The free-energy self: a predictive coding account of self-recognition

The Effect of a Single Session Rubber Hand Illusion on Pressure Pain Is Not Long-Lasting

BACKGROUND

Rubber hand illusion (RHI) is an experience that causes changes in body perception and awareness as a result of the integration of simultaneous perceived visual and tactile stimuli. After synchronous brush strokes with rubber and real hands, the person perceives the rubber hand as their own. RHI is known to alter pain perception. In this study, it was aimed to evaluate the effects of RHI on pressure pain threshold and continuity of this effect.

METHODS

Twenty-three volunteers who developed RHI were included in our study and two conditions, illusion (synchronous) and control (asynchronous), were applied. The illusion condition was created by synchronous brush strokes, while the control condition was created by asynchronous brush application using different frequency and different finger areas in the same individuals. In both conditions, pressure pain threshold measurements with an algometer were performed at four times: baseline/1st measurement, during the brush stroke/2nd measurement, at the end of the brush stroke/3rd measurement and after the hand was removed from the environment/4th measurement.

RESULTS

It was shown that RHI increased the pressure-pain threshold (p = 0.004) in healthy volunteers. Asynchronous brush strokes arranged as a control trial significantly decreased the pressure pain threshold (p = 0.002).

CONCLUSIONS

It was found that the threshold values that change during the brush strokes return to the initial state after the brush strokes are terminated and the rubber hand is removed from the environment so that the effect of the illusion does not last for a long time with a single session application.

The paradox of the self-studying brain

The paradox of a brain trying to study itself presents a conundrum, raising questions about self-reference, consciousness, psychiatric disorders, and the boundaries of scientific inquiry. By which means can this complex organ shift the focus of study towards itself? We aim at unpacking the intricacies of this paradox. Historically, this question has been raised by philosophers under different frameworks. Thanks to the development of novel techniques to study the brain on a functional and structural level - as well as neurostimulation protocols that can modulate its activity in selected areas - we now possess advanced methods to progress this intricate inquiry. Nonetheless, the broader implications of the brain's pursuit of understanding itself remain unclear to this day. Ultimately, the need to employ both perception and introspection has led to different formulations of consciousness. This creates a challenge, as evidence supporting one formulation does not necessarily support the other. By deconstructing the paradoxical nature of self understanding - from a philosophical and neuroscientific point of view - we may gain insights into the human brain, which could lead to improved understanding of self-awareness and consciousness.

Gesture sonification for enhancing agency: an exploratory study on healthy participants

Background

Body awareness (BA) and proprioception, which are essential components of the sense of agency (SA), are often altered in various mental disorders such as posttraumatic stress disorder (PTSD). However, the relationship between BA, proprioception, and SA, as well as the methods to manipulate them, remain unclear. This study explored using real-time gesture sonification (GS), i.e., wearable technology transforming body movements into sounds, to enhance proprioception, BA, and thus the SA.

Methods

In this within-subjects design, 17 healthy adults (mean age = 25.5 years) with varying dance expertise (novice, amateur, expert) improvised movements to match sounds with and without auditory feedback from motion sensors on wrists/ankles modulated by their gestures. BA, immersion, pleasure, and self-efficacy were measured.

Results

Sonification significantly increased body awareness, reward, and immersion (all p < 0.05).

Conclusion

GS can enhance BA and the SA, pleasure, and control during physical activity. This highlights potential mental health applications, such as agency-based therapies for PTSD. Manipulating bodily perception could improve symptoms and embodiment. Further research should replicate this in clinical populations and explore neurocognitive mechanisms.

The visuomotor synchronization immersive virtual reality of a depression avatar in a stigma context experience mobilizes the fronto-parietal cortex and anterior insula

Introduction

The gradual synchronization of the movement of one's real hand with a virtual one can effectively induce a sense of embodiment (SoE) with an avatar with depression. Although neuroimaging studies have explored the neural correlates of some SoE subcomponents of visuomotor synchronization, the neural correlates of individual differences in SoE and how humans acquire virtual body representations through SoE subcomponents remain to be investigated.

Methods

Here, we used the right hand of a virtual patient with depression in immersive virtual reality (IVR) to induce SoE in participants and measured whole brain activity using functional magnetic resonance imaging (fMRI). Participants were instructed to listen to the audio recording of the IVR experience and visualize movements during the fMRI scan. fMRI data were acquired before and immediately after the visuomotor synchronization IVR experience (target condition) or an asynchronized video experience (control condition), followed by embodiment measures related to the two types of experiences.

Results

All five subcomponents of SoE (sense of ownership, sense of agency, sense of localization, appearance, and response to stimuli) were significantly increased during the visuomotor synchronization IVR experience compared with the asynchronized video experience. A significant negative effect of the SoE score was identified in the frontoparietal and anterior insula only for the visuomotor synchronization IVR experience of guiding the virtual right hand of the avatar with depression, implicating interoceptive and multisensory integration.

Discussion

We demonstrated that all five subcomponents of the SoE were present, and that decreased activity in the frontoparietal and anterior insula were crucial brain regions for the virtual human body to be perceived as one's own body and promote conscious feelings of embodiment.

