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Using Visual Guides to Reduce Virtual Reality Sickness in First-Person Shooter Games: Correlation Analysis

Using Visual Guides to Reduce Virtual Reality Sickness in First-Person Shooter Games: Correlation... Background: The virtual reality (VR) content market is rapidly growing due to an increased supply of VR devices such as head-mounted displays (HMDs), whereas VR sickness (reported to occur while experiencing VR) remains an unsolved problem. The most widely used method of reducing VR sickness is the use of a rest frame that stabilizes the user's viewpoint by providing fixed visual stimuli in VR content (including video). However, the earth-fixed grid and natural independent visual background that are widely used as rest frames cannot maintain VR fidelity, as they reduce the immersion and the presence of the user. A visual guide is a visual element (eg, a crosshair of first-person shooter [FPS]) that induces a user's gaze movement within the VR content while maintaining VR fidelity, whereas there are no studies on the correlation of visual guide with VR sickness. Objective: This study aimed to analyze the correlation between VR sickness and crosshair, which is widely used as a visual guide in FPS games. Methods: Eight experimental scenarios were designed and evaluated, including having the visual guide on/off, the game controller on/off, and varying the size and position of the visual guide to determine the effect of visual guide on VR sickness. Results: The results showed that VR sickness significantly decreased when visual guide was applied in an FPS game. In addition, VR sickness was lower when the visual guide was adjusted to 30% of the aspect ratio and positioned in the head-tracking direction. Conclusions: The experimental results of this study indicate that the visual guide can achieve VR sickness reduction while maintaining user presence and immersion in the virtual environment. In other words, the use of a visual guide is expected to solve the existing limitation of distributing various types of content due to VR sickness. (JMIR Serious Games 2021;9(3):e18020) doi: 10.2196/18020 KEYWORDS virtual reality; motion sickness; VR sickness; visual guide; VR fidelity disorientation caused while experiencing an HMD-based VR Introduction [1]. To investigate the causes of VR sickness, various theories are being studied in a cognitive science approach. The popular Recently, virtual reality (VR) content based on head-mounted sensory conflict theory [1] proposes that VR sickness is induced display (HMD) has been expanded to various industrial fields by an inconsistency between the visual and the vestibular or such as sports, medical care, education, and social network. proprioceptive senses. In particular, the vection that occurs Moreover, such content has been used in video games. However, during the VR experience is the biggest cause of sensory conflict most users have experienced “VR sickness” while using [2-4]. Additionally, the postural instability theory posits that HMD-based VR content. VR sickness has symptoms similar to VR sickness is caused by changes in human balance [5]. motion sickness, including nausea, oculomotor discomfort, and https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 1 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Seok et al Furthermore, VR sickness may also be induced by various games was reduced when cockpits were added to the IVB, while individual characteristics, such as age, gender, prior user the VR fidelity of the users was disturbed [24]. experience, concentration, medical history, mental rotation, To overcome the problem of IVB, we discuss another visual perceptual style, and dominant eye [6]. element applied to VR FPS games called the visual guide, which Until now, various studies have only been partially successful refers to a visual element that induces a user's gaze movement in attempting to reduce HMD-induced VR sickness by focusing within VR content. To our knowledge, there is no study on the device and the content. A typical method focusing on investigating the effect of visual guide on the reduction of VR the device is the optimization of the delay time caused by head sickness while maintaining VR fidelity in VR FPS games. movement tracking response, rendering, image transmission, Therefore, in this study, we investigated how VR sickness and display response speed [7]. Studies have also been reduction is affected by visual guide in FPS games. To do this, conducted to reduce VR sickness in device elements such as we performed experiments on a VR FPS game consisting of resolution, frame rate, viewing angle, binocular parallax, and eight scenarios, including visual guide on/off, game controller flicker fusion frequency [8-13]. Recent studies have evaluated on/off, and varying the size and position of the visual guide. methods focusing on content. These methods investigated the use of dynamic blurring with retinal tracking [14], optical flow Methods reduction of peripheral vision [15], field of view control [16], Visual Guide Design in VR FPS Games and viewpoint snapping [17]. In this section, we describe the visual guide used in this study. However, there is a disadvantage that these dynamic blurring In VR FPS games, crosshairs, character path indicators, and methods limit the user's experience. Therefore, in other studies, maps are used as visual guides to provide situational awareness VR sickness has been reduced by adding fixed or dynamic visual for the user to spatially determine their position in a virtual stimuli regardless of the motion of objects in the content [18-20]. environment. In this study, we used crosshair as a visual guide This visual stimulus includes a rest frame that serves as a to induce a user's gaze movement while maintaining VR fidelity reference frame designed to induce a user's effective spatial in a space-environment FPS game. Crosshair is a 2D image perception. In particular, VR sickness was reduced by applying composed of color, shape, line thickness, depth, size, and a virtual human nose as a rest frame to the content [21]. position elements. Figure 1 shows an example of crosshair used However, this artificial rest frame could not maintain VR in the VR FPS game. The brilliant color, complex shape, bold fidelity, as it reduced user presence and immersion and provided line, and depth of a visual guide can reduce the presence and a strong sense of heterogeneity to the user. VR sickness has immersion of the user by increasing the visual stimulation [18]. further been reduced using the earth-fixed grid or the natural Therefore, these elements are fixed, and they are designed as a independent visual background (IVB) with rest frames, whereas white, circle, 1.0 px, and 0, respectively by referring to it did not increase the presence and immersion of the user commercial VR FPS games. Table 1 shows various crosshair [22,23]. Particularly, VR sickness in first-person shooter (FPS) in commercial VR FPS games. Figure 1. Example of crosshair used in the virtual reality first-person shooter game. HMD: head-mounted display; SSQ: Simulator Sickness Questionnaire. https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 2 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Seok et al Table 1. Various crosshair in commercial virtual reality (VR) first-person shooter (FPS) games. No. Name