Abstract
BackgroundEven though virtual reality (VR) is increasingly used in rehabilitation, the implementation of walking navigation in VR still poses a technological challenge for current motion tracking systems. Different metaphors simulate locomotion without involving real gait kinematics, which can affect presence, orientation, spatial memory and cognition, and even performance. All these factors can dissuade their use in rehabilitation. We hypothesize that a marker-based head tracking solution would allow walking in VR with high sense of presence and without causing sickness. The objectives of this study were to determine the accuracy, the jitter, and the lag of the tracking system and its elicited sickness and presence in comparison of a CAVE system.MethodsThe accuracy and the jitter around the working area at three different heights and the lag of the head tracking system were analyzed. In addition, 47 healthy subjects completed a search task that involved navigation in the walking VR system and in the CAVE system. Navigation was enabled by natural locomotion in the walking VR system and through a specific device in the CAVE system. An HMD was used as display in the walking VR system. After interacting with each system, subjects rated their sickness in a seven-point scale and their presence in the Slater-Usoh-Steed Questionnaire and a modified version of the Presence Questionnaire.ResultsBetter performance was registered at higher heights, where accuracy was less than 0.6 cm and the jitter was about 6 mm. The lag of the system was 120 ms. Participants reported that both systems caused similar low levels of sickness (about 2.4 over 7). However, ratings showed that the walking VR system elicited higher sense of presence than the CAVE system in both the Slater-Usoh-Steed Questionnaire (17.6 ± 0.3 vs 14.6 ± 0.6 over 21, respectively) and the modified Presence Questionnaire (107.4 ± 2.0 vs 93.5 ± 3.2 over 147, respectively).ConclusionsThe marker-based solution provided accurate, robust, and fast head tracking to allow navigation in the VR system by walking without causing relevant sickness and promoting higher sense of presence than CAVE systems, thus enabling natural walking in full-scale environments, which can enhance the ecological validity of VR-based rehabilitation applications.
Highlights
Even though virtual reality (VR) is increasingly used in rehabilitation, the implementation of walking navigation in VR still poses a technological challenge for current motion tracking systems
Instrumentation Walking VR system The experimental system presented in this paper consisted of 1) an head mounted display (HMD), the Oculus DK2 (Oculus VR, Irvine, CA); 2) a RGB camera, the PlayStation®Eye Camera (Sony® Corporation, Tokyo, Japan) with an additional lens (4.3 mm, 70° FOV); 3) a pattern of markers fixed to the ceiling at 2.65 cm of height; 4) and a laptop (Fig. 1)
This paper presents an experimental VR system that enables head tracking through a fiducial marker-based solution, accurate, robust, and fast enough to allow natural navigation in the virtual environment (VE) by walking in the real world without causing relevant sickness or vertigo
Summary
Even though virtual reality (VR) is increasingly used in rehabilitation, the implementation of walking navigation in VR still poses a technological challenge for current motion tracking systems. Different metaphors simulate locomotion without involving real gait kinematics, which can affect presence, orientation, spatial memory and cognition, and even performance. All these factors can dissuade their use in rehabilitation. The technologymediated simulation of enriched environments and the provision of controlled sensory stimulation enable immersion in potentially hazardous and ecologically valid environments. These characteristics can be specially interesting for rehabilitation because they may allow to exceed the boundaries of the clinical setting and provide customized training to each participant [5, 6]
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