York Conference 2001: Levels of Perception, L. Harris and M. Jenkin, Eds, Springer Verlag Human Visual Orientation in Weightlessness Charles m. oman Man vehicle laboratory massachusetts institute of Technology cambridge, MA 02139 Abstract An astronaut's sense of self-orientation is relatively labile, since the gravitational""cues provided by gravity are absent and visual cues to orientation are often ambiguous, and familiar objects can be difficult to recognize when viewed from an unfamiliar aspect. This chapter surveys the spatial orientation problems encountered in weightlessness including O-G inversion illusions, visual reorientation illusions, EVA height vertigo, and spatial memory problems described by astronauts. We consider examples from Shuttle, Mir, and International Space Station. A vector model for sensory cue interaction is synthesized which includes gravity, gravireceptor bias, frame(architectural symmetry), and polarity cues, and an intrinsic diotropic" tendency to perceive the visual vertical in a footward direction. Experimental evidence from previous studies and recent research by our York and MIt teams in orbital flight is summarized Supported by NASA Cooperative Agreement NCC9-58 with the National Space Biomedical Research Institute, and NASA Grant NAG9-1004 from Johnson Space Center 1. Introduction Understanding how humans maintain spatial orientation in the absence of gravity is of practical importance for astronauts and flight surgeons. It is also of fundamental interest to neurobiologists and cognitive scientists, since the force of gravity is a universal constant in normal evolution and development. Gravireceptor information plays a major role in the coordination of all types of body movement, and anchors the coordinate frame of our place and direction sense, as neurally coded in the limbic system his chapter reviews four related types of spatial orientation problems, as described by crewmembers on the Us Shuttle and Russian and international space stations. We synthesize a set of working hypotheses which account for static orientation illusions in 0-G and 1-G, thei relationship to height vertigo and spatial memory, and the role of visual cues, and summarize supporting evidence from ground, parabolic, and orbital flight experiments. There is evidence astronauts are more susceptible to dynamic(circular-and linear-vection)self-motion illusions during the first weeks of spaceflight, but for reasons of brevity, these dynamic illusions are not considered here This year's symposium honors Professor lan Howard, who has made so many contributions to the understanding of human perception. Human spatial orientation has been a longstandingYork Conference 2001: Levels of Perception, L. Harris and M. Jenkin, Eds., Springer Verlag Human Visual Orientation in Weightlessness Charles M. Oman Man Vehicle Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139 Abstract: An astronaut's sense of self-orientation is relatively labile, since the gravitational “down” cues provided by gravity are absent and visual cues to orientation are often ambiguous, and familiar objects can be difficult to recognize when viewed from an unfamiliar aspect. This chapter surveys the spatial orientation problems encountered in weightlessness including 0-G inversion illusions, visual reorientation illusions, EVA height vertigo, and spatial memory problems described by astronauts. We consider examples from Shuttle, Mir, and International Space Station. A vector model for sensory cue interaction is synthesized which includes gravity, gravireceptor bias, frame (architectural symmetry), and polarity cues, and an intrinsic “idiotropic” tendency to perceive the visual vertical in a footward direction. Experimental evidence from previous studies and recent research by our York and MIT teams in orbital flight is summarized. Supported by NASA Cooperative Agreement NCC9-58 with the National Space Biomedical Research Institute, and NASA Grant NAG9-1004 from Johnson Space Center. 1. Introduction Understanding how humans maintain spatial orientation in the absence of gravity is of practical importance for astronauts and flight surgeons. It is also of fundamental interest to neurobiologists and cognitive scientists, since the force of gravity is a universal constant in normal evolution and development. Gravireceptor information plays a major role in the coordination of all types of body movement, and anchors the coordinate frame of our place and direction sense, as neurally coded in the limbic system. This chapter reviews four related types of spatial orientation problems, as described by crewmembers on the US Shuttle and Russian and international space stations. We synthesize a set of working hypotheses which account for static orientation illusions in 0-G and 1-G, their relationship to height vertigo and spatial memory, and the role of visual cues, and summarize supporting evidence from ground, parabolic, and orbital flight experiments. There is evidence astronauts are more susceptible to dynamic (circular- and linear-vection) self-motion illusions during the first weeks of spaceflight, but for reasons of brevity, these dynamic illusions are not considered here. This year’s symposium honors Professor Ian Howard, who has made so many contributions to the understanding of human perception. Human spatial orientation has been a longstanding