The effect of rest frames on simulator sickness reduction by Zekun Cao Department of Mechanical Engineering and Material Science Duke University Date: Approved: Regis Kopper, Supervisor Mary Cummings Michael Zavlanos Jason Jerald Thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in the Department of Mechanical Engineering and Material Science in the Graduate School of Duke University 2017 Abstract The effect of rest frames on simulator sickness reduction by Zekun Cao Department of Mechanical Engineering and Material Science Duke University Date: Approved: Regis Kopper, Supervisor Mary Cummings Michael Zavlanos Jason Jerald An abstract of a dissertation submitted in partial fulfillment of the requirements for the degree of Master of Science in the Department of Mechanical Engineering and Material Science in the Graduate School of Duke University 2017 Copyright c 2017 by Zekun Cao All rights reserved except the rights granted by the Creative Commons Attribution-Noncommercial Licence Abstract With increasing prevalence and capabilities of Virtual Reality (VR) as a part of education, entertainment, data analysis and industrial applications, the consideration of constructing a more user-friendly virtual environment becomes more important, which requires the reduction or elimination of simulator sickness (SS) -- a discomfort caused in simulated environment. As a form of motion sickness (MS) -- caused by movement in travel, some signs and symptoms of SS are the same as those of MS's, such as pallor, cold sweating, nausea, and vomiting. Several convincing theories or hypothesis to explain the cause of SS have been advanced, such as Sensory Conflict Theory, Postural Instability Theory and Rest Frames Hypothesis. Based on the first two theories aforementioned, high-quality tracking systems (Pierre et al., 2015) and modification of field of view (FOV) (Fernandes and Feiner, 2016) have been proposed to reduce the mismatch between visual perception and vestibular system in virtual environment (VE). Two main drawbacks exist in these techniques: (1) They will make uses weary in VE needs long distance physical navigation; (2) Modifying the field of view will decrease immersion. To this end, inspired by the rest frame hypothesis (Prothero, 1998; Prothero and Parker, 2003) and previous study on field of view (Fernandes and Feiner, 2016), the goal of this research is to evaluate the effect of rest frames -- portions of the virtual environment that remain fixed in relation to the real world and do not move as the user moves around -- on SS reduction. A study was performed in this research, in iv which all participants experienced two different VR sessions: one with rest frames and the other without rest frames. The rest frames were developed by using a trans- parent cockpit attached with a black metal net in our experimental environment. A questionnaire asking users' discomfort was shown periodically in the VE during the study, which allowed us to record the level of participants' comfort in real time. Par- ticipants were required to finish a Simulator Sickness Questionnaire (SSQ) (Kennedy et al., 1993) and a presence questionnaire (Slater et al., 1994) after completing either session, to analyze the influence of rest frames on presence and their overall sickness induced by VR. Through comparing the time spent in VE, the real-time subjects' discomfort levels and scores of SSQ and presence questionnaire from both sessions, we found that rest frames have advantages as follows: (1) Users could experience VEs without physical navigation; (2) Rest frames significantly helped users acclimate to VR; (3) The level of discomfort in VR was reduced; (4) The level of presence was not impacted. v To my parents who supported me, taught me the value of working with schedule and happiness, and provided me with the opportunity to receive a great education. To Dr. Regis Kopper and Dr. Jason Jerald who revealed the charm of virtual reality, and for their guidance, support, and ability to lend sound technical advice without a moments notice vi Contents Abstract iv List of Figures ix List of Abbreviations and Symbolsx 1 Introduction1 1.1 Motivation.................................2 1.2 Research Approach............................4 1.3 Research Questions............................5 1.4 Outline of Master's Thesis........................5 1.5 Summary.................................6 2 Literature Review7 2.1 Theories on Motion Sickness.......................8 2.1.1 Sensory conflict theory......................8 2.1.2 Postural instability theory....................9 2.2 Current Simulator Sickness Reduction Techniques........... 11 2.2.1 Motion simulation........................ 11 2.2.2 Visual Methods.......................... 