Self-Awareness from Whole-Body Movements

Humans can recognize their whole-body movements even when displayed as dynamic dot patterns. The sparse depiction of whole-body movements, coupled with a lack of visual experience watching ourselves in the world, has long implicated nonvisual mechanisms to self-action recognition. Using general linear modeling and multivariate analyses on human brain imaging data from male and female participants, we aimed to identify the neural systems for this ability. First, we found that cortical areas linked to motor processes, including frontoparietal and primary somatomotor cortices, exhibit greater engagement and functional connectivity when recognizing self-generated versus other-generated actions. Next, we show that these regions encode self-identity based on motor familiarity, even after regressing out idiosyncratic visual cues using multiple regression representational similarity analysis. Last, we found the reverse pattern for unfamiliar individuals: encoding localized to occipitotemporal visual regions. These findings suggest that self-awareness from actions emerges from the interplay of motor and visual processes.

Body as First Teacher: The Role of Rhythmic Visceral Dynamics in Early Cognitive Development

Embodied cognition-the idea that mental states and processes should be understood in relation to one's bodily constitution and interactions with the world-remains a controversial topic within cognitive science. Recently, however, increasing interest in predictive processing theories among proponents and critics of embodiment alike has raised hopes of a reconciliation. This article sets out to appraise the unificatory potential of predictive processing, focusing in particular on embodied formulations of active inference. Our analysis suggests that most active-inference accounts invoke weak, potentially trivial conceptions of embodiment; those making stronger claims do so independently of the theoretical commitments of the active-inference framework. We argue that a more compelling version of embodied active inference can be motivated by adopting a diachronic perspective on the way rhythmic physiological activity shapes neural development in utero. According to this visceral afferent training hypothesis, early-emerging physiological processes are essential not only for supporting the biophysical development of neural structures but also for configuring the cognitive architecture those structures entail. Focusing in particular on the cardiovascular system, we propose three candidate mechanisms through which visceral afferent training might operate: (a) activity-dependent neuronal development, (b) periodic signal modeling, and (c) oscillatory network coordination.

Nature heals: An informational entropy account of self-organization and change in field psychotherapy

This paper reviews biophysical models of psychotherapeutic change based on synergetics and the free energy principle. These models suggest that introducing sensory surprise into the patient-therapist system can lead to self-organization and the formation of new attractor states, disrupting entrenched patterns of thoughts, emotions, and behaviours. We propose that the therapist can facilitate this process by cultivating epistemic trust and modulating embodied attention to allow surprising affective states to enter shared awareness. Transient increases in free energy enable the update of generative models, expanding the range of experiences available within the patient-therapist phenomenal field. We hypothesize that patterns of disorganization at behavioural and physiological levels, indexed by increased entropy, complexity, and lower determinism, are key markers and predictors of psychotherapeutic gains. Future research should investigate how the therapist's openness to novelty shapes therapeutic outcomes.

A normative framework dissociates need and motivation in hypothalamic neurons

Physiological needs evoke motivational drives that produce natural behaviors for survival. In previous studies, the temporally intertwined dynamics of need and motivation have made it challenging to differentiate these two components. On the basis of classic homeostatic theories, we established a normative framework to derive computational models for need-encoding and motivation-encoding neurons. By combining the model-based predictions and naturalistic experimental paradigms, we demonstrated that agouti-related peptide (AgRP) and lateral hypothalamic leptin receptor (LHLepR) neuronal activities encode need and motivation, respectively. Our model further explains the difference in the dynamics of appetitive behaviors induced by optogenetic stimulation of AgRP or LHLepR neurons. Our study provides a normative modeling framework that explains how hypothalamic neurons separately encode need and motivation in the mammalian brain.

Synthesizing the temporal self: robotic models of episodic and autobiographical memory

Episodic memories are experienced as belonging to a self that persists in time. We review evidence concerning the nature of human episodic memory and of the sense of self and how these emerge during development, proposing that the younger child experiences a persistent self that supports a subjective experience of remembering. We then explore recent research in cognitive architectures for robotics that has investigated the possibility of forms of synthetic episodic and autobiographical memory. We show that recent advances in generative modeling can support an understanding of the emergence of self and of episodic memory, and that cognitive architectures which include a language capacity are showing progress towards the construction of a narrative self with autobiographical memory capabilities for robots. We conclude by considering the prospects for a more complete model of mental time travel in robotics and the implications of this modeling work for understanding human episodic memory and the self in time. This article is part of the theme issue 'Elements of episodic memory: lessons from 40 years of research'.

Viewed touch influences tactile detection by altering decision criterion

Our tactile perception is shaped not only by somatosensory input but also by visual information. Prior research on the effect of viewing touch on tactile processing has found higher tactile detection rates when paired with viewed touch versus a control visual stimulus. Therefore, some have proposed a vicarious tactile system that activates somatosensory areas when viewing touch, resulting in enhanced tactile perception. However, we propose an alternative explanation: Viewing touch makes the observer more liberal in their decision to report a tactile stimulus relative to not viewing touch, also resulting in higher tactile detection rates. To disambiguate between the two explanations, we examined the effect of viewed touch on tactile sensitivity and decision criterion using signal detection theory. In three experiments, participants engaged in a tactile detection task while viewing a hand being touched or approached by a finger, a red dot, or no stimulus. We found that viewing touch led to a consistent, liberal criterion shift but inconsistent enhancement in tactile sensitivity relative to not viewing touch. Moreover, observing a finger approach the hand was sufficient to bias the criterion. These findings suggest that viewing touch influences tactile performance by altering tactile decision mechanisms rather than the tactile perceptual signal.

