Effect of sickness severity on habituation to repeated motion challenges in aircrew referred for airsickness treatment.

The aim of this study was to determine whether varying the predetermined malaise level at which provocative motion challenges were stopped would affect the habituation rate. At the rate of 2 per day, 21 motion challenges were delivered, stopping either at initial symptoms or at moderate nausea, on a cross-over design randomized between subjects (n = 20). The cross-coupled motion challenge had an incrementing profile of rotational velocity from 2-90 degrees.s-1 in steps of 2 degrees.s-1 every 30 s, with 8 head movements per 30 s, of approximately 45 degrees. The number of head movements tolerated before the onset of nausea increased over the 21 challenges, but the effects of the treatment variation on habituation were not significant. The number of motion challenges, rather than the severity of malaise level achieved, was the more important factor determining habituation.