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 longstanding
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 “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
Oman York Conference(2001 in press)11/2/0 interest of lans. His 1982 book Human Visual Orientation", though out of print, remains the students best introduction to this subject. Over the subsequent two decades, he and his students built a set of unique stimulus devices in the basements of three buildings the now legendary rotating sphere, vection sled, mirrored bed and two tumbling rooms. They did a series of experiments on static and dynamic visual orientation which are landmarks in this field. Ian has al ways been fascinated by the orientation illusions reported by astronauts, and has done experiments in parabolic flight. In the early 1990s, he accepted my challenge to help me write the first NASa proposal for what has since become a series of continuing space flight investigations on human visual orientation on the Shuttle and the International Space Station employing virtual reality technology in space for the first time. both in the laboratory and in the field, Ian's discipline, intellect, curiosity, creativity, infectious scientific passion, and adaptability to Tex-Mex food inspired everyone including our astronauts. Some of the results from Neurolab-our first flight-are included here. Our laboratories also continue to collaborate in ground based research sponsored by the NAsA National Space Biomedical Research Institute .Human orientation problems In space Flight. Vision plays a critical role in maintaining spatial orientation in weightlessness. One of the most striking things about entering 0-G is that if the observers are in a windowless cabin, usually no one has any sensation of falling. Obviously"falling sensations are visually and cognitively mediated. If the observers make normal head movements, the visual surround seems quite stable. Oscillopsia(apparent motion of the visual environment), so common among patients who have inner ear disease, is only rarely reported in weightlessness. What can change -often dramatic fashion- is one's perception of static orientation with respect to the cabin and the environment beyond 2. 10-G Inversion Illusions. Ever since the second human orbital spaceflight by the late Gherman Titov in 1961, crewmembers in both the US and Russian space programs have described a bizarre sensation of feeling continuously inverted in O-G, even though in a familiar visually upright orientation in the cabin( Gazenko, 1964; Oman, et al, 1986)."The only way I can describe it', some say, "is that though I'm floating upright in the cabin in weightlessness both the spacecraft and I seem to somehow be flying upside down". Visual cues clearly play a role in the strength of the illusion, but in contrast with visual reorientation illusions( Sect. 2. 2) inversion illusions are relatively persistent, and continue after eyes are closed. Some report the illusion is stronger in the visually symmetrical mid-deck area of the Shuttle than when on the flight deck, or in the asymmetrical Spacelab module. Inversion illusion is sometimes reversible by belting or pulling yourself firmly into a seat, or looking at yourself in a mirror. The illusion is quite common among shuttle crewmembers in the first minutes of weightlessness, continuing or recurring for minutes to hours thereafter, but reports are rare after the second day in orbit. It is almost universal in parabolic flight among blindfolded volunteers entering weightlessness for the first time (Lackner, 1992). As detailed later, inversion illusion in 0-G has been attributed to the combined effects of gravitational unloading of the inner ear otolith organs, elevation of viscera, and to the sensations of facial fullness and nasal stuffiness caused by sitting with feet elevated prior to launch, launch accelerations, and 0-G fluid shift
Oman York Conference (2001 in press) 11/2/01 Page 2 interest of Ian’s. His 1982 book “Human Visual Orientation”, though out of print, remains the student’s best introduction to this subject. Over the subsequent two decades, he and his students built a set of unique stimulus devices in the basements of three buildings: the now legendary rotating sphere, vection sled, mirrored bed and two tumbling rooms. They did a series of experiments on static and dynamic visual orientation which are landmarks in this field. Ian has always been fascinated by the orientation illusions reported by astronauts, and has done experiments in parabolic flight. In the early 1990s, he accepted my challenge to help me write the first NASA proposal for what has since become a series of continuing space flight investigations on human visual orientation on the Shuttle and the International Space Station, employing virtual reality technology in space for the first time. Both in the laboratory and in the field, Ian’s discipline, intellect, curiosity, creativity, infectious scientific passion, and adaptability to Tex-Mex food inspired everyone, including our astronauts. Some of the results from Neurolab - our first flight - are included here. Our laboratories also continue to collaborate in ground based research sponsored by the NASA National Space Biomedical Research Institute. 