12 2.2.3 Medication............................ 14 2.3 Rest Frame Hypothesis and Related Works............... 15 vii 3 Material and Method 17 3.1 Design and Implementation....................... 17 3.2 Equipment................................. 19 3.3 Procedure................................. 22 3.4 Participants and Groups......................... 23 4 Results and Analysis 26 4.1 Discomfort Score............................. 27 4.1.1 Interaction Effects........................ 27 4.2 Exposure Time.............................. 32 4.3 Simulator Sickness............................ 32 4.4 Presence.................................. 37 5 Discussion 39 6 Conclusion and Future Work 42 A SIMULATOR SICKNESS QUESTIONAIRE (SSQ) 44 B PRESENCE QUESTIONNAIRE 48 C VIDEO GAME EXPERIENCE QUESTIONNAIRE 50 D STATISTICS DATA 53 Bibliography 56 viii List of Figures 2.1 Neural mismatch model of sensory conflict theory........... 10 3.1 Rest frames (black metal net)...................... 19 3.2 No rest frames............................... 20 3.3 Map of Path with Arrows and Arches in Application......... 20 3.4 Question Shown at Each Waypoint................... 21 3.5 Waypoint in Virtual Environment.................... 21 3.6 Travel Paused and Question Shown at Waypoints........... 22 3.7 Out of Path Warnings.......................... 24 3.8 Seated study participant with Oculus and holding gamepad used for virtual navigation............................. 24 3.9 Design of two-session experiment.................... 25 4.1 Discomfort scores over time for individual participants and mean dis- comfort scores over waypoints by session................ 30 4.2 Mean discomfort scores over time by session. (Same color coding as Figure 4.1.)................................ 31 4.3 Number of participants finished all laps at each session........ 33 4.4 Overall SS score over two orderings................... 34 4.5 Cluster score over two orderings..................... 36 4.6 Presence score over two orderings.................... 37 ix List of Abbreviations and Symbols Abbreviations DS Discomfort Score FOV Field of view HMD Head Mounted Display MS Motion Sickness NR No Rest Frames PI Postural Instability RF Rest Frames SC Sensory Conflict SS Simulator Sickness. VR Virtual Reality VE Virtual Environment x 1 Introduction Virtual reality (VR) is rapidly being adopted in high-risk or high-cost environments for its capability in simulating real environment distinctly, modularizing the soft- ware used, creating additional worlds less expensively and ensuring controllability. For example, VR has been developed as a psychological therapy with which psy- chotherapists treat those patients with phobias, who require specific treatments that are hard to be achieved via regular methods in real world (Carlin et al., 1997; Miloff et al., 2016). In addition to employment in psychotherapy, VR also can act as an auxiliary remedy for rehabilitation (Borrego et al., 2016) or a substitute to simplify and reinforce traditional military, surgical or industrial trainings(Baumann, 1993; Seymour et al., 2002; Kozak et al., 1993). Despite the rising use of VR, and the boom in popularity within the mass con- sumer world, such as Oculus Rift, HTC Vive and Samsung Gear VR (OculusVR, 2016; HTCVive, 2016), all these advanced devices are facing a common problem -- simulator sickness (SS). Appliance of auxiliary devices, including walking simula- tors, also known as treadmills, and modification in field of view are proven significant success on SS reduction (Jaeger and Mourant, 2001; Fernandes and Feiner, 2016). 1 1.1 Motivation Current tactics of exacerbating SS can be summarized as two main styles: motion simulators (Mourant and Yin, 2010), which involve interaction techniques that allow users to receive vestibular stimulation, and modification of field-of-view (FOV), such as dynamic FOV restriction (Fernandes and Feiner, 2016). However, they to some extent also need extra investments on devices or sacrifice display fidelity. Motion simulators works well when the VE is small which does not require travel over long distances. However, problems emerge when users pass through a large scene such as a convoluted city. Long distance physical navigation, similar to a long-term hiking in real world, can cause users physical weariness and impair users` experience. The utilization of VR in military training requires much higher level of imitation to reality, which means any modifications on FOV may increase possibilities of judgments in critical tasks. Although the influence of motion simulators and modification of FOV have such potential shortcomings, we still cannot deny their effects on SS reduction. There should be a third option, that can alleviate SS without depending much on users vestibular systems