安価なHMDの発売に始まり，モデルの更新もあり，視聴覚のVR体験は飛躍的に向上しました．バーチャルリアリティの用途もエンタテインメントのみならず，リハビリやメンタルセラピーなどの医療分野，スポーツトレーニング，コミュニケーションなど多岐に渡ります．特にコロナ禍においては，遠隔での教育やコミュニケーションの手法としてメタバース空間が利用され，VR体験の質向上が求められました．各体験の質を向上させる手法として複数の感覚を提示するマルチモーダルや，複数の感覚を提示することで，新たな感覚を知覚させるクロスモーダルが用いられ，注目されています．

このような背景のもと，本特集も2018年以来の3回目となり，VRへの応用を見据えたマルチモーダル/クロスモーダルの基礎研究から，マルチモーダル/クロスモーダルを用いたVR体験や応用研究に関する基礎論文，コンテンツ論文，総説論文を広く募集しました．募集の結果，11件（基礎研究5件，応用研究5件，コンテンツ1件）と多くの投稿をいただき，本分野の研究が活発に行われていることを強く感じました．厳正なる査読の結果，7件採択，3件返戻，1件取り下げとなりました．採択論文の内訳は，基礎論文4件，応用論文3件でした．いずれの論文も査読者の皆さまとの建設的な議論を経て非常にクオリティの高いものが出揃ったと考えています．今回の特徴としては，触覚や体性感覚を利用した新たな体験や人間の知覚に関する研究が多く投稿され，多くの研究者がこれらの感覚に着目していることが伺えました．

最後に，本特集にご投稿いただきました著者の皆様，査読を引き受けてくださった皆様，ならびに本特集号の機会を与えていただきました論文委員会の皆様，その他関係者の皆様に心よりお礼申し上げます．

We explored how augmented reality (AR) can reduce motion sickness during unpredictable vehicle movements by overlaying precise motion prediction cues onto real environments. Participants highly susceptible to motion sickness viewed video see-through images on head-mounted displays and were exposed to varying rotational patterns to block motion anticipation. AR-based motion prediction cues showing rotation direction and stopping points were used to reduce conflicts between predicted and actual multimodal sensations, including visual, vestibular, and somatosensory sensations, which often cause motion sickness. The AR-based motion prediction cues significantly reduced motion sickness. Future research should evaluate the effectiveness of multimodal sensory presentation in reducing motion sickness.

In recent years, various attempts have been made to create immersive experiences by combining electric wheelchairs, used as motion platforms (MP), with Virtual Reality (VR) visuals presented through Head Mounted Displays (HMDs). However, due to constraints posed by the size of the physical space and safety considerations, it is challenging to directly map the movement and speed of the virtual space in VR to the physical space. Therefore, designing a more immersive VR experience requires appropriately designing the VR ride’s trajectory, considering the speed and safety constraints of the physical space and the MP. This study focuses on the teacup ride, a classic amusement park attraction, as the VR experience to be provided. We investigated the trajectory for constructing a VR ride that combines HMDs and electric wheelchairs. We compared and evaluated nine different wheelchair trajectories by altering the translational and rotational speeds in the VR visuals by factors of 1, 0.5, and 0.The results suggest that the wheelchair trajectory, which incorporates the rotational speed present in the teacup VR visuals, does not significantly diminish passengers’ consistency evaluations even when the translational speed is reduced.

We focused on the residual numbness sensation experienced after receiving vibration stimulation for a particular duration. In this study, we investigated the conditions conducive to numbness occurrence and the intensity of numbness and its duration under those conditions. Our findings revealed that numbness occurred and vibration perception diminished following vibration exposure for 40 to 80 seconds, gradually subsiding within 10 to 30 seconds post-stimulation. Additionally, we observed that after 10 seconds from the onset of numbness, stimuli below 10 dB were less perceptible due to residual numbness, whereas vibration perception remained intact for stimuli above 20 dB. Although this experiment primarily assessed the impact of numbness on vibration perception, exploring its effects on tactile sensations beyond vibration perception could broaden the potential applications and interactions, considering the optimal vibration exposure time and duration of residual numbness identified in this study.

A hit-stop is a technique used mainly in fighting games to highlight the impact felt by a player when the target’s movement temporarily pauses at the moment of contact. This technique can induce a sense of pseudo-impact in users when applied in virtual reality (VR). However, previous studies have only looked at its effects on a single user, leaving the impact of hit-stops on multiple users in a shared virtual environment unexamined. Concerns exist that hit-stops might cause discomfort and degrade the VR experience due to unpredictable movements of other players. This study aims to explore how hit-stops affect user discomfort in multi-user VR and whether presenting hit-stops asymmetrically can reduce such discomfort. We conducted an experiment where two players engaged in a virtual tennis rally under four conditions: each player’s hit-stop adjusted motion (symmetric condition) or real motion (asymmetric condition) shown to the opponent, and the opponent’s hit-stop adjusted or real motion shown to the player. The findings indicated that asymmetric presentation of hit-stops can alleviate discomfort with the other player while still providing a pseudo-impact sensation.

