The Sense of embodiment in virtual reality

What does it feel like to own, to control, and to be inside a body? The multidimensional nature of this experience together with the continuous presence of one's biological body, render both theoretical and experimental approaches problematic. Nevertheless, exploitation of immersive virtual reality has allowed a reframing of this question to whether it is possible to experience the same sensations towards a virtual body inside an immersive virtual environment as toward the biological body, and if so, to what extent. The current paper addresses these issues by referring to the Sense of Embodiment (SoE). Due to the conceptual confusion around this sense, we provide a working definition which states that SoE consists of three subcomponents: the sense of self-location, the sense of agency, and the sense of body ownership. Under this proposed structure, measures and experimental manipulations reported in the literature are reviewed and related challenges are outlined. Finally, future experimental studies are proposed to overcome those challenges, toward deepening the concept of SoE and enhancing it in virtual applications

Is my hand connected to my body? The impact of body continuity and arm alignment on the virtual hand illusion

When a rubber hand is placed on a table top in a plausible position as if part of a person"s body, and is stroked synchronously with the person"s corresponding hidden real hand, an illusion of ownership over the rubber hand can occur (Botvinick and Cohen 1998). A similar result has been found with respect to a virtual hand portrayed in a virtual environment, a virtual hand illusion (Slater et al. 2008). The conditions under which these illusions occur have been the subject of considerable study. Here we exploited the flexibility of virtual reality to examine four contributory factors: visuo-tactile synchrony while stroking the virtual and the real arms, body continuity, alignment between the real and virtual arms, and the distance between them. We carried out three experiments on a total of 32 participants where these factors were varied. The results show that the subjective illusion of ownership over the virtual arm and the time to evoke this illusion are highly dependent on synchronous visuo-tactile stimulation and on connectivity of the virtual arm with the rest of the virtual body. The alignment between the real and virtual arms and the distance between these were less important. It was found that proprioceptive drift was not a sensitive measure of the illusion, but was only related to the distance between the real and virtual arms

Touching is believing: creating illusions and feeling of embodiment with mid-air haptic technology

Over the last two decades, the sense of touch has received new attention from the scientific community.Several haptic devices have been developed to address the complexity of the sense of touch, the latest addition being mid-air (contactless) haptic technology. An interesting series of previous research has suggested an easier way to tackle the complexity of designing convincing tactile sensations by exploiting tactile illusions. Tactile illusions rely on perceptual shortcuts based on the psychophysics of the tactile receptors. Currently, studies exploring the perceptual space of mid-air haptics and its applicability in the tactile illusions field are still limited in number. This thesis aims to contribute to the field of Human-Computer Interaction (HCI) by investigating the perceptual design space of ultrasonic mid-air haptics technology. Specifically, in a first set of three studies, we investigate the absolute thresholds (minimal amount of a property of astimulus that a user can detect) for control points (CP) at different frequencies on the hand and arm (Study 1). Then we investigate the optimal sampling rate needed to drive the device in an optimal fashion and its relationship with shape size (Study 2). Next, we apply a new technique to increase users’ performance in a shape discrimination task (Study 3). In Study 4, we start the exploration of a tactile illusion of movement using contact touch and later, we apply a similar procedure to investigate the feasibility of creating a tactile illusion of movement between the two non-interconnected hands by using mid-air touch (Study 5). Finally, in Study 6, we explore our sense of touch in VR, while providing an illusion of rain drops through mid-air haptics, to recreate a virtual hand illusion (VHI) to explore the boundaries of our sense of embodiment. Therefore, the contribution of this work is threefold: a) we contribute by adding new knowledge on the psychophysical space for mid-air haptics, b) we test the potential to create realistic tactile sensations by exploiting tactile illusions with mid-air haptic technology, and c) we demonstrate how tactile illusions mediated by mid-air haptics can convey a sense of embodiment in VR environments

I’m sensing in the rain: spatial incongruity in visual-tactile mid-air stimulation can elicit ownership in VR users