Crosshair image 1 Super Stardust Ultra VR 2 End Space VR 3 Elite: Dangerous 4 Gunjack 5 Sublevel Zero 6 VR Galaxy Wars 7 Fusion Wars 8 EVE: Valkyrie 9 Rez Infinite 10 EVERSPACE The size and position of the visual guide is considered a variable is no visual guide. If the position is “H,” then the position of for VR sickness measurements. Therefore, we designed it as a the visual guide is synchronized with the head-tracking direction variable. First, the size was designed to be 0%, 10%, 30%, and by the HMD operation. If the position is “G,” then the position 50% of the size of the aspect ratio (with 0% implying that there of the visual guide is synchronized in the direction of forwarding is no visual guide). Second, the position was synchronized to movement, pitch, yaw, and roll rotation by the game controller “none,” “head-tracking direction with HMD (H),” “movement operation. Finally, if the position is “H & G,” then the position direction with game controller (G),” and “head-tracking of the visual guide is synchronized with the head-tracking direction with HMD and movement direction with game direction by the HMD operation and the direction of forwarding controller (H & G).” That is, if the position is “none,” then there movement, pitch, yaw, and roll by the game controller operation. https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 3 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Seok et al of answers in the SSQ. Experimental content is a VR FPS game Experiments in space environment because it easily causes VR sickness due In this section, we describe the experimental environment and to multiaxis movement. The user uses the HMD and the game methods used to examine the effect of visual guide on VR controller operations to trace the enemy target and score it with sickness. The experimental environment consisted of the the missile. participant, experiment device, and experimental content. The experimental protocol consisted of preliminary experiment We used a paired t test method to analyze the results. This (M2), eight experimental scenarios (S1–S8), SSQ, and rest requires the experimental results to approximate the normal videos. Figure 2 shows the experimental protocol for VR distribution. Therefore, the minimum sample size was set to 30 sickness measurement. In the preliminary experiment (M2), the to satisfy a central limit theorem [25]. Eventually, 32 individuals participants were taught how to operate the HMD and the game (male: 23, female: 9) participated in the experiment. controller. The eight experimental scenarios were designed to All the participants were in their twenties without any HMD measure VR sickness. If a participant is exposed to VR content VR experience, and none had a medical history of hearing or for a long time, the VR sickness level will potentially increase. balancing disorder. We received an institutional review board [28] Therefore, each scenario was composed of content of 60 approval for testing of VR sickness by KOREATECH. s for the safety of the participants. These eight experimental scenarios were designed to have the visual guide on/off, the Before performing the experiment, each participant was game controller on/off, and to vary sizes and positions of the administered a preliminary questionnaire (M1) comprising the visual guide to determine its effect on VR sickness. Table 2 Simulator sickness Questionnaire (SSQ) items, such as shows the features of these eight scenarios. measurement, reliability, validity, score interpretation, etc [26,27], to evaluate their current motion sickness state. After In addition, the experimental scenarios were randomly placed the SSQ (M1) was completed, the participant wore the HMD, and used to ensure reliability. For 240 s after each experimental and the experiment was initiated. scenario (including M2) ended, participants entered SSQ and watched the rest video to relax VR sickness. All participants The experimental equipment used was a head-tracking interface were equally exposed to this rest video. When the experiment device HTC VIVE HMD and an Xbox One Wireless Controller. was completed, the SSQ data for the eight scenarios were With these devices, the participants played the VR FPS game automatically saved. From the VR sickness measurement and answered the SSQ. The game controller has several experiment, preexperimental SSQ data (M1) and functionalities including forward movement; rotation based on postexperimental SSQ data (S1-S8) were collected for each pitch, yaw and roll axes; missile launch targeting; and selection participant. Figure 2. Experimental protocol for virtual reality sickness measurement. HMD: head-mounted display; SSQ: Simulator Sickness Questionnaire. https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 4 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Seok et al Table 2. Features of eight scenarios used in the experiment. Feature S1 S2 S3 S4 S5 S6 S7 S8 Game controller Off On On On On On On On Visual guide size (%) 0 0 0 10 30 50 30 30 a b c Visual guide position None None None H H H G H & G H: head-tracking direction with head-mounted display. G: movement direction with game controller. H & G: head-tracking direction with head-mounted display and movement direction with game controller. Using these experimental protocols, we conducted two Experiment II investigated the effects of the visual guide’s size experiments to examine the effect of the visual guide on VR and position on VR sickness. In the first step of experiment II, sickness. Experiment I investigated the effect of visual guide we investigated the effect of the visual guide’s size with the on/off on VR sickness. In the first step of experiment I, we game controller on. Thus, the SSQ data of S4, S5, and S6 and investigated the effect of VR sickness when the visual guide is the SSQ data of S3 were used for the comparison of VR on/off with the game controller off. Thus, the SSQ data of S1 sickness. Figure 5 shows the S3, S4, S5, and S6 used in the first and S2 were used for the comparison of VR sickness. Figure 3 step of experiment II. shows the S1 and S2 used in the first step of experiment I. In the second step of experiment II, we investigated the effect In the second step of experiment I, we investigated the effect of the visual guide’s position with the game controller on. Thus, of visual guide on/off with the game controller on. Thus, the the SSQ data of S5, S7, and S8 using a visual guide with SSQ data of S3 and S5 were used for the comparison of VR different positions at 30% of the size of the aspect ratio and the sickness. Figure 4 shows the S3 and S5 used in the second step SSQ data of S3 were used for comparison of VR sickness. of experiment I. Figure 6 shows the shows S3, S5, S7, and S8 used in the second step of experiment II. Figure 3. S1 and S2 used in the first step of experiment I. VG: visual guide. https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 5 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Seok et al Figure 4. S3 and S5 used in the second step of experiment I. VG: visual guide. Figure 5. S3, S4, S5, and S6 used in the first step of experiment II. VG: visual guide. https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 6 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Seok et al Figure 6. S3, S5, S7, and S8 used in the second step of Experiment II. VG: visual guide. to visual guide on/off