## 2 Background and Related Works  
In this section, we will review relevant related works. We reviewed works related to the research of rest and reference frames in VR applications. In a study by [PERSON] et al. [18], the authors analyzed the impact of a virtual nose (head-centric) rest-frame on VR sickness and game experience in a virtual reality jump'n'run game. This was the only previous study that analyzed the effects of head-centric rest-frames in virtual reality. They found out that using a virtual nose reduced VR sickness, while it did not affect the game experience. They also investigated the rest-frame salience's significance, which showed no significant impact, either on simulator sickness or on the game experience. They concluded that a rest-frame in the form of a virtual nose could be used in virtual reality applications to reduce VR sickness. [PERSON] et al. [15] analyzed the effects of static and dynamic rest-frames on VRISE, assessed by the Simulator Sickness Questionnaire (SSQ) and discomfort level. As a rest-frame, they used a see-through metal net surrounding users above and below their seat, which was kept stationary relative to the real world. The rest-frame moved virtually with the cockpit and did not move with the user's head or virtual motion. The participants were seated in a physical chair and also virtually seated in a cockpit while navigating through the virtual environment. While static rest-frames have fixed opacities, dynamic rest-frame opacities change in response to visually perceived motion as users virtually traverse the VE. The scale of discomfort level ranged from 0 to 10 (0 being most comfortable and ten being the most uncomfortable). The participants reported their discomfort levels six times during the gameplay while passing through a waypoint. The results showed that a VE with a static or dynamic rest-frame allowed users to travel through more waypoints before stopping due to discomfort compared to a virtual environment without a rest-frame. Further, a virtual environment with a static rest-frame was also found to result in more real-time reported comfort than when there was no rest-frame. In the study of [PERSON] et al. [17], the authors investigated the effects of simulated reference frames on spatial orientation. They used two different types (an allocentric reference frame--simulated room and an egocentric reference frame--simulated CAVE) of visually simulated reference frames in a navigational search task in a mixed-method study. The results showed that an allocentric reference frame significantly improved the user performance in navigational search time and overall travel distance, while an egocentric reference frame did not help significantly. They also analyzed the effect on VRISE using a single question method to assess the level of overall motion sickness. They found out that a simulated CAVE (body-centric rest-frame) significantly reduced the level of motion sickness compared to no reference frame. [PERSON] et al. [16] concluded the experiment where they investigated the effects of rest-frames on VRISE and oscillatory brain activity. In a roller coaster simulation, the participants experienced a rest-frame condition and a non-rest-frame condition. The rest-frame was presented as a grid of white lines, consisting of two horizontal and two vertical lines superimposed on the simulator's display. Based on the VRISE levels and EEG changes, they suggested that rest-frames may reduce or delay the onset of VRISE by alleviating users' attention or perception load. An independent visual background (IVB) that never moves relative to the individual was utilized in a within-subjects design study by [PERSON] et al. [24], where the subjects were exposed at two scene motion frequencies and three IVB conditions in a projection-based system. The rolling scene used was a cartoon scene, and over the entire scene, the IVB was superimposed at two brightness levels--dim and bright.