We found that an illusory force of the finger was induced in flexion and extension direction by applying electrical stimulation to the proximal phalanx of the finger of the palm and dorsal sides. In this paper, we investigated illusory force directions when changing the polarity of electrical stimulation and finger posture. The force sensation was also evaluated quantitatively under conditions in which the largest extension and flexion force illusions were induced. As a result, this force illusion had a relatively large dependency on the finger posture. We found that our approach could induce force sensation from 1 N to 2 N in both directions.

Electrical muscle stimulation (EMS)-based systems have been proposed in human augmentation studies for augmenting motor skills while playing sports and musical instruments. Healthy people with such EMS-based systems perform voluntary muscle contractions while the EMS is superimposed on their muscles. However, few studies have investigated the effect superimposed electrical stimulation has on voluntary contractions for muscle coordination (i.e., the intentional, orchestrated movement of multiple body parts) in particular. Therefore, we investigate the effect of superimposed electrical stimulation on muscle coordination when users perform maximal grip force, in which muscle coordination of the forearm and shoulder muscles occurs. We conducted a user study with 20 participants to assess the effect by measuring their maximal grip force under three conditions: no-EMS, EMS application to the forearm, and EMS application to the shoulder. The mean results were 33.4 kgw (327 N) for no-EMS, 30.9 kgw (303 N) for EMS to the forearm, and 32.4 kgw (318 N) for EMS to the shoulder, and the medians were 34.7 kgw (340 N), 30.3 kgw (296 N), and 33.5 kgw (328 N), respectively. We determined that electrical stimulation superimposed on muscle coordination diminished grip force, and the effect size differed depending on where EMS was applied. The results suggest that we should consider users’ muscle coordination when designing EMS-based systems for human augmentation to avoid unintentionally diminishing their ability.

The stochastic resonance phenomenon has been proposed to improve the tactile sensitivity of a finger by presenting a weak vibration on the fingernail. In the present study, we focused on the spread of sensory nerve action potentials in order to further strengthen the effect of the stochastic resonance phenomenon caused by vibration stimulation on the nail on improving tactile sensitivity. When a stimulus is presented to the hand, sensory nerve action potentials spread from the target nerve at the stimulation site to another adjacent nerve. Therefore, in order to verify the effect of improving tactile sensitivity by spread from the ulnar nerve to the median nerve, we conducted a test piece detection test with the middle finger when a vibration stimulus was presented on the nail of the little finger or ring finger. As a result, it was obtained that vibration stimulation on the ring fingernail affects the tactile sensitivity of the middle finger, suggesting that it is possible to reduce the constraint of the vibrator on fingers that are frequently used in manual work.

GVS expects a current path along the direction of display vestibular sensation, and by applying a penetrating current to the vestibular organs, it achieves vestibular sensory presentation in that direction. Conventional GVS method, for presentation the sensation of rotation around the Roll axis, is also cased the sensation of rotation around the Yaw axis. It is a reason that it is caused by wraparound current flow in an unexpected direction, in addition to the sensation of rotation around the Roll axis. In this paper, in order to suppress the sensory impression in the secondary direction, we proposed a method of suppressing the current by shorting between electrodes and succeeded in maintaining the amount of roll axis rotation while suppressing the sensation of Yaw axis rotation.

In previous studies, GVS has achieved vestibular sensory presentation by applying a penetrating current to the vestibular organs in the direction in which vestibular sensation is desired to be presented. However, currents in the head have taken only limited current pathways due to impedance gradients, and as a result, the direction of vestibular sensation presentation has been limited. In this paper, we propose a new method of presenting vestibular sensory based on current pathways, which is time-division multiplexing of multiple basis vectors. The method extends the direction of vestibular sensory presentation, which has been limited by current pathways. By using the method, simultaneous energization of multiple current sources and current pathways can be avoided, and it is expected that mutual interference between them can be avoided. In addition, we succeeded in separating anisotropy of body sway and of vestibular sensitivity to GVS, which have not been discussed in vestibular sensory presentation display with GVS.

Head-up display (HUD) is a technology that is expected to be applied to automotive driver assistance. While driving, drivers input visual information into their brains by turning their eyes from the road environment to the HUD image. We investigated whether the time required for this eye-turning process is influenced by the HUD projection method. We found that the virtual image projection tended to take longer than the real image projection. The reason is probably that the positional relationship between the display body and the HUD image affected the spatial localization of the image.