when game controller was off; there was Results a negligible difference in nausea, oculomotor discomfort, disorientation, and total score values. In other words, there was Overview no effect of visual guide with game controller off (watching First, we compared the SSQ preexperiment (M1) and video) on VR sickness. Table 3 shows the results of the paired postexperiment (S1-S8) data to verify that the experimental t test of visual guide on/off with game controller off. Figure 7 protocol for VR sickness measurement was well designed. From shows the results of the first step of experiment I (ie, difference the paired t test results, a significant difference was observed in VR sickness with respect to visual guide on/off with game in VR sickness between M1 and S1-S8. Significantly higher controller off). nausea and disorientation symptoms were noted in S1-S8 than In the second step of Experiment I, the paired t test showed a in M1. Hence, we confirmed that the participants had significant difference in VR sickness with visual guide on/off experienced nausea and disorientation. In addition, oculomotor and game controller on: nausea and total score values were discomfort in S1-S8 did not significantly increase because many significantly decreased, whereas oculomotor discomfort and participants had eye fatigue from M1. From the different SSQ disorientation values had no significant differences. Table 4 values before and after VR exposure, the increase in the values shows the results of the paired t test of visual guide on/off with of nausea and disorientation symptoms of the participants was the game controller on. Figure 8 shows the results of the second confirmed. It was concluded that the scenarios for the VR step of Experiment I (difference in VR sickness of visual guide sickness experiment were appropriately produced. on/off with game controller on). Experiment I: Effects of Visual Guide On/Off In the first step of experiment I, the results of the paired t test showed no significant difference in VR sickness with respect Table 3. Results of the paired t test of the visual guide on/off with game controller off. Scenario (state) Simulator Sickness Questionnaire Nausea Oculomotor discomfort Disorientation Total score Score t (df) P value Score t (df) P value Score t (df) P value Score t (df) P value S1 (visual guide off) 8.65 N/A 12.08 N/A N/A 17.84 N/A N/A 14.14 N/A N/A N/A S2 (visual guide on) 8.65 0 (31) >.99 13.50 –.649 (31) .52 16.97 .360 (31) .72 14.61 –.235 (31) .82 N/A: not applicable. https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 7 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Seok et al Figure 7. Results of the first step of experiment I (difference in virtual reality sickness with respect to visual guide on/off with game controller off). SSQ: Simulator Sickness Questionnaire; VG: visual guide. Table 4. Results of the paired t test of the visual guide on/off with game controller on. Scenario (state) Simulator Sickness Questionnaire Nausea Oculomotor discomfort Disorientation Total score Score t (df) P value Score t (df) P value Score t (df) P value Score t (df) P value S3 (visual guide off) 9.24 N/A 15.87 N/A N/A 20.45 N/A N/A 16.95 N/A N/A N/A S5 (visual guide on) 5.66 2.547 (31) 13.03 1.359 (31) .18 14.79 1.815 (31) .08 12.62 2.183 (31) .04 N/A: not applicable. Italicized values indicate statistical significance. Figure 8. Results of the second step of experiment I (difference in virtual reality sickness of visual guide on/off with game controller on). SSQ: Simulator Sickness Questionnaire; VG: visual guide. of visual guide used in S5: nausea and total score values were Experiment II: Effect of Visual Guide Size and Position significantly decreased, whereas oculomotor discomfort and In the first step of Experiment II, the paired t test showed that disorientation values had no significant differences. However, there was a significant difference in VR sickness with the size there was no significant difference in VR sickness with the size https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 8 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Seok et al of visual guide used in S4 and S6. Table 5 shows the results of were significantly decreased, whereas oculomotor discomfort the paired t test of the visual guide size with the game controller and disorientation values had no significant differences. on. As shown in Figure 9, VR sickness was lower than that However, there was no significant difference in VR sickness observed with other sizes when the visual guide was 30% of with the position of the visual guide used in S7 and S8. Table the size of the aspect ratio. Figure 9 shows the results of the 6 shows the results of the paired t test of the visual guide first step of Experiment II (ie, difference in VR sickness with position with the game controller on. As shown in Figure 10, respect to the visual guide size when the game controller was VR sickness was lower than that observed with other positions on). when visual guide was in the head-tracking direction. Figure 10 shows the results of the second step of Experiment II (ie, In the second step of Experiment II, the paired t test showed difference in VR sickness with respect to visual guide position that there was a significant difference in VR sickness with the when the game controller is on). position of visual guide used in S5: nausea and total score values Table 5. Results of the paired t test of visual guide size with game controller on. Scenario (size) Simulator Sickness Questionnaire Nausea Oculomotor discomfort Disorientation Total score Score t (df) P value Score t (df) P value Score t (df) P value Score t (df) P value S3 (0%) 9.24 N/A 15.87 N/A N/A 20.45 N/A N/A 16.95 N/A N/A N/A S4 (10%) 7.45 1.063 (31) .296 12.55 1.422 (31) .17 16.53 1.359 (31) .18 13.56 1.674 (31) .10 S5 (30%) 5.66 2.547 (31) 13.03 1.359 (31) .18 14.79 1.815 (31) .08 12.62 2.183 (31) .04 S6 (50%) 7.16 0.980 (31) .34 12.79 1.200 (31) .24 15.23 1.615 (31) .12 13.21 1.447 (31) .16 N/A: not applicable. Italicized values indicate statistical significance. Figure 9. Results of the first step of experiment II (difference in virtual reality sickness with respect to visual guide size when game controller was on). SSQ: Simulator Sickness Questionnaire; VG: visual guide. https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 9 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Seok et al Table 6. Results of the paired t test of the visual guide position with game controller on. Scenario (position) Simulator Sickness Questionnaire Nausea Oculomotor discomfort Disorientation Total score Score t (df) P value Score t (df) P value Score t (df) P value Score t (df) P value S3 (none) 9.24 N/A 15.87 N/A N/A 20.45 N/A N/A 16.95 N/A N/A N/A S5 (H) 5.66 2.547 (31) 13.03 1.359 (31) 18 14.79 1.815 (31) .08 12.62 2.183 (31) .04 S7 (G) 9.24 0 (31) >.99 18.71 –1.099 (31) .28 18.71 0.436 (31) .67 17.88 –0.323 (31) .75 S8 (H & G) 7.75 0.645 (31) .52 14.69 0.456 (31) .65 19.14 0.317 (31) .75 15.43 0.517 (31) .61 N/A: not applicable. Italicized values indicate statistical significance. Figure 10. Results of the second step of Experiment II (difference in virtual reality sickness with respect to visual guide position when game controller is on). SSQ: Simulator Sickness Questionnaire; VG: visual guide. 