# Correlations between SSQ Scores and ECG Data during Virtual Reality Walking by Display Type
## 3 Experimental Results  
Figure 4 presents a graph of the SSQ scores of the two groups under the two experimental conditions (screen-assisted walking and HMD-assisted walking). The score of the no-motion-sickness group was 2.3 for screen-assisted walking and 4.2 for HMD-assisted walking, that is, the score with the HMD was higher by 1.9. In the motion-sickness group, the score was 21 with the screen and 34.6 with the HMD, that is, an increase of 13.6. Statistical analysis confirmed that the increase in the SSQ scores between the two groups was significant (\(p<0.001\)). The \(t\)-test showed significant results under the two conditions for the motion-sickness group (\(p=0.005\)), and there was a significant difference in the SSQ score between the two groups during the HMD-assisted walking phase (\(p<0.001\)).  
Table 1 presents the HR, RMSSD, and LF/HF ratio differences for the two groups (no motion sickness and motion sickness) under the two conditions. Figure 5a shows the HR difference between the two groups (no motion sickness and motion sickness) under the two conditions. The results of a two-way ANOVA showed that only the difference in HR was significant between the two groups (\(p=0.047\)). That is, there was a significant increase in HR difference in the motion-sickness group when compared with that in the no-motion-sickness group. In addition, the \(t\)-test results showed that there was a significant increase in HR when the HMD was used compared to when the screen was used in the motion-sickness group (\(p=0.04\)). Moreover, the motion-sickness group showed a significant increase in HR difference when compared with that of the no-motion-sickness group when wearing the HMD (\(p=0.006\)).  
Figure 5b shows the RMSSD data results for the two conditions (HMD and screen) and two groups. The two-way ANOVA results confirmed the difference in RMSSD between the two groups (\(p\) = 0.037). That is, the reduction in the RMSSD of the motion-sickness group when compared with that of the no-motion-sickness group was significant. The \(t\)-test results showed that the RMSSD decreased by a greater extent during walking with the HMD than during walking with the screen in the motion-sickness group (\(p\) = 0.027). In addition, the RMSSD decreased by a greater extent in the motion-sickness group than in the no-motion-sickness group when wearing the HMD (\(p\) = 0.012).  
Figure 5c shows the LF/HF ratios; the analysis of the LH/HF ratios for the two groups under the two conditions did not show statistical significance for the groups or conditions. The \(t\)-test results showed that the increase in the LF/HF ratio in the motion-sickness group was greater during screen-assisted walking than during HMD-assisted walking (\(p\) = 0.04), and the increase in the LF/HF ratio was greater in the motion-sickness group than in the non-motion-sickness group when walking with the HMD (\(p\) = 0.05).  
In the linear regression analysis, a stepwise method was used, and the SSQ scores were designated as dependent variables, whereas the HR, RMSSD, and LF/HF ratio were designated as independent variables. From the analysis, the RMSSD was selected as the variable of interest, and the results were significant at \(p\) < 0.001 (Table 2). These results were found to have an explanatory power of approximately 62%, with R\({}^{2}\) = 0.617 (Figure 6).  
Figure 4: SSQ score difference for the two groups and two conditions. (** and *** indicates statistical difference at the \(p\) < 0.01, and \(p\) < 0.001 levels, respectively).