Immersed false vertical room. A new motion sickness model.

We evaluated a new model of motion sickness--an enclosure decorated with visual cues to upright which was immersed either inverted or "front"-wall down, in Johnson Space Center's Weightless Environment Training Facility (WETF) pool. This "WETF False Vertical Room" (WFVR) was tested with 19 male and 3 female SCUBA diver subjects, aged 23 to 57, who alternately set clocks mounted near the room's 8 corners and made exaggerated pitch head movements. We found that (1) the WFVR test runs produced motion sickness symptoms in 56% and 36% of subjects in the room-inverted and room-front-down positions, respectively. (2) Pitch head movements were the most provocative acts, followed closely by setting the clocks--particularly when a clock face filled the visual field. (3) When measured with a self-ranking questionnaire, terrestrial motion sickness susceptibility correlated strongly (P < 0.005) with WFVR sickness susceptibility. (4) Standing instability, measured with a modified Fregly-Graybiel floor battery, also correlated strongly (P < 0.005) with WFVR sickness susceptibility. This result may reflect a relationship between visual dominance and WFVR sickness. (5) A control study demonstrated that the inverted and front-down positions produced WFVR sickness, but the upright position did not, and that adaptation may have occurred in some subjects with repeated exposure. The WFVR could become a useful terrestrial model of space motion sickness (SMS) because it duplicates the nature of the gravity-dependent sensory conflicts created by microgravity (visual and otolith inputs conflict while somatosensory gravity cues are minimized), and it also duplicates the nature of the provocative stimulus (sensory environment "rule change" versus application of motion to passive subject) more closely than any other proposed terrestrial SMS model. Also, unlike any other proposed terrestrial SMS model, the WFVR incorporates whole-body movement in all three spatial dimensions. However, the WFVR's sensory environment differs from that created by spaceflight in several respects, including the presence of frictional drag on limb movement, magnification at the face-mask-water interface, greater otolith conflict, exhaled bubbles, and the presence of some gravity-dependent somatosensory inputs.