50% and positions G and H & G of the visual guide was not Discussion significant, whereas VR sickness according to size 30% and position H of the visual guide was significant. Moreover, VR Principal Findings sickness was lower when the visual guide was 30% of the size In this study, we analyzed the correlation between VR sickness of the aspect ratio and positioned in the head-tracking direction and crosshair, which is widely used as a visual guide in an FPS compared with other sizes and positions. The various sizes of game. To do this, eight scenarios were designed: visual guide the visual guide reduced nausea, oculomotor discomfort, on/off, game controller on/off, and various sizes and positions disorientation symptom, and total score when compared to of visual guide. Experiments were performed using a protocol scenarios when a visual guide was not used. In particular, the that consisted of the abovementioned eight scenarios, SSQ, and visual guide at 30% the size of the aspect ratio further reduced rest video. Results of Experiment I showed no reduction of VR these symptoms to a larger extent than other sizes. The visual sickness of the visual guide when the game controller was not guide at 50% of the size of the aspect ratio reduced the operated, whereas there was a reduction when the game disorientation symptom, showing that disorientation was controller was operated. While the user operated the HMD and minimized due to the high synergy with the gaze movement the game controller in the game, the user's gaze movement was when the visual guide size increased. However, if the size of synchronized with the motion of the visual guide, thereby the visual guide increases, the VR fidelity cannot be maintained reducing VR sickness. The results suggest that visual guide can because it lowers the immersion and presence of the user. The reduce VR sickness caused by sensory conflicts between content visual guide positioned in the head-tracking direction reduced and users when manipulating content. It can be interpreted that the symptoms of nausea, oculomotor discomfort, disorientation, visual guide should be used effectively to reduce VR sickness and total score more than other positions. As mentioned above, because most VR content requires a game controller. Results crosshair was the visual guide function to reduce VR sickness, of experiment II confirmed a difference in VR sickness with as well as maintain VR fidelity in FPS games. respect to the size and position of the visual guide with game controller operation. VR sickness according to sizes 10% and https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 10 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Seok et al When recruiting participants, we tried to keep the number of to be significantly correlated with visual guide on/off, and the men and women the same. As a result, the number of male use of a visual guide was very effective in reducing VR sickness (n=23) participants exceeded the number of female (n=9) when using a game controller. VR sickness was reduced by participants recruited. This may have affected the results of the synchronizing the user's gaze movement to the motion of the experiments, as it is reported that men are stronger than women visual guide while operating the HMD and game controller with regard to motion sickness [29]. Therefore, the effects of within the game. In addition, VR sickness reduced when the the proposed method in a same-gender ratio environment should visual guide was 30% of the size of the aspect ratio and be included in further study. positioned in the head-tracking direction. From these findings, it is confirmed that using a visual guide can be an effective Conclusions method to reduce VR sickness. The experimental results of this In this study, we used an experimental protocol consisting of study indicate that the visual guide can achieve VR sickness scenarios such as visual guide on/off, game controller on/off, reduction while maintaining user presence and immersion in and various sizes and positions of the visual guide to analyze the virtual environment. In other words, the use of visual guide the correlation between VR sickness and crosshair that is widely is expected to solve the existing difficulty in disseminating used as a visual guide in FPS games. VR sickness was found various VR content due to VR sickness. Acknowledgments This work was supported by Institute for Information & communications Technology Promotion (IITP) grant funded by the Korea government (Ministry of Science and ICT [MSIT]) (No. 2017-0-00289-001). This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. NRF-2020R1F1A1076114). In addition, this study was partially supported by the Sabbatical Year Research Program of KOREATECH in 2019. Conflicts of Interest None declared. References 1. LaViola JJ. A discussion of cybersickness in virtual environments. SIGCHI Bull 2000 Jan 01;32(1):47-56. [doi: 10.1145/333329.333344] 2. Hettinger LJ, Berbaum KS, Kennedy RS, Dunlap WP, Nolan MD. Vection and simulator sickness. Mil Psychol 1990;2(3):171-181. [doi: 10.1207/s15327876mp0203_4] [Medline: 11537522] 3. Bonato F, Bubka A, Palmisano S, Phillip D, Moreno G. Vection change exacerbates simulator sickness in virtual environments. 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An “independent visual background” reduced balance disturbance envoked by visual scene motion: implication for alleviating simulator sickness. 2001 Presented at: The SIGCHI Conference on Human Factors in Computing Systems; March 31 - April 5, 2001; Seattle Washington USA p. 85-89. [doi: 10.1145/365024.365051] 23. Lin JJ, Abi-Rached H, Kim D, Parker DE, Furness TA. A “natural” independent visual background reduced simulator sickness. Proceedings of the Human Factors and Ergonomics Society Annual Meeting 2002 Sep 1;46(26):2124-2128. [doi: 10.1177/154193120204602605] 24. Prothero J. The role of rest frames in vection, presence and motion sickness. Doctoral Dissertation. University of Washington. Seattle, Washington: University of Washington; 1998. 25. Rosenblatt M. A central limit theorem and a strong mixing condition. Proc Natl Acad Sci U S A 1956 Jan;42(1):43-47 [FREE Full text] [doi: 10.1073/pnas.42.1.43] [Medline: 16589813] 26. Kennedy RS, Lane NE, Berbaum KS, Lilienthal MG. Simulator sickness questionnaire: An enhanced method for quantifying simulator sickness. Int J Aviat Psychol 1993 Jul;3(3):203-220. [doi: 10.1207/s15327108ijap0303_3] 27. Kennedy R, Drexler J, Compton D, Stanney K, Lanham D, Harm D. Configural scoring of simulator sickness, cybersickness and space adaptation syndrome: similarities and differences. In: Virtual and adaptive environments: applications, implications, and human performance issues. Boca Raton, Florida: CRC Press; 2003:247. 