Embodiment Illusion Research Articles

Measuring Embodiment: Movement Complexity and the Impact of Personal Characteristics.

A user's personal experiences and characteristics may impact the strength of an embodiment illusion and affect resulting behavioral changes in unknown ways. This paper presents a novel re-analysis of two fully-immersive embodiment user-studies (n = 189 and n = 99) using structural equation modeling, to test the effects of personal characteristics on subjective embodiment. Results demonstrate that individual characteristics (gender, participation in science, technology, engineering or math - Experiment 1, age, video gaming experience - Experiment 2) predicted differing self-reported experiences of embodiment Results also indicate that increased self-reported embodiment predicts environmental response, in this case faster and more accurate responses within the virtual environment. Importantly, head-tracking data is shown to be an effective objective measure for predicting embodiment, without requiring researchers to utilize additional equipment.

Whose body is it anyway? Cultural reflections on embodiment illusion research in eating disorders and body dysmorphic disorder.

Whose body is it anyway? Cultural reflections on embodiment illusion research in eating disorders and body dysmorphic disorder.

Novel online enfacement illusion for investigating self-perception in mental disorders: an experimental study protocol

BackgroundRemote research methods and interventions for mental health disorders have become increasingly important, particularly for conditions like eating disorders (EDs). Embodiment illusions, which induce feelings of ownership over another person?s body or body parts, offer valuable insights into the mechanisms underlying self-perception issues in EDs and potential interventions. However, existing research using these illusions has been limited to face-to-face settings. We illustrate a novel online protocol to induce the enfacement illusion (embodiment illusion principles applied to one’s face) in an ED-based sample.MethodsParticipants complete a 2-hr virtual session with a researcher. First, baseline trait/state ED psychopathology measures and a self-face recognition task occur. Second, participants experience two testing blocks of the enfacement illusion involving synchronously and asynchronously mimicking a pre-recorded actor’s facial expressions. After each block, subjective and objective enfacement illusion measures occur alongside state ED psychopathology reassessment.DiscussionSuccessfully inducing enfacement illusions online could provide an affordable, accessible virtual approach to further elucidate the mechanistic role of self-perception disturbances across psychopathologies such as EDs. Moreover, this protocol may represent an innovative, remotely-delivered intervention strategy, as ‘enfacement’ over another face could update negative self-representations in a cost-effective, scalable manner.

Your body, my experience: A systematic review of embodiment illusions as a function of and method to improve body image disturbance.

Your body, my experience: A systematic review of embodiment illusions as a function of and method to improve body image disturbance.

Supplemental Material for Your Body, My Experience: A Systematic Review of Embodiment Illusions as a Function of and Method to Improve Body Image Disturbance

Supplemental Material for Your Body, My Experience: A Systematic Review of Embodiment Illusions as a Function of and Method to Improve Body Image Disturbance

Development and validation of a pictographic assessment embodiment scale.

Embodiment is a complex concept related to the subjective perception of an object as it belongs to its own body. In general, this construct has been evaluated by means of questionnaires, but validation studies in other cultures and limitations related with barriers of language received little attention. The purpose of the present investigation was twofold: to validate the factorial structure of embodiment questionnaire (EQ) and to construct a pictographic scale (PAE) to measure embodiment without relapse verbal representations. In the first experiment, 136 participants underwent a Rubber Hand Illusion (RHI) procedure following both congruent and incongruent (control) visuo-tactile stimulations. Then, they evaluated embodiment illusion in EQ using a Likert-type scale to rate their agreement or disagreement with 27 statements and with a pictographic scale designed to assess their subjective experience of the illusion. Principal components analysis in EQ scores identified four components that emerged in both conditions: Embodiment, Disembodiment, Affect and Deafference. PAE scale was highly correlated with embodiment factor and can differentiate between conditions. In a second experiment, 30 participants underwent the RHI procedure, and they were assessed using PAE and proprioceptive drift. Results indicate a high positive correlation between PAE and post-illusion drift score. These results provide evidence about the consistency of the factorial structure of EQ across cultures, and we also provide a new pictographic tool that allows quick measurement of embodiment overcoming language barriers.

