The sense of embodiment in Virtual Reality and its assessment methods

The sense of embodiment refers to the sensations of being inside, having, and controlling a body. In virtual reality, it is possible to substitute a person’s body with a virtual body, referred to as an avatar. Modulations of the sense of embodiment through modifications of this avatar have perceptual and behavioural consequences on users that can influence the way users interact with the virtual environment. Therefore, it is essential to define metrics that enable a reliable assessment of the sense of embodiment in virtual reality to better understand its dimensions, the way they interact, and their influence on the quality of interaction in the virtual environment. In this review, we first introduce the current knowledge on the sense of embodiment, its dimensions (senses of agency, body ownership, and self-location), and how they relate the ones with the others. Then, we dive into the different methods currently used to assess the sense of embodiment, ranging from questionnaires to neurophysiological measures. We provide a critical analysis of the existing metrics, discussing their advantages and drawbacks in the context of virtual reality. Notably, we argue that real-time measures of embodiment, which are also specific and do not require double tasking, are the most relevant in the context of virtual reality. Electroencephalography seems a good candidate for the future if its drawbacks (such as its sensitivity to movement and practicality) are improved. While the perfect metric has yet to be identified if it exists, this work provides clues on which metric to choose depending on the context, which should hopefully contribute to better assessing and understanding the sense of embodiment in virtual reality

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Manipulating the Sense of Embodiment in Virtual Reality: a study of the interactions between the senses of agency, self-location and ownership

International audienceIn Virtual Reality (VR), the Sense of Embodiment (SoE) corresponds to the feeling of controlling and owning a virtual body, usually referred to as an avatar. The SoE is generally divided into three components: the Sense of Agency (SoA) which characterises the level of control of the user over the avatar, the Sense of Self-Location (SoSL) which is the feeling to be located in the avatar and the Sense of Body-Ownership (SoBO) that represents the attribution of the virtual body to the user. While previous studies showed that the SoE can be manipulated by disturbing either the SoA, the SoBO or the SoSL, the relationships and interactions between these three components still remain unclear. In this paper, we aim at extending the understanding of the SoE and the interactions between its components by 1) experimentally manipulating them in VR via a biased visual feedback, and 2) understanding if each sub-component can be selectively altered or not. To do so, we designed a within-subject experiment where 47 right-handed participants had to perform movements of their right-hand under different experimental conditions impacting the sub-components of embodiment: the SoA was modified by impacting the control of the avatar with visual biased feedback, the SoBO was altered by modifying the realism of the virtual right hand (anthropomorphic cartoon hand or non-anthropomorphic stick ``fingers'') and the SoSL was controlled via the user's point of view (first or third person). After each trial, participants rated their level of agency, ownership and self-location on a 7-item Likert scale. Results' analysis revealed that the three components could not be selectively altered in this experiment. Nevertheless, these preliminary results pave the way to further studies

The sense of embodiment in Virtual Reality and its assessment methods

International audienceThe sense of embodiment refers to the sensations of being inside, having, and controlling a body. In virtual reality, it is possible to substitute a person's body with a virtual body, referred to as an avatar. Modulations of the sense of embodiment through modifications of this avatar have perceptual and behavioural consequences on users that can influence the way users interact with the virtual environment. Therefore, it is essential to define metrics that enable a reliable assessment of the sense of embodiment in virtual reality to better understand its dimensions, the way they interact, and their influence on the quality of interaction in the virtual environment. In this review, we first introduce the current knowledge on the sense of embodiment, its dimensions (senses of agency, body ownership, and self-location), and how they relate the ones with the others. Then, we dive into the different methods currently used to assess the sense of embodiment, ranging from questionnaires to neurophysiological measures. We provide a critical analysis of the existing metrics, discussing their advantages and drawbacks in the context of virtual reality. Notably, we argue that real-time measures of embodiment, which are also specific and do not require double tasking, are the most relevant in the context of virtual reality. Electroencephalography seems a good candidate for the future if its drawbacks (such as its sensitivity to movement and practicality) are improved. While the perfect metric has yet to be identified if it exists, this work provides clues on which metric to choose depending on the context, which should hopefully contribute to better assessing and understanding the sense of embodiment in virtual reality

Manipulating the Sense of Embodiment in Virtual Reality: a study of the interactions between the senses of agency, self-location and ownership

International audienceIn Virtual Reality (VR), the Sense of Embodiment (SoE) corresponds to the feeling of controlling and owning a virtual body, usually referred to as an avatar. The SoE is generally divided into three components: the Sense of Agency (SoA) which characterises the level of control of the user over the avatar, the Sense of Self-Location (SoSL) which is the feeling to be located in the avatar and the Sense of Body-Ownership (SoBO) that represents the attribution of the virtual body to the user. While previous studies showed that the SoE can be manipulated by disturbing either the SoA, the SoBO or the SoSL, the relationships and interactions between these three components still remain unclear. In this paper, we aim at extending the understanding of the SoE and the interactions between its components by 1) experimentally manipulating them in VR via a biased visual feedback, and 2) understanding if each sub-component can be selectively altered or not. To do so, we designed a within-subject experiment where 47 right-handed participants had to perform movements of their right-hand under different experimental conditions impacting the sub-components of embodiment: the SoA was modified by impacting the control of the avatar with visual biased feedback, the SoBO was altered by modifying the realism of the virtual right hand (anthropomorphic cartoon hand or non-anthropomorphic stick ``fingers'') and the SoSL was controlled via the user's point of view (first or third person). After each trial, participants rated their level of agency, ownership and self-location on a 7-item Likert scale. Results' analysis revealed that the three components could not be selectively altered in this experiment. Nevertheless, these preliminary results pave the way to further studies

