Bioengineering Graduate Program - PhD Thesis Presentation - Phase Synchronization of Regional Electroencephalograph and Postural Stability Indicator for Susceptibility to Visually Induced Motion Sickness Validated with Habituation Training

Susceptibility to visually induced motion sickness (VIMSS) can prevent people from enjoying 3D films, VR games, and many other entertainments involving self-motion illusion (vection). The mechanism of VIMSS has not been completely understood. In particular, little is known on how the brains of susceptible and resistant individuals differ in responding to VIMS-provoking stimulations. This research investigates the effects of habituation training and determines objective indicators for VIMSS through measurements of VIMS symptoms, postural stability, and electroencephalographs (EEG). In the current study, rotating random dots around roll and pitch axes were utilized to provoke VIMS and to elicit EEG activities. Thirty-four participants were classified into resistant and susceptible groups. To investigate the effect of habituation on VIMSS, participants went through a 7-to-10-day training. Training significantly reduced rated levels of VIMS. Before training, when watching rotating dots in both axes, EEG phase synchronization between the signal from the right parietal region (P4) and signals from central, parietal, and occipital regions was significantly higher among the resistant group, while phase synchronization between signals from two central sites (C3-C4) was significantly higher among the susceptible group. Besides, the synchronization to P4 negatively correlated with VIMS and could be related to neural coordination to relieve VIMS. Positive correlations were found between VIMS and the interhemispheric synchronization (C3-C4), which could indicate a direct neural response to sensory conflict or VIMS severity. After the training, there was a significant increment in phase synchronizations of parietal signals (P4-P7) among individuals trained to be resistant from the susceptible group. The phase synchronization of interhemispheric signals (C3-C4) was also lower after training. For the first time, we have uncovered EEG synchronization indictors that are associated with susceptibility and resistance to VIMS, respectively. The two opposite EEG indicators suggest that VIMS could be the consequence of two antagonistic neural activities, and habituation training could reduce the VIMS response by affecting both. Furthermore, less visual dependence and a narrower postural sway range along the x-axis (left to right) were found among the susceptible group after training. The newly discovered EEG phase synchronization indicators offer a new method to predict VIMS susceptibility.