Around the (Virtual) World

Infinite Walking in Virtual Reality Using Electrical Muscle Stimulation

Paper by Jonas Auda, Max Pascher, and Stefan Schneegass.

Link to the paper: https://doi.org/10.1145/3290605.3300661

This work will be presented at CHI 2019, Glasgow at 7th May 2019, 11 am during the Virtual Reality session (https://chi2019.acm.org/).

Virtual worlds are infinite environments in which the user can move or walk around freely. Currently, users use handheld controllers to walk in virtual environments. This artificial way of walking poses the risk of breaking the immersion of the user in the virtual experience. Up to now this was, however, the most practical solution, since, when shifting from controller-based movement to regular walking, spatial properties of the real world limit the virtual world. For example, the size of the room the user is in while interacting with the VR world highly influences the VR scenery.

Figure 1: The Infinite Walker System with the Step Detector below the foot of the user. The EMS electrodes attached to his leg. The Oculus GO to see the virtual environment and the OptiTrack camera system to track the movement of the user while he is walking (staged scene).

We tackled this challenge by proposing the use of EMS to reduce the necessary real-world space to create an unlimited walking experience in VR environments. To do so, electrical signals were used to actuate the user’s legs in a way that users unnoticeably deviate from their straight route and, thus, walk in circles in the real world while still walking straight in the virtual world. We compared this approach to vision shift (i.e., a state-of-the-art approach that slightly shifts the vision of the user to one direction so that the user walks in circles to correct this shift) as well as a combination of both approaches. The results show that particularly combining both approaches yield high potential to create an infinite walking experience.

Electrical Muscle Stimulation

We chose to use EMS to create the experience of an unlimited walking in virtual reality, because EMS lets the user perform certain movements by actuating muscles through an electrical signal. This signal is applied via self-adhesive electrodes to the body of the user mimicking the signal generated by the human body itself (see setup in Figure 1). This allows for artificial influence and control of certain movements of a user. In particular, we slightly twist the legs outwards by actuating the sartorius muscle so that the user unnoticeably walks in circles instead of in a straight line.

While current methods either use room-sized setups (e.g., Cyberith Virtualizer) or modify the visual experiences (e.g., vision shift), EMS is an on-body system that requires relatively low energy to actuate the legs of the user.

Evaluation

To evaluate our system we conducted a user study comparing the EMS approach to the vision shift approach, as well as evaluated a combination of both (EMS and vision shift).

Figure 2: The VR scene we used for the system evaluation. The user can walk between two rows of trees.

In this evaluation, the users were walking through an alley of trees in virtual reality (see Figure 2). They could naturally walk down this alley while we manipulated their view (vision shift), actuated their legs (EMS), or both to let them walk infinitely in VR.

Figure 3: Left: The top view on the path one user was walking while the vision was shifted slightly to the left. The user was walking almost in a perfect circle. Middle: The user was walking while EMS actuated the left leg. The path is not that circular anymore, but one can see semicircles. Right: The combination of the shifted vision and the EMS reduced the space needed for walking in a circle drastically compared to the other paths.

We analyzed the walking paths for all participants in all three conditions (see Figure 3: Shift: left, EMS: middle, Shift + EMS: right). The results show that the combination of both EMS and vision shift reduced the space needed for walking drastically as shown on the right-hand side of Figure 3.

Conclusion

With this approach, we provided an additional mean to enrich the experience of large virtual environments in limited real-world environments. While providing a basic method in this very first step, future systems might build upon this to provide an illusion of a truly endless environment.

Future Work

While this project focuses on walking straight, future work could investigate how EMS can be used to enable users to freely walk in virtual reality. As soon as a user approaches an obstacle (e.g., a wall), EMS is actuating the user in a way that he or she starts walking a circle.

Further readings:

Max Pfeiffer, Tim Dünte, Stefan Schneegass, Florian Alt, and Michael Rohs. 2015. Cruise Control for Pedestrians: Controlling Walking Direction using Electrical Muscle Stimulation. In Proceedings of the 33rd Annual ACM Conference on Human Factors in Computing Systems (CHI ‘15). ACM, New York, NY, USA, 2505–2514. DOI: https://doi.org/10.1145/2702123.2702190

Stefan Schneegass, Albrecht Schmidt, and Max Pfeiffer. 2016. Creating user interfaces with electrical muscle stimulation. Interactions 24, 1 (December 2016), 74–77. DOI: https://doi.org/10.1145/3019606