28. Häkkinen J, Ohta F, Kawai T. Time course of sickness symptoms with HMD viewing of 360-degree Videos. Electronic Imaging 2019 Jan 13;2019(3):60403-1-60403-11. [doi: 10.2352/j.imagingsci.technol.2018.62.6.060403] 29. Stanney KM, Kennedy RS, Drexler JM, Harm DL. Motion sickness and proprioceptive aftereffects following virtual environment exposure. Applied Ergonomics 1999 Feb;30(1):27-38. [doi: 10.1016/s0003-6870(98)00039-8] Abbreviations FPS: first-person shooter G: movement direction with game controller H: head-tracking direction with head-mounted display H & G: head-tracking direction with head-mounted display and movement direction with game controller HMD: head-mounted display IITP: Institute for Information & Communications Technology Promotion IVB: independent visual background MSIT: Ministry of Science and ICT SSQ: Simulator Sickness Questionnaire VR: virtual reality https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 12 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Seok et al Edited by N Zary; submitted 29.01.20; peer-reviewed by C Johnson, R Haghighi Osgouei; comments to author 30.06.20; revised version received 25.03.21; accepted 30.04.21; published 15.07.21 Please cite as: Seok KH, Kim Y, Son W, Kim YS JMIR Serious Games 2021;9(3):e18020 URL: https://games.jmir.org/2021/3/e18020 doi: 10.2196/18020 PMID: 34264196 ©Kwang-Ho Seok, YeolHo Kim, Wookho Son, Yoon Sang Kim. Originally published in JMIR Serious Games (https://games.jmir.org), 15.07.2021. This is an open-access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work, first published in JMIR Serious Games, is properly cited. The complete bibliographic information, a link to the original publication on https://games.jmir.org, as well as this copyright and license information must be included. https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 13 (page number not for citation purposes) XSL FO RenderX http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png JMIR Serious Games JMIR Publications

Using Visual Guides to Reduce Virtual Reality Sickness in First-Person Shooter Games: Correlation Analysis

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Abstract

Background: The virtual reality (VR) content market is rapidly growing due to an increased supply of VR devices such as head-mounted displays (HMDs), whereas VR sickness (reported to occur while experiencing VR) remains an unsolved problem. The most widely used method of reducing VR sickness is the use of a rest frame that stabilizes the user's viewpoint by providing fixed visual stimuli in VR content (including video). However, the earth-fixed grid and natural independent visual background that are widely used as rest frames cannot maintain VR fidelity, as they reduce the immersion and the presence of the user. A visual guide is a visual element (eg, a crosshair of first-person shooter [FPS]) that induces a user's gaze movement within the VR content while maintaining VR fidelity, whereas there are no studies on the correlation of visual guide with VR sickness. Objective: This study aimed to analyze the correlation between VR sickness and crosshair, which is widely used as a visual guide in FPS games. Methods: Eight experimental scenarios were designed and evaluated, including having the visual guide on/off, the game controller on/off, and varying the size and position of the visual guide to determine the effect of visual guide on VR sickness. Results: The results showed that VR sickness significantly decreased when visual guide was applied in an FPS game. In addition, VR sickness was lower when the visual guide was adjusted to 30% of the aspect ratio and positioned in the head-tracking direction. Conclusions: The experimental results of this study indicate that the visual guide can achieve VR sickness reduction while maintaining user presence and immersion in the virtual environment. In other words, the use of a visual guide is expected to solve the existing limitation of distributing various types of content due to VR sickness. (JMIR Serious Games 2021;9(3):e18020) doi: 10.2196/18020 KEYWORDS virtual reality; motion sickness; VR sickness; visual guide; VR fidelity disorientation caused while experiencing an HMD-based VR Introduction [1]. To investigate the causes of VR sickness, various theories are being studied in a cognitive science approach. The popular Recently, virtual reality (VR) content based on head-mounted sensory conflict theory [1] proposes that VR sickness is induced display (HMD) has been expanded to various industrial fields by an inconsistency between the visual and the vestibular or such as sports, medical care, education, and social network. proprioceptive senses. In particular, the vection that occurs Moreover, such content has been used in video games. However, during the VR experience is the biggest cause of sensory conflict most users have experienced “VR sickness” while using [2-4]. Additionally, the postural instability theory posits that HMD-based VR content. VR sickness has symptoms similar to VR sickness is caused by changes in human balance [5]. motion sickness, including nausea, oculomotor discomfort, and https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 1 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Seok et al Furthermore, VR sickness may also be induced by various games was reduced when cockpits were added to the IVB, while individual characteristics, such as age, gender, prior user the VR fidelity of the users was disturbed [24]. experience, concentration, medical history, mental rotation, To overcome the problem of IVB, we discuss another visual perceptual style, and dominant eye [6]. element applied to VR FPS games called the visual guide, which Until now, various studies have only been partially successful refers to a visual element that induces a user's gaze movement in attempting to reduce HMD-induced VR sickness by focusing within VR content. To our knowledge, there is no study on the device and the content. A typical method focusing on investigating the effect of visual guide on the reduction of VR the device is the optimization of the delay time caused by head sickness while maintaining VR fidelity in VR FPS games. movement tracking response, rendering, image transmission, Therefore, in this study, we investigated how VR sickness and display response speed [7]. Studies have also been reduction is affected by visual guide in FPS games. To do this, conducted to reduce VR sickness in device elements such as we performed experiments on a VR FPS game consisting of resolution, frame rate, viewing angle, binocular parallax, and eight scenarios, including visual guide on/off, game controller flicker fusion frequency [8-13]. Recent studies have evaluated on/off, and varying the size and position of the visual guide. methods focusing on content. These methods investigated the use of dynamic blurring with retinal tracking [14], optical flow Methods reduction of peripheral vision [15], field of view control [16], Visual Guide Design in VR FPS Games and viewpoint snapping [17]. In this section, we describe the visual guide used in this study. However, there is a disadvantage that these dynamic blurring In VR FPS games, crosshairs, character path indicators, and methods limit the user's experience. Therefore, in other studies, maps are used as visual guides to provide situational awareness VR sickness has been reduced by adding fixed or dynamic visual for the user to spatially determine their position in a virtual stimuli regardless of the motion of objects in the content [18-20]. environment. In this study, we used crosshair as a visual guide This visual stimulus includes a rest frame that serves as a to induce a user's gaze movement while maintaining VR fidelity reference frame designed to induce a user's effective spatial in a space-environment FPS game. Crosshair is a 2D image perception. In particular, VR sickness was reduced by applying composed of color, shape, line thickness, depth, size, and a virtual human nose as a rest frame to the content [21]. position elements. Figure 1 shows an example