Meditation and interoception: a conceptual framework for the narrative and experiential self

The concept of the self is complex and there is no consensus on what the self is. However, there are emerging patterns in the literature that point to two different selves, the narrative and experiential self. The narrative self refers to a conceptual or representational knowledge of the self that extends across time and manifests in self-reflection and personality assessments. The experiential self refers to first-person perception, moment-to-moment awareness, embodiment, and a sense of agency. These two selves are reliably linked to two distinct neural circuits, the default mode network (DMN) and the insula and salience network (SN). One of the consistent themes in the meditative and mindfulness literature is a change in the perspective of the self. In this paper, I will review how meditation alters those neural circuits providing a plausible mechanism that can explain the changes in the self. I also propose a rudimentary conceptual framework to account for some of the mixed results found throughout meditation literature.

Embodiment in the enfacement illusion is mediated by self-other overlap

The enfacement illusion is a facial version of the rubber hand illusion, in which participants experience tactile stimulation of their own faces synchronously with the observation of the same stimulation applied to another's face. In previous studies, participants have reported experiencing an illusory embodiment of the other's face following synchronous compared to asynchronous stimulation. In a series of three experiments, we addressed the following three questions: (i) how does similarity between the self and the other, operationalized here as being of the same or different gender to the other, impact the experience of embodiment in the enfacement illusion; (ii) does the experience of embodiment result from alterations to the self-concept; and (iii) is susceptibility to the experience of embodiment associated with interoceptive processing, i.e. perception of the internal state of the body? Results indicate that embodiment is facilitated by the similarity between the self and the other and is mediated by the incorporation of the other into the self-concept, but sensitivity to one's own internal states does not impact upon embodiment within the enfacement illusion. This article is part of the theme issue 'Minds in movement: embodied cognition in the age of artificial intelligence'.

Social exclusion in a virtual Cyberball game reduces the virtual hand illusion

Sense of ownership and agency are two important aspects of the minimal self, but how self-perception is affected by social conditions remains unclear. Here, we studied how social inclusion or exclusion of participants in the course of a virtual Cyberball game would affect explicit judgments and implicit measures of ownership and agency (proprioceptive drift, skin conductance responses, and intentional binding, respectively) in a virtual hand illusion paradigm, in which a virtual hand moved in or out of sync with the participants' own hand. Results show that synchrony affected all four measures. More importantly, this effect interacted with social inclusion/exclusion in the Cyberball game for both ownership and agency measure, showing that social exclusion reduces perceived agency and ownership.

Eliciting the rubber hand illusion by the activation of nociceptive C and Aδ fibers

ABSTRACT

The coherent perceptual experience of one's own body depends on the processing and integration of signals from multiple sensory modalities, including vision, touch, and proprioception. Although nociception provides critical information about damage to the tissues of one's body, little is known about how nociception contributes to own-body perception. A classic experimental approach to investigate the perceptual and neural mechanisms involved in the multisensory experience of one's own body is the rubber hand illusion (RHI). During the RHI, people experience a rubber hand as part of their own body (sense of body ownership) caused by synchronized stroking of the rubber hand in the participant's view and the hidden participant's real hand. We examined whether the RHI can be elicited by visual and "pure" nociceptive stimulation, ie, without tactile costimulation, and if so, whether it follows the basic perceptual rules of the illusion. In 6 separate experiments involving a total of 180 healthy participants, we used a Nd:YAP laser stimulator to specifically target C and Aδ fibers in the skin and compared the illusion condition (congruent visuonociceptive stimulation) to control conditions of incongruent visuonociceptive, incongruent visuoproprioceptive, and no nociceptive stimulation. The illusion was quantified through direct (questionnaire) and indirect (proprioceptive drift) behavioral measures. We found that a nociceptive rubber hand illusion (N-RHI) could be elicited and that depended on the spatiotemporal congruence of visuonociceptive signals, consistent with basic principles of multisensory integration. Our results suggest that nociceptive information shapes multisensory bodily awareness and contributes to the sense of body ownership.

