Ownership Illusion Research Articles

Body ownership and response to threat.

A virtual-reality setup was used to investigate the relationship between perceived body ownership and subjective anxiety, as assessed by an anxiety inventory (SA-I). A pilot study confirmed that synchrony between the participant’s real hand movements and the movements of a virtual effector induced perceived ownership illusions. The illusions were comparable for virtual human hands and virtual cat claws, even though the overall acceptance was greater for human hands. In Experiment 1, participants used the virtual effector to collect coins and avoid knives descending on a screen before anxiety was measured. The level of anxiety increased with synchrony and was higher for human hands than for cat claws, but these two effects were independent. Experiment 2 separated effects of coin catching and knife avoiding by means of a between-participant design. The outcome of Experiment 1 was replicated in the knife-avoiding task but not in the coin-catching task, in which anxiety levels were low and not systematically affected by the type of virtual effector. Taken altogether, our findings suggest that subjective anxiety and ownership are strongly related.

Sensations of skin infestation linked to abnormal frontolimbic brain reactivity and differences in self-representation

Some patients experience skin sensations of infestation and contamination that are elusive to proximate dermatological explanation. We undertook a functional magnetic resonance imaging study of the brain to demonstrate, for the first time, that central processing of infestation-relevant stimuli is altered in patients with such abnormal skin sensations. We show differences in neural activity within amygdala, insula, middle temporal lobe and frontal cortices. Patients also demonstrated altered measures of self-representation, with poorer sensitivity to internal bodily (interoceptive) signals and greater susceptibility to take on an illusion of body ownership: the rubber hand illusion. Together, these findings highlight a potential model for the maintenance of abnormal skin sensations, encompassing heightened threat processing within amygdala, increased salience of skin representations within insula and compromised prefrontal capacity for self-regulation and appraisal.

The role of agency for perceived ownership in the virtual hand illusion.

The rubber hand illusion shows that people can perceive artificial effectors as part of their own body under suitable conditions, and the virtual hand illusion shows the same for virtual effectors. In this study, we compared a virtual version of the rubber-hand setup with a virtual-hand setup, and manipulated the synchrony between stimulation or movement of a virtual "effector" and stimulation or movement of people's own hand, the similarity between virtual effector and people's own hand, and the degree of agency (the degree to which the virtual effector could be controlled by people's own movements). Synchrony-induced ownership illusion was strongly affected by agency but not similarity, which is inconsistent with top-down modulation approaches but consistent with bottom-up approaches to ownership. However, both agency and similarity induce a general bias towards perceiving an object as part of one's body, suggesting that ownership judgments integrate various sources of information.

Alexithymia modulates the experience of the rubber hand illusion.

Alexithymia is associated with lower awareness of emotional and non-emotional internal bodily signals. However, evidence suggesting that alexithymia modulates body awareness at an external level is scarce. This study aimed to investigate whether alexithymia is associated with disrupted multisensory integration by using the rubber hand illusion task. Fifty healthy individuals completed the Toronto Alexithymia Scale and underwent the rubber hand illusion measure. In this measure, one watches a rubber hand being stroked synchronously or asynchronously with one’s own hand, which is hidden from view. Compared to the asynchronous stimulation, the synchronous stimulation results in the illusion that the rubber hand and the participant’s hand are closer together than they really are and that the rubber hand belongs to them. Results revealed that higher levels of alexithymia are associated with a lower ownership illusion over the rubber hand. In conclusion, our findings demonstrate that high alexithymia scorers integrate two simultaneous sensory and proprioceptive events into a single experience (lower multisensory integration) to a lesser extent than low alexithymia scorers. Higher susceptibility to the illusion in high alexithymia scorers may indicate that alexithymia is associated with an abnormal focus of one’s own body.

Over my fake body: body ownership illusions for studying the multisensory basis of own-body perception.

