# The Effect of Retinal Eccentricity on Visually Induced Motion Sickness and Postural Control
## 2 Materials and Methods  
**Participants**. Thirty-six participants, all undergraduates and graduates from Keimyung University, volunteered for the experiment. All participants had normal or corrected-to-normal vision, with no previous history of postural or vestibular dysfunction. Participants were randomly assigned to one of three experimental groups (central vision, peripheral vision, or full vision). Participants in the full vision group served as controls. Each group was comprised of 12 participants (6 males and 6 females). Participants were asked to refrain from eating for a minimum of three hours prior to the experiment. The study was approved by the Keimyung University's Institutional Review Board, and written informed consent was obtained from participants prior to their participation. **Stimulus**. Participants watched _The Great Wall_ (Niceberg Studios, Belgium). This VR application conveyed a first-person perspective of a rocket powered rickshaw ride over The Great Wall of China in a highly immersive stereoscopic 3D environment. The VR ride took 4.17 min. **Apparatus**. A Samsung Gear VR (SM-R324, Samsung, Suwon, Korea) headset and a Samsung Galaxy S8 smartphone (Samsung, Suwon, Korea) which acted as the headset's display and processor were used to present the VR exposure. S8 is equipped with a 5.8 inch display panel. The display had a refresh rate of 60 Hz and a pixel resolution of 1280 H x 1440 V per eye, which yielded a 101\({}^{\circ}\) horizontal field of view. Head-tracking was enabled, providing a 360\({}^{\circ}\) field of view. In the central vision condition, each eye's view was masked except for the central 10\({}^{\circ}\) while, in the peripheral vision condition, the central 10\({}^{\circ}\) of each eye's view was masked. The control group viewed the display via an unmasked HMD. A Polhemus G4 (Polhemus, Colchester, VT, USA) wireless motion tracking system was used to record the postural sway of participants. Three sensors were attached to each participant's head, cervical spine (C7-T1 junction), and base of the spine (lumbo-sacral junction) to collect the six degrees of freedom position data at 120 Hz. VIMS symptoms were assessed using the Simulator Sickness Questionnaire (SSQ) [33]. The 16-item questionnaire rates symptom intensities on a four-point scale (0 = none, 1 = slight, 2 = moderate, or 3 = severe). The SSQ scores are grouped under three subscales (nausea, oculomotor distress, and disorientation), yielding four scores: three sub-scores and a total score that serves as an indicator of overall severity of the simulator sickness. The SSQ was administered at the beginning and end of the experiment. The pre-exposure administration was to familiarize participants with the symptons of VIMS and to provide a baseline level of symptoms for comparison with the scores from post-exposure administration. **Procedure**. After completing the informed consent procedure, participants filled out the pre-exposure SSQ. After donning the Gear VR, participants were allowed to explore the virtual environment briefly while standing comfortably. With head tracking enabled, the HMD provided a 360\({}^{\circ}\) field of view. However, head movements during VR exposure have been found to increase the likelihood of VIMS [2; 31]. Thus, to avoid having their head movements provoke or aggravate VIMS, participants were advised to keep their heads still and look directly at the center of the display during the VR ride. Upon termination of the VR ride, participants completed the post-exposure SSQ. **Data analysis**. Each SSQ administration yielded, for each participant, four scores consisting of one total and three subscale scores obtained using methods and weighting factors as described by [33]. Each set of scores was combined by subtracting the pre-SSQ score from the post-SSQ score, and the combined score was subjected to a Kruskal-Wallis test to assess differences among the three groups.