We challenge Gallagher’s distinction between the sense of ownership (SO) and the sense of agency (SA) as two separable modalities of experience of the minimal self and argue that a careful investigation of the examples provided to promote this distinction in fact reveals that SO and SA are intimately related and modulate each other. We propose a way to differentiate between the various notions of SO and SA that are currently used interchangeably in the debate, and suggest a more gradual (...) reading of the two that allows for various blends of SO and SA. Such an approach not only provides us with a richer phenomenology but also with a more parsimonious view of the minimal self. (shrink)

Schilbach et al. contrast second-person and third-person approaches to social neuroscience. We discuss relations between second-person and first-person approaches, arguing that they cannot be studied in isolation. Contingency is central for converging first- and second-person approaches. Studies of embodiment show how contingencies scaffold first-person perspective and how the transition from a third- to a second-person perspective fundamentally involves first-person contributions.

Multisensory stimulation has been shown to alter the sense of body-ownership. Given that perceived similarity between one’s own body and those of others is crucial for social cognition, we investigated whether multisensory stimulation can lead participants to experience ownership over a hand of different skin colour. Results from two studies using introspective, behavioural and physiological methods show that, following synchronous visuotactile stimulation, participants can experience body-ownership over hands that seem to belong to a different racial group. Interestingly, a baseline measure (...) of implicit racial bias did not predict whether participants would experience the RHI, but the overall strength of experienced body-ownership seemed to predict the participants’ post-illusion implicit racial bias with those who experienced a stronger RHI showing a lower bias. These findings suggest that multisensory experiences can override strict ingroup/outgroup distinctions based on skin colour and point to a key role for sensory processing in social cognition. (shrink)

An argument is developed for the conclusion that certain neurological conditions and disorders are directly relevant for understanding the self?'s embodiment and the ownership of conscious experience enjoyed by such an embodied self. Since these neurological conditions and disorders provide evidence that there can be shifts of, and compromises to, ownership, they help identify neural substrates and realizers of such ownership. However, even if recent neuroimaging and neuropsychological nominees for neural substrates of ownership unity are core realizers of ownership, they (...) are not its total realizers. Implications of the distinction between core and total realizers are discussed. (shrink)

This study reviews research about the recognition of one’s own face and discusses scientific techniques to investigate differences in brain activation when looking at familiar faces compared to unfamiliar ones. Our analysis highlights how people do not possess a perception of their own face that corresponds precisely to reality, and how the awareness of one’s face can also be modulated by means of the enfacement illusion. This illusion allows one to maintain a sense of self at the expense of a (...) precise discrimination of self-face. The internal dynamics of different brain processes, associated with the construction of bodily identity and the sense of self and capable of integrating signals from different sensory channels, particularly visual and tactile, create a mirror-mask effect. According to this effect, the self-face reflected by a mirror becomes a mask for the self, which has the features of the subject’s face, but nonetheless does not correspond perfectly to its characteristics. This poses interesting questions about the nature and construction of one’s self, as self-face reflections allow the mind to mediate between analogue and virtual reality, between past and future events, between memories and plans of action and, most importantly, between beliefs about our identities. (shrink)