Embodiment illusions and eating disorders: snapshot of implications for research and interventions

In recent years, researchers have increasingly used the embodiment illusion paradigm in subclinical and clinical eating disorder (ED) populations. This has important implications for understanding and ultimately improving bodily misperception. Here, we provide a brief overview of the current 'state of the art' of these implications while highlighting challenges and future directions.

Investigating the perceptual attribution of a virtual robotic limb synchronizing with hand and foot simultaneously

Introduction: Incorporating an additional limb that synchronizes with multiple body parts enables the user to achieve high task accuracy and smooth movement. In this case, the visual appearance of the wearable robotic limb contributes to the sense of embodiment. Additionally, the user’s motor function changes as a result of this embodiment. However, it remains unclear how users perceive the attribution of the wearable robotic limb within the context of multiple body parts (perceptual attribution), and the impact of visual similarity in this context remains unknown.Methods: This study investigated the perceptual attribution of a virtual robotic limb by examining proprioceptive drift and the bias of visual similarity under the conditions of single body part (synchronizing with hand or foot motion only) and multiple body parts (synchronizing with average motion of hand and foot). Participants in the conducted experiment engaged in a point-to-point task using a virtual robotic limb that synchronizes with their hand and foot motions simultaneously. Furthermore, the visual appearance of the end-effector was altered to explore the influence of visual similarity.Results: The experiment revealed that only the participants’ proprioception of their foot aligned with the virtual robotic limb, while the frequency of error correction during the point-to-point task did not change across conditions. Conversely, subjective illusions of embodiment occurred for both the hand and foot. In this case, the visual appearance of the robotic limbs contributed to the correlations between hand and foot proprioceptive drift and subjective embodiment illusion, respectively.Discussion: These results suggest that proprioception is specifically attributed to the foot through motion synchronization, whereas subjective perceptions are attributed to both the hand and foot.

"To Be or Not to Be Me?": Exploration of Self-Similar Effects ofAvatars on Social Virtual Reality Experiences.

The growing interest in the self-similarity effect of avatars in virtual reality (VR) has spurred the creation of realistic avatars that closely mirror their users. However, despite extensive research on the self-similarity effect in single-user VR environments, our understanding of its impact in social VR settings remains underdeveloped. This shortfall exists despite the unique socio-psychological phenomena arising from the illusion of embodiment that could potentially alter these effects. To fill this gap, this paper provides an in-depth empirical investigation of how avatars' self-similarity influences social VR experiences. Our research uncovers several notable findings: 1) A high level of avatar self-similarity boosts users' sense of embodiment and social presence but has minimal effects on the overall presence and even slightly hinders immersion. These results are driven by increased self-awareness. 2) Among various factors that contribute to the self-similarity of avatars, voice stands out as a significant influencer of social VR experiences, surpassing other representational factors. 3) The impact of avatar self-similarity shows negligible differences between male and female users. Based on these findings, we discuss the pros and cons of incorporating self-similarity into social VR avatars. Our study serves as a foundation for further research in this field.

Immersive Virtual Reality Avatars for Embodiment Illusions in People With Mild to Borderline Intellectual Disability: User-Centered Development and Feasibility Study.

Immersive virtual reality (IVR) has been investigated as a tool for treating psychiatric conditions. In particular, the practical nature of IVR, by offering a doing instead of talking approach, could support people who do not benefit from existing treatments. Hence, people with mild to borderline intellectual disability (MBID; IQ=50-85) might profit particularly from IVR therapies, for instance, to circumvent issues in understanding relevant concepts and interrelations. In this context, immersing the user into a virtual body (ie, avatar) appears promising for enhancing learning (eg, by changing perspectives) and usability (eg, natural interactions). However, design requirements, immersion procedures, and proof of concept of such embodiment illusion (ie, substituting the real body with a virtual one) have not been explored in this group. Our study aimed to establish design guidelines for IVR embodiment illusions in people with MBID. We explored 3 factors to induce the illusion, by testing the avatar's appearance, locomotion using IVR controllers, and virtual object manipulation. Furthermore, we report on the feasibility to induce the embodiment illusion and provide procedural guidance. We conducted a user-centered study with 29 end users in care facilities, to investigate the avatar's appearance, controller-based locomotion (ie, teleport, joystick, or hybrid), and object manipulation. Overall, 3 iterations were conducted using semistructured interviews to explore design factors to induce embodiment illusions in our group. To further understand the influence of interactions on the illusion, we measured the sense of embodiment (SoE) during 5 interaction tasks. IVR embodiment illusions can be induced in adults with MBID. To induce the illusion, having a high degree of control over the body outweighed avatar customization, despite the participants' desire to replicate their own body image. Similarly, the highest SoE was measured during object manipulation tasks, which required a combination of (virtual) locomotion and object manipulation behavior. Notably, interactions that are implausible (eg, teleport and occlusions when grabbing) showed a negative influence on SoE. In contrast, implementing artificial interaction aids into the IVR avatar's hands (ie, for user interfaces) did not diminish the illusion, presuming that the control was unimpaired. Nonetheless, embodiment illusions showed a tedious and complex need for (control) habituation (eg, motion sickness), possibly hindering uptake in practice. Balancing the embodiment immersion by focusing on interaction habituation (eg, controller-based locomotion) and lowering customization effort seems crucial to achieve both high SoE and usability for people with MBID. Hence, future studies should investigate the requirements for natural IVR avatar interactions by using multisensory integrations for the virtual body (eg, animations, physics-based collision, and touch) and other interaction techniques (eg, hand tracking and redirected walking). In addition, procedures and use for learning should be explored for tailored mental health therapies in people with MBID.

