Oman York Conference (2001 in press)11/2/01 Many astronauts are familiar with aerobatic"inversion illusion, a sensation of inversion ulting from the eyeballs up acceleration component involved in an aerobatic pushd over or inverted flight. Since the us shuttle thrusts into orbit into an inverted attitude. and crewmembers experience eyeballs-in and up"acceleration, it is not surprising crewmember experience aerobatic inversion illusion during launch. Perhaps the aerobatic inversion illusion due to the launch profile primes the onset of o-G inversion illusion after entering weightlessness 2.2 Visual Reorientation Illusions. Unlike their predecessors in the Mercury, Gemini, and Apollo programs, Skylab and Shuttle astronauts no longer routinely worked in their seats Instead their tasks fre move around. and work in orientations relative to the spacecraft interior, which were physically impossible to practice in simulators beforehand Fundamental symmetries in the visual scene can create an ambiguity in the perceived identity of surrounding surfaces. When floating horizontally or upside down, they discovered that the spacecraft floor, ceiling, and walls ould fre know intellectually what is on but somehow whichever surface is seen beneath your feet seems like a floor","surfaces parallel to your body axis are walls", surfaces overhead are ceilings".(Figure 1). Interior architectural asymmetries and familiar objects in fixed tions provided tended to prevent or reverse the illusion However, the human body is also a familiar form, viewed on Earth primarily in a gravitationally upright position. Astronauts Figure 1. Crewmember with feet toward found that catching sight Spacelab ceiling seems right side up. Note crewmember floating inverted nearby would canted"upper racks in the lower part of the sometimes make they themselves suddenly feel ide down( Figure 2). The Earth a powerful"down "orienting stimulus when viewed out a porthole or when on a spacewalk. In crew debriefings, other examples abound: Astronauts working inverted on the flight deck, photographing the Earth through the overhead windows felt they were looking"down"through windows in the floor of a gondola Crewmembers working close to the canted upper racks in the Spacelab module were surprised to look down and see the lower racks tilting outward beneath them. Astronauts in the nodes and aboratory modules of the US portions of the International Space Station sometimes find it difficult to distinguish walls from ceiling from floor, since the modules have a square cross section, and interchangable rack systems. Crewmembers passing headfirst through the horizontalOman York Conference (2001 in press) 11/2/01 Page 3 Many astronauts are familiar with “aerobatic” inversion illusion, a sensation of inversion resulting from the “eyeballs up” acceleration component involved in an aerobatic pushover or inverted flight. Since the US Shuttle thrusts into orbit into an inverted attitude, and crewmembers experience “eyeballs-in and up” acceleration, it is not surprising crewmembers experience aerobatic inversion illusion during launch. Perhaps the aerobatic inversion illusion due to the launch profile primes the onset of 0-G inversion illusion after entering weightlessness. 2.2 Visual Reorientation Illusions. Unlike their predecessors in the Mercury, Gemini, and Apollo programs, Skylab and Shuttle astronauts no longer routinely worked in their seats. Instead, their tasks frequently required them to move around, and work in orientations relative to the spacecraft interior, which were physically impossible to practice in simulators beforehand. Fundamental symmetries in the visual scene can create an ambiguity in the perceived identity of surrounding surfaces. When floating horizontally or upside down, they discovered that the spacecraft floor, ceiling, and walls would frequently exchange identities: “You know intellectually what is going on but somehow whichever surface is seen beneath your feet seems like a floor”; “surfaces parallel to your body axis are walls”; “surfaces overhead are ceilings”. (Figure 1). Interior architectural asymmetries and familiar objects in fixed locations provided important landmarks which tended to prevent or reverse the illusion. However, the human body is also a familiar form, viewed on Earth primarily in a gravitationally upright position. Astronauts Figure 1. Crewmember with feet toward found that catching sight of another Spacelab ceiling seems right side up. Note crewmember floating inverted nearby would canted “upper racks in the lower part of the sometimes make they themselves suddenly feel photo. upside down (Figure 2). The Earth can provide a powerful “down” orienting stimulus when viewed out a porthole or when on a spacewalk. In crew debriefings, other examples abound: Astronauts working inverted on the flight deck, photographing the Earth through the overhead windows felt they were looking “down” through windows in the floor of a gondola. Crewmembers working close to the canted upper racks in the Spacelab module were surprised to look down and see the lower racks tilting outward beneath them. Astronauts in the nodes and laboratory modules of the US portions of the International Space Station sometimes find it difficult to distinguish walls from ceiling from floor, since the modules have a square cross section, and interchangable rack systems. Crewmembers passing headfirst through the horizontal