Malleability of the sense of bodily self in early childhood: 5- and 6-year-old children show the enfacement illusion

The mechanisms underlying the developing sense of bodily self are debated. Whereas some scholars stress the role of sensory factors, others propose the importance of contextual factors. By manipulating multisensory stimulation and social familiarity with the other person, we explored two factors that are proposed to relate to young children's developing sense of bodily self. Including an adult sample allowed us to investigate age-related differences of the malleability of the bodily self. To this end, the study implemented an enfacement illusion with children (N = 64) and adults (N = 33). Participants were exposed to one trial with synchronous interpersonal multisensory stimulation and one trial with asynchronous interpersonal multisensory stimulation-either with a stranger or with the mother as the other person. A self-recognition task using morph videos of self and other and an enfacement questionnaire were implemented as dependent measures. Results revealed evidence for the presence of the enfacement effect in children in both measures. The identity of the other person had a significant effect on the self-recognition task. Contrary to our hypothesis, the effect was significantly smaller in the caregiver condition. No significant differences between children and adults emerged. Our results demonstrate the role of both multisensory stimulation and contextual-here social familiarity-factors for the construction and development of a bodily self. The study provides developmental science with a novel approach to the bodily self by showing the validity of the self-recognition task in a child sample. Overall, the study supports proposals that the sense of bodily self is malleable early in development.

Meeting the multidimensional self: fostering selfhood at the interface of Creative Arts Therapies and neuroscience

Intriguing explorations at the intersection of the fields of neuroscience and psychology are driven by the quest to understand the neural underpinnings of "the self" and their psychotherapeutic implications. These translational efforts pertain to the unique Creative Arts Therapies (CATs) and the attributes and value of the self-related processes they offer. The self is considered as a multi-layered complex construct, comprising bodily and mental constituents, subjective-objective perspectives, spatial and temporal dimensions. Neuroscience research, mostly functional brain imaging, has proposed cogent models of the constitution, development and experience of the self, elucidating how the multiple dimensions of the self are supported by integrated hierarchical brain processes. The psychotherapeutic use of the art-forms, generating aesthetic experiences and creative processes, touch upon and connect the various layers of self-experience, nurturing the sense of self. The present conceptual analysis will describe and interweave the neural mechanisms and neural network configuration suggested to lie at the core of the ongoing self-experience, its deviations in psychopathology, and implications regarding the psychotherapeutic use of the arts. The well-established, parsimonious and neurobiologically plausible predictive processing account of brain-function will be discussed with regard to selfhood and consciousness. The epistemic affordance of the experiential CATs will further be portrayed, enabling and facilitating the creation of updated self-models of the body in the world. The neuropsychological impact of the relational therapeutic encounter will be delineated, acknowledging the intersubjective brain synchronization through communicative verbal and non-verbal means and aesthetic experiences. The recognition and assimilation of neuroscientific, phenomenological and clinical perspectives concerning the nested dimensionality of the self, ground the relational therapeutic process and the neuroplastic modulations that CATs have to offer on the premise of fostering, shaping and integrating selfhood.

The Many Roles of Precision in Action

Active inference describes (Bayes-optimal) behaviour as being motivated by the minimisation of surprise of one's sensory observations, through the optimisation of a generative model (of the hidden causes of one's sensory data) in the brain. One of active inference's key appeals is its conceptualisation of precision as biasing neuronal communication and, thus, inference within generative models. The importance of precision in perceptual inference is evident-many studies have demonstrated the importance of ensuring precision estimates are correct for normal (healthy) sensation and perception. Here, we highlight the many roles precision plays in action, i.e., the key processes that rely on adequate estimates of precision, from decision making and action planning to the initiation and control of muscle movement itself. Thereby, we focus on the recent development of hierarchical, "mixed" models-generative models spanning multiple levels of discrete and continuous inference. These kinds of models open up new perspectives on the unified description of hierarchical computation, and its implementation, in action. Here, we highlight how these models reflect the many roles of precision in action-from planning to execution-and the associated pathologies if precision estimation goes wrong. We also discuss the potential biological implementation of the associated message passing, focusing on the role of neuromodulatory systems in mediating different kinds of precision.

Prior Context and Individual Alpha Frequency Influence Predictive Processing during Language Comprehension

The extent to which the brain predicts upcoming information during language processing remains controversial. To shed light on this debate, the present study reanalyzed Nieuwland and colleagues' (2018) [Nieuwland, M. S., Politzer-Ahles, S., Heyselaar, E., Segaert, K., Darley, E., Kazanina, N., et al. Large-scale replication study reveals a limit on probabilistic prediction in language comprehension. eLife, 7, e33468, 2018] replication of DeLong and colleagues (2015) [DeLong, K. A., Urbach, T. P., & Kutas, M. Probabilistic word pre-activation during language comprehension inferred from electrical brain activity. Nature Neuroscience, 8, 1117-1121, 2005]. Participants (n = 356) viewed sentences containing articles and nouns of varying predictability, while their EEG was recorded. We measured ERPs preceding the critical words (namely, the semantic prediction potential), in conjunction with postword N400 patterns and individual neural metrics. ERP activity was compared with two measures of word predictability: cloze probability and lexical surprisal. In contrast to prior literature, semantic prediction potential amplitudes did not increase as cloze probability increased, suggesting that the component may not reflect prediction during natural language processing. Initial N400 results at the article provided evidence against phonological prediction in language, in line with Nieuwland and colleagues' findings. Strikingly, however, when the surprisal of the prior words in the sentence was included in the analysis, increases in article surprisal were associated with increased N400 amplitudes, consistent with prediction accounts. This relationship between surprisal and N400 amplitude was not observed when the surprisal of the two prior words was low, suggesting that expectation violations at the article may be overlooked under highly predictable conditions. Individual alpha frequency also modulated the relationship between article surprisal and the N400, emphasizing the importance of individual neural factors for prediction. The present study extends upon existing neurocognitive models of language and prediction more generally, by illuminating the flexible and subject-specific nature of predictive processing.

