Eight 26-35 yr olds, wearing left-right vision reversing goggles, executed sequences of controlled active head movements to provoke motion sickness. Ss reported the level of discomfort experienced by using a magnitude estimation technique derived from S. S. Stevens's (1956) ratio scaling method. Using this approach, it was demonstrated that the time course of subjective discomfort exhibited a profile characterized by both fast and slow response components. (27 ref)