Force feedback to the hand is essential for enhancing immersion in VR and facilitating skill transfer. However, no existing method allows unconstrained hand and arm positions while keeping the fingertips free. We present a novel fingertip-free technique that induces directional force illusions on the entire hand by applying asymmetric vibrations to antagonistic dorsal and palmar tendons. Through two user studies, we demonstrate that directional accuracy is significantly above chance level under dual-point asymmetric vibration, in contrast single-point or symmetric vibration. By integrating effective haptic feedback with unconstrained hand interaction, our approach offers a promising avenue toward richer VR experiences.

We present a pseudo-haptic technique that modulates perceived weight in full-body virtual reality by jointly scaling virtual-hand motion and user viewpoint. Unlike prior study that manipulates the hand alone, our method leverages visual self-motion cues, extending pseudo-haptics beyond seated interactions. A threshold study isolated perceptually salient gains, and a within-subjects lifting experiment ($N=23$) crossed the two factors. Both manipulations significantly modulated perceived weight ratings ($p<.001$), and their effects combined additively. However, presence ratings declined specifically under conditions designed to produce strong lightness illusions-namely, when the virtual hand moved more than its real-world counterpart, while the virtual viewpoint moved less ($p_{\text {Holm }}<.05$). In contrast, when the virtual hand moved more slowly or matched the real hand's motion, manipulating the virtual viewpoint had relatively little impact on presence, which remained stable. Hand scaling thus serves as a low-cost primary cue and viewpoint manipulation as a complementary channel for modulating the perceived weight without sacrificing presence. The technique provides actionable guidance for VR training, rehabilitation, and exergames that demand convincing sensations of physical effort.

The mirroring effect has been demonstrated to facilitate smooth social interactions. Digital technology can automatically implement mirroring to achieve more natural interactions in contexts where spontaneous mirroring is challenging, such as remote human communication or dialogue with non-human agents. However, many existing automatic mirroring systems replicate a user’s movements with a time delay, and when applied to full-body interactions between human users, such systems often result in excessive and unnatural mimicry. To address this issue, this study examines the effectiveness of Co-embodiment, a technique that blends the movements of a user and their partner in real-time, as a method for achieving both the benefits of mimicry and the naturalness of interaction. We examined how varying the blending ratios (0%, 25%, 50%) affects social impressions in a two-person interaction in the VE. Results showed that moderate blending (25%, 50%) enabled natural and comfortable interactions, comparable to no blending (0%). However, we did not observe significant improvements in perceived closeness or trustworthiness. Semi-structured interviews helped explain these results, revealing that participants differed in their interpretations of subtle synchronized movements. Some viewed them as signs of mutual understanding or cooperation, while others experienced discomfort. In some cases, this discomfort seemed specific to virtual contexts, as subtle similarities made participants doubt the presence of a real human behind the avatar. These findings highlight that impressions depend on whether blended movements feel socially responsive or merely imitative, stressing the need for interaction designs that enhance the sense of social presence.

Redirected walking (RDW) is a method for exploring virtual spaces larger than physical spaces while preserving a natural walking sensation. Expanding the range of visual manipulation gains that can be applied without causing discomfort is necessary to apply RDW in practice. Ankle tendon electrical stimulation (TES) can expand the range by inducing body tilt sensation and sway. Therefore, in this study, we proposed a locomotion method that applies ankle TES to RDW. In Experiment 1, we evaluated the effect of TES on the detection threshold (DT), which is the maximal gain at which visual manipulation remains unnoticed. The results indicated that the DT was expanded when TES was applied to induce the body tilt sensation in the same direction as the RDW's visual manipulation. Specifically, the pooled mean of the DT was expanded by more than 18%. In Experiment 2, we evaluated the applicability, a supplementary index for assessing locomotion techniques. The results demonstrated that ankle TES mitigates the reduction of the applicability, especially under a curvature gain of $\pm 0.3 [m^{-1}]$±0.3[m-1].