Sense of body ownership and body agency in schizophrenia

Recent research suggests that embodiment sensations (sense of body ownership and sense of body agency) are altered in schizophrenia. Using a mirror box illusion setup, we tested if the anomalous embodiment experience depends on deficient processing of visuomotor synchrony, disrupted processing of movement mode, or both. The task required participants to press a lever with their index while looking at the image of the experimenter’s hand moving on a similar lever. The illusion of embodiment could arise because looking toward the direction of their own hand the participant saw the reflection of the experimenter’s hand visually superimposed to his own one through a mirror. During the illusion induction, we systematically varied visuomotor asynchrony (4 delays were imposed on the movement of the experimenter’s hand) and the mode of movement (the participant could perform active vs. passive movements). The strength of the illusion of embodiment of the external hand was assessed with explicit judgments of ownership and agency. Patients’ data showed an anomalous modulation of ownership with respect to visuomotor synchrony manipulation and an altered modulation of agency with respect to both visuomotor synchrony and movement mode manipulations. Results from the present study suggest that impairments affecting both the processing of temporal aspects of visuomotor signals and the processing of type of movement underlie anomalous embodiment sensations in schizophrenia. Hypotheses about potential deficits accounting for our results are proposed.

Feeling of Ownership over an Embodied Avatar's Hand Brings About Fast Changes of Fronto-Parietal Cortical Dynamics.

When we look at our body parts, we are immediately aware that they belong to us and we rarely doubt about the integrity, continuity, and sense of ownership of our body. Despite this certainty, immersive virtual reality (IVR) may lead to a strong feeling of embodiment over an artificial body part seen from a first-person perspective (1PP). Although such feeling of ownership (FO) has been described in different situations, it is not yet understood how this phenomenon is generated at neural level. To track the real-time brain dynamics associated with FO, we delivered transcranial magnetic stimuli over the hand region in the primary motor cortex (M1) and simultaneously recorded electroencephalography (EEG) in 19 healthy volunteers (11 male/8 female) watching IVR renderings of anatomically plausible (full-limb) versus implausible (hand disconnected from the forearm) virtual limbs. Our data show that embodying a virtual hand is temporally associated with a rapid drop of cortical activity of the onlookers' hand region in the M1 contralateral to the observed hand. Spatiotemporal analysis shows that embodying the avatar's hand is also associated with fast changes of activity within an interconnected fronto-parietal circuit ipsilateral to the brain stimulation. Specifically, an immediate reduction of connectivity with the premotor area is paralleled by an enhancement in the connectivity with the posterior parietal cortex (PPC) which is related to the strength of ownership illusion ratings and thus likely reflects conscious feelings of embodiment. Our results suggest that changes of bodily representations are underpinned by a dynamic cross talk within a highly-plastic, fronto-parietal network.SIGNIFICANCE STATEMENT Observing an avatar's body part from a first-person perspective (1PP) induces an illusory embodiment over it. What remains unknown are the cortical dynamics underpinning the embodiment of artificial agents. To shed light on the physiological mechanisms of embodiment we used a novel approach that combines noninvasive stimulation of the cortical motor-hand area and whole-scalp electroencephalographic (EEG) recordings in people observing an embodied artificial limb. We found that just before the illusion started, there is a decrease of activity of the motor-hand area accompanied by an increase of connectivity with the parietal region ipsilateral to the stimulation that reflects the ratings of the embodiment illusion. Our results suggest that changes of bodily representations are underpinned by a dynamic cross talk within a fronto-parietal circuit.