2. Human orientation problems in space flight. Vision plays a critical role in maintaining spatial orientation in weightlessness. One of the most striking things about entering 0-G is that if the observers are in a windowless cabin, usually no one has any sensation of falling. Obviously “falling” sensations are visually and cognitively mediated. If the observers make normal head movements, the visual surround seems quite stable. Oscillopsia (apparent motion of the visual environment), so common among patients who have inner ear disease, is only rarely reported in weightlessness. What can change – often in dramatic fashion – is one’s perception of static orientation with respect to the cabin and the environment beyond: 2.1 0-G Inversion Illusions. Ever since the second human orbital spaceflight by the late Gherman Titov in 1961, crewmembers in both the US and Russian space programs have described a bizarre sensation of feeling continuously inverted in 0-G, even though in a familiar “visually upright” orientation in the cabin (Gazenko, 1964; Oman, et al, 1986). “The only way I can describe it”, some say, “is that though I’m floating upright in the cabin in weightlessness, both the spacecraft and I seem to somehow be flying upside down ”. Visual cues clearly play a role in the strength of the illusion, but in contrast with visual reorientation illusions (Sect. 2.2), inversion illusions are relatively persistent, and continue after eyes are closed. Some report the illusion is stronger in the visually symmetrical mid-deck area of the Shuttle than when on the flight deck, or in the asymmetrical Spacelab module. Inversion illusion is sometimes reversible by belting or pulling yourself firmly into a seat, or looking at yourself in a mirror. The illusion is quite common among shuttle crewmembers in the first minutes of weightlessness, continuing or recurring for minutes to hours thereafter, but reports are rare after the second day in orbit. It is almost universal in parabolic flight among blindfolded volunteers entering weightlessness for the first time (Lackner, 1992). As detailed later, inversion illusion in 0-G has been attributed to the combined effects of gravitational unloading of the inner ear otolith organs, elevation of viscera, and to the sensations of facial fullness and nasal stuffiness caused by sitting with feet elevated prior to launch, launch accelerations, and 0-G fluid shift
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 horizontal
Oman 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
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 abou
Oman 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
Oman York Conference(2001 in press)11/2/01 any axis, particularly in pitch, are the dominant stimulus causing space sickness. However, it is clear from crewmember reports that inversion illusions and VRIs-when they occur -often increase nausea. Crewmembers experiencing Inversion Illusions are reportedly continually aware of the sensory cue discrepancy. Apparently it is the onset of a VRI-and the sudden change in perceived self-orientation without a concurrent change in semicircular canal or otolith cue-which provides the nauseogenic stimulus. For example, one Shuttle pilot awoke, removed the sleep shades from the flight deck windows, saw the earth above instead of below where he had previously seen it, and vomited immediately after. Other crewmembers described vomiting attacks after seeing other crewmembers-or doffed space suits- floating inverted nearby, and suddenly feeling tilted or uncertain about their orientation. One astronaut who was feelin nauseous described"getting it over with simply by deliberately cognitively inducing VRIs This causal relationship makes sense in terms of what we know about the role of vestibular sensory conflict in motion sickness(Reason, 1978; Oman, 1982, 1990). Once we recognized the etiologic role of VRIs in space sickness(Oman, et al, 1984, 1986: Oman, 1986),we suggested that whenever anyone on board was suffering from space sickness, everyone-not just the afflicted-should try to work"visually upright"in the cabin. This advice has since been broadly accepted by Shuttle