realize that e.g. you are facing east, not west. On Earth, gravity constrains our body orientation, and provides an omnipresent “down” cue, so we normally only experience VRIs about a vertical axis. However, VRIs can be easily created about the gravitational horizontal in a 1-G laboratory using real or virtual tumbling rooms (Howard and Childerson, 1994; Oman and Skwersky, 1997) 2.3 Inversion Illusions, VRIs, and Space Sickness. There is relatively strong circumstantial and scientific evidence (reviewed by Oman and Shubentsov, 1992) that head movements made about