Predicting vection and visually induced motion sickness based on spontaneous postural activity

Evidence is mounting that differences in postural instability can be used to predict who will experience strong illusory self-motions (vection) and become sick when exposed to global patterns of optical flow (e.g., Apthorp et al., PLoS One 9(12):e113897, 2014; Stoffregen and Smart, Brain Res Bull 47:437-448, 1998). This study compared the predictive ability of traditional and recurrence quantification analysis (RQA) based measures of postural activity. We initially measured spontaneous fluctuations in the centre of foot pressure (CoP) of our subjects as they stood quietly with their eyes open and closed. They were then repeatedly exposed to two different types of self-motion display. As expected, the oscillating self-motion displays were found to induce stronger vection and greater sickness than the smooth self-motion displays. RQA based measures of spontaneous postural activity proved to be superior predictors of both vection strength and visually induced motion sickness (VIMS). Participants who had displayed lower CoP recurrence rates when standing quietly were more likely to later report stronger vection and VIMS when exposed to both types of optical flow. Vection strength (but not VIMS) was also found to correlate significantly with three other RQA based measures of postural activity (determinism, entropy, and average diagonal line length). We propose that these RQA based measures of spontaneous postural activity could serve as useful diagnostic tools for evaluating who will benefit the most/least from exposure to virtual environments.