Which is my body and how do I distinguish it from the bodies of others, or from objects in the surrounding environment? The perception of our own body and more particularly our sense of body ownership is taken for granted. Nevertheless, experimental findings from body ownership illusions (BOIs), show that under specific multisensory conditions, we can experience artificial body parts or fake bodies as our own body parts or body, respectively. The aim of the present paper is to discuss how and why BOIs are induced. We review several experimental findings concerning the spatial, temporal, and semantic principles of crossmodal stimuli that have been applied to induce BOIs. On the basis of these principles, we discuss theoretical approaches concerning the underlying mechanism of BOIs. We propose a conceptualization based on Bayesian causal inference for addressing how our nervous system could infer whether an object belongs to our own body, using multisensory, sensorimotor, and semantic information, and we discuss how this can account for several experimental findings. Finally, we point to neural network models as an implementational framework within which the computational problem behind BOIs could be addressed in the future.

Vestibular contributions to a right-hemisphere network for bodily awareness: Combining galvanic vestibular stimulation and the “Rubber Hand Illusion”

An altered sense of one's own body is a common consequence of vestibular damage, and also of damage to vestibular networks in the right hemisphere. However, few experimental studies have investigated whether vestibular signals contribute to bodily awareness. We addressed this issue by combining an established experimental model of bodily awareness (Rubber Hand Illusion -RHI) with galvanic vestibular stimulation (GVS) in healthy participants. Brief left anodal and right cathodal GVS (which predominantly activates vestibular networks in the right hemisphere), or right anodal and left cathodal GVS, or sham stimulation were delivered at random, while participants experienced either synchronous or asynchronous visuo-tactile stimulation of a rubber hand and their own hand. The drift in the perceived position of the participant’s hand towards the rubber hand was used as a proxy measure of the resulting multisensory illusion of body ownership. GVS induced strong polarity-dependent effects on this measure of RHI: left anodal and right cathodal GVS produced significantly lower proprioceptive drift than right anodal and left cathodal GVS. We suggest that vestibular inputs influence the multisensory weighting functions that underlie bodily awareness: the right hemisphere vestibular projections activated by the left anodal and right cathodal GVS increased the weight of intrinsic proprioceptive signals about hand position, and decreased the weight of visual information responsible for visual capture during the RHI.

The Empathy Quotient (EQ) predicts perceived strength of bodily illusions and illusion-related sensations of pain

In this study we test the possible implications of high empathising skills on bodily self–other distinction by measuring the strength of a body ownership illusion and a related experience of illusory pain. One-hundred adult participants completed the Empathy Quotient (EQ) questionnaire. Twenty participants from the top quintile and 20 participants from the bottom quintile of the EQ distribution took part in a laboratory experiment. In the experiment, a classical Rubber Hand Illusion (RHI) was induced followed by the presentation of a series of painful stimuli to the rubber hand. Participants were asked to self-rate the strength of their subjective experience of the RHI and of the illusory pain. A proprioceptive location judgment on the position of the hidden hand was also required before and after RHI induction, to record drifts towards the rubber hand. We found a significant difference between high- and low-empathy participants in RHI and pain score. The EQ was not related with the proprioceptive location judgement drift. It thus appears to be a better predictor of subjective ownership feelings and phenomenological self–other merging than of the behavioural components of bodily illusions.

How to Build an Embodiment Lab: Achieving Body Representation Illusions in Virtual Reality

Advances in computer graphics algorithms and virtual reality (VR) systems, together with the reduction in cost of associated equipment, have led scientists to consider VR as a useful tool for conducting experimental studies in fields such as neuroscience and experimental psychology. In particular virtual body ownership, where the feeling of ownership over a virtual body is elicited in the participant, has become a useful tool in the study of body representation, in cognitive neuroscience and psychology, concerned with how the brain represents the body. Although VR has been shown to be a useful tool for exploring body ownership illusions, integrating the various technologies necessary for such a system can be daunting. In this paper we discuss the technical infrastructure necessary to achieve virtual embodiment. We describe a basic VR system and how it may be used for this purpose, and then extend this system with the introduction of real-time motion capture, a simple haptics system and the integration of physiological and brain electrical activity recordings.

Body ownership causes illusory self-attribution of speaking and influences subsequent real speaking.

