Background: The sense of embodiment (SoE) is the feeling of one’s own body, and research on the SoE extends from the rubber hand illusion to the full-body ownership illusion with a virtual avatar.Objective: The key to utilizing a virtual avatar is understanding and controlling the SoE, and it can be extended to several medical applications. In this study, we aimed to clarify these aspects by considering the following three subcomponents of SoE: sense of agency, ownership, and self-location.Methods: We defined a human avatar (HA), point light avatar (PLA), and out-of-body point light avatar (OBPLA) and compared them in three user studies. In study 1, 28 participants were recruited and the three avatar conditions (HA, PLA, and OBPLA) were compared. In study 2, 29 new participants were recruited, and there were two avatar conditions (HA ad PLA) and two motion synchrony conditions (synchrony and asynchrony). In study 3, 29 other participants were recruited, and there were two avatar conditions (PLA and OBPLA) and two motion synchrony conditions (synchrony and asynchrony). Dependent measures included sense of agency, ownership, and self-location; emotional response; presence; and simulator sickness.Results: The findings of study 1 showed that the three avatar generation methodologies can control the sense of ownership and self-location in a stepwise manner while maintaining a high sense of agency. In studies 2 and 3, we found dependencies among the three subcomponents of SoE and observed that they affected users’ subjective experiences.Conclusions: Our findings may have implications for boosting the effects of virtual avatar applications in medical areas, by understanding and controlling the SoE with a full-body illusion.

Conditional autonomous vehicles have attracted significant attention, and their wide-spread use is expected to further increase in the near future. However, such vehicles can send take-over requests (TORs) to a driver who may struggle to accommodate the request while immersed in non-driving-related tasks. Previous studies have focused on TOR times and cues; however, the effects of environmental conditions have not been examined rigorously. This study, with the aim of addressing the aforementioned issue, is divided into two parts: in Study 1, we examine driver responses to TORs under different environmental conditions (i.e., sunny, rainy, snowy, foggy, and night-time), and in Study 2, we examine the effects of the proposed TOR cues (augmented reality $+$ smartphone alert) under different environmental conditions. For this investigation, a driving simulator was used for the participants’ safety. Each study involves 33 participants. The results of Study 1 indicate significant differences in the take-over time, lane-change time, time-to-collision, maximum acceleration, and subjective mental workload corresponding to different environmental conditions. Furthermore, the results of Study 2 suggest that the proposed TOR cues significantly reduce the effects of environmental conditions on various take-over performances. We discuss the implication of these results in terms of the improvements in responses to TORs and investigation of the effects of environmental conditions on the responses to TORs.

A radial arm maze (RAM) is an essential tool for assessing spatial learning and memory. Although this tool is widely used to study deficits in spatial memory in animal models, it has several restrictions that prevent its adaptation to human research and training. Therefore, we developed a head-mounted-display RAM (HMD-RAM) program for humans and verified its validity by comparing it to the results obtained by previous RAM studies. We also compared the HMD and a flat monitor as experimental devices. Forty participants were recruited for the current study (Study 1: 20 participants with the HMD device; Study 2: 20 participants with the flat monitor). They navigated a virtual room as a first-person viewer and used environmental landmarks to remember their spatial position and orientation. The main dependent measures were working memory error, reference memory error, detection time, travel distance, and participant's head movements. To validate the program, participants also conducted neuropsychological assessments and self-reported measures. The results for HMD-RAM tasks were consistent with the results of previous research conducted on animals, and the HMD elicited a higher sense of presence, immersion, and simulator sickness than the flat monitor. According to post-experiment questions on navigation strategy, creating landmarks was important when people were discovering locations in their environment, and an HMD was beneficial for better navigation strategy. These results suggest that the HMD-RAM is valuable for estimating spatial learning and memory in humans and may be a useful tool for early diagnosis of deficits in spatial learning and memory, including amnestic mild cognitive impairment and Alzheimer's disease.

The current study sought to investigate the effects of matching body movement and body size between an avatar and a participant on the body ownership illusion (BOI), the body size illusion, the sense of presence, simulator sickness, and emotional responses within an immersive virtual reality (IVR). Forty participants experienced their life-sized virtual avatars from a first-person perspective using a full-body motion-capture system. The experiment used a 2 (Motion: Synchrony and Asynchrony) × 2 (Size: Matched and Unmatched) within-subject design. Each participant completed a self-reported questionnaire that evaluated BOI, body size illusion, presence, simulator sickness, and emotional valence. Results showed that matching participant's motion to that of an avatar increased the BOI and sense of presence, while reducing simulator sickness. Furthermore, participants reported more positive emotions when motion was synchronized to the virtual avatar. Most notably, synchronizing body movement between participants and avatars resulted in strong body size illusion even when the body size of an avatar was larger than the one of a participant. To the best of our knowledge, this is the first study to directly link synchronization of user motion and body size to a virtual avatar with user's subjective experience (BOI, body size illusion, sense of presence, simulator sickness, and valence) in IVR. Our findings suggest beneficial effects of synchronized body motion and matched body size between a user and avatar on user's subjective experience in IVR, which can possibly boost the effects of virtual reality applications in the fields of entertainment, psychotherapy, and education.

Background: Embodiment through a virtual avatar is a key element for people to feel that they are in the virtual world. Objective: This study aimed to elucidate the interaction between 2 methods of eliciting embodiment through a virtual avatar: motion synchronization and appearance similarity between a human and avatar, to understand embodiment (agency, body ownership, and self-location) and subjective experience (presence, simulator sickness, and emotion) in virtual reality. Methods: Using a full-body motion capture system, 24 participants experienced their virtual avatars with a 3D-scanned face and size-matched body from a first-person perspective. This study used a 2 (motion; sync and async) × 2 (appearance; personalized and generic) within-subject design. Results: The results indicated that agency and body ownership increased when motion and appearance were matched, whereas self-location, presence, and emotion were affected by motion only. Interestingly, if the avatar’s appearance was similar to the participants (personalized avatar), they formed an agency toward the avatar’s motion that was not performed by themselves. Conclusions: Our findings would be applicable in the field of behavioral therapy, rehabilitation, and entertainment applications, by eliciting higher agency with a personalized avatar.