crews 2.4 EVA Height Vertigo. Over the past decade, there have been anecdotal reports from several crewmembers that while working inverted in the Shuttle payload bay, or while standing in foot restraints on the end of the Shuttle robot arm(Figure 3) or hanging at the end of a pole used as a mobility aid, they experienced a sudden attack of height anxiety, and fear of falling toward Earth somewhat resembling the physiological height vertigo many people experience on Earth when standing at the edge of a cliff or the roof of a tall building Some report experience enhanced orbital motion awareness and a sensation of lling down". The associated anxiety is igure 3. Spacewalking Shuttle crewmember standing disturbing, or in some cases even In foot restraints on the end of the canadian robotic arm disable ausing crewmembers to"han on for dear life" A Nasa astronaut flying on Mir published a vivid account (Linenger, 2000; see also Richards. et al 2001). We do not yet have prospective or retrospective statistical data on the incidence of the phenomenon. However height vertigo is clearly a potential problem which will become more important during the Iss construction era, when many more EVAs are being made
Oman York Conference (2001 in press) 11/2/01 Page 5 any axis, particularly in pitch, are the dominant stimulus causing space sickness. However, it is clear from crewmember reports that inversion illusions and VRIs – when they occur - often increase nausea. Crewmembers experiencing Inversion Illusions are reportedly continually aware of the sensory cue discrepancy. Apparently it is the onset of a VRI – and the sudden change in perceived self-orientation without a concurrent change in semicircular canal or otolith cue – which provides the nauseogenic stimulus. For example, one Shuttle pilot awoke, removed the sleep shades from the flight deck windows, saw the Earth above instead of below where he had previously seen it, and vomited immediately after. Other crewmembers described vomiting attacks after seeing other crewmembers – or doffed space suits – floating inverted nearby, and suddenly feeling tilted or uncertain about their orientation. One astronaut who was feeling nauseous described “getting it over with” simply by deliberately cognitively inducing VRIs. This causal relationship makes sense in terms of what we know about the role of vestibular sensory conflict in motion sickness (Reason, 1978; Oman, 1982, 1990). Once we recognized the etiologic role of VRIs in space sickness (Oman, et al, 1984, 1986; Oman, 1986), we suggested that whenever anyone on board was suffering from space sickness, everyone – not just the afflicted – should try to work “visually upright” in the cabin. This advice has since been broadly accepted by Shuttle crews. 2.4 EVA Height Vertigo. Over the past decade, there have been anecdotal reports from several crewmembers that while working inverted in the Shuttle payload bay, or while standing in foot restraints on the end of the Shuttle robot arm (Figure 3), or hanging at the end of a pole used as a mobility aid, they experienced a sudden attack of height anxiety, and fear of falling toward Earth somewhat resembling the physiological height vertigo many people experience on Earth when standing at the edge of a cliff or the roof of a tall building. Some report experience enhanced orbital motion awareness, and a sensation of falling “down”. The associated anxiety is Figure 3. Spacewalking Shuttle crewmember standing disturbing, or in some cases even In foot restraints on the end of the Canadian robotic arm. disabling, causing crewmembers to “hang on for dear life”. A NASA astronaut flying on Mir published a vivid account (Linenger, 2000; see also Richards, et al, 2001). We do not yet have prospective or retrospective statistical data on the incidence of the phenomenon. However height vertigo is clearly a potential problem which will become more important during the ISS construction era, when many more EVAs are being made
Oman York Conference(2001 in press)11/2/01 2.5 3D spatial memory and navigation difficulties. The US and Russian space program gradually evolved to using larger vehicles with more complex three dimensional architectures For practical reasons, the local visual verticals in different modules are not universally coaligned Ground trainer modules are not al ways physically connected in the same way as they are in the actual vehicle. Therefore, occupants say that they have difficulty visualizing the spatial relationships between landmarks on the interiors of the two modules. They cannot point in the direction of familiar interior landmarks in other modules the way they say they could when in their homes on Earth. They often do not instinctively