# Correlations between SSQ Scores and ECG Data during Virtual Reality Walking by Display Type
## 4 Discussion
[PERSON] and [PERSON] (2019) presented virtual environments in which 16 subjects attempted to locate five objects for five minutes under two conditions (using PCs and HMDs) and measured their HRs and SSQ scores [19]. Motion sickness symptoms in HMD-equipped walking were stronger, and there was a significant reduction in the mean value of NN intervals (NNMean), standard deviation of the NN intervals (SDNN), and RMSSD in the HMD conditions when compared with PC-equipped walking. Although these variables can be potential indicators of cybersickness, their correlation with the intensity of motion sickness remains uncertain. [PERSON] et al. (2017) used the data from 12 subjects in their 20s and 30s who experienced a virtual roller coaster via HMDs (including scenes of embarking, moving forward, and moving backward) to determine the resulting degree of motion sickness symptoms (nausea) and measured the skin conductivity and ECGs [20]. Based on the results, they reported that the intensity of motion sickness was higher during forward-moving scenes than during backward-moving scenes, and the skin conductivity increased when motion sickness occurred, confirming the correlation between skin conductivity and motion sickness. In addition, there was an inverse correlation between the RMSSD and motion sickness symptoms, and the RMSSD was significantly reduced when the symptom level was high. In this study, RMSSD reflected the short-term variability in the HR and was a measurement of the parasympathetic nervous control of the heart. The RMSSD decreased to a greater extent in the motion-sickness group than in the no-motion-sicknessgroup. Moreover, the difference was greater during HMD-assisted walking than during screen-assisted walking in the motion-sickness group. That is, it was found that the subjects became unstable during walking when motion sickness symptoms occurred, and the instability was greater when the stimuli were presented via an HMD than a screen. The LF/HF ratio compares the relative power of the low-frequency band (0.04-0.15 Hz) to that of the high-frequency band (0.15-0.4 Hz). Under controlled conditions, this ratio can be used to estimate the ratio of sympathetic nervous system activity to parasympathetic nervous system activity [21]. [PERSON] et al. (2022) used HMDs to present 360\({}^{\circ}\) VR scenes to 28 subjects for ten minutes and assessed motion sickness using the HRV and SSQ questionnaire [22]. Ten patients had scores of 20 points or less, indicating mild simulator sickness, and the frequency of the SS symptoms increased as the screen speed increased. The SSQ scores showed a positive correlation with the very low frequency (VLF) band, and the VLF power was higher in the motion-sickness group than in the no-motion-sickness group, with a greater difference occurring in the 6-10 min interval. [PERSON] and [PERSON] (2014) divided 15 male participants in their 20s into motion-sickness and no-motion-sickness groups according to the difference in the SSQ scores before and after repeated (five times) exposure to visual first-person-perspective motion sickness-inducing content [23]. The LF and HF time series data were acquired, and the LF values of 120% or above and HF values of below 80% were recorded as peak values. The motion sickness symptoms clearly increased as the frequency of the peaks increased. This study aimed to confirm that the LF/HF ratio is correlated with cybersickness by comparing the amount of change in the frequency of peaks and the amount of change in the LF/HF ratio at the peaks. The results showed that the LF/HF ratio increased when the frequency of the peak values increased, confirming the correlation between the LF/HF ratio and cybersickness. In addition, because the increase in the LF/HF ratio decreases over time when the frequency of the peaks decreases, it is expected that cybersickness is likely to have occurred because of a specific cybersickness-inducing trigger factor rather than simply because of prolonged exposure to virtual stimuli. [PERSON] et al.