Keeping up with ourselves: Multimodal processes underlying body ownership across the lifespan

The sense of a bodily self is thought to depend on adaptive weighting and integration of bodily afferents and prior beliefs. While the physical body changes in shape, size, and functionality across the lifespan, the sense of body ownership remains relatively stable. Yet, little is known about how multimodal integration underlying such sense of ownership is altered in ontogenetic periods of substantial physical changes. We aimed to study this link for the motor and the tactile domain in a mixed-realty paradigm where participants ranging from 7 to 80 years old saw their own body with temporally mismatching multimodal signals. Participants were either stroked on their hand or moved it, while they saw it in multiple trials with different visual delays. For each trial, they judged the visuo-motor/tactile synchrony and rated the sense of ownership for the seen hand. Visual dependence and proprioceptive acuity were additionally assessed. The results show that across the lifespan body ownership decreases with increasing temporal multisensory mismatch, both in the tactile and the motor domain. We found an increased sense of ownership with increasing age independent of delay and modality. Delay sensitivity during multisensory conflicts was not consistently related to age. No effects of age were found on visual dependence or proprioceptive accuracy. The results are at least partly in line with an enhanced weighting of top-down and a reduced weighting of bottom-up signals for the momentary sense of bodily self with increasing age.

Causal Roles of Ventral and Dorsal Neural Systems for Automatic and Control Self-Reference Processing: A Function Lesion Mapping Study

Background: Humans perceive and interpret the world through the lens of self-reference processes, typically facilitating enhanced performance for the task at hand. However, this research has predominantly emphasized the automatic facet of self-reference processing, overlooking how it interacts with control processes affecting everyday situations. Methods: We investigated this relationship between automatic and control self-reference processing in neuropsychological patients performing self-face perception tasks and the Birmingham frontal task measuring executive functions. Results: Principal component analysis across tasks revealed two components: one loaded on familiarity/orientation judgments reflecting automatic self-reference processing, and the other linked to the cross task and executive function indicating control processing requirements. Voxel-based morphometry and track-wise lesion-mapping analyses showed that impairments in automatic self-reference were associated with reduced grey matter in the ventromedial prefrontal cortex and right inferior temporal gyrus, and white matter damage in the right inferior fronto-occipital fasciculus. Deficits in executive control were linked to reduced grey matter in the bilateral inferior parietal lobule and left anterior insula, and white matter disconnections in the left superior longitudinal fasciculus and arcuate fasciculus. Conclusions: The causal evidence suggests that automatic and control facets of self-reference processes are subserved by distinct yet integrated ventral prefrontal-temporal and dorsal frontal-parietal networks, respectively.

Embodiment of underweight and normal-weight avatars affects bodily self-representations in anorexia nervosa

Body image distortion (BID) is a crucial aspect of anorexia nervosa (AN), leading to body overestimation, dissatisfaction, and low self-esteem. BID significantly influences the onset, maintenance, and relapse of the pathology. We assessed whether a Full Body Illusion (FBI) using under and normal-weight avatars' bodies affects perceptual body image and body schema estimations in both individuals with anorexia nervosa (AN) and healthy controls (HC). After each embodiment procedure, we asked participants to estimate the width of their hips (Perceptual Body Image Task) and the minimum aperture width of a virtual door necessary to pass through it (Body Schema Task). Additionally, we asked participants to rate the avatars in terms of self-similarity, attractiveness, and implicit disgust (i.e., pleasant/unpleasant body odour). Whereas participants with AN (N = 26) showed changes in body schema estimations after embodying the normal-weight avatar, no changes were found in HC (N = 25), highlighting increased bodily self-plasticity in AN. Notably, individuals with AN rated the normal weight avatar as the most similar to their real body, which was also considered the least attractive and the most repulsive. These ratings correlated with BID severity. Furthermore, at the explicit level, all participants reported feeling thinner than usual after embodying the underweight avatar. Overall, our findings suggest that BID in AN engages multiple sensory channels (from visual to olfactory) and components (from perceptual to affective), offering potential targets for innovative non-invasive treatments aimed at modifying flexible aspects of body representation.

Predicting the bodily self in space and time

To understand how the human brain distinguishes itself from external stimulation, it was examined if motor predictions enable healthy adult volunteers to infer self-location and to distinguish their body from the environment (and other agents). By uniquely combining a VR-setup with full-body motion capture, a full-body illusion paradigm (FBI) was developed with different levels of motion control: (A) a standard, passive FBI in which they had no motion control; (B) an active FBI in which they made simple, voluntary movements; and (C) an immersive game in which they real-time controlled a human-sized avatar in third person. Systematic comparisons between measures revealed a causal relationship between (i) motion control (prospective agency), (ii) self-other identification, and (iii) the ability to locate oneself. Healthy adults could recognise their movements in a third-person avatar and psychologically align with it (action observation); but did not lose a sense of place (self-location), time (temporal binding), nor who they are (self/other). Instead, motor predictions enabled them to localise their body and to distinguish self from other. In the future, embodied games could target and strengthen the brain's control networks in psychosis and neurodegeneration; real-time motion simulations could help advance neurorehabilitation techniques by fine-tuning and personalising therapeutic settings.