We examined the effects of hand avatar and grasping on vection. The scene that an observer moves upward in the space surrounded by many buildings was simulated. The virtual hand corresponding to the observer’s real hand movement was presented. The observer grasped the cylindrical object by both the virtual and real hand. The virtual grasping object connected to many balloons that evokes floating to sky. The real grasping object was pulled upward using a weight and two pulleys. The force to real hand was modified by changing weight or not grasping the real object. We found that virtual hand avatar (hand, cylindrical object, and balloons) and the force to real hand shortened the vection latency and increased the vection duration and subjective strength. This result suggests that increasing the consistency between visual stimuli and observer’s body movement in semantic meaning facilitates vection.

To reproduce haptic sensations with slightly varying roughness, we propose a robust approach based on a three-dimensional (3D) surface image captured by a 3D microscope. This approach had a good effect on the reproduction of sandpaper. To confirm the versatility of other materials, this study attempts to reproduce the soft skin model and compare the reproduction effects of conventional and proposed approaches. The skin models were commercially available and prepared by copying the cheek skin of females in three age groups. Experiments were conducted under conditions in which only skin models were reproduced, and skin models and sandpapers with similar roughness were simultaneously reproduced. The results revealed that the proposed approach is effective in reproducing not only the macroscopic difference between sandpaper and skin models but also the fine difference in roughness within either of them with good reproducibility and discernibility.

In this research, we proposed VR content with a function to feed back the state of conducting, with the aim of making the experienced person aware of the fun and difficulty of conducting. Focusing on the expression by the movement of the arm, which is the basis of conducting, the tempo of conducting is carved while drawing a figure with the right hand, and the left hand has the role of controlling the strength of the sound. Audiovisual measures were taken to make the experienced person aware of whether the four-beat conductor is swinging accurately or not. Visually, the conductor’s baton and the trajectory depicted by the experiencer are presented in the VR space. The color of the trajectory is changed according to the number of times it is swung accurately, and the shape and color of the trajectory are changed when it fails. Also, aurally, the music will be disturbed when it fails.

Two fingers coming into contact with each other at the same speed sometimes produces the sensation of contact with a flat rigid surface. This illusory sensation is considered to be caused by skin deformation and kinesthesia similar to those that would be produced by contact with a hard surface. We speculated that it would be possible to produce the same tactile sensation as that of contact with a flat rigid plate by placing a soft sphere with the same curvature and hardness as a finger against a finger and moving it at a speed equal to that of the finger. We conducted an experiment to verify the modulation effect of perceived curvature by comparison with various curvature samples. In addition, we developed a prototype of an encountered-type haptic display using this illusion and verified the applicability of the illusion.

The robotic limbs using a body remapping approach often followeither a user’s reference frame 1) fixed outside a user’s body (Space frame), 2) centered on a user’s torso (Torso frame), or 3) centered on a user’s head (Head frame). In this study, we investigate the effect of the reference frame on the embodiment of robotic limbs and the user’s motor control process. We asked 12 participants to perform point-to-point tasks with the virtual robotic limbs remapped to the participants’ feet. The virtual robotic limb tips followed the participants’ feet and each reference frame condition (Space frame, Torso frame, and Head frame). As a result, we found higher task performance in the Torso frame condition than the Head frame condition on the reaction time and movement straightness of the virtual robotic limbs. The virtual robotic limbs’ movement straightness and jerk based on the natural human behavior showed that participants manipulated the virtual robotic limbs as their own body in the Torso frame condition. The sense of agency and body ownership showed that the reference frame condition affected their occurrence and attribution.

Various haptic devices for application to virtual reality have been developed. Most of them have to be stationary on a desk, thus users cannot move around. To overcome this shortcoming, we propose a wearable force feedback device that uses air jet. In this paper, a prototype for hand position guidance which is able to provide force in any direction is developed, and its performance to guide the wearer’s hand is evaluated by experiments.

This study comprehensively evaluates the user experience of walking in a virtual space in a seated position. Walking is a common means of transportation in virtual reality (VR), and research has been conducted on devices for walking in virtual space (locomotion interface) or devices for presenting the walking sensation. However, there has been little research on the appropriate use of these devices in contents. In this experiment, the effects of walking sensation presentation (using motion platform), foot-stepping locomotion interface, and virtual walkers on the user experience were examined with the aim of using them in VR contents. As a result, it was found that each element has various effects on the user experience, and it is important to select devices and components of the virtual space according to the production intention when creating virtual walking contents.