The walking sensation is a result of the synthesis of multisensory inputs from various systems. The vestibular system, typically used for detecting acceleration, is a crucial component of the walking sensation. This study investigated the use of galvanic vestibular stimulation(GVS) to enhance the sensation of walking in virtual reality (VR) environments, particularly when users are seated and not engaged in active movements. GVS is a transcutaneous electric stimulation technique to evoke vestibular sensory responses and involves the application of a penetrating current to vestibular afferents. This study revealed that the pseudo-walking sensation can be intensified by applying lateral GVS. However, no difference was observed when it was synchronized with the walking rhythm represented by foot-sole vibration patterns. Furthermore, the study compares the effectiveness of lateral versus anterior-posterior GVS in enhancing walking sensations in VR. The findings provide novel perspectives on enhancing the VR walking experience through vestibular stimulation, even in scenarios in which the user is seated.

As a redirected walking technique, a method has been proposed to enable users to walk in an undulating virtual space even in a flat physical environment by setting the slope of the floor in the virtual environment to be different from that in the physical environment without causing discomfort. However, the slope range in which discrepancies between visual and proprioceptive sensations are not perceived is limited, restricting the slopes that can be presented. In this study, we proposed redirected walking using electrical stimulation of the Achilles and tibialis anterior muscle tendons, extending the applicable slope range of redirected walking without compromising the natural gait sensation. Electrical stimulation of the ankle tendons affects the proprioceptive sensation and gives the illusion of tilting in the standing posture, expanding the applicable slope range. Two experiments showed that the proposed method improved the experience of uphill and downhill walking in terms of the range of the virtual slope where a high naturalness of gait and a high congruency of visual and proprioceptive sensations are maintained. Notably, electrical stimulation of the Achilles tendons significantly improved the naturalness of the walking experience during virtual downhill walking, which has been considered more challenging in previous studies.

Pseudo-haptic techniques are used to modify haptic perception by appropriately changing visual feedback to body movements. Based on the knowledge that tendon vibration can affect our somatosensory perception, this article proposes a method for leveraging tendon vibration to enhance pseudo-haptics during free arm motion. Three experiments were performed to examine the impact of tendon vibration on the range and resolution of pseudo-haptics. The first experiment investigated the effect of tendon vibration on the detection threshold of the discrepancy between visual and physical motion. The results indicated that vibrations applied to the inner tendons of the wrist and elbow increased the threshold, suggesting that tendon vibration can augment the applicable visual motion gain by approximately 13% without users detecting the visual/physical discrepancy. Furthermore, the results demonstrate that tendon vibration acts as noise on haptic motion cues. The second experiment assessed the impact of tendon vibration on the resolution of pseudo-haptics by determining the just noticeable difference in pseudo-weight perception. The results suggested that the tendon vibration does not largely compromise the resolution of pseudo-haptics. The third experiment evaluated the equivalence between the weight perception triggered by tendon vibration and that by visual motion gain, that is, the point of subjective equality. The results revealed that vibration amplifies the weight perception and its effect was equivalent to that obtained using a gain of 0.64 without vibration, implying that the tendon vibration also functions as an additional haptic cue. Our results provide design guidelines and future work for enhancing pseudo-haptics with tendon vibration.

To capture a remote 3D image, conventional stereo cameras attached to a robot head have been commonly used. However, when the head and cameras rotate, the captured image in buffers is degraded by latency and motion blur, which may cause VR sickness. In the present study, we propose a method named TwinCam in which we use two 360° cameras spaced at the standard interpupillary distance and keep the direction of the lens constant in the world coordinate even when the camera bodies are rotated to reflect the orientation of the observer's head and the position of the eyes. We consider that this method can suppress the image buffer size to send to the observer because each camera captures the omnidirectional image without lens rotation. This paper introduces the mechanical design of our camera system and its potential for visual telepresence through three experiments. Experiment 1 confirmed the requirement of a stereoscopic rather than monoscopic camera for highly accurate depth perception, and Experiments 2 and 3 proved that our mechanical camera setup can reduce motion blur and VR sickness.