When we carry out an act, we typically attribute the action to ourselves, the sense of agency. Explanations for agency include conscious prior intention to act, followed by observation of the sensory consequences; brain activity that involves the feed-forward prediction of the consequences combined with rapid inverse motor prediction to fine-tune the action in real time; priming where there is, e.g., a prior command to perform the act; a cause (the intention to act) preceding the effect (the results of the action); and common-sense rules of attribution of physical causality satisfied. We describe an experiment where participants falsely attributed an act to themselves under conditions that apparently cannot be explained by these theories. A life-sized virtual body (VB) seen from the first-person perspective in 3D stereo, as if substituting the real body, was used to induce the illusion of ownership over the VB. Half of the 44 experimental participants experienced VB movements that were synchronous with their own movements (sync), and the other half asynchronous (async). The VB, seen in a mirror, spoke with corresponding lip movements, and for half of the participants this was accompanied by synchronous vibrotactile stimulation on the thyroid cartilage (Von) but this was not so for the other half. Participants experiencing sync misattributed the speaking to themselves and also shifted the fundamental frequency of their later utterances toward the stimulus voice. Von also contributed to these results. We show that these findings can be explained by current theories of agency, provided that the critical role of ownership over the VB is taken into account.

What can body ownership illusions tell us about minimal phenomenal selfhood?

Illusions have become an invaluable tool for investigating how the sense of a body as one's own is constructed and maintained: During the rubber hand illusion (RHI, Botvinick and Cohen, 1998), congruent touch to one's hidden hand and a fake counterpart produces an illusion of feeling the touch on the fake hand and, more strikingly, an experience of the fake hand as part of one's body (Ehrsson et al., 2004; Tsakiris, 2010). The principles of the RHI paradigm have been extended to various body parts (Petkova et al., 2011), including even the face (Tsakiris, 2008; Apps et al., 2013); most notably, the RHI has been induced for the entire body (full body illusion, FBI), producing similar behavioral and neural responses (anxiety responses, ownership of the fake body, misperception of one's physical location; Ehrsson, 2007; Lenggenhager et al., 2007; Maselli and Slater, 2013). Such body ownership illusions (BOIs) have generated a substantial amount of research and invaluable insights into the mechanisms of body ownership (Tsakiris, 2010; Blanke, 2012; Moseley et al., 2012). The special importance of these illusions lies in the fact that what they manipulate—the sense of having a body—is one of the enabling conditions of minimal phenomenal selfhood (MPS, Gallagher, 2000; Blanke and Metzinger, 2009; Metzinger, 2013a). MPS is defined as the most basic possible kind of self-consciousness or self-awareness (Blanke and Metzinger, 2009; Gallagher and Zahavi, 2010), and investigating its enabling conditions may help us understand what it takes for an organism to have the experience of being a self. Nevertheless, in this paper I will argue that it is still unclear what exactly the mechanisms revealed by BOIs tell us about MPS, and that this needs to be clarified via a joint effort of phenomenological analysis and formal accounts of self-modeling. BOIs rest on the induction of some crossmodal conflict (e.g., touch seen on a fake hand but felt on one's real hand), which violates the predictions of one's body-model about the unity of one's body (Hohwy, 2007). This conflict is resolved by the brain by remapping modality-specific body part-centered reference frames onto each other (e.g., proprioception onto vision), so that the multimodal representation of the body and the space surrounding it remains coherent (Holmes and Spence, 2004; Makin et al., 2008; Tsakiris, 2010; Blanke, 2012). Thereby the spatio-temporal and anatomical constraints of BOIs (touch needs to occur simultaneously at corresponding locations and on a congruent body part in an anatomically plausible posture) suggest that multisensory input has to be compatible with a prior representation of the body (Tsakiris and Haggard, 2005; De Preester and Tsakiris, 2009; Tsakiris, 2010; Moseley et al., 2012). The brain seems to make a probabilistic either-or decision based on current sensory input under a prior body model, which during BOIs results in the replacement of the real body part by the “owned” fake body part (Longo et al., 2008; Moseley et al., 2012). And indeed, the neural mechanisms integrating multisensory information during the RHI may be similarly employed for one's real body parts (Gentile et al., 2013). When the rubber hand is threatened or injured, participants show behavioral, and neural anxiety responses similar as for one's real body part (Ehrsson et al., 2007). BOIs may even affect the regulation of one's physiological states: During illusory ownership, one's real limb's temperature may be downregulated (Moseley et al., 2008), and even the immune system may decrease “protection” of the own limb (Barnsley et al., 2011; Costantini, 2014). In sum, there is compelling evidence that BOIs interfere with the representation of one's body. Upon closer inspection, however, the fact that BOIs isolate “the various components that converge in the holistic experience of our bodies” (Maselli and Slater, 2013) may be a fundamental limitation when it comes to relating them to MPS.

