Assessing (dis)comfort: measuring motion sickness progression

Motion sickness has a dominant contribution to the broader concept of discomfort when self-motion is at issue, for example when travelling in a self-driving car. Recent studies are devoted to finding ways to mitigate motion sickness even though the relationship between the different types of scales
used to measure motion sickness is largely overlooked. For this reason, we here compared two major types of self-report rating scales: those measuring general unpleasantness and those measuring specific symptomatology. For up to 30 minutes of ongoing motion stimulation, we found that 1) symptoms generally manifested in a fixed order, while unpleasantness seemed to increase
non-monotonically, and 2) symptoms that manifested later were generally reported as more unpleasant, except for nausea onset. The onset of nausea was systematically rated less unpleasant than the preceding pre-nausea symptoms. This indicates that unpleasantness does not monotonically increase during the progression of motion sickness symptoms. Studies having used the two different
types of scales can accordingly not directly be compared, particularly at nausea onset. Our results imply that rating how bad someone feels is not the equivalent of rating how close someone is to the point of vomiting.