This paper describes a passive stimulation of a body to evoke a walking sensation using a vestibular and haptic device while the real body of the user is sitting. It imparts a pseudo body image to the user through the real (physical) body of the user as a part of the virtual reality (VR) display system. The created walking sensation was evaluated by nine factors to analyze the complex nature of the walking sensation.

The Five Senses Theatre project was established for the development of a basic technology that enables the user to relive a spatial motion of other persons as if the user him/her-self experienced it in person. This technology aims to duplicate a bodily experience performed in the real space and to pass it to the other person. In other words, the user experiences another person's body that moved in a real space as if the user moved in that real space. The spatial motion may be a walking tour to the world heritage, a legend run of a top athlete, and etc. More specifically, the system creates the sensation of a self-body motion without a voluntary motion of the user by providing physical motion to the real body. The sensation of self-body motion is generated by not only a visually induced vection but proprioceptive and tactile sensations of the body passively evoked. The Five Senses Theatre provides multisensory stimuli to the user to make use of the user's body as medium to project the valuable experience from others to the user's cognition. The research issues include the following: 1) Cognitive mechanism of passive stimulation perceived as an active motion sensation (pseudo agency), and body ownership transfer (virtual body). 2) Device development of the mutisensory display system, rendering/projection algorithms, and a lifelog data system.

The present paper describes the system to present a pseudo-walking sensation to a sitting participant. The vibration was added to the heel and toe to imitate cutaneous sensation of the sole during walking. The sound of footsteps was also provided to the participant through headphones simultaneously. In this sound presentation, we used a spatial sound of footsteps of another walker as well as own footstep sound. Another walker's sound was moved along several trajectories in a VR space. We conducted an experiment to elucidate the effect of third person's footstep sound moved differently on the walking sensation of a participant. The result showed that third person's sound enhanced not only walking sensation but also translational sensation of a sitting participant. Furthermore, the effect was the highest when third person's sound came from front to backward of the participant in a VR space.

This paper describes rendering characteristics of a virtual walk by a motion seat. The motion seat creates a small body motion in three dof (lift, roll, and pitch directions) to make the user feel as if the user him-/herself is walking despite sitting own body. We consider the actual self body is a medium to render the virtual body to share experiences of others by using the motion seat as part of the multisensory display. After setting the motion to optimally present a walking sensation, basic characteristics of perception levels of the virtual walk by the seat motion were measured and compared with those for a real walk. The result indicated that the perception levels of the virtual walk were around those of a real walk.

This paper describes an approach to interpolate the wind direction and velocity using two fans. Firstly, maps of the angle and velocity of the wind in relation to the speeds of the two fans are created. It was found that changes in the speeds of the two fans in the interpolation were not necessarily linear to the directional angles from the fans. Next, in the generation of wind, the speeds of the fans are inversely referenced from the maps using the target direction and velocity. An experiment confirmed that wind can be generated from an intermediate direction between the two fans. Through an evaluation using subjects, it was proven that a change in the direction of the wind could be recognized to some extent, although great differences in accuracy were observed among individuals.

We developed a computer-vision-based position and orientation tracking system for pedestrian navigation with a mobile haptic display. Our developed system tracks the user's hand and provides the user with a haptic directional cue for way-finding. An off-the-shelf web camera is rigidly affixed to the haptic display the user holds and faces the ceiling where fiducial markers are displayed. The three-dimensional position and orientation of the device can be calculated from the known position and orientation of the fiducial markers that appear in the captured image. The performance of the system was verified using simultaneous measurement comparisons with a high-precision commercial motion capture system.

We conducted a user study to clarify whether a tactile flow created by a matrix of vibrators in a seat pan simultaneously presented with an optical flow in peripheral vision enhances the perceived forward velocity of self-motion. A brief tactile motion stimulus consisted of four successive rows of vibration, and the inter-stimulus onset between the tactile rows was varied to change the velocity of the tactile motion. The experimental results show that the velocity of self-motion is significantly overestimated for rapid tactile flows and underestimated for slow tactile flows, compared with only optical flow or non-motion vibrotactile stimulation conditions.

