Oman York Conference (2001 in press)11/2/01 Page 16 4.6 EVA Height Vertigo. Height vertigo, experienced by many people when standing on top of a high structure, is generally seen as a normal physiological aversive response to a potentially dangerous situation. Symptoms include subjective instability of posture and locomotion coupled with a fear or sensation of falling, and autonomic symptoms. Brandt, et al(1980)found the intensity of symptoms was greatest when the subject was standing, intermediate when sitting and least when lying. It was strong when there were no stationary objects in front of the subject within 15-20 meters. They noted that when a standing observer looks out over a distant vista, the threshold. The observer must depend on other vestibular and proprioceptive sources on ow visual subtle visual cues resulting from small translations of the body s center of mass fall bele information to be sure his center of gravity does not slip forward of his point of support. If the subject increases postural reflex gains in response to this uncertainty, his postural sway amplitude may actually increase, increasing his anxiety further. Of course height vertigo is not limited to situations in which subjects stand erect. The training director of a major New England area telephone company has estimated that fully one third of lineman trainees drop out due to height vertigo experienced while learning to climb telephone poles(personal communication) Height workers generally say that habituation usually occurs after repeated, graded exposures It makes sense to think that eva height vertigo is triggered by visual reorientation illusions resulting from seeing the Earth"below", as described in Section 3, and Figure 9. If subjects feel they are"standing"on the end of the Shuttle robot arm looking down at Earth, the lack of visual cues from nearby Shuttle-stationary objects in response to body movement may seem disturbing Based on this interpretation obvious EVA height vertigo countermeasures include immediately rotating body to face the spacecraft, and if possible working right side up "relative to the spacecraft with the Earth nadir is in the upper visual vield. Use body and hand restraints in addition to foot restraints may be helpful. Preflight practice with these techniques or even may be required since using conventional underwater EVA training techniques, the pool wallo es graded preflight habituation of the susceptible is possible, but the use of virtual reality technic nearby are readily visible 4.7 3D spatial memory and navigation difficulties. Given that the interior architectures of space station modules and nodes are so symmetrical, and VRIs happen often, is not surprising crewmembers occasionally have difficulty maintaining a exocentric reference frame veridically aligned with the vehicle. However there is a second problem which relates to the way that we establish local spatial frameworks, and the difficulty we apparently have in vehicles like the Mir station or ISS when we have to turn the spatial frameworks -originally learned in 1-G simulators over in our minds, connect them together, and make spatial judgements. It is not so easy Humans appear to choose salient spatial reference points to define a"spatial framework and use this to remember the location of other objects and places in hierarchical fashion( Sadalla, et al, 1980: MCNamara, 1986, Franklin and Tversky, 1990), often employing their body axes to help establish referent directions. Observers can use mental imagery to change viewpoint location and direction. Creem, et al (in press)recently found that observers can more easily rotate memories of previously seen external object arrays about their body axis- perhaps because we have do it in everyday life-though the relative orientation of the gravity vector was unimportant. We recently studied how observers establish a spatial framework inside a cubic virtual room and recognize targets after the room had been rotated 90 or 180 degrees about any of the three axes, not just the body axis(Oman, et al, submitted ) Observers had to memorize theOman York Conference (2001 in press) 11/2/01 Page 16 4.6 EVA Height Vertigo. Height vertigo, experienced by many people when standing on top of a high structure, is generally seen as a normal physiological aversive response to a potentially dangerous situation. Symptoms include subjective instability of posture and locomotion, coupled with a fear or sensation of falling, and autonomic symptoms. Brandt, et al (1980) found the intensity of symptoms was greatest when the subject was standing, intermediate when sitting and least when lying. It was strong when there were no stationary objects in front of the subject within 15-20 meters. They noted that when a standing observer looks out over a distant vista, the subtle visual cues resulting from small translations of the body’s center of mass fall below visual threshold. The observer must depend on other vestibular and proprioceptive sources of information to be sure his center of gravity does not slip forward of his point of support. If the subject increases postural reflex gains in response to this uncertainty, his postural sway amplitude may actually increase, increasing his anxiety further. Of course height vertigo is not limited to situations in which subjects stand erect. The training director of a major New England area telephone company has estimated that fully one third of lineman trainees drop out due to height vertigo experienced while learning to climb telephone poles (personal communication). Height workers generally say that habituation usually occurs after repeated, graded exposures. It makes sense to think that EVA height vertigo is triggered by visual reorientation illusions resulting from seeing the Earth “below”, as described in Section 3, and Figure 9. If subjects feel they are “standing” on the end of the Shuttle robot arm looking down at Earth, the lack of visual cues from nearby Shuttle-stationary objects in response to body movement may seem disturbing. Based on this interpretation obvious EVA height vertigo countermeasures include immediately rotating body to face the spacecraft, and if possible working “right side up” relative to the spacecraft with the Earth nadir is in the upper visual vield. Use body and hand restraints in addition to foot restraints may be helpful. Preflight practice with these techniques or even graded preflight habituation of the susceptible is possible, but the use of virtual reality techniques may be required since using conventional underwater EVA training techniques, the pool walls nearby are readily visible . 4.7 3D spatial memory and navigation difficulties. Given that the interior architectures of space station modules and nodes are so symmetrical, and VRIs happen often, is not surprising crewmembers occasionally have difficulty maintaining a exocentric reference frame veridically aligned with the vehicle. However there is a second problem which relates to the way that we establish local spatial frameworks, and the difficulty we apparently have in vehicles like the Mir station or ISS when we have to turn the spatial frameworks – originally learned in 1-G simulators - over in our minds, connect them together, and make spatial judgements. It is not so easy. Humans appear to choose salient spatial reference points to define a “spatial framework” and use this to remember the location of other objects and places in hierarchical fashion (Sadalla, et al, 1980; McNamara, 1986, Franklin and Tversky, 1990), often employing their body axes to help establish referent directions. Observers can use mental imagery to change viewpoint location and direction. Creem, et al (in press) recently found that observers can more easily rotate memories of previously seen external object arrays about their body axis – perhaps because we have do it in everyday life – though the relative orientation of the gravity vector was unimportant. We recently studied how observers establish a spatial framework inside a cubic virtual room and recognize targets after the room had been rotated 90 or 180 degrees about any of the three axes, not just the body axis (Oman, et al, submitted). Observers had to memorize the