Many haptic feedback methods have been proposed to enhance realism in virtual reality (VR). However, friction on the feet in VR, which renders feedback as if walking on different terrains or ground textures or stepping on objects is still less explored. Herein, we propose a wearable device, FrictShoes a pair of foot accessories, to provide multilevel nonuniform friction feedback to feet. This is achieved by the independent functioning of six brakes on six wheels underneath each FrictShoe, which allows the friction levels of the wheels from each to be either matched or to vary. We conducted a magnitude estimation study to understand users' distinguishability of friction force magnitudes (or levels). Based on the results, we performed an exploratory study to realize how users adjust and map the multilevel nonuniform friction patterns to common VR terrains or ground textures. Finally, a VR experience study was conducted to evaluate the performance of the proposed multilevel nonuniform friction feedback to the feet in VR experiences.

For haptic guidance, vibrotactile feedback is a commonly-used mechanism, but requires users to interpret its complicated patterns especially in 3D guidance, which is not intuitive and increases their mental effort. Furthermore, for haptic guidance in virtual reality (VR), not only guidance performance but also realism should be considered. Since vibrotactile feedback interferes with and reduces VR realism, it may not be proper for VR haptic guidance. Therefore, we propose a wearable device, GuideBand, to provide intuitive 3D multilevel force guidance upon the forearm, which reproduces an effect that the forearm is pulled and guided by a virtual guider or telepresent person in VR. GuideBand uses three motors to pull a wristband at different force levels in 3D space. Such feedback usually requires much larger and heavier robotic arms or exoskeletons. We conducted a just-noticeable difference study to understand users’ force level distinguishability. Based on the results, we performed a study to verify that compared with state-of-the-art vibrotactile guidance, GuideBand is more intuitive, needs a lower level of mental effort, and achieves similar guidance performance. We further conducted a VR experience study to observe how users combine and complement visual and force guidance, and prove that GuideBand enhances realism in VR guidance.

Force feedback is commonly used to enhance realism in virtual reality (VR). However, current works mainly focus on providing different force types or patterns, but do not investigate how a proper point of application of force (PAF), which means where the resultant force is applied to, affects users' experience. For example, users perceive resistive force without torque when pulling a virtual bow, but with torque when pulling a virtual slingshot. Therefore, we propose a set of handheld controllers, ElastiLinks, to provide force feedback between controllers with dynamic PAFs.A rotatable track on each controller provides a dynamic PAF, and two common types of force feedback, resistive force and impact, are produced by two links, respectively. We performed a force perception study to ascertain users' resistive and impact force level distinguishability between controllers. Based on the results, we conducted another perception study to understand users' distinguishability of PAF offset and rotation differences. Finally, we performed a VR experience study to prove that force feedback with dynamic PAFs enhances VR experience.