Feasibility of a walking virtual reality system for rehabilitation: objective and subjective parameters

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.

Comparison of Oculus Rift and HTC Vive: Feasibility for Virtual Reality-Based Exploration, Navigation, Exergaming, and Rehabilitation

“…At each point of the grid, accuracy (e) was estimated as the mean difference between the position of the HMD measured in the real world and its estimated position. Jitter (j) was calculated as the standard deviation in the estimated position in the time interval as follows 17 :…”

“…The HMDs were sequentially placed in all the grid's intersection and border points (121 points in total) at 1.7 and 1.3 m, the approximate heights of a subject's head in the standing and sitting positions, respectively, using a spe-cially designed device that prevented movement and allowed height adjustment. 17,20 For the points where tracking data were available, the positions of both HMDs, always oriented in the Àŷ direction ( Fig. 2), were registered for 5 seconds at 50 Hz.…”

“…From the clinical point of view, the possibility to move and walk as in the real world could maximize the ecological validity of virtual environments and tasks that require users to move, such as walking and navigating simulations or exergaming and serious games for motor rehabilitation. [14][15][16][17] These tasks could also increase skill transference from the virtual to the real world. 18 Although the HMDs' tracking features might be determinant for these applications, their characteristics and feasibility still remain unknown.…”

Virtual reality in medicine: a brief overview and future research directions

“…The development of VR in recent years has resulted in the emergence of many different systems, including the CAVE-type environments. The CAVE system, also called a 'virtual cave,' allows for placing the patient in the 'centre of the virtual world' [25]. The user has the impression of being present in the world generated by computers.…”

The New Era of Virtual Reality Locomotion: A Systematic Literature Review of Techniques and a Proposed Typology

“…The user's position and orientation are determined, usually by tracking the HMD's position [22,33] or the user's limb movements [44,46,50].…”