In this study, we proposed to promote the user’s motivation to start work using multiple virtual agents to present their behaviors and include (good or bad) familiarity with the user as a social relationship. For the verification, we used the agent that represented the relationship in terms of the color of its clothing. Based on balance theory and cognitive dissonance theory, we hypothesized that the agents’ presence, relationship with the user, and behavior would change the user’s motivation to start work. As a result of the verification, we found that presenting agents in a good relationship with the user engaging in work improves the user’s motivation to start work.

To enhance the flexibility of haptic feedback in virtual reality (VR), hand redirection (HR) has been introduced to alter the virtual position of the hand from its real position. To extend the applications of HR, it is necessary to broaden the detection threshold (DT), the maximum shift that can be applied without the user noticing. We propose a method to increase the DTs of HR by boosting visual dominance in the integration of vision and proprioception, achieved by introducing noise to proprioception through weak Gaussian white noise electrical stimulation. A user study with 22 participants demonstrated that this noisy electrical stimulation significantly increases the DTs of HR. Participants generally found the electrical stimulation tolerable, and it did not negatively impact their sense of embodiment or presence.

In this study, a VR theater was developed to explore the “Standing Prince Shōtoku in His Youth” statue at Kōshō-ji, Hiroshima, offering a unique insight into Buddha statuary. The project involved digitizing the statue’s exterior through photogrammetry with 143 images and modeling the interior based on fiberscope imagery, including carving marks and crystal eyes details. This VR system, featuring head-mounted display and hand tracking for gesture-based interactions, allowed users to simulate carving with a chisel in VR. The system was exhibited at the museum and was tested by 90 visitors, showing its ease of use and effectiveness in enhancing understanding of the statue.

In the field of horticultural therapy, which utilizes gardening activities as a means of therapy, positive psychological and physiological effects of physical contact with plants have been reported. However, especially for urban people, opportunities and motivation for regular contact with plants are limited even if indoor plants are installed at home, school, or office. This paper presents a smart plant pot that detects user touch on the plant and imparts kinetic energy to the plant to provide vibrotactile feedback to the user. The experiments demonstrated that the vibrotactile stimuli generated via waves propagated from the plant are perceptible to users who make contact with the plant while the implemented capacitive sensing technique detects human touch with less than 25-ms delay. We also propose some examples of augmented human-plant interactions using the developed pot to facilitate the positive effects, where a plant appears to voluntarily react to human touch by moving its body.

This study aims to develop a tactile display reproducing fine tactile perception during finger tracing. We have developed a haptic display, SVA-D (Soft Vibration Actuator-Display), independently providing high-resolution vibrotactile stimulation across various frequencies. We have evaluated high-resolution stimulation by SVA-D, focusing on tactile apparent movement in the narrow interval. The experimental results are significant, indicating that SVA-D provides stimulation with spatial information at an interval as narrow as 2 mm between two points on the fingertip. Previous studies have found providing various tactile sensations challenging at this interval, making our findings particularly noteworthy.

Despite numerous reports on using 360° videos for medical education, there is little evidence that they provide more educational effects than 2D videos, especially in practical surgical techniques. We compared the impact and effectiveness of a 360° video and a two-dimensional (2D) video for training veterinary students on conducting canine sterilization surgery. After the video learning using 360° or 2D videos, we conducted a mini-exam and a questionnaire and compared the data of recorded head motion while watching VR videos. The results showed that the 360° VR group reported a more significant presence and achieved a better understanding of anatomical terms than the 2Dgroup. Our findings suggest that 360° videos have more potential for learning than 2D videos and increase students’ knowledge and motivation.

Pupil synchronization, in which the size of one’s pupil changes in the same way as the pupil of observing person, has been reported, and is interpreted as a mimetic behavior in communication. Most of the previous studies have focused on the conditions under which this phenomenon occurs (race, ethnicity, age, etc.). Few studies have examined the impression of the person when pupil synchronization occurs. In this study, we investigated the effect of pupil synchronization on the facial impressions by manipulating pupil synchronization/asynchronization. In Experiment 1, the pupil variability increased activity rating, although the effect of pupil synchronization was not clear. In Experiment 2, we confirmed pupil synchronization occurs when observing with the enlarged pupil diameter, and the impression due to the difference in pupil diameter was also shown in each evaluation point.

Humans can estimate properties of a swung object, such as its moment of inertia and viscous resistance by feeling applied forces in their hands. This study aims to replicate these perceived properties by dynamically altering forces using a device equipped with Control Moment Gyroscopes. Without grounding, it provides three degrees of freedom in torque feedback. By adjusting torque feedback according to the user’s angular acceleration and velocity, we simulated changes in effective inertia and viscosity. Experiments showed the device can amplify inertia by roughly 2.5 times and viscosity by about 1000 times. Considering Weber fractions, it can differentiate approximately six inertia levels and eleven viscosity levels.