# Correlations between SSQ Scores and ECG Data during Virtual Reality Walking by Display Type
## 4 Discussion  
Following recent research results that showed that walking in virtual environments is effective for rehabilitation, this study aimed to analyze the correlations between HR, HRV, \begin{table}
\begin{tabular}{c c c c} \hline \hline Entered Variables & B & t & Sig. \\ \hline RMSSD & \(-1.045\) & \(-5.676\) & \(0.000\) \\ \hline Excluded Variables & B & t & Sig. \\ \hline HR & \(0.223\) & \(1.515\) & \(0.146\) \\ LF/HF & \(-0.93\) & \(-0.605\) & \(0.552\) \\ \hline \end{tabular}
\end{table} 
Table 2: Regression analysis results for SSQ scores and difference of HR, RMSSD, and LF/HF ratio (stepwise): entered variables and excluded variables. Figure 5: (a) HR, (b) RMSSD, and (c) LF/HF ratio difference for the two groups and two conditions. (* and ** indicates statistical difference at the \(p\) < 0.05 and \(p\) < 0.01 levels, respectively). Figure 6: Graph of regression analysis results for SSQ scores and RMSSD values. and SSQ scores with regard to motion sickness symptoms that can occur when walking, which is the most basic human movement, in a virtual environment. The HR difference was higher in the motion-sickness group than in the no-motion-sickness group, and the increase in HR difference was higher during HMD-assisted walking than during screen-assisted walking in the motion-sickness group. In addition, the RMSSD difference was lower in the motion-sickness group than in the no-motion-sickness group, and the decrease was greater during HMD-assisted walking than during screen-assisted walking in the motion-sickness group. The increase in the LF/HF ratio was greater during HMD-assisted walking than during screen-assisted walking in the motion-sickness group. The results of a regression analysis of the HR, HRV difference, and SSQ scores, which differentiated the motion-sickness and no-motion-sickness groups, showed that there was a high negative correlation between the SSQ scores and RMSSD difference. [PERSON] et al. (2015) asked 26 subjects to view a virtual roller coaster, evaluated the degree of motion sickness symptoms through an MSSQ survey, and measured their HRs and finger temperatures [17]. The results showed that there was little change in the HR for patients with nausea scores of less than five. However, the HR increased overall in patients with scores of five or greater (occurrence of cybersickness), and their finger temperatures were higher. [PERSON] et al. (2018) presented three types of virtual environments to 25 subjects and asked the subjects to provide their motion sickness scores [7]. The changes in the symptoms were confirmed based on the HR and HRV of the group that experienced motion sickness and the group that did not experience motion sickness based on their motion sickness scores. As a result, it was found that the HR increased as the symptom scores increased, and the HRV was higher for the sickness group. [PERSON] et al. (2022) presented VR content to 16 subjects, performed an SSQ survey, and measured the biosignals (blood pressure, cortisol, and HR) before and after viewing of the content [18]. It was found that the HR and cortisol levels were greatly increased in subjects who experienced cybersickness. Although the stimuli conditions differed from those in previous studies, the present study also found that the HR increased in the motion-sickness group when compared with that in the no-motion-sickness group during VR-assisted walking, which was the focus of this study, and the change in the HR of the motion-sickness group was greater during HMD-assisted walking than during screen-assisted walking. Particularly, it was found that the sympathetic nerves were activated more intensively during HMD-assisted walking than during screen-assisted walking in the motion-sickness group. The RMSSD is the primary measure used to predict the beat-to-beat variability in the high-frequency band of the HRV; a larger RMSSD value indicates a more stable condition.