Comparison of SSVEP BCI and Eye Tracking for Controlling a Humanoid Robot in a Social Environment

Recent advances in humanoid robot technologies have made it possible to inhabit a humanlike form located at a remote place. This allows the participant to interact with others in that space and experience the illusion that the participant is actually present in the remote space. Moreover, with these humanlike forms, it may be possible to induce a full-body ownership illusion, where the robot body is perceived to be one's own. We show that it is possible to induce the full-body ownership illusion over a remote robotic body with a highly robotic appearance. Additionally, our results indicate that even with nonmanual control of a remote robotic body, it is possible to induce feelings of agency and illusions of body ownership. Two established control methods, an SSVEP-based BCI and eye tracking, were tested as a means of controlling the robot's gesturing. Our experience and the results indicate that both methods are tractable for immersive control of a humanoid robot in a social telepresence setting.

Sliding perspectives: dissociating ownership from self-location during full body illusions in virtual reality.

Bodily illusions have been used to study bodily self-consciousness and disentangle its various components, among other the sense of ownership and self-location. Congruent multimodal correlations between the real body and a fake humanoid body can in fact trigger the illusion that the fake body is one's own and/or disrupt the unity between the perceived self-location and the position of the physical body. However, the extent to which changes in self-location entail changes in ownership is still matter of debate. Here we address this problem with the support of immersive virtual reality. Congruent visuotactile stimulation was delivered on healthy participants to trigger full body illusions from different visual perspectives, each resulting in a different degree of overlap between real and virtual body. Changes in ownership and self-location were measured with novel self-posture assessment tasks and with an adapted version of the cross-modal congruency task. We found that, despite their strong coupling, self-location and ownership can be selectively altered: self-location was affected when having a third person perspective over the virtual body, while ownership toward the virtual body was experienced only in the conditions with total or partial overlap. Thus, when the virtual body is seen in the far extra-personal space, changes in self-location were not coupled with changes in ownership. If a partial spatial overlap is present, ownership was instead typically experienced with a boosted change in the perceived self-location. We discussed results in the context of the current knowledge of the multisensory integration mechanisms contributing to self-body perception. We argue that changes in the perceived self-location are associated to the dynamical representation of peripersonal space encoded by visuotactile neurons. On the other hand, our results speak in favor of visuo-proprioceptive neuronal populations being a driving trigger in full body ownership illusions.

Effect of biased feedback on motor imagery learning in BCI-teleoperation system.

Feedback design is an important issue in motor imagery BCI systems. Regardless, to date it has not been reported how feedback presentation can optimize co-adaptation between a human brain and such systems. This paper assesses the effect of realistic visual feedback on users' BCI performance and motor imagery skills. We previously developed a tele-operation system for a pair of humanlike robotic hands and showed that BCI control of such hands along with first-person perspective visual feedback of movements can arouse a sense of embodiment in the operators. In the first stage of this study, we found that the intensity of this ownership illusion was associated with feedback presentation and subjects' performance during BCI motion control. In the second stage, we probed the effect of positive and negative feedback bias on subjects' BCI performance and motor imagery skills. Although the subject specific classifier, which was set up at the beginning of experiment, detected no significant change in the subjects' online performance, evaluation of brain activity patterns revealed that subjects' self-regulation of motor imagery features improved due to a positive bias of feedback and a possible occurrence of ownership illusion. Our findings suggest that in general training protocols for BCIs, manipulation of feedback can play an important role in the optimization of subjects' motor imagery skills.