know which way to turn when moving between modules through symmetrical multi-ported nodes. Shuttle crew visiting the Mir station (Figure 4)often had difficulty finding their way back, without assistance from Mir crewmembers, or arrows fashioned and positioned to help them( richards, et al, 2001) Comparable problems have not been described within the US Shuttle itself, probably because the flight deck, mid-deck, and payload bay research modules have coaligned and less ambiguous internal visual verticals. Maintaining spatial orientation during EVA activity on the outside of the Mir and International Space Station was sometimes also difficult, particularly during the dark half of each orbit, due to the lack of easily recognizable visual landmarks Several operational crises which occurred in 1997 aboard the Russian mir station convinced crewmembers and human factors specialists that the ability to make three dimensional spatial judgements is important in emergency situations and critical if an emergency evacuation Is necessary in darkness or when smoke obscures the cabin Twice when collisions with Progress spacecraft were imminent, crewmembers moved from module to module and window to window, unsuccessfully trying to locate the inbound spacecraft. Another emergency required the crew to reorient the entire station using thrusters on a docked Soyuz spacecraft Members of the crew in the mir base block module discovered they had great difficulty mentally visualizing the orientation of another crewmember in the differently oriented Soyuz cockpit, and verbally rel the appropriate commands( Burrough, 1998) 4. Russian mi e station had four research modules connected to a central node Related difficulties are being encountered on Visual verticals of some modules were not the new International Space Station. Egress routes to Shuttle and Soyuz require turns in potentially disorienting nodes. Emergency gress Is comp of rescue vehicles, so different crewmembers are assigned different vehicles and egress routes One early station crew placed emergency Exit signs beside the node hatches, but subsequently
Oman York Conference (2001 in press) 11/2/01 Page 6 2.5 3D spatial memory and navigation difficulties. The US and Russian space program gradually evolved to using larger vehicles with more complex three dimensional architectures. For practical reasons, the local visual verticals in different modules are not universally coaligned. Ground trainer modules are not always physically connected in the same way as they are in the actual vehicle. Therefore, occupants say that they have difficulty visualizing the spatial relationships between landmarks on the interiors of the two modules. They cannot point in the direction of familiar interior landmarks in other modules the way they say they could when in their homes on Earth. They often do not instinctively know which way to turn when moving between modules through symmetrical multi-ported nodes. Shuttle crew visiting the Mir station (Figure 4) often had difficulty finding their way back, without assistance from Mir crewmembers, or arrows fashioned and positioned to help them (Richards, et al, 2001) Comparable problems have not been described within the US Shuttle itself, probably because the flight deck, mid-deck, and payload bay research modules have coaligned and less ambiguous internal visual verticals. Maintaining spatial orientation during EVA activity on the outside of the Mir and International Space Station was sometimes also difficult, particularly during the dark half of each orbit, due to the lack of easily recognizable visual landmarks. Figure 4. Russian Mir space station had four research modules connected to a central node. Visual verticals of some modules were not coaligned. Several operational crises which occurred in 1997 aboard the Russian MIR station convinced crewmembers and human factors specialists that the ability to make three dimensional spatial judgements is important in emergency situations and critical if an emergency evacuation is necessary in darkness, or when smoke obscures the cabin. Twice when collisions with Progress spacecraft were imminent, crewmembers moved from module to module and window to window, unsuccessfully trying to locate the inbound spacecraft. Another emergency required the crew to reorient the entire station using thrusters on a docked Soyuz spacecraft. Members of the crew in the MIR base block module discovered they had great difficulty mentally visualizing the orientation of another crewmember in the differently oriented Soyuz cockpit, and verbally relaying the appropriate commands (Burrough, 1998). Related difficulties are being encountered on the new International Space Station. Egress routes to Shuttle and Soyuz require turns in potentially disorienting nodes. Emergency egress is complicated by the limited capacity of rescue vehicles, so different crewmembers are assigned different vehicles and egress routes. One early station crew placed emergency “Exit” signs beside the node hatches, but subsequently