Forgetting ourselves in flow: an active inference account of flow states and how we experience ourselves within them

Flow has been described as a state of optimal performance, experienced universally across a broad range of domains: from art to athletics, gaming to writing. However, its phenomenal characteristics can, at first glance, be puzzling. Firstly, individuals in flow supposedly report a loss of self-awareness, even though they perform in a manner which seems to evince their agency and skill. Secondly, flow states are felt to be effortless, despite the prerequisite complexity of the tasks that engender them. In this paper, we unpick these features of flow, as well as others, through the active inference framework, which posits that action and perception are forms of active Bayesian inference directed at sustained self-organisation; i.e., the minimisation of variational free energy. We propose that the phenomenology of flow is rooted in the deployment of high precision weight over (i) the expected sensory consequences of action and (ii) beliefs about how action will sequentially unfold. This computational mechanism thus draws the embodied cognitive system to minimise the ensuing (i.e., expected) free energy through the exploitation of the pragmatic affordances at hand. Furthermore, given the challenging dynamics the flow-inducing situation presents, attention must be wholly focussed on the unfolding task whilst counterfactual planning is restricted, leading to the attested loss of the sense of self-as-object. This involves the inhibition of both the sense of self as a temporally extended object and higher-order, meta-cognitive forms of self-conceptualisation. Nevertheless, we stress that self-awareness is not entirely lost in flow. Rather, it is pre-reflective and bodily. Our approach to bodily-action-centred phenomenology can be applied to similar facets of seemingly agentive experience beyond canonical flow states, providing insights into the mechanisms of so-called selfless experiences, embodied expertise and wellbeing.

The role of identity priming on the (unconscious) bodily self-attribution

It has been recently demonstrated that hand stimuli presented in a first-, with respect to a third-, person perspective were prioritized before awareness independently from their identity (i.e., self, or other). This pattern would represent an unconscious advantage for self-related bodily stimuli rooted in spatial perspective. To deeper investigate the role of identity, we employed a breaking-Continuous Flash Suppression paradigm in which a self- or other-hand presented in first- or third-person perspective was displayed after a conscious identity-related prime (i.e., self or other face). We replicated the unconscious advantage of the first-person perspective but, crucially, we reported that within the first-person perspective, other-hand stimuli preceded by other-face priming slowed down the conscious access with respect to the other conditions. These findings demonstrate that a top-down conscious identity context modulates the unconscious self-attribution of bodily stimuli. Within a predictive processing framework, we suggest that, by adding ambiguous information, the prime forces a prediction update that slows conscious access.

Metaverse in Mental Health: The Beginning of a Long History

PURPOSE OF REVIEW

We review the first pilot studies applying metaverse-related technologies in psychiatric patients and discuss the rationale for using this complex federation of technologies to treat mental diseases. Concerning previous virtual-reality applications in medical care, metaverse technologies provide the unique opportunity to define, control, and shape virtual scenarios shared by multi-users to exploit the "synchronized brains" potential exacerbated by social interactions.

RECENT FINDINGS

The application of an avatar-based sexual therapy program conducted on a metaverse platform has been demonstrated to be more effective concerning traditional sexual coaching for treating female orgasm disorders. Again, a metaverse-based social skills training program has been tested on children with autism spectrum disorders, demonstrating a significant impact on social interaction abilities. Metaverse-related technologies could enable us to develop new reliable approaches for treating diseases where behavioral symptoms can be addressed using socio-attentive tasks and social-interaction strategies.

Balancing the Senses: Electrophysiological Responses Reveal the Interplay between Somatosensory and Visual Processing During Body-Related Multisensory Conflict

In the study of bodily awareness, the predictive coding theory has revealed that our brain continuously modulates sensory experiences to integrate them into a unitary body representation. Indeed, during multisensory illusions (e.g., the rubber hand illusion, RHI), the synchronous stroking of the participant's concealed hand and a fake visible one creates a visuotactile conflict, generating a prediction error. Within the predictive coding framework, through sensory processing modulation, prediction errors are solved, inducing participants to feel as if touches originated from the fake hand, thus ascribing the fake hand to their own body. Here, we aimed to address sensory processing modulation under multisensory conflict, by disentangling somatosensory and visual stimuli processing that are intrinsically associated during the illusion induction. To this aim, we designed two EEG experiments, in which somatosensory- (SEPs; Experiment 1; N = 18; F = 10) and visual-evoked potentials (VEPs; Experiment 2; N = 18; F = 9) were recorded in human males and females following the RHI. Our results show that, in both experiments, ERP amplitude is significantly modulated in the illusion as compared with both control and baseline conditions, with a modality-dependent diametrical pattern showing decreased SEP amplitude and increased VEP amplitude. Importantly, both somatosensory and visual modulations occur in long-latency time windows previously associated with tactile and visual awareness, thus explaining the illusion of perceiving touch at the sight location. In conclusion, we describe a diametrical modulation of somatosensory and visual processing as the neural mechanism that allows maintaining a stable body representation, by restoring visuotactile congruency under the occurrence of multisensory conflicts.