The Journal of Physiology Annual Report 2013–14:Another year of progress

We have just completed another busy and fruitful year for The Journal of Physiology as we continue our mission to promote excellence in the communication of physiology to the world. The Journal is without international boundaries, and below is a summary of where we have recently been, and where we plan to go in 2014–15. We value the support of our readers and those who publish their outstanding findings with us. At the beginning of 2013, The Journal of Physiology Consulting Editor Carol Robinson FRS was made a Dame Commander of the Most Excellent Order of the British Empire (DBE) for Services to Science and Industry. She is widely recognised for her ground-breaking research in mass spectrometry and as a role model for women scientists. In the 2014 New Year Honours list, Peter Ratcliffe FRS, another of The Journal's esteemed Consulting Editors, was awarded a knighthood for his services to clinical medicine. Sir Peter is Head of the Nuffield Department of Clinical Medicine based at the Henry Wellcome Building for Molecular Physiology in Oxford. His laboratory works on understanding the mechanisms by which cells sense and signal hypoxia. In 2013 we published a paper based on the Annual Review Prize Lecture which Peter delivered at Physiology 2012 (the annual meeting of The Physiological Society), Edinburgh, UK, 4 July 2012. Oxygen sensing and hypoxia signalling pathways in animals: the implications of physiology for cancer Ratcliffe PJ (2013) J Physiol 591, 2027–2042 http://jp.physoc.org/content/591/8/2027.full Sadly in 2013 we said goodbye to one of the legends in the field of physiology who had his Nobel Prize winning work in The Journal. David H. Hubel FRS passed away in October after a long and distinguished career in visual neuroscience. Physiology lost one of its giants. The Journal of Physiology lost one of its heroes. David H. Hubel – A man of vision J Physiol 592, issue 1. http://jp.physoc.org/content/592/1.toc

Modulation of pain threshold by virtual body ownership

Appropriate sensorimotor correlations can result in the illusion of ownership of exogenous body parts. Nevertheless, whether and how the illusion of owning a new body part affects human perception, and in particular pain detection, is still poorly investigated. Recent findings have shown that seeing one's own body is analgesic, but it is not known whether this effect is transferable to newly embodied, but exogenous, body parts. In recent years, results from our laboratory have demonstrated that a virtual body can be felt as one's own, provided realistic multisensory correlations. The current work aimed at investigating the impact of virtual body ownership on pain threshold. An immersive virtual environment allowed a first-person perspective of a virtual body that replaced the own. Passive movement of the index finger congruent with the movement of the virtual index finger was used in the 'synchronous' condition to induce ownership of the virtual arm. The pain threshold was tested by thermal stimulation under four conditions: (1) synchronous movements of the real and virtual fingers; (2) asynchronous movements; (3) seeing a virtual object instead of an arm; and (4) not seeing any limb in real world. Our results show that, independently of attentional and stimulus adaptation processes, the ownership of a virtual arm per se can significantly increase the thermal pain threshold. This finding may be relevant for the development and improvement of digital solutions for rehabilitation and pain treatment.

Measuring the Effects through Time of the Influence of Visuomotor and Visuotactile Synchronous Stimulation on a Virtual Body Ownership Illusion

Previous studies have examined the experience of owning a virtual surrogate body or body part through specific combinations of cross-modal multisensory stimulation. Both visuomotor (VM) and visuotactile (VT) synchronous stimulation have been shown to be important for inducing a body ownership illusion, each tested separately or both in combination. In this study we compared the relative importance of these two cross-modal correlations, when both are provided in the same immersive virtual reality setup and the same experiment. We systematically manipulated VT and VM contingencies in order to assess their relative role and mutual interaction. Moreover, we present a new method for measuring the induced body ownership illusion through time, by recording reports of breaks in the illusion of ownership ('breaks') throughout the experimental phase. The balance of the evidence, from both questionnaires and analysis of the breaks, suggests that while VM synchronous stimulation contributes the greatest to the attainment of the illusion, a disruption of either (through asynchronous stimulation) contributes equally to the probability of a break in the illusion.