Oman York Conference(2001 in press)11/2/01 discovered that one the signs had been misplaced probably as a result of a visual reorientation illusion. Improved egress signs are in development, and"you are here"maps, inflight practice, and preflight virtual reality based spatial memory training are under consideration 3. A model for human visual orientation Based on prior research on human visual orientation in 1-G(reviewed by Howard, 1982), and synthesizing more recent theories and experiments of Mittelstaedt(1983, 1988), Young, et al (1986), Oman(1986), Oman et al (1986), and Howard and Childerson(1993), the following heuristic model for static orientation perception emerges 3.1 Beginning with a 1-G model On Earth in 1-G, the direction of the subjective vertical (sv) is the nonlinear sum of three ectors G, the gravitational stimulus to the otoliths, cardiovascular, and kidney gravireceptors B, a net gravireceptor bias acting in the direction of the bodys major axis. The magnitude and headward vs footward direction is presumed to be an individual characteristic V. the tual visual vertical. is normally determined by F,frame"(architectural symmetry) visual cues, disambiguated by P,polarity"cues, associated with the recognition of top/bottom of familiar objects in view, and the visual vertical as oriented along the body axis in a footward direction Note that as is the convention in eering and physics, the defining the gravitational"vertical Floor= Subject SV depicted pointing"down", as are the Figure 5. Model for 1-G"Tilted Room" illusion
Oman York Conference (2001 in press) 11/2/01 Page 7 discovered that one the signs had been misplaced, probably as a result of a visual reorientation illusion. Improved egress signs are in development, and “you are here” maps, inflight practice, and preflight virtual reality based spatial memory training are under consideration. 3. A model for human visual orientation Based on prior research on human visual orientation in 1-G (reviewed by Howard, 1982), and synthesizing more recent theories and experiments of Mittelstaedt (1983, 1988), Young, et al (1986), Oman (1986), Oman et al (1986), and Howard and Childerson (1993), the following heuristic model for static orientation perception emerges: 3.1 Beginning with a 1-G Model: On Earth in 1-G, the direction of the subjective vertical (SV) is the nonlinear sum of three vectors: G, the gravitational stimulus to the otoliths, cardiovascular, and kidney gravireceptors. B, a net gravireceptor bias acting in the direction of the body’s major axis. The magnitude and headward vs. footward direction is presumed to be an individual characteristic. V, the perceptual visual vertical, is normally determined by: F, “frame” (architectural symmetry) visual cues, disambiguated by P, “polarity” cues, associated with the recognition of top/bottom of familiar objects in view, and M, an “idiotropic” tendency to perceive the visual vertical as oriented along the body axis in a footward direction. Note that as is the convention in engineering and physics, the G vector defining the gravitational “vertical” is depicted pointing “down”, as are the Figure 5. Model for 1-G “Tilted Room” illusion
Oman York Conference(2001 in press)11/2/01 corresponding v, P, and M vectors. (Mittelstaedt has adopted the opposite convention ). The idiotropic vector is denoted"M" in recognition of Mittelstaedt's many contributions(Young et al,1986) The Sv in complete darkness(sometimes called the postural vertical) is determined only by the G and B vectors. The Sv of gravitationally horizontal observers who have a headward gravireceptor bias is tilted slightly in a headward direction, i.e. they report feeling tilted slightly head down, and conversely. Measurement of the postural vertical provides a convenient way to assess a persons gravireceptor bias B-at least in one G The"idiotropic"tendency M affects all judgements of sV when any visual cues are present. The idiotropic effect a usually stronger than gravireceptor bias, even when the latter is in a headward direction. Hence the Sv of a horizontally recumbent subject is deviated footward. When no F or Pcues are present, the resultant of M and B deviates the Sv footward. Hence an observer perceives a dimly lit gravitationally vertical line as rotated in the opposite direction to body tilt the well known aubert illusion Figure 5 shows a horizontally recumbent observer viewing