# A Study on Visually Induced VR Reduction Method for Virtual Reality Sickness
## 2 Materials and Methods  
### Design of a Visually Induced VR Sickness Reduction Method  
This section describes a visually induced VR sickness reduction method based on a VG. A VG is an independent element in the form of a guide to visually induce gaze movement. This has a role in reducing the level of a user's concentration on VR sickness' causes: fast movement and rotation speed of the camera, the complexity of the background, unpredictable object movement, and fast screen transitions. This VG can have various properties in position, size, shape, color, etc. However, it is difficult to determine which of these various properties are most effective for VR sickness reduction In commercial VR games, a VG of white color, circle shape, and 1 pixel line thickness was commonly used. Also, the main properties that directly affect the user's gaze movement, position and size, were being used in a wide variety of ways. Thus, the color, shape, and the thickness of VG to be used for VR sickness reduction methods were fixed to white, circle, and 1 pixel based on existing references. The remaining two properties (size and position) were set as parameters of VR sickness reduction method.  
We confirmed from a pilot study [12] that among the various sizes of VG, a size 30% that of the aspect ratio [13] was more effective in reducing VR sickness than other sizes. Therefore, based on this result, five VR sickness reduction methods were designed by changing the two properties of VGs which have a size 30% that of the aspect ratio. First, a VG was designed to maintain size 30% that of the aspect ratio or designed to vary its size from 0% to 30% that of the aspect ratio. Then, a VG was designed to have a position synchronized with the user's head or gaze movement direction or moving along in the clockwise (CW)/counterclockwise (CCW) direction.  
The VG of the first VR sickness reduction method had a size 30% that of the aspect ratio, and a position synchronized to the user's head movement direction. Figure 1 shows the first VR sickness reduction method (M1).  
The VG of the second VR sickness reduction method had a size that changes from 0% to 30% that of the aspect ratio, and a position synchronized to the user's head movement direction. This was a way to temporarily attract the user's gaze. In other words, as the VG was no longer visible when the size of the VG reached 0%, this allowed users to focus more on the content. Figure 2 shows the second VR sickness reduction method (M2).  
The VG of the third VR sickness reduction method had a size 30% that of the aspect ratio, and a position that moves CW every second along the eight points. This method induced CW gaze movement through the movement of the VG. Figure 3 shows the third VR sickness reduction method (M3).  
The VG of the fourth VR sickness reduction method had a size 30% that of the aspect ratio, and a position that moves CCW every second along the eight points. This method  
Figure 1: The first VR sickness reduction method (M1).  
Figure 3: The third VR sickness reduction method (M3).  
Figure 2: The second VR sickness reduction method (M2).  
induced CCW gaze movement through the movement of the VG. Figure 4 shows the fourth VR sickness reduction method (M4).  
The VG of the fifth VR sickness reduction method had a size 30% that of the aspect ratio, and a position synchronized to the user's gaze movement direction. This method continuously induced the user's gaze by positioning the VG in the user's gaze direction. Figure 5 shows the fifth VR sickness reduction method (M5).