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 madeOman 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