Exploring the use of augmented reality in fitness on innovation, embodiment, and communication

Virtual representations of humans have been explored heavily and used widely in the realms of game development and virtual reality. Motivated by a desire for convenience and privacy in an age of pursuing a healthy life and self-improvement, many augmented reality (AR) and virtual reality (VR) technologies are used for developing better fitness products (e.g., smart fitness mirror). ​​This research aims to investigate the potential for the usage of AR in smart fitness mirrors to affect emotions, assist embodiment illusions, and accordingly influence cognitive function by applying it to the domain of innovative thinking. In addition, the research wants to further evaluate how the perception changes that results in distinct linguistic functionality with the long-term interaction with virtual characters and staying in the cross-boundary space. Our final goal is to develop an AR system which could empower learners to benefit from both cognitive learning and the effective fitness exercises, encouraging the innovation while taking the courses.

Embodiment in Virtual Reality Intensifies Emotional Responses to Virtual Stimuli

Modulating emotional responses to virtual stimuli is a fundamental goal of many immersive interactive applications. In this study, we leverage the illusion of illusory embodiment and show that owning a virtual body provides means to modulate emotional responses. In a single-factor repeated-measures experiment, we manipulated the degree of illusory embodiment and assessed the emotional responses to virtual stimuli. We presented emotional stimuli in the same environment as the virtual body. Participants experienced higher arousal, dominance, and more intense valence in the high embodiment condition compared to the low embodiment condition. The illusion of embodiment thus intensifies the emotional processing of the virtual environment. This result suggests that artificial bodies can increase the effectiveness of immersive applications psychotherapy, entertainment, computer-mediated social interactions, or health applications.

The toolish hand illusion: embodiment of a tool based on similarity with the hand

A tool can function as a body part yet not feel like one: Putting down a fork after dinner does not feel like losing a hand. However, studies show fake body-parts are embodied and experienced as parts of oneself. Typically, embodiment illusions have only been reported when the fake body-part visually resembles the real one. Here we reveal that participants can experience an illusion that a mechanical grabber, which looks scarcely like a hand, is part of their body. We found changes in three signatures of embodiment: the real hand’s perceived location, the feeling that the grabber belonged to the body, and autonomic responses to visible threats to the grabber. These findings show that artificial objects can become embodied even though they bear little visual resemblance to the hand.

Towards a Common Framework for Mediated Embodiment

Mediated embodiment (ME) is the technologically generated illusion of substituting a person’s body with an avatar body. Virtual reality is the most representative technology of ME. However, other forms of embodiment are emerging and need to be examined. The inclusion of all ME technologies under a common paradigm would largely facilitate their study. Here, I develop a unified conceptual framework of ME and integrate robot embodiment as part of the phenomenon. I first describe the central component of ME: avatars. I extend the concept of avatar used in virtual reality to other forms of ME. I then outline the minimum conditions necessary to induce the embodiment illusion as well as the technical principles used to create this illusion. Next, I suggest that ME technologies can be regarded as tools that increase human capabilities in four directions: embodiment of a new self, expansion of traveling capabilities, expansion of body capabilities, and the reach of immortality. I connect the principal research conducted in the field to these categories and suggest potential research directions to promote the positive applied uses of ME. I conclude with the importance to also address ethical issues related to this phenomenon.

Visual feedback from a virtual body modulates motor illusion induced by tendon vibration.