of crosshair used However, this artificial rest frame could not maintain VR in the VR FPS game. The brilliant color, complex shape, bold fidelity, as it reduced user presence and immersion and provided line, and depth of a visual guide can reduce the presence and a strong sense of heterogeneity to the user. VR sickness has immersion of the user by increasing the visual stimulation [18]. further been reduced using the earth-fixed grid or the natural Therefore, these elements are fixed, and they are designed as a independent visual background (IVB) with rest frames, whereas white, circle, 1.0 px, and 0, respectively by referring to it did not increase the presence and immersion of the user commercial VR FPS games. Table 1 shows various crosshair [22,23]. Particularly, VR sickness in first-person shooter (FPS) in commercial VR FPS games. Figure 1. Example of crosshair used in the virtual reality first-person shooter game. HMD: head-mounted display; SSQ: Simulator Sickness Questionnaire. https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 2 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Seok et al Table 1. Various crosshair in commercial virtual reality (VR) first-person shooter (FPS) games. No. Name Crosshair image 1 Super Stardust Ultra VR 2 End Space VR 3 Elite: Dangerous 4 Gunjack 5 Sublevel Zero 6 VR Galaxy Wars 7 Fusion Wars 8 EVE: Valkyrie 9 Rez Infinite 10 EVERSPACE The size and position of the visual guide is considered a variable is no visual guide. If the position is “H,” then the position of for VR sickness measurements. Therefore, we designed it as a the visual guide is synchronized with the head-tracking direction variable. First, the size was designed to be 0%, 10%, 30%, and by the HMD operation. If the position is “G,” then the position 50% of the size of the aspect ratio (with 0% implying that there of the visual guide is synchronized in the direction of forwarding is no visual guide). Second, the position was synchronized to movement, pitch, yaw, and roll rotation by the game controller “none,” “head-tracking direction with HMD (H),” “movement operation. Finally, if the position is “H & G,” then the position direction with game controller (G),” and “head-tracking of the visual guide is synchronized with the head-tracking direction with HMD and movement direction with game direction by the HMD operation and the direction of forwarding controller (H & G).” That is, if the position is “none,” then there movement, pitch, yaw, and roll by the game controller operation. https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 3 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Seok et al of answers in the SSQ. Experimental content is a VR FPS game Experiments in space environment because it easily causes VR sickness due In this section, we describe the experimental environment and to multiaxis movement. The user uses the HMD and the game methods used to examine the effect of visual guide on VR controller operations to trace the enemy target and score it with sickness. The experimental environment consisted of the the missile. participant, experiment device, and experimental content. The experimental protocol consisted of preliminary experiment We used a paired t test method to analyze the results. This (M2), eight experimental scenarios (S1–S8), SSQ, and rest requires the experimental results to approximate the normal videos. Figure 2 shows the experimental protocol for VR distribution. Therefore, the minimum sample size was set to 30 sickness measurement. In the preliminary experiment (M2), the to satisfy a central limit theorem [25]. Eventually, 32 individuals participants were taught how to operate the HMD and the game (male: 23, female: 9) participated in the experiment. controller. The eight experimental scenarios were designed to All the participants were in their twenties without any HMD measure VR sickness. If a participant is exposed to VR content VR experience, and none had a medical history of hearing or for a long time, the VR sickness level will potentially increase. balancing disorder. We received an institutional review board [28] Therefore, each scenario was composed of content of 60 approval for testing of VR sickness by KOREATECH. s for the safety of the participants. These eight experimental scenarios were designed to have the visual guide on/off, the Before performing the experiment, each participant was game controller on/off, and to vary sizes and positions of the administered a preliminary questionnaire (M1) comprising the visual guide to determine its effect on VR sickness. Table 2 Simulator sickness Questionnaire (SSQ) items, such as shows the features of these eight scenarios. measurement, reliability, validity, score interpretation, etc [26,27], to evaluate their current motion sickness state. After In addition, the experimental scenarios were randomly placed the SSQ (M1) was completed, the participant wore the HMD, and used to ensure reliability. For 240 s after each experimental and the experiment was initiated. scenario (including M2) ended, participants entered SSQ and watched the rest video to relax VR sickness. All participants The experimental equipment used was a head-tracking interface were equally exposed to this rest video. When the experiment device HTC VIVE HMD and an Xbox One Wireless Controller. was completed, the SSQ data for the eight scenarios were With these devices, the participants played the VR FPS game automatically saved. From the VR sickness measurement and answered the SSQ. The game controller has several experiment, preexperimental SSQ data (M1) and functionalities including forward movement; rotation based on postexperimental SSQ data (S1-S8) were collected for each pitch, yaw and roll axes; missile launch targeting; and selection participant. Figure 2. Experimental protocol for virtual reality sickness measurement. HMD: head-mounted display; SSQ: Simulator Sickness Questionnaire. https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 4 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Seok et al Table 2. Features of eight scenarios used in the experiment. Feature S1 S2 S3 S4 S5 S6 S7 S8 Game controller Off On On On On On On On Visual guide size (%) 0 0 0 10 30 50 30 30 a b c Visual guide position None None None H H H G H & G H: head-tracking direction with head-mounted display. G: movement direction with game controller. H & G: head-tracking direction with head-mounted display and movement direction with game controller. Using these experimental protocols, we conducted two Experiment II investigated the effects of the visual guide’s size experiments to examine the effect of the visual guide on VR and position on VR sickness. In the first step of experiment II, sickness. Experiment I investigated the effect of visual guide we investigated the effect of the visual guide’s size with the on/off on VR sickness. In the first step of experiment I, we game controller on. Thus, the SSQ data of S4, S5, and S6 and investigated the effect of VR sickness when the visual guide is the SSQ data of S3 were used for the comparison of VR on/off with the game controller off. Thus, the SSQ data of S1 sickness. Figure 5 shows the S3, S4, S5, and S6 used in the first and S2 were used for the comparison of VR sickness. Figure 3 step of experiment II. shows the S1 and S2 used in the first step of experiment I. In the second step of experiment