Users are often seated in the real environment, while their virtual avatars either remain standing stationary or move in virtual reality (VR). This creates posture inconsistencies between the real and virtual embodiment representations. The relationship between posture consistency in locomotion techniques and sense of presence in VR is still unclear. This study investigates how visual and somatosensory integration affects the sense of standing (SoSt) and the sense of self-motion (SoSm) when the sitting posture is varied slightly, including highlighting the importance of sitting posture for locomotion design in VR. The degree and occurrence of SoSt and SoSm were assessed by subjective experiments, and it was found that higher sitting and lower sitting postures present higher SoSt and lower SoSm, respectively. Invocation of SoSt also influences postural perception. Perception of travel distance varied according to the posture condition when identical visual flow was presented. The findings suggest that visual and somatosensory integration related to posture enhances SoSt and SoSm, and a sitting posture with a higher seating position is recommended in seated VR locomotion design.

Hap’n’Roll is a wearable device that leverages the concept of a scroll to present, with a single motor, tactile sensations of various sizes, shapes, and textures. Hap’n’Roll is composed of two axes, a sheet, and one motor. By changing the number of sheet wraps, the thickness within the user’s hand can be adjusted. Additionally, using holes on the sheet to secure the fingertips, it can present a wide range of sizes and shapes. Unlike typical existing handheld shape-changing devices, Hap’n’Roll is not limited to cylindrical forms. Furthermore, by moving different materials attached on the sheet to the fingertips, it can also express different textures. A user study showed that Hap’n’Roll can convey at least three sizes (small, medium, and large) and four types of shapes (a cylinder, a rectangle, a cone, and a cup), with a shape and size identification accuracy of approx. 76.1%. The identification accuracy for shape alone was approx. 98.5%. Moreover, several applications were developed to showcase the effectiveness of Hap’n’Roll’s mechanism for various haptic feedback.

Although a variety of haptic devices are used for virtual reality (VR) and augmented reality (AR) experiences, few can present a wide range of softness-hardness of the surface of the virtual objects. We propose a haptic device that can present a wide range of softness-hardness by using a two-layered structure consisting of a pneumatic balloon and a mechanical piston. Through a series of user studies, we confirmed that the prototype can present five levels of softness and three levels of hardness, and that the prototype device improves the VR experience in terms of realism, enjoyment, and comfort for virtual objects with a variety of softness/hardness.

In recent years, human augmentation has attracted much attention. One type of human augmentation, motion augmentation makes perceived motion larger than in reality, and it can be used for a variety of applications such as rehabilitation of motor functions of stroke patients and a more realistic experience in virtual reality (VR) such as redirected walking (RDW). However, as augmented motion becomes larger than the real motion, a variety of senses that accompany will be more inconsistent with those perceived from somatic sensations, which will cause a severe sense of discomfort. To address the problem, we focus on kinesthetic illusions that are psychological phenomena where a person feels as if his or her own body is moving. Kinesthetic illusions are expected to fill the gap between the intended augmented motion and perceived physical motion. However, it has not been explored if and how large kinesthetic illusions are produced while a user is moving their limbs voluntarily in VR. To expand the knowledge on kinesthetic illusions, we have conducted two user studies on the impact of tendon vibration and visual stimuli on kinesthetic illusions. First experiment confirmed that the perceived elbow angle becomes larger than the actual angle when presented with tendon vibration. Second experiment revealed that the increase of the perceived elbow angle was about 20 degrees when both tendon vibration and visual stimuli were presented whereas it was about 10 degrees when only visual stimuli were presented. Through these experiments, it has been confirmed that combining tendon vibration and visual stimulation enhances kinesthetic illusions.

In virtual reality (VR) systems, a user avatar is typically manipulated based on actual body motion in order to present natural immersive sensations resulted from proprioceptors. It is useful to be able to feel a large body motion in a virtual environment while it is actually smaller in the real environment. As a method to achieve this, we have been working on kinesthetic illusions induced by tendon vibration. In this article, we report on a user study focusing on the effects of a combination of visual stimulus and tendon vibration. In the user study, we measured subjects' perceived elbow angles while they observed the corresponding virtual arm bending to 90 degrees, with different rotation amplification ratios between 1.0 and 1.5, with and without tendon vibration on the wrist joint. The results show that the perceived angle is increased by up to 8 degrees when tendon vibration is applied, roughly in proportion to the rotation amplification ratio. Our study suggests that the vision-induced kinesthetic illusion is further increased by tendon vibration, and that our technique can be applied to VR applications to make users feel larger body motion than that in the real environment.