Kizashi Nakano

Head-Mounted Displays (HMDs) allow users to move freely in virtual environments and interact with various objects. However, existing HMDs have a limited downward Field of View (FOV), restricting visibility of the feet and nearby virtual objects unless users tilt their heads downward. This limitation complicates walking in HMDs, leading to increased difficulty and apprehension, and constrains interaction with virtual objects. In this study, we investigate how the area near the user’s body affects presence, walking, and interactions such as avoiding or stepping over virtual objects, using an HMD with an expanded downward FOV. We also examined whether these effects were present in both Virtual Reality (VR) and Video See-Through Augmented Reality (VST-AR), which typically has narrower FOVs and higher latencies than VR. When the downward FOV was expanded, users could walk and avoid virtual objects more easily without needing to tilt their heads downward. Notably, participants moved their feet significantly while avoiding the virtual objects by stepping over them. Exploratory analyses further suggested that the increased downward FOV may enhance the realism and the perceived three-dimensionality of the virtual objects.

Cross-modal correspondence, exemplified by the Bouba/Kiki effect, which refers to the association between linguistic sounds and visual shape impressions, is known to influence taste perception. Previous studies have shown that taste perception varies with the visual features of foods, beverages, and tableware. However, it remains unclear how embodying a self-avatar in virtual reality (VR) whose visual features are associated with Bouba/Kiki influences taste perception. We conducted two studies to investigate the effects of cross-modal correspondence between VR self-avatar characteristics and taste perception using lemon-flavored carbonated beverages that elicit both sweetness and sourness. Study 1 directly compared Bouba avatars (round shapes, red colors, slow animations) and Kiki avatars (angular shapes, yellow colors, fast animations) in a within-participants design ($N = 36$). Study 2 examined the effects of each avatar type separately by comparing them with neutral control conditions ($N = 72$). In Study 1, the Bouba avatar led participants to perceive the beverage as mellower compared to the Kiki avatar. However, this effect was not significant when compared with a neutral control avatar in Study 2. In contrast, the Kiki avatar produced robust effects, increasing perceived sourness and sharpness in both studies. These findings suggest that the observed changes in taste are primarily driven by the congruence between avatar characteristics and the intrinsic sensory properties of the beverage. This study demonstrates the potential for avatar-mediated congruence effects to alter perceived taste in VR, highlighting the importance of the alignment between the user's virtual body and the consumed stimulus.

Studies that split the avatar into left and right halves induce a sense of body splitting, but that sensation is weak. In mirror-based body illusions, translating the mirror shifts the reflected body image, causing the body behind the mirror to be perceived as if it were moving. However, the self-motion and splitting sensations that arise when the observer’s viewpoint moves together with one body segment remain unclear. When the viewpoint translates with one half-body, the other half remains in its original position, and from the observer’s perspective the stationary half appears to move relatively. This relative displacement is expected to generate the sensation that both halves are moving, thereby evoking a strong sense of body splitting. In the present study, we divide the avatar into upper and lower halves and translate either half horizontally in synchrony with the participant’s viewpoint to provide strong sensations of body splitting and sense of drift. Additionally, by employing a head-mounted display with a wide downward field of view, we enhance the clear presentation of the lower half and strengthen the sense of self-motion.

In the real world, the body typically remains within the downward field of view (FOV) irrespective of whether it is consciously or unconsciously observed. However, with head-mounted displays (HMDs) that have restricted viewing angles, users are unable to see their own avatars directly unless they tilt their heads significantly downward. To overcome this, virtual mirrors are commonly employed in virtual environments (VEs) to provide users with a full-body view of their avatars, which ultimately enhances the viewer's sense of embodiment (SoE). However, positioning users directly in front of a virtual mirror may restrict their movement and reduce their sense of presence. To overcome this limitation, we developed an HMD with an extended downward field of view (FOV) integrated with eye-tracking. We compared the impact of using virtual mirrors alone versus the extended downward FOV in terms of several parameters, including the head pitch angle, perceived SoE, presence, and task difficulty during a reaching task that involves both hand and foot movements. The results demonstrated that the extended downward FOV offered by the proposed HMD improved the users' sense of agency toward their avatars and enhanced their sense of presence compared to when only virtual mirrors are used. In addition, the participants tended to use the virtual mirror for hand movements and relied on the extended downward FOV for foot movements, often maintaining a stable head angle. Both the virtual mirror and extended downward FOV facilitated easier and faster completion of a reaching task while encouraging an upward head angle. However, the combined use of virtual mirrors and extended downward FOV did not have a significant impact on the SoE or presence. Notably, the extended downward FOV alone, without the integration of the virtual mirror, was more effective in increasing both SoE and presence.

The Proteus effect is known as the effect that the self-image evoked by an avatar influences the behavior. Previous studies have shown that the Proteus effect influences food-related behaviors, but it is not clear whether it influences perceptions of food. Therefore, in this study, we investigated whether the avatar’s body shape affects beverage perception when drinking a beverage in a virtual environment. Specifically, we measured the sense of body ownership toward the avatar, the taste of the beverage, the amount of the beverage consumed, and the purchase intention of the beverage. The results showed that a gradual transition in body shape with drinking produced a significant improvement in the sense of body ownership, particularly in terms of feeling that the virtual body belonged to oneself. We also report the larger body shape significantly increases the purchase intention. Furthermore, we found that image congruence between the avatar and cola induces better taste perception.