Relationship between selected orientation rest frame, circular vection andspace motion sickness

Space motion sickness (SMS) and spatial orientation and motion perception d isturbances occur in 70-80% of astronauts. People select "rest frames" to c reate the subjective sense of spatial orientation. In microgravity, the ast ronaut's rest frame may be based on visual scene polarity cues and on the i nternal head and body z axis (vertical body axis). The data reported here a ddress the following question: Can an astronaut's orientation rest frame be related and described by other variables including circular vection respon se latencies and space motion sickness? The astronaut's microgravity spatia l orientation rest frames were determined from inflight and postflight verb al reports. Circular vection responses were elicited by rotating a virtual room continuously at 35 degrees/s in pitch, roll and yaw with respect to th e astronaut. Latency to the onset of vection was recorded from the time the crew member opened their eyes to the onset of vection. The astronauts who used visual cues exhibited significantly shorter vection latencies than tho se who used internal z axis cues. A negative binomial regression model was used to represent the observed total SMS symptom scores for each subject fo r each flight day. Orientation reference type had a significant effect, res ulting in an estimated three-fold increase in the expected motion sickness score on flight day 1 for astronauts who used visual cues. The results demo nstrate meaningful classification of astronauts' rest frames and their rela tionships to sensitivity to circular vection and SMS. Thus, it may be possi ble to use vection latencies to predict SMS severity and duration. (C) 1999 Elsevier Science Inc.