An Overview of the Bodily Awareness Representation and Interoception: Insights and Progress in the Field of Neurorehabilitation Research

In the last two decades, the scientific literature on so-called body representations has been increasing, and the notion of body awareness (BA) is particularly interesting for neurorehabilitation. In this article, we present results derived from recent studies on this representation, considering the different definitions and explicative models proposed as well as the empirical settings used to test it, providing an extensive overview of these issues. This article discusses the challenge of understanding how we integrate the sensory experiences of proprioception (knowing where our body is in space) and interoception (sensing internal bodily sensations, like hunger of thirst) with our perception of self. This is a difficult problem to analyze because our awareness of our body is inherently linked to our perspective, since the body is the means through which we interact with the world. Presenting the different viewpoints offered by recent theories on this concern, we highlighted that the neurorehabilitation and psychiatric settings offer two important fields useful for the study of BA because in them it is possible to analyze bodily representations by inducing/observing a controlled discrepancy between dysfunctional content and sensory inputs.

Fluid face but not gender: Enfacement illusion through digital face filters does not affect gender identity

It has been shown that observing a face being touched or moving in synchrony with our own face increases self-identification with the former which might alter both cognitive and affective processes. The induction of this phenomenon, termed enfacement illusion, has often relied on laboratory tools that are unavailable to a large audience. However, digital face filters applications are nowadays regularly used and might provide an interesting tool to study similar mechanisms in a wider population. Digital filters are able to render our faces in real time while changing important facial features, for example, rendering them more masculine or feminine according to normative standards. Recent literature using full-body illusions has shown that participants' own gender identity shifts when embodying a different gendered avatar. Here we studied whether participants' filtered faces, observed while moving in synchrony with their own face, may induce an enfacement illusion and if so, modulate their gender identity. We collected data from 35 female and 33 male participants who observed a stereotypically gender mismatched version of themselves either moving synchronously or asynchronously with their own face on a screen. Our findings showed a successful induction of the enfacement illusion in the synchronous condition according to a questionnaire addressing the feelings of ownership, agency and perceived similarity. However, we found no evidence of gender identity being modulated, neither in explicit nor in implicit measures of gender identification. We discuss the distinction between full-body and facial processing and the relevance of studying widely accessible devices that may impact the sense of a bodily self and our cognition, emotion and behaviour.

Disturbed interoception in body dysmorphic disorder: A framework for future research

Body dysmorphic disorder is a severe psychiatric condition characterised by a preoccupation with a perceived appearance flaw or flaws that are typically not observable to others. Although significant advances in understanding the disorder have been made in the past decade, current explanations focus on cognitive, behavioural and visual perceptual disturbances that contribute to the disorder. Such a focus does not consider how perception of the internal body or interoception may be involved, despite (1) clinical observations of disturbed perception of the body in body dysmorphic disorder and (2) disturbed interoception being increasingly recognised as a transdiagnostic factor underlying a wide range of psychopathologies. In this paper, we use an existing model of hierarchical brain function and neural (predictive) processing to propose that body dysmorphic disorder involves defective interoception, with perceived appearance flaws being the result of 'interoceptive prediction errors' that cause body parts to be experienced as 'not just right'. We aim to provide a framework for interoceptive research into body dysmorphic disorder, and outline areas for future research.

Feeling our place in the world: an active inference account of self-esteem

Self-esteem, the evaluation of one's own worth or value, is a critical aspect of psychological well-being and mental health. In this paper, we propose an active inference account of self-esteem, casting it as a sociometer or an inferential capacity to interpret one's standing within a social group. This approach allows us to explore the interaction between an individual's self-perception and the expectations of their social environment.When there is a mismatch between these perceptions and expectations, the individual needs to adjust their actions or update their self-perception to better align with their current experiences. We also consider this hypothesis in relation with recent research on affective inference, suggesting that self-esteem enables the individual to track and respond to this discrepancy through affective states such as anxiety or positive affect. By acting as an inferential sociometer, self-esteem allows individuals to navigate and adapt to their social environment, ultimately impacting their psychological well-being and mental health.

Examining the role of self-reported somatosensory sensations in body (dis)ownership: A scoping review and empirical study of patients with a disturbed sense of limb ownership

Patients with a disturbed sense of limb ownership (DSO) offer a unique window of insight into the multisensory processes contributing to the sense of body ownership. A limited amount of past research has examined the role of sensory deficits in DSO, and even less is known regarding the role of patient self-reported somatosensory sensations in the pathogenesis of DSO. To address this lack of knowledge we first conducted a systematic scoping review following PRISMA-SR guidelines, examining current research into somatosensory deficits and patient self-reported somatosensory sensations in patients with DSO. Eighty studies, including 277 DSO patients, were identified. The assessment of sensory deficits was generally limited in scope and quality, and deficits in tactile sensitivity and proprioception were most frequently found. The reporting of somatosensory sensations was even less frequent, with instances of paraesthesia (pins-and-needles), stiffness/rigidity, numbness and warmth, coldness and heaviness amongst the deficits recorded. In a second part of the study, we sought to directly address the lack of evidence concerning the impact of patient self-reported somatosensory sensations in DSO by measuring DSO and self-reported somatosensory sensations in a large (n = 121) sample of right-hemisphere stroke patients including N = 65 with DSO and N = 56 hemiplegic controls. Results show that feelings of coldness and stiffness modulate DSO symptoms. Sense of heaviness and numbness are more frequent in patients with DSO but do not have a clear impact on disownership symptomology. Although preliminary, these results suggest a role of subjective sensations about the felt body in the sense of limb ownership.