Frequency-specific tendon vibration (TV) elicits illusory kinesthetic sensations around the vibrated body parts. Studies indicate that vision plays a fundamental role in modulating such illusions. In our current study, we used immersive virtual reality (IVR) to investigate the role of body-related visual feedback in modulating illusory sensation of movement in the left arm. Thirty healthy participants were asked to evaluate the onset of motor illusion and four illusion-related features (vividness, duration, extension andaftereffect), in the presence and absence of real and virtual visual feedback. Additionally, subjective reports of the embodiment illusion (the sense of embodying a virtual surrogate) were collected in virtual conditions. Results showed a progressive decrease in the perception of the motor illusion along a continuum ranging from the absence of visual feedback (maximal illusory perception) to the observation of one's own real arm (minimal illusory perception). Interestingly, the appearance of the virtual limbs affected the movement illusion differently. Specifically, TV evoked a stronger kinesthetic illusion when observing the virtual handdetached from thelimb than during the observation of the virtual full limb and virtual object. This suggests that a closer visual resemblance between the virtual and real limb results in a greater effect on proprioceptive processing. However, no significant correlation was found between the illusion of arm movement and the illusion of embodiment, indicating that the two phenomena may not be directly related. These findings provide new insight into the role of body-related visual feedback in modulating motor illusions.

Defective Embodiment of Alien Hand Uncovers Altered Sensorimotor Integration in Schizophrenia.

The observation that people with schizophrenia misattribute the source of their own actions has led to the hypothesis that they suffer from altered sensorimotor processes underlying sense of agency. Furthermore, rubber hand studies suggest an abnormal experience of embodiment in schizophrenia. However, this latter finding is based on a procedure that elicits ownership sensations for a fake hand by visuo-tactile stimulation, leaving the agency subcomponent of embodiment relatively untouched. By using a visuo-motor version of the embodiment illusion able to actively elicit also sense of agency for an alien hand, we tested whether the putative sensorimotor deficits are also involved in altering embodiment sensations in schizophrenia. Subjective (questionnaire) and perceptual (forearm bisection performance) indexes of the embodiment illusion were collected. Differently from controls, both the explicit agency component and the implicit body metrics update were not modulated by the extent of visuo-motor congruency in participants with schizophrenia. We conclude that motor prediction and/or temporal binding window impairments may alter the feeling of embodiment and body representation in schizophrenia.

Avatar Embodiment. Towards a Standardized Questionnaire.

Inside virtual reality, users can embody avatars that are collocated from a first-person perspective. When doing so, participants have the feeling that the own body has been substituted by the self-avatar, and that the new body is the source of the sensations. Embodiment is complex as it includes not only body ownership over the avatar, but also agency, co-location, and external appearance. Despite the multiple variables that influence it, the illusion is quite robust, and it can be produced even if the self-avatar is of a different age, size, gender, or race from the participant's own body. Embodiment illusions are therefore the basis for many social VR experiences and a current active research area among the community. Researchers are interested both in the body manipulations that can be accepted, as well as studying how different self-avatars produce different attitudinal, social, perceptual, and behavioral effects. However, findings suggest that despite embodiment being strongly associated with the performance and reactions inside virtual reality, the extent to which the illusion is experienced varies between participants. In this paper, we review the questionnaires used in past experiments and propose a standardized embodiment questionnaire based on 25 questions that are prevalent in the literature. We encourage future virtual reality experiments that include first-person virtual avatars to administer this questionnaire in order to evaluate the degree of embodiment.

Effects of Augmented Reality on the Performance of Teleoperated Industrial Assembly Tasks in a Robotic Embodiment

Teleoperation in robotic embodiments allows operators to perform and program manipulation tasks with better accuracy, dexterity, and visualization than what is possible with traditional human-robot interaction paradigms. However, the perception of cues (e.g., egocentric distances) relevant to task execution, is known to be distorted in virtual environments due to many factors, which can be grouped into technical, human, and methodological categories. This phenomenon becomes more pronounced in a low-cost/encumbrance setup, where the dynamic environment is captured with color and depth (RGB-D) cameras and presented in a virtual environment. In this paper, the effects of augmented reality (AR) are evaluated as a tool to deliver additional information, which helps in overcoming the differences in perception between telepresence and actual presence. The AR feedback is used to improve the embodiment illusion and to guide the operator during task execution. The AR setup, comprising an RGB-D camera and a head-mounted display, is integrated with the Baxter robot and evaluated by involving 22 participants in an experiment while they execute a pick-and-place task, taking into account their expertise in AR/virtual reality (VR) and gaming. The use of AR results in enhancing the accuracy and efficiency of the task performance, besides significantly reducing the effect of the differences in skillfulness between the participants. Furthermore, it is found that the sense of presence and embodiment for the participant is positively affected by different types of AR.