The Effects of Rotating the Self Out of the Body in the Full Virtual Body Ownership Illusion

It has been shown that it is possible to induce a strong illusion that a virtual body (VB) is one's own body. However, the relative influence of a first-person-perspective (1PP) view of the VB and spatial coincidence of the real body and VB remains unclear. We demonstrate a method that permits separation of these two factors. It provides a 1PP view of a VB, supporting visuomotor synchrony between real body and VB movements, but where the entire scene including the body is rotated 15 degrees upwards through the axis connecting the eyes, so that the VB and real body are coincident only through this axis. In a within-subjects study that compared this 15 degrees rotation with a 0 degrees rotation condition, participants reported only slightly diminished levels of perceived ownership of the VB in the rotated condition and did not detect the rotation of the scene. These results indicate that strong spatial coincidence of the virtual and real bodies is not necessary for a full-body ownership illusion. The rotation method used, similar to the effects of vertical prisms, did not produce significant negative side-effects, thus providing a useful methodology for further investigations of body ownership.

Supplementary Material for: “Measuring the Effects through Time of the Influence of Visuomotor and Visuotactile Synchronous Stimulation on a Virtual Body Ownership Illusion”

<i>Supplementary Material for:</i> “Measuring the Effects through Time of the Influence of Visuomotor and Visuotactile Synchronous Stimulation on a Virtual Body Ownership Illusion”

The Human Touch: Skin Temperature during the Rubber Hand Illusion in Manual and Automated Stroking Procedures

A difference in skin temperature between the hands has been identified as a physiological correlate of the rubber hand illusion (RHI). The RHI is an illusion of body ownership, where participants perceive body ownership over a rubber hand if they see it being stroked in synchrony with their own occluded hand. The current study set out to replicate this result, i.e., psychologically induced cooling of the stimulated hand using an automated stroking paradigm, where stimulation was delivered by a robot arm (PHANToMTM force-feedback device). After we found no evidence for hand cooling in two experiments using this automated procedure, we reverted to a manual stroking paradigm, which is closer to the one employed in the study that first produced this effect. With this procedure, we observed a relative cooling of the stimulated hand in both the experimental and the control condition. The subjective experience of ownership, as rated by the participants, by contrast, was strictly linked to synchronous stroking in all three experiments. This implies that hand-cooling is not a strict correlate of the subjective feeling of hand ownership in the RHI. Factors associated with the differences between the two designs (differences in pressure of tactile stimulation, presence of another person) that were thus far considered irrelevant to the RHI appear to play a role in bringing about this temperature effect.

The extrastriate body area is involved in illusory limb ownership

The Rubber Hand Illusion (RHI) is an established paradigm for studying body ownership, and several studies have implicated premotor and temporo-parietal brain regions in its neuronal foundation. Here we used an automated setup to induce a novel multi-site version of the RHI in healthy human participants inside an MR-scanner, with a RHI and control condition that were matched in terms of synchrony of visual and tactile stimulation. Importantly, as previous research has shown that most of the ownership-related brain areas also respond to observed human actions and touch, or body parts of others, here such potential effects of the experimenter were eliminated by the automated procedure. The RHI condition induced a strong ownership illusion; we found correspondingly stronger brain activity during the RHI versus control condition in contralateral middle occipital gyrus (mOCG) and bilateral anterior insula, which have previously been related to illusory body ownership. Using independent functional localizers, we confirmed that the activity in mOCG was located within the body-part selective extrastriate body area (EBA). Crucially, activity differences in participants' peak voxels within the left EBA correlated strongly positively with their behavioral illusion scores. Thus EBA activity also reflected interindividual differences in the experienced intensity of illusory limb ownership. Moreover, psychophysiological interaction analyses (PPI) revealed that contralateral primary somatosensory cortex had stronger brain connectivity with EBA during the RHI versus control condition, while EBA was more strongly interacting with temporo-parietal multisensory regions. In sum, our findings demonstrate a direct involvement of EBA in limb ownership.