II, we investigated the effect In the second step of experiment I, we investigated the effect of the visual guide’s position with the game controller on. Thus, of visual guide on/off with the game controller on. Thus, the the SSQ data of S5, S7, and S8 using a visual guide with SSQ data of S3 and S5 were used for the comparison of VR different positions at 30% of the size of the aspect ratio and the sickness. Figure 4 shows the S3 and S5 used in the second step SSQ data of S3 were used for comparison of VR sickness. of experiment I. Figure 6 shows the shows S3, S5, S7, and S8 used in the second step of experiment II. Figure 3. S1 and S2 used in the first step of experiment I. VG: visual guide. https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 5 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Seok et al Figure 4. S3 and S5 used in the second step of experiment I. VG: visual guide. Figure 5. S3, S4, S5, and S6 used in the first step of experiment II. VG: visual guide. https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 6 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Seok et al Figure 6. S3, S5, S7, and S8 used in the second step of Experiment II. VG: visual guide. to visual guide on/off when game controller was off; there was Results a negligible difference in nausea, oculomotor discomfort, disorientation, and total score values. In other words, there was Overview no effect of visual guide with game controller off (watching First, we compared the SSQ preexperiment (M1) and video) on VR sickness. Table 3 shows the results of the paired postexperiment (S1-S8) data to verify that the experimental t test of visual guide on/off with game controller off. Figure 7 protocol for VR sickness measurement was well designed. From shows the results of the first step of experiment I (ie, difference the paired t test results, a significant difference was observed in VR sickness with respect to visual guide on/off with game in VR sickness between M1 and S1-S8. Significantly higher controller off). nausea and disorientation symptoms were noted in S1-S8 than In the second step of Experiment I, the paired t test showed a in M1. Hence, we confirmed that the participants had significant difference in VR sickness with visual guide on/off experienced nausea and disorientation. In addition, oculomotor and game controller on: nausea and total score values were discomfort in S1-S8 did not significantly increase because many significantly decreased, whereas oculomotor discomfort and participants had eye fatigue from M1. From the different SSQ disorientation values had no significant differences. Table 4 values before and after VR exposure, the increase in the values shows the results of the paired t test of visual guide on/off with of nausea and disorientation symptoms of the participants was the game controller on. Figure 8 shows the results of the second confirmed. It was concluded that the scenarios for the VR step of Experiment I (difference in VR sickness of visual guide sickness experiment were appropriately produced. on/off with game controller on). Experiment I: Effects of Visual Guide On/Off In the first step of experiment I, the results of the paired t test showed no significant difference in VR sickness with respect Table 3. Results of the paired t test of the visual guide on/off with game controller off. Scenario (state) Simulator Sickness Questionnaire Nausea Oculomotor discomfort Disorientation Total score Score t (df) P value Score t (df) P value Score t (df) P value Score t (df) P value S1 (visual guide off) 8.65 N/A 12.08 N/A N/A 17.84 N/A N/A 14.14 N/A N/A N/A S2 (visual guide on) 8.65 0 (31) >.99 13.50 –.649 (31) .52 16.97 .360 (31) .72 14.61 –.235 (31) .82 N/A: not applicable. https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 7 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Seok et al Figure 7. Results of the first step of experiment I (difference in virtual reality sickness with respect to visual guide on/off with game controller off). SSQ: Simulator Sickness Questionnaire; VG: visual guide. Table 4. Results of the paired t test of the visual guide on/off with game controller on. Scenario (state) Simulator Sickness Questionnaire Nausea Oculomotor discomfort Disorientation Total score Score t (df) P value Score t (df) P value Score t (df) P value Score t (df) P value S3 (visual guide off) 9.24 N/A 15.87 N/A N/A 20.45 N/A N/A 16.95 N/A N/A N/A S5 (visual guide on) 5.66 2.547 (31) 13.03 1.359 (31) .18 14.79 1.815 (31) .08 12.62 2.183 (31) .04 N/A: not applicable. Italicized values indicate statistical significance. Figure 8. Results of the second step of experiment I (difference in virtual reality sickness of visual guide on/off with game controller on). SSQ: Simulator Sickness Questionnaire; VG: visual guide. of visual guide used in S5: nausea and total score values were Experiment II: Effect of Visual Guide Size and Position significantly decreased, whereas oculomotor discomfort and In the first step of Experiment II, the paired t test showed that disorientation values had no significant differences. However, there was a significant difference in VR sickness with the size there was no significant difference in VR sickness with the size https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 8 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Seok et al of visual guide used in S4 and S6. Table 5 shows the results of were significantly decreased, whereas oculomotor discomfort the paired t test of the visual guide size with the game controller and disorientation values had no significant differences. on. As shown in Figure 9, VR sickness was lower than that However, there was no significant difference in VR sickness observed with other sizes when the visual guide was 30% of with the position of the visual guide used in S7 and S8. Table the size of the aspect ratio. Figure 9 shows the results of the 6 shows the results of the paired t test of the visual guide first step of Experiment II (ie, difference in VR sickness with position with the game controller on. As shown in Figure 10, respect to the visual guide size when the game controller was VR sickness was lower than that observed with other positions on). when visual guide was in the head-tracking direction. Figure 10 shows the results of the second step of Experiment II (ie, In the second step of Experiment II, the paired t test showed difference in VR sickness with respect to visual guide position that there was a significant difference in VR sickness with the when the game controller is on). position of visual guide used in S5: nausea and total score values Table 5. Results of the paired t test of visual guide size with game controller on. Scenario (size) Simulator Sickness Questionnaire Nausea Oculomotor discomfort Disorientation Total score Score t (df) P value Score t (df) P value Score t (df) P value Score t (df) P value S3 (0%) 9.24 N/A 15.87 N/A N/A 20.45 N/A N/A 16.95 N/A N/A N/A S4 (10%) 7.45 1.063 (31) .296 12.55 1.422 (31) .17 16.53 1.359 (31) .18 13.56 1.674 (31) .10 S5 (30%) 5.66 2.547 (31) 13.03 1.359 (31) .18 14.79 1.815 (31) .08 12.62 2.183 (31) .04 S6 (50%) 7.16 0.980 (31) .34 12.79 1.200 (31) .24 15.23 1.615 (31) .12 13.21 1.447 (31) .16 N/A: not applicable. Italicized values indicate statistical significance. Figure 9. Results of the first step of experiment II (difference in virtual reality sickness