## 2 Materials and Methods
### Design of the Fuzzy-Control Anti-Cybersickness Intelligent System (FCACIS)
#### 2.2.1 Fuzzy Sets
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Age**} & \multirow{2}{*}{**Sex**} & \multirow{2}{*}{**Visual Ability**} & \multicolumn{2}{c}{**Susceptibility**} \\ \cline{3-5}  & & & **Emotion** & **Depth Perception Ability** \\ \hline \(\leq\)39 years old & Male & Stereoscopic aberration: & Happiness: & Distance between the two \\ (0.3) & (0.2) & 0 errors (0.0) & Happy to Sad & pillars \\  & & & (0.02–0.1) & \(\leq\)1 cm (0.1) \\
40–59 years old & Female & Stereoscopic aberration: & Excitement: & Distance between the two \\ (0.5) & (0.3) & 1 error (0.1) & High to Low (0.02–0.1) & pillars \\ \(\geq\)60 years old & & Stereoscopic aberration: & Control desire: & Distance between the two \\ (0.7) & & 2 errors (0.2) & Strong to Weak (0.02–0.1) & pillars \\  & & Stereo motion: 0 error & & \(\geq\)4 cm (0.3) \\  & & (0.0) & & \\  & & Stereo motion: 1 error & & \\  & & (0.1) & & \\  & & Stereo motion: 2 errors & & \\  & & (0.2) & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Personal characteristic score sheet. Figure 2: Emotion assessment system: (**a**) happy mood: the user checks the optimal state corresponding to the current happiness level; (**b**) excited mood: the user evaluates the excitement level before entering the 3D virtual store; (**c**) control desire: the user indicates the extent to which he or she wants to control store navigation after entering the 3D virtual store. (2)  
The hardware interface fuzzy set \(\mu D_{n}\) (\(d\)) integrates the fuzzy set variables of the display devices and control devices and includes three membership functions: \(\widetilde{D}_{1}\), \(\widetilde{D}_{2}\), and \(\widetilde{D}_{3}\). These are defined as follows: \(\widetilde{D}_{1}\) is defined as a good hardware interface (Good) with a slight impact on cybersickness, \(\widetilde{D}_{2}\) is defined as a fair hardware interface (Fair) with a moderate impact on cybersickness, and \(\widetilde{D}_{3}\) is defined as a poor hardware interface (Poor) with a significant impact on cybersickness. All of these functions are trapezoidal membership functions. Accordingly, the defined domain of the hardware interface is [0, 1], where \"0\" indicates that the induction of cybersickness is very low, \"1\" indicates that the induction of cybersickness is very high, and 0.3, 0.5, and 0.7 are used as segment points. According to previous studies, regarding the display interface, an HMD is considered to have a greater impact on the occurrence of cybersickness than a flat display does. Regarding the control interface, wireless hand controllers that are commonly used to operate in VR have two forms: 3 DOF and 6 DOF. They have relatively little impact on the occurrence of cybersickness [18]. Therefore, in this study, the scores for the impact of the hardware interface on cybersickness are defined as follows: display device--HMD (0.5); display device--flat display (0.2); and control device--wireless hand controller 3 DOF (0.2) and 6 DOF (0.1). The sum of the display device and control device scores is the hardware interface fuzzy set input value. (3)  
[PERSON] and [PERSON] (2019) reported that there is a strong positive correlation between the duration of exposure and cybersickness [20]. During active operation with an HMD, there are almost no symptoms in the first 2 min, and then the symptoms begin to gradually increase; after 8 min, more obvious symptoms will arise. [PERSON] (2009) used the TFT-LCD as the display device and reported that the subjects' cybersickness increased rapidly 10 min after the experiment, continued to a certain extent for 20 min, and became very uncomfortable after 30 min [36]. Therefore, for the exposure time fuzzy set \(\mu T_{x}\) (\(t\)), three membership functions are defined: \(\widetilde{T}_{1}\), \(\widetilde{T}_{2}\), and \(\widetilde{T}_{3}\). \(\widetilde{T}_{1}\) is defined as a short exposure time (Short), which has a slight effect on cybersickness. \(\widetilde{T}_{2}\) is defined as a medium exposure time (Medium), which has a moderate impact on cybersickness.