This study investigates how the sense of embodiment in virtual environments can be enhanced by multisensory feedback related to body movements. In particular, we analyze the effect of combined vestibular and proprioceptive afferent signals on the perceived embodiment within an immersive walking scenario. These feedback signals were applied by means of a motion platform and by tendon vibration of lower limbs, evoking illusory leg movements. Vestibular and proprioceptive feedback were provided congruently with a rich virtual scenario reconstructing a real city, rendered on a head-mounted display (HMD). The sense of embodiment was evaluated through both self-reported questionnaires and physiological measurements in two experimental conditions: with all active sensory feedback (highly embodied condition), and with visual feedback only. Participants' self-reports show that the addition of both vestibular and proprioceptive feedback increases the sense of embodiment and the individual's feeling of presence associated with the walking experience. Furthermore, the embodiment condition significantly increased the measured galvanic skin response and respiration rate. The obtained results suggest that vestibular and proprioceptive feedback can improve the participant's sense of embodiment in the virtual experience.

It is well known by the virtual hand illusion (VHI) that simultaneous and synchronous visuotactile sensory feedback within a virtual environment elicits the feeling of ownership of a virtual hand, by observing for some seconds in a scene a virtual hand being touched while at the same time receiving tactile stimulation on the real hand in the corresponding positions. In this paper, we investigate possible modulations in the feeling of ownership (sensation of owning a virtual hand) and of agency (sensation of owning virtual movements and actions) according to whether or not the participant's own motor acts (1) induce coherent self-activated visuotactile sensory stimulations; and (2) generate plausible consequences in the simulated environment. For this purpose, we elicited the VHI within a group of participants through a cross-modal integration of visuo-tactile sensory stimulations within a dynamic and physically plausible immersive virtual environment, where they were able to perform natural tasks in both passive and active agency conditions. Our results indicate that both feelings of ownership and agency can be achieved in immersive virtual environments, when the subject is realistically interacting and performing natural upper limb movements. We did not observe any significant difference in the VHI in terms of ownership and agency between the active and passive conditions, but we observed that a physically incongruent simulated interaction with the virtual world can lead to a significant disruption of ownership. Moreover, in the passive agency condition, a plausible physical behavior of the virtual hand was sufficient to elicit a partially complete sense of ownership, if measured in terms of proprioceptive drift, even in the presence of an asynchronous visuotactile sensory feedback. All these findings suggest that the multisensory feedback associated with a subject's own actions and the physical plausibility of the environment both act as determinant factors, influencing and modulating the vividness of the VHI.

Haptic interaction in a virtual world can be tool mediated or direct; and, among direct interactions, the encountered haptic interfaces provide physical contact only when there is contact with a virtual object. This paper deals with the haptic rendering of the catching and throwing of objects by means of this type of interface. A general model for the rendering of the impact is discussed with the associated formalism for managing multiple objects and multiple devices. Next, a key parameter for simulating the impact is selected by means of a psychophysical test. Finally, a working system is presented with the application of the rendering strategy to the case of haptic juggling, showing the possibility of effectively performing basic juggling patterns with two balls.

The use of virtual environments (VE) for training sports is quite natural when considering strategic or cognitive aspects. Using VE for sensorimotor training is more challenging, in particular with the difficulty of transferring the task learned in the virtual world to the real. Of special concern for the successful transfer is the adequate combination of training experience protocols and the delivery modes of multimodal feedback. Analyzing feedback in terms of information exchange, this work discusses different feedback combinations and their application to virtual reality training of rowing skills.

This paper presents results and experiences coming from 10 years of development and use of XVR, a flexible, general-purpose framework for virtual reality (VR) development. The resulting architecture, that comes under the form of a self-sufficient integrated development environment (IDE) organized around a dedicated scripting language and a virtual machine, is able to accommodate a wide range of applications needs, ranging from simple Web3D applications to motion-based simulators or complex cluster-based immersive visualization systems. Within the framework a common, archetypical structure is used for any application, showing how inhomogeneous needs and technologies can be effectively covered by using a single, rather simple, system organization. We also show how the framework flexibility allows for innovative development techniques such as multiple frameworks coexisting within a single, tightly integrated, VR application.

This work refers to the study of thermal contact phenomena modeling for tactile feedback in virtual environments applications. The results of the modeling aspects for thermal replication are collected in specific functions that are used by the renderer of a virtual application. The finger temperature distribution versus time and contacted object temperature are the fundamental ways to approach, according to a specific modeling technique, the computation of the contact temperature occurring at the interface between the virtual hand and virtual object. Finger temperature distribution is then used for the control of thermal effectors. The modeling of the spatial and temporal distribution of the temperature in the human finger, when contact occurs with an external object at a defined temperature, is carried out in two phases: (a) determination of the temperature distribution in the finger when no contact is detected; and (b) determination of the temperature distribution in the finger when contact is detected. Results of the modeling are given and a procedure describing how these results can be used in the framework of a real application is presented.