With hand on heart: A cardiac Rubber Hand Illusion

Body illusions such as the Rubber Hand Illusion (RHI) have highlighted how multisensory integration underpins the sense of one's own body. Much of this research has focused on senses arising from outside the body (e.g. vision and touch), but sensations from within the body may also play a role. In a pre-registered study, participants completed a cardiac variation of the RHI, where taps to the finger occurred in or out of time with the heartbeat. We replicated the RHI effect, showing that synchronous but not asynchronous taps to the real and rubber hand increased sensations of embodiment over the rubber hand and caused a shift in the perceived hand location. However, there were no significant influences of cardiac timing on embodiment, nor did it interact with visuo-tactile synchrony. An exploratory analysis found a three-way interaction between synchrony, cardiac timing and interoceptive accuracy as measured by a heartbeat counting task, such that greater interoceptive accuracy was associated with lower embodiment ratings in the systole condition compared to diastole, but only during synchronous stimulation. Although our novel methodology successfully replicated the RHI, our findings suggest that the cooccurence of vision and touch with cardiac signals may make little contribution to the sense of one's body.

Nested Selves: Self-Organization and Shared Markov Blankets in Prenatal Development in Humans

The immune system is a central component of organismic function in humans. This paper addresses self-organization of biological systems in relation to-and nested within-other biological systems in pregnancy. Pregnancy constitutes a fundamental state for human embodiment and a key step in the evolution and conservation of our species. While not all humans can be pregnant, our initial state of emerging and growing within another person's body is universal. Hence, the pregnant state does not concern some individuals but all individuals. Indeed, the hierarchical relationship in pregnancy reflects an even earlier autopoietic process in the embryo by which the number of individuals in a single blastoderm is dynamically determined by cell- interactions. The relationship and the interactions between the two self-organizing systems during pregnancy may play a pivotal role in understanding the nature of biological self-organization per se in humans. Specifically, we consider the role of the immune system in biological self-organization in addition to neural/brain systems that furnish us with a sense of self. We examine the complex case of pregnancy, whereby two immune systems need to negotiate the exchange of resources and information in order to maintain viable self-regulation of nested systems. We conclude with a proposal for the mechanisms-that scaffold the complex relationship between two self-organising systems in pregnancy-through the lens of the Active Inference, with a focus on shared Markov blankets.

Brain-inspired bodily self-perception model for robot rubber hand illusion

The core of bodily self-consciousness involves perceiving ownership of one's body. A central question is how body illusions like the rubber hand illusion (RHI) occur. Existing theoretical models still lack satisfying computational explanations from connectionist perspectives, especially for how the brain encodes body perception and generates illusions from neuronal interactions. Moreover, the integration of disability experiments is also neglected. Here, we integrate biological findings of bodily self-consciousness to propose a brain-inspired bodily self-perception model by which perceptions of bodily self are autonomously constructed without any supervision signals. We successfully validated the model with six RHI experiments and a disability experiment on an iCub humanoid robot and simulated environments. The results show that our model can not only well-replicate the behavioral and neural data of monkeys in biological experiments but also reasonably explain the causes and results of RHI at the neuronal level, thus contributing to the revelation of mechanisms underlying RHI.

Inhabiting the body: Exploring the link between embodiment and identity in community adolescents

The intricate relationship between the body and identity has been highlighted in previous studies. However, a holistic approach to the body that focuses on embodiment is lacking in research examining body - identity linkages. The current study (N = 917 adolescents; 58% female; Mage = 16.17, range = 14-19 years) examined the psychometric properties of a Dutch translation of the Experience of Embodiment Scale (EES) and explored the link between embodiment and personal identity. First, confirmatory factor analysis revealed a second-order factor structure for the EES and adequate reliability coefficients were obtained. Metric invariance across gender was demonstrated for the first- and second-order factors. Second, path analysis demonstrated that experiencing embodiment was positively associated with adaptive identity work. Third, five identity statuses emerged using cluster analysis. Adolescents in statuses reflecting less adaptive identity functioning displayed lower levels of embodiment. The EES shows promising indications of reliability and factor structure for assessing adolescents' Experience of Embodiment, and the present study demonstrates that embodiment is meaningfully related to identity functioning. These findings support the call for the adoption of a positive psychology framework within this research field, with attention given to more broadly defined body-related concepts such as embodiment.

Specificity in the processing of a subject's own name

Subject's own name (SON) is widely used in both daily life and the clinic. Event-related potