Measurement Accuracy of the HTC VIVE Tracker 3.0 Compared to Vicon System for Generating Valid Positional Feedback in Virtual Reality.

For realistic and reliable full-body visualization in virtual reality, the HTC VIVE Tracker could be an alternative to highly complex and cost- and effort-intensive motion capture systems such as Vicon. Due to its lighter weight and smaller dimensions, the latest generation of trackers is proving to be very promising for capturing human movements. The aim of this study was to investigate the accuracy of the HTC VIVE Tracker 3.0 compared to the gold-standard Vicon for different arrangements of the base stations and various velocities during an athletic movement. Therefore, the position data from three trackers attached to the hip, knee and ankle of one sporty participant were recorded while riding a bicycle ergometer at different pedaling frequencies and different base station arrangements. As parameters for the measurement accuracy, the trajectories of the linear motion of the knee and the circular motion of the ankle were compared between VIVE and Vicon by calculating the spatial distance from the raw data at each point in time. Both the pedaling frequency and the arrangement of the base stations significantly affected the measurement accuracy, with the lowest pedaling frequency of 80 rpm and the rectangular arrangement recommended by the manufacturer showing the smallest spatial differences of 10.4 mm ± 4.5 mm at the knee and 11.3 mm ± 5.1 mm at the ankle. As the pedaling frequency increased gradually (120 rpm and 160 rpm), the measurement accuracy of the trackers per step decreased less at the knee (approximately 5 mm) than at the ankle (approximately 10 mm). In conclusion, the measurement accuracy for various athletic skills was high enough to enable the visualization of body limbs or the entire body using inverse kinematics in VR on the one hand and, on the other hand, to provide initial insights into the quality of certain techniques at lower speeds in sports science research. However, the VIVE trackers are not suitable for exact biomechanical analyses.

Gymnastic skills on a balance beam with simulated height.

Virtual reality (VR) is a valuable tool for simulating dangerous situations and training under these conditions with a reduced possibility of injury. This could be beneficial within different sports scenarios. In gymnastics, the height of the balance beam can be dangerous and frightening, especially for beginners. Here, a simulated height can reduce the participant's risk of injury and facilitate entry to balance beam gymnastics. However, the investigation of sports performance in a virtual environment is rare. Therefore, the current study aims to compare beginners' performance in balance beam tasks between the real world (RW) and VR. 34 sports students executed gymnastic balancing forward, backward and the extension of one leg to the front, the side and the back on a regular balance beam in the RW and on a balance beam with simulated height in VR (using a head-mounted display). We analyzed beginners' performance in both conditions (RW and VR) regarding different criteria for each balance beam task. Statistical analyses show significant differences in performance with better results in RW (p < .05). Especially the body tension and the upper body posture were superior in RW. One explanation can be the more difficult regulation of the balance in VR. For the tasks where the motion took part in a fixed position on the beam, the further performance aspects were similar for RW and VR. When the participants moved along the beam, further performance aspects, like the leg extension, were better in RW. In total, the participants executed the VR balance beam tasks with decreased danger of injury due to the simulated height of the balance beam, but their performance was slightly limited. We conclude that for the first contact with the height of a balance beam, VR is a suitable tool to reduce the danger of injury occurring from falling off the beam and facilitate entry to balance beam gymnastics.

Influence of body visualization in VR during the execution of motoric tasks in different age groups.

Virtual reality (VR) has become a common tool and is often considered for sport-specific purposes. Despite the increased usage, the transfer of VR-adapted skills into the real-world (RW) has not yet been sufficiently studied, and it is still unknown how much of the own body must be visible to complete motoric tasks within VR. In addition, it should be clarified whether older adults also need to perceive their body within VR scenarios to the same extent as younger people extending the usability. Therefore, younger (18-30 years old) and elderly adults (55 years and older) were tested (n = 42) performing a balance-, grasping- and throwing task in VR (HMD based) accompanied with different body visualization types in VR and in the RW having the regular visual input of body's components. Comparing the performances between the age groups, the time for completion, the number of steps (balance task), the subjective estimation of difficulty, the number of errors, and a rating system revealing movements' quality were considered as examined parameters. A one-way ANOVA/Friedmann with repeated measurements with factor [body visualization] was conducted to test the influence of varying body visualizations during task completion. Comparisons between the conditions [RW, VR] were performed using the t-Tests/Wilcoxon tests, and to compare both age groups [young, old], t-Tests for independent samples/Mann-Whitney-U-Test were used. The analyses of the effect of body visualization on performances showed a significant loss in movement's quality when no body part was visualized (p < .05). This did not occur for the elderly adults, for which no influence of the body visualization on their performance could be proven. Comparing both age groups, the elderly adults performed significantly worse than the young age group in both conditions (p < .05). In VR, both groups showed longer times for completion, a higher rating of tasks' difficulty in the balance and throwing task, and less performance quality in the grasping task. Overall, the results suggest using VR for the elderly with caution to the task demands, and the visualization of the body seemed less crucial for generating task completion. In summary, the actual task demands in VR could be successfully performed by elderly adults, even once one has to reckon with losses within movement's quality. Although more different movements should be tested, basic elements are also realizable for elderly adults expanding possible areas of VR applications.

Effects of body visualization on performance in head-mounted display virtual reality.

Although there are many virtual reality (VR) applications in sports, only a handful of studies visualized the whole body. There is still a lack of understanding, how much of the own body must be visualized in the head-mounted display (HMD) based VR, to ensure fidelity and similar performance outcome as in the real-world. In the current study, 20 young and healthy participants completed three tasks in a real and virtual environment: balance task, grasping task, and throwing task with a ball. The aim was to find out the meaning of the visualization of different body parts for the quality of movement execution and to derive future guidelines for virtual body presentation. In addition, a comparison of human performance between reality and VR, with whole-body visualization was made. Focusing on the main goal of the current study, there were differences within the measured parameters due to the visualization of different body parts. In the balance task, the differences within the VR body visualization consisted mainly through no-body visualization (NB) compared to the other visualization types defined as whole-body (WB), WB except feet (NF), as well as WB except feet and legs (NLF). In the grasping task, the different body visualization seemed to have no impact on the participants' performances. In the throwing task, the whole-body visualization led to higher accuracy compared to the other visualization types. Regarding the comparison between the conditions, we found significant differences between reality and VR, which had a large effect on the parameters time for completion in the balance and grasping task, the number of foot strikes on the beam in the balance task, as well as the subjective estimation of the difficulty for all tasks. However, the number of errors and the quality of the performances did not differ significantly. The current study was the first study comparing sports-related tasks in VR and reality with further manipulations (occlusions of body parts) of the virtual body. For studies analyzing perception and sports performance or for VR sports interventions, we recommend the visualization of the whole body in real-time.

How are cognitive and physical difficulty compared?

Tasks that require less physical effort are generally preferred over more physically demanding alternatives. Similarly, tasks that require less mental effort are generally preferred over more mentally demanding alternatives. But what happens when one must choose between tasks that entail different kinds of effort, one mainly physical (e.g., carrying buckets) and the other mainly mental (e.g., counting)? We asked participants to choose between a bucket-carrying task and a counting task. Our participants were less likely to choose the bucket task when it required a long reach rather than a short reach, and our participants were also less likely to choose the bucket task the smaller the final count value. We tested the hypothesis that subjective task durations provided a common currency for comparing the difficulties of the two kinds of tasks. We found that this hypothesis provided a better account of the task choice data than did an account that relied on objective task durations. Our study opens the door to a new problem in the study of attention, perception, and psychophysics-judging the difficulty of different kinds of tasks. The approach we took to this problem, which relies on two-alternative forced choice along with modeling the basis for the choice, may prove useful in future investigations.