with respect to visual guide size when game controller was on). SSQ: Simulator Sickness Questionnaire; VG: visual guide. https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 9 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Seok et al Table 6. Results of the paired t test of the visual guide position with game controller on. Scenario (position) Simulator Sickness Questionnaire Nausea Oculomotor discomfort Disorientation Total score Score t (df) P value Score t (df) P value Score t (df) P value Score t (df) P value S3 (none) 9.24 N/A 15.87 N/A N/A 20.45 N/A N/A 16.95 N/A N/A N/A S5 (H) 5.66 2.547 (31) 13.03 1.359 (31) 18 14.79 1.815 (31) .08 12.62 2.183 (31) .04 S7 (G) 9.24 0 (31) >.99 18.71 –1.099 (31) .28 18.71 0.436 (31) .67 17.88 –0.323 (31) .75 S8 (H & G) 7.75 0.645 (31) .52 14.69 0.456 (31) .65 19.14 0.317 (31) .75 15.43 0.517 (31) .61 N/A: not applicable. Italicized values indicate statistical significance. Figure 10. Results of the second step of Experiment II (difference in virtual reality sickness with respect to visual guide position when game controller is on). SSQ: Simulator Sickness Questionnaire; VG: visual guide. 50% and positions G and H & G of the visual guide was not Discussion significant, whereas VR sickness according to size 30% and position H of the visual guide was significant. Moreover, VR Principal Findings sickness was lower when the visual guide was 30% of the size In this study, we analyzed the correlation between VR sickness of the aspect ratio and positioned in the head-tracking direction and crosshair, which is widely used as a visual guide in an FPS compared with other sizes and positions. The various sizes of game. To do this, eight scenarios were designed: visual guide the visual guide reduced nausea, oculomotor discomfort, on/off, game controller on/off, and various sizes and positions disorientation symptom, and total score when compared to of visual guide. Experiments were performed using a protocol scenarios when a visual guide was not used. In particular, the that consisted of the abovementioned eight scenarios, SSQ, and visual guide at 30% the size of the aspect ratio further reduced rest video. Results of Experiment I showed no reduction of VR these symptoms to a larger extent than other sizes. The visual sickness of the visual guide when the game controller was not guide at 50% of the size of the aspect ratio reduced the operated, whereas there was a reduction when the game disorientation symptom, showing that disorientation was controller was operated. While the user operated the HMD and minimized due to the high synergy with the gaze movement the game controller in the game, the user's gaze movement was when the visual guide size increased. However, if the size of synchronized with the motion of the visual guide, thereby the visual guide increases, the VR fidelity cannot be maintained reducing VR sickness. The results suggest that visual guide can because it lowers the immersion and presence of the user. The reduce VR sickness caused by sensory conflicts between content visual guide positioned in the head-tracking direction reduced and users when manipulating content. It can be interpreted that the symptoms of nausea, oculomotor discomfort, disorientation, visual guide should be used effectively to reduce VR sickness and total score more than other positions. As mentioned above, because most VR content requires a game controller. Results crosshair was the visual guide function to reduce VR sickness, of experiment II confirmed a difference in VR sickness with as well as maintain VR fidelity in FPS games. respect to the size and position of the visual guide with game controller operation. VR sickness according to sizes 10% and https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 10 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Seok et al When recruiting participants, we tried to keep the number of to be significantly correlated with visual guide on/off, and the men and women the same. As a result, the number of male use of a visual guide was very effective in reducing VR sickness (n=23) participants exceeded the number of female (n=9) when using a game controller. VR sickness was reduced by participants recruited. This may have affected the results of the synchronizing the user's gaze movement to the motion of the experiments, as it is reported that men are stronger than women visual guide while operating the HMD and game controller with regard to motion sickness [29]. Therefore, the effects of within the game. In addition, VR sickness reduced when the the proposed method in a same-gender ratio environment should visual guide was 30% of the size of the aspect ratio and be included in further study. positioned in the head-tracking direction. From these findings, it is confirmed that using a visual guide can be an effective Conclusions method to reduce VR sickness. The experimental results of this In this study, we used an experimental protocol consisting of study indicate that the visual guide can achieve VR sickness scenarios such as visual guide on/off, game controller on/off, reduction while maintaining user presence and immersion in and various sizes and positions of the visual guide to analyze the virtual environment. In other words, the use of visual guide the correlation between VR sickness and crosshair that is widely is expected to solve the existing difficulty in disseminating used as a visual guide in FPS games. VR sickness was found various VR content due to VR sickness. 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[doi: 10.1016/s0003-6870(98)00039-8] Abbreviations FPS: first-person shooter G: movement direction with game controller H: head-tracking direction with head-mounted display H & G: head-tracking direction with head-mounted display and movement direction with game controller HMD: head-mounted display IITP: Institute for Information & Communications Technology Promotion IVB: independent visual background MSIT: Ministry of Science and ICT SSQ: Simulator Sickness Questionnaire VR: virtual reality https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 12 (page number not for citation purposes) XSL FO RenderX JMIR SERIOUS GAMES Seok et al Edited by N Zary; submitted 29.01.20; peer-reviewed by C Johnson, R Haghighi Osgouei; comments to author 30.06.20; revised version received 25.03.21; accepted 30.04.21; published 15.07.21 Please cite as: Seok KH, Kim Y, Son W, Kim YS JMIR Serious Games 2021;9(3):e18020 URL: https://games.jmir.org/2021/3/e18020 doi: 10.2196/18020 PMID: 34264196 ©Kwang-Ho Seok, YeolHo Kim, Wookho Son, Yoon Sang Kim. Originally published in JMIR Serious Games (https://games.jmir.org), 15.07.2021. This is an open-access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work, first published in JMIR Serious Games, is properly cited. The complete bibliographic information, a link to the original publication on https://games.jmir.org, as well as this copyright and license information must be included. https://games.jmir.org/2021/3/e18020 JMIR Serious Games 2021 | vol. 9 | iss. 3 | e18020 | p. 13 (page number not for citation purposes) XSL FO RenderX

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JMIR Serious Games – JMIR Publications

Published: Jul 15, 2021

Keywords: virtual reality; motion sickness; VR sickness; visual guide; VR fidelity

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