Our understanding of body ownership largely relies on the Rubber Hand Illusion (RHI) paradigm where synchronous stroking of the real and fake hands leads to an illusion of ownership of RH provided its physical, anatomical, and spatial plausibility. Self-attribution of a fake hand also occurs during visuomotor synchrony, when the visual feedback of self-initiated movements follows the trajectory of the instantiated motor command. In both cases, the experience of ownership is established through bottom-up integration and top-down prediction of multisensory (proximodistal) (...) cues within the peripersonal space. It seems, however, that depending on whether the signals are externally or self-generated, top-down expectation signals are qualitatively different. On the one hand, in RHI, the sensory correlations are modulated by empirically induced priors about the internal model of the body. On the other hand, in mRHI, body ownership is actively shaped by processes allowing for continuous comparison between the actual and predicted sensory consequences of the actions. Ample research demonstrates that the differential processing of the predicted and the actual reafferent information is addressed by the central nervous system via an internal Forward Model (FM). Indeed, results from mRHI suggest that in action-contexts mechanism underlying body ownership could be similar to the FM. Crucially FMs integrate across all sensory input including not only proximodistal (visuomotor) but also purely distal sensory signals (visuoauditory). Thus if body ownership results from a consistency of FM, it would be affected by the (in)congruency of purely distal signals provided that they inform about the action-consequences relevant to the task. Here we explicitly address this question. To test our hypothesis, we devise an embodied VR-based task where action outcomes were signaled by distinct auditory cues. By manipulating the cues with respect to their spatial, temporal and semantic congruency, we show that purely distal feedback violating predictions about action outcomes compromises both body ownership and performance. These results demonstrate that body ownership is influenced by cues which not only pertain to the body itself but also those arising outside of the body, and suggest that in goal-oriented tasks body ownership might result from the consistency of forward models. (shrink)

This paper investigates the role of a pre-existing body-model that is an enabling constraint for the incorporation of objects into the body. This body-model is also a basis for the distinction between body extensions (e.g., in the case of tool-use) and incorporation (e.g., in the case of successful prosthesis use). It is argued that, in the case of incorporation, changes in the sense of body-ownership involve a reorganization of the body-model, whereas extension of the body with tools does not involve (...) changes in the sense of body-ownership. (shrink)

Emerging evidence is now challenging the view that patients diagnosed with schizophrenia experience a selective deficit in their sense of agency. Additional disturbances seem to exist in their sense of body ownership. However, the factors underlying this disturbance in body ownership remain elusive. Knowledge of these factors, and increased understanding of how body ownership is related to other abnormalities seen in schizophrenia, could ultimately advance development of new treatments. Research on body ownership in schizophrenia has mainly been investigated with the (...) rubber hand illusion (RHI). Schizophrenia patients show higher susceptibility to the RHI, which may be explained by a stronger reliance on multisensory information over weaker stored body representations. This review shows that a coherent sense of body ownership arises from the integration of both bottom-up sensory processes and higher order, top-down bodily- and perceptual representations. Multisensory integration, temporal binding, anticipation, intention and efferent signals all partly modulate the complex experience of body ownership. Specifically, we propose that patients with schizophrenia have weaker stored body representations, and rely to a greater extent on external stimuli, such as visual information, due to imprecise or highly variable internal predictions on the consequences of action. Moreover, the reduced sense of agency in schizophrenia may additionally contribute to the disturbed sense of body ownership, as evidence from healthy participants suggests that agency and body ownership are interrelated. Vice versa, a reduced sense of body ownership may also contribute to a reduced sense of agency. Future studies should explicitly target the precise relation between the two in schizophrenia. (shrink)

The effect of the body transfer illusion on the perceived strength of self- and externally-generated “tickle” sensations was investigated. As expected, externally generated movement produced significantly higher ratings of tickliness than those associated with self-generated movements. Surprisingly, the body transfer illusion had no influence on the ratings of tickliness, suggesting that highly surprising, and therefore hard to predict, experiences of body image and first-person perspective do not abolish the attenuation of tickle sensations. In addition, evidence was found that a version (...) of the rubber hand illusion exists within the body transfer illusion. We situate our findings within the larger debate over sensory attenuation: there is an attenuation of prediction errors that depends upon the context in which sensory input is predicted , and sensory attenuation is a necessary consequence of self-generated movement irrespective of context . The results support the notion of active inference. (shrink)