Major virtual reality (VR) companies are trying to enhance the sense of immersion in virtual environments by implementing haptic feedback in their systems (e.g., Oculus Touch). It is known that tactile stimulation adds realism to a virtual environment. In addition, when users are not limited by wearing any attachments (e.g., gloves), it is even possible to create more immersive experiences. Mid-air haptic technology provides contactless haptic feedback and offers the potential for creating such immersive VR experiences. However, one of the limitations of mid-air haptics resides in the need for freehand tracking systems (e.g., Leap Motion) to deliver tactile feedback to the user's hand. These tracking systems are not accurate, limiting designers capability of delivering spatially precise tactile stimulation. Here, we investigated an alternative way to convey incongruent visual-tactile stimulation that can be used to create the illusion of a congruent visual-tactile experience, while participants experience the phenomenon of the rubber hand illusion in VR

Vestibular contribution to bodily self-consciousness and multisensory cortical processing

How does the self relate to the body? Bodily self-consciousness, i.e. the sense of being a subject bound to a body, involves a first-person perspective (1PP), i.e. the sense of being directed at the world. Prior research suggests that bodily self-consciousness depends on brain mechanisms integrating multisensory bodily signals. However, the specific multisensory mechanisms of 1PP are poorly understood. Here, I defend the thesis that the vestibular system, i.e. the sensory system encoding rotational and linear accelerations of the head, contributes to 1PP and related multisensory processing in the brain. The first part of my thesis presents experimental evidence showing that 1PP was influenced by multisensory conflict about the direction of gravity and the location of the body. 1PP depended on integrated visual-vestibular signals and was functionally distinct from another aspect of bodily self-consciousness: self-identification, i.e. the feeling that a particular body is âmineâ. The second part of my thesis presents the electrical neural correlates by which vestibular stimulation affected somatosensory and visual cortical processing. Passive whole-body yaw rotation naturally and selectively stimulated the vestibular system while the evoked responses to somatosensory or visual stimuli were recorded by electroencephalography. Electrical neuroimaging analysis showed temporal-specific vestibular effects on somatosensory and visual evoked potentials, localized by source estimations to distinct regions of the somatosensory, visual, and vestibular cortical networks. Collectively, the results from my thesis suggest that the vestibular system contributes to 1PP and multisensory cortical processing and imply that the vestibular system should not be neglected when studying higher brain function and neurobiological mechanisms of consciousness

I'm sensing in the rain: Spatial incongruity in visual-tactile mid-air stimulation can elicit ownership in VR users

Major virtual reality (VR) companies are trying to enhance the sense of immersion in virtual environments by implementing haptic feedback in their systems (e.g., Oculus Touch). It is known that tactile stimulation adds realism to a virtual environment. In addition, when users are not limited by wearing any attachments (e.g., gloves), it is even possible to create more immersive experiences. Mid-air haptic technology provides contactless haptic feedback and offers the potential for creating such immersive VR experiences. However, one of the limitations of mid-air haptics resides in the need for freehand tracking systems (e.g., Leap Motion) to deliver tactile feedback to the user's hand. These tracking systems are not accurate, limiting designers capability of delivering spatially precise tactile stimulation. Here, we investigated an alternative way to convey incongruent visual-tactile stimulation that can be used to create the illusion of a congruent visual-tactile experience, while participants experience the phenomenon of the rubber hand illusion in VR

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Vestibular Contributions to the Sense of Body, Self, and Others

There is increasing evidence that vestibular signals and the vestibular cortex are not only involved in oculomotor and postural control, but also contribute to higher-level cognition. Yet, despite the effort that has recently been made in the field, the exact location of the human vestibular cortex and its implications in various perceptional, emotional, and cognitive processes remain debated. Here, we argue for a vestibular contribution to what is thought to fundamentally underlie human consciousness, i.e., the bodily self. We will present empirical evidence from various research fields to support our hypothesis of a vestibular contribution to aspects of the bodily self, such as basic multisensory integration, body schema, body ownership, agency, and self-location. We will argue that the vestibular system is especially important for global aspects of the self, most crucially for implicit and explicit spatiotemporal self-location. Furthermore, we propose a novel model on how vestibular signals could not only underlie the perception of the self but also the perception of others, thereby playing an important role in embodied social cognition

Haptics: Science, Technology, Applications

This open access book constitutes the proceedings of the 12th International Conference on Human Haptic Sensing and Touch Enabled Computer Applications, EuroHaptics 2020, held in Leiden, The Netherlands, in September 2020. The 60 papers presented in this volume were carefully reviewed and selected from 111 submissions. The were organized in topical sections on haptic science, haptic technology, and haptic applications. This year's focus is on accessibility