Manipulating the Sense of Embodiment in Virtual Reality: a study of the interactions between the senses of agency, self-location and ownership

International audienceIn Virtual Reality (VR), the Sense of Embodiment (SoE) corresponds to the feeling of controlling and owning a virtual body, usually referred to as an avatar. The SoE is generally divided into three components: the Sense of Agency (SoA) which characterises the level of control of the user over the avatar, the Sense of Self-Location (SoSL) which is the feeling to be located in the avatar and the Sense of Body-Ownership (SoBO) that represents the attribution of the virtual body to the user. While previous studies showed that the SoE can be manipulated by disturbing either the SoA, the SoBO or the SoSL, the relationships and interactions between these three components still remain unclear. In this paper, we aim at extending the understanding of the SoE and the interactions between its components by 1) experimentally manipulating them in VR via a biased visual feedback, and 2) understanding if each sub-component can be selectively altered or not. To do so, we designed a within-subject experiment where 47 right-handed participants had to perform movements of their right-hand under different experimental conditions impacting the sub-components of embodiment: the SoA was modified by impacting the control of the avatar with visual biased feedback, the SoBO was altered by modifying the realism of the virtual right hand (anthropomorphic cartoon hand or non-anthropomorphic stick ``fingers'') and the SoSL was controlled via the user's point of view (first or third person). After each trial, participants rated their level of agency, ownership and self-location on a 7-item Likert scale. Results' analysis revealed that the three components could not be selectively altered in this experiment. Nevertheless, these preliminary results pave the way to further studies

The role of agency in neurofeedback performance

Neurofeedback (NF) aims to elicit voluntary modulation of neural activity by providing online feedback (FB). In Motor Imagery (MI) NF, participants reduce sensorimotor activity by imagining movements. Providing FB improves modulation relative to simple MI. Yet, a lot of NF participants fail to learn to modulate targeted activity. Most studies feature abstract FB obscuring the causal link between the MI task and the FB. This may reduce the sense of agency, which is rooted in the consistency between predicted and actual sensory outcomes. FB transparency could increase this consistency, yielding better sense of agency and in turn better NF performance. In this study, we tested this hypothesis in a MI-NF EEG-based protocol with different FB conditions

Manipulating the Sense of Embodiment in Virtual Reality: a study of the interactions between the senses of agency, self-location and ownership

International audienceIn Virtual Reality (VR), the Sense of Embodiment (SoE) corresponds to the feeling of controlling and owning a virtual body, usually referred to as an avatar. The SoE is generally divided into three components: the Sense of Agency (SoA) which characterises the level of control of the user over the avatar, the Sense of Self-Location (SoSL) which is the feeling to be located in the avatar and the Sense of Body-Ownership (SoBO) that represents the attribution of the virtual body to the user. While previous studies showed that the SoE can be manipulated by disturbing either the SoA, the SoBO or the SoSL, the relationships and interactions between these three components still remain unclear. In this paper, we aim at extending the understanding of the SoE and the interactions between its components by 1) experimentally manipulating them in VR via a biased visual feedback, and 2) understanding if each sub-component can be selectively altered or not. To do so, we designed a within-subject experiment where 47 right-handed participants had to perform movements of their right-hand under different experimental conditions impacting the sub-components of embodiment: the SoA was modified by impacting the control of the avatar with visual biased feedback, the SoBO was altered by modifying the realism of the virtual right hand (anthropomorphic cartoon hand or non-anthropomorphic stick ``fingers'') and the SoSL was controlled via the user's point of view (first or third person). After each trial, participants rated their level of agency, ownership and self-location on a 7-item Likert scale. Results' analysis revealed that the three components could not be selectively altered in this experiment. Nevertheless, these preliminary results pave the way to further studies

The role of agency in neurofeedback performance

Neurofeedback (NF) aims to elicit voluntary modulation of neural activity by providing online feedback (FB). In Motor Imagery (MI) NF, participants reduce sensorimotor activity by imagining movements. Providing FB improves modulation relative to simple MI. Yet, a lot of NF participants fail to learn to modulate targeted activity. Most studies feature abstract FB obscuring the causal link between the MI task and the FB. This may reduce the sense of agency, which is rooted in the consistency between predicted and actual sensory outcomes. FB transparency could increase this consistency, yielding better sense of agency and in turn better NF performance. In this study, we tested this hypothesis in a MI-NF EEG-based protocol with different FB conditions

The role of agency in neurofeedback performance

Neurofeedback (NF) aims to elicit voluntary modulation of neural activity by providing online feedback (FB). In Motor Imagery (MI) NF, participants reduce sensorimotor activity by imagining movements. Providing FB improves modulation relative to simple MI. Yet, a lot of NF participants fail to learn to modulate targeted activity. Most studies feature abstract FB obscuring the causal link between the MI task and the FB. This may reduce the sense of agency, which is rooted in the consistency between predicted and actual sensory outcomes. FB transparency could increase this consistency, yielding better sense of agency and in turn better NF performance. In this study, we tested this hypothesis in a MI-NF EEG-based protocol with different FB conditions