This paper discusses the design of a knocking force display to induce the kinesthetic illusion of being pulled. Previously, we have found that when a hand-held object oscillates in the hand, if the acceleration pattern is lopsided, one feels a pulling force sensation, although the object does move in two opposite directions. Here, we designed and developed a new force display to generate two imbalanced acceleration patterns in opposing directions. In the display, an internal mass repetitively collides against a wall, to create a spikier pulse than the previous force display could produce. We determined the circumstances under which the sensation of being pulled was perceived by varying the pulse width, i.e., by attaching materials of different stiffnesses to the wall.

When visually impaired pedestrians walk from one place to another by themselves, they must update their orientation and position to find their way and avoid obstacles and hazards. We present the design of a new haptic direction indicator, whose purpose is to help blind pedestrians travel a path and avoid hazards intuitively and safely by means of haptic navigation. The haptic direction indicator uses a novel kinesthetic perception method called the "pseudo-attraction force" technique, which exploits the nonlinear relationship between perceived and physical acceleration to generate a force sensation. In an experiment performed to evaluate with the haptic direction indicator, we found that visually impaired users could safely walk along a predefined route at their usual walking pace, independent of the existence of auditory information. These results demonstrate the utility and usability of the haptic direction indicator, but there is still room for improvement.

This paper discusses the effect of acceleration profiles on the kinesthetic illusion of being pulled (pseudo-attraction force perception). We have found that when a hand-held object oscillates in the hands, if the acceleration pattern is lopsided, one feels a pulling force sensation, although the object does move in two opposite directions. Our previous findings indicate that the pulse frequency of a lopsided oscillation determines the effective generation of the pseudo-attraction force. The object of this study is to clarify the effect of pulse width and pulse interval on force perception at the pulse frequency. The experimental results suggest that (i) there were no significant difference between pulse widths as regards perceiving a pseudo-attraction force, and (ii) there was a depressive interaction between pulse width and pulse interval with respect to force perception.

We have proposed a haptic direction indicator that will help visually impaired pedestrians to travel a path and avoid hazards areas intuitively and safely by means of force-based navigation. The haptic direction indicator uses the pseudo-attraction force technique, which generates a pulling or pushing force in portable or mobile devices by exploiting the nonlinear relationship between perceived acceleration and physical acceleration. We have investigated the angular resolution of the pseudo-attraction force for the visually impaired in a static posture to design a practical haptic direction indicator. This paper describes a prototype of a crosshair haptic direction indicator based on our previous findings. An experiment was performed to clarify the perceptual characteristics when a visually impaired pedestrian is navigated by perceiving force sensation. The results show that most of the visually impaired participants could walk in a predetermined cardinal direction with the haptic direction indicator. Finally, we discuss the drawbacks of our system and design improvements.

When a small mass in a hand-held device oscillates along a single axis with asymmetric acceleration (strongly peaked in one direction and diffuse in the other), the holder typically experiences a kinesthetic illusion characterized by the sensation of being continuously pushed or pulled by the device. This effect was investigated because of its potential application to a hand-held, nongrounded, haptic device that can convey a sense of a continuous translational force in one direction, which is a key missing piece in haptic research. A 1 degree-of-freedom (DOF) haptic device based on a crank-slider mechanism was constructed. The device converts the constant rotation of an electric motor into the constrained movement of a small mass with asymmetric acceleration. The frequency that maximizes the perceived movement offered by the haptic device was investigated. Tests using three subjects showed that for the prototype, the best frequencies were 5 and 10 cycles per second.

When a small object in a hand-held device moves periodically and prismatically with asymmetric acceleration (strong in one direction and weak in the other), the holder typically experiences the kinesthetic illusion of being pushed or pulled continuously by the held device. We investigated this perceptual effect for its potential application to a hand-held, non-grounded, haptic device that can convey a sense of a continuous translational force in one direction, which is a yet missing tile in haptics research. A one-degree of freedom haptic device based on two symmetric slider-crank mechanism was constructed to convert the single-speed rotational cyclic movement of a motor into asymmetric translational cyclic movement with asymmetric acceleration and to cancel unwanted side acceleration. We verified our previous results with the haptic device and investigated the effect of the gross weight of the device on force perception.