the interior of a tilted, barnlike room in 1-G. The major and minor axes of symmetry of the visual environment are depicted with the array of bidirectional vectors F. Since the room interior has a familiar shape, and readily distinguishable ceiling(top) and floor(bottom), it is also said to possess visual polarity, depicted by the vector P. The visual vertical v lies along one of the major the axes of symmetry in a direction closest to P and M. Here V points in the direction of the true floor, so it is subjectively perceived as a floor. The direction of the subjective vertical SV is determined by a nonlinear interaction of the visual V and gravireceptor(G+B)vectors. How the vectors combine depend on the orientation of the subject. For relatively small static tilts of the subject or the environment as shown in the figure -up to a limit of perhaps 45 degrees-the SV lies in a direction intermediate between V and(G+B) However, if the subject is not in the normal erect position, but instead recumbent, supine or prone with respect to gravity, and V aligns with M, the SV can be"captured by (i.e. align with )the F B V and M vectors. Thus a supine subject feels gravitationally upright if the environment is tilted so p and v align with the body axis 3.2 Extending the model to o-g: how shown in Figure 6. The physical stimulus to the body's gravireceptors G is absent, but a headward or footward bias b remains. As in 1-G. the direction of the visual vertical v True Ceilin Subjective Floor Figure 6. Model for 0-G Visual Reorientation Illusion. Crewmember inverted in a Spacelab module feels right side u
Oman York Conference (2001 in press) 11/2/01 Page 8 corresponding V, P, and M vectors. (Mittelstaedt has adopted the opposite convention). The idiotropic vector is denoted “M” in recognition of Mittelstaedt’s many contributions (Young et al, 1986). The SV in complete darkness (sometimes called the postural vertical) is determined only by the G and B vectors. The SV of gravitationally horizontal observers who have a headward gravireceptor bias is tilted slightly in a headward direction, i.e. they report feeling tilted slightly head down, and conversely. Measurement of the postural vertical provides a convenient way to assess a person’s gravireceptor bias B – at least in one G. The “idiotropic” tendency M affects all judgements of SV when any visual cues are present. The idiotropic effect a usually stronger than gravireceptor bias, even when the latter is in a headward direction. Hence the SV of a horizontally recumbent subject is deviated footward. When no F or P cues are present, the resultant of M and B deviates the SV footward. Hence an observer perceives a dimly lit gravitationally vertical line as rotated in the opposite direction to body tilt – the well known Aubert illusion. Figure 5 shows a horizontally recumbent observer viewing the interior of a tilted, barnlike room in 1-G. The major and minor axes of symmetry of the visual environment are depicted with the array of bidirectional vectors F. Since the room interior has a familiar shape, and readily distinguishable ceiling (top) and floor (bottom), it is also said to possess visual polarity, depicted by the vector P. The visual vertical V lies along one of the major the axes of symmetry in a direction closest to P and M. Here V points in the direction of the true floor, so it is subjectively perceived as a floor. The direction of the subjective vertical SV is determined by a nonlinear interaction of the visual V and gravireceptor (G+B) vectors. How the vectors combine depends on the orientation of the subject. For relatively small static tilts of the subject or the environment as shown in the figure – up to a limit of perhaps 45 degrees – the SV lies in a direction intermediate between V and (G+B). However, if the subject is not in the normal erect position, but instead recumbent, supine or prone with respect to gravity, and V aligns with M, the SV can be “captured”by (i.e. align with) the V and M vectors. Thus a supine subject feels gravitationally upright if the environment is tilted so P and V align with the body axis M. 3.2 Extending the model to 0-G: How the model applies in weightlessness is shown in Figure 6. The physical stimulus to the body’s gravireceptors G is absent, but a headward or footward bias B remains. As in 1-G, the direction of the visual vertical V is Figure 6. Model for 0-G Visual Reorientation Illusion. Crewmember inverted in a Spacelab module feels right side up
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 Illusion
Oman 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
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 up
Oman 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