How do we acquire a mental representation of our own face? Recently, synchronous, but not asynchronous, interpersonal multisensory stimulation between one’s own and another person’s face has been used to evoke changes in self-identification . We investigated the conscious experience of these changes with principal component analyses that revealed that while the conscious experience during synchronous IMS focused on resemblance and similarity with the other’s face, during asynchronous IMS it focused on multisensory stimulation. Analyses of the identified common factor structure (...) revealed significant quantitative differences between synchronous and asynchronous IMS on self-identification and perceived similarity with the other’s face. Experiment 2 revealed that participants with lower interoceptive sensitivity experienced stronger enfacement illusion. Overall, self-identification and body-ownership rely on similar basic mechanisms of multisensory integration, but the effects of multisensory input on their experience are qualitatively different, possibly underlying the face’s unique role as a marker of selfhood. (shrink)

Visual, somatosensory, and perspectival cues normally provide congruent information about where the self is experienced. Separating those cues by virtual reality techniques, recent studies found that self-location was systematically biased to where a visual–tactile event was seen. Here we developed a novel, repeatable and implicit measure of self-location to compare and extend previous protocols. We investigated illusory self-location and associated phenomenological aspects in a lying body position that facilitates clinically observed abnormal self-location . The results confirm that the self is (...) located to where touch is seen. This leads to either predictable lowering or elevation of self-localization, and the latter was accompanied by sensations of floating, as during out-of-body experiences. Using a novel measurement we show that the unitary and localized character of the self can be experimentally separated from both the origin of the visual perspective and the location of the seen body, which is compatible with clinical data. (shrink)

According to Peter Halligan, […] it is important to consider that the experience of our body is largely the product of a continuously updated „phantom” generated by the brain. (Halligan 2002, 266). Next, he adds: I will argue (not withstanding pathology to the physical body) that the prevalent common sense assumption of phantom experience as pathological is wrongheaded and largely based on a long-standing and pernicious folk assumption that the physical body is necessary for experience of a body. (Halligan 2002, (...) 252). These two remarks can serve as a backdrop for a discussion of the problem of bodily self-consciousness presented in the article. If experiencing a phantom of an amputated limb is indeed not pathological, and if normal bodily experience is de facto based on the body phantom constructed by the brain, then our conception of this very phantom should prove relevant when trying to explain bodily self-consciousness. (shrink)

Artificial stimulation of the peripheral vestibular system has been shown to improve ownership of body parts in neurological patients, suggesting vestibular contributions to bodily self-consciousness. Here, we investigated whether galvanic vestibular stimulation interferes with the mechanisms underlying ownership, touch, and the localization of one’s own hand in healthy participants by using the “rubber hand illusion” paradigm. Our results show that left anodal GVS increases illusory ownership of the fake hand and illusory location of touch. We propose that these changes are (...) due to vestibular interference with spatial and/or temporal mechanisms of visual-tactile integration leading to an enhancement of visual capture. As only left anodal GVS lead to such changes, and based on neurological data on body part ownership, we suggest that this vestibular interference is mediated by the right temporo-parietal junction and the posterior insula. (shrink)

The experience of owning a body is built upon the integration of exteroceptive, interoceptive, and proprioceptive signals. Recently, it has been suggested that motor signals could be particularly important in producing the feeling of body part ownership. One thus may hypothesize that the strength of this feeling may not be spatially uniform; rather, it could vary as a function of the degree by which different body parts are involved in motor behavior. Given that our dominant hand plays a leading role (...) in our motor behavior, we hypothesized that it could be more strongly associated with one’s self compared to its non-dominant counterpart. To explore whether this possible asymmetry manifests as a stronger implicit association of the right hand (vs left hand) with the self, we administered the Implicit Association Test to a group of 70 healthy individuals. To control whether this asymmetric association is human-body specific, we further tested whether a similar asymmetry characterizes the association between a right (vs left) animal body part with the concept of self, in an independent sample of subjects (N= 70, 140 subjects total). Our results revealed a linear relationship between the magnitude of the implicit association between the right hand with the self and the subject’s handedness. In detail, the strength of this association increased as a function of hand preference. Critically, the handedness score did not predict the association of the right-animal body part with the self. These findings suggest that, in healthy individuals, the dominant and non-dominant hands are differently perceived at an implicit level as belonging to the self. We argue that such asymmetry may stem from the different roles that the two hands play in our adaptive motor behavior. (shrink)

This paper presents a gamified motor imagery brain-computer interface (MI-BCI) training in immersive virtual reality. Aim of the proposed training method is to increase engagement, attention, and motivation in co-adaptive event-driven MI-BCI training. This was achieved using gamification, progressive increase of the training pace, and virtual reality design reinforcing the body ownership transfer (embodiment) into the avatar. From the 20 healthy participants performing 6 runs of 2-class MI-BCI training (left/right hand), 19 were trained for a basic level of MI-BCI operation, (...) with average peak accuracy in the session equal to 75.84\%. This confirms the proposed training method succeeded in improvement of the MI-BCI skills; moreover, participants were leaving the session in high positive affect. Although the performance was not directly correlated to the degree of embodiment, subjective magnitude of the body ownership transfer illusion correlated with the abilities to modulate the sensorimotor rhythm. (shrink)

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. (shrink)

A recent report in Consciousness and Cognition provided evidence from a study of the rubber hand illusion that supports the multisensory principle of inverse effectiveness . I describe two methods of assessing the principle of inverse effectiveness , and discuss how the post-hoc method is affected by the statistical artefact of ‘regression towards the mean’. I identify several cases where this artefact may have affected particular conclusions about the PoIE, and relate these to the historical origins of ‘regression towards the (...) mean’. Although the conclusions of the recent report may not have been grossly affected, some of the inferential statistics were almost certainly biased by the methods used. I conclude that, unless such artefacts are fully dealt with in the future, and unless the statistical methods for assessing the PoIE evolve, strong evidence in support of the PoIE will remain lacking. (shrink)

We challenge Gallagher’s distinction between the sense of ownership and the sense of agency as two separable modalities of experience of the minimal self and argue that a careful investigation of the examples provided to promote this distinction in fact reveals that SO and SA are intimately related and modulate each other. We propose a way to differentiate between the various notions of SO and SA that are currently used interchangeably in the debate, and suggest a more gradual reading of (...) the two that allows for various blends of SO and SA. Such an approach not only provides us with a richer phenomenology but also with a more parsimonious view of the minimal self. (shrink)

To offer engaging neurorehabilitation training to neurologic patients, motor tasks are often visualized in virtual reality. Recently introduced head-mounted displays allow to realistically mimic the body of the user from a first-person perspective in a highly immersive VR environment. In this immersive environment, users may embody avatars with different body characteristics. Importantly, body characteristics impact how people perform actions. Therefore, alternating body perceptions using immersive VR may be a powerful tool to promote motor activity in neurologic patients. However, the ability (...) of the brain to adapt motor commands based on a perceived modified reality has not yet been fully explored. To fill this gap, we “tricked the brain” using immersive VR and investigated if multisensory feedback modulating the physical properties of an embodied avatar influences motor brain networks and control. Ten healthy participants were immersed in a virtual environment using an HMD, where they saw an avatar from first-person perspective. We slowly transformed the surface of the avatar from human to stone. We enforced this visual change by repetitively touching the real arm of the participant and the arm of the avatar with a hammer, while progressively replacing the sound of the hammer against skin with stone hitting sound via loudspeaker. We applied single-pulse transcranial magnetic simulation to evaluate changes in motor cortical excitability associated with the illusion. Further, to investigate if the “stone illusion” affected motor control, participants performed a reaching task with the human and stone avatar. Questionnaires assessed the subjectively reported strength of embodiment and illusion. Our results show that participants experienced the “stone arm illusion.” Particularly, they rated their arm as heavier, colder, stiffer, and more insensitive when immersed with the stone than human avatar, without the illusion affecting their experienced feeling of body ownership. Further, the reported illusion strength was associated with enhanced motor cortical excitability and faster movement initiations, indicating that participants may have physically mirrored and compensated for the embodied body characteristics of the stone avatar. Together, immersive VR has the potential to influence motor brain networks by subtly modifying the perception of reality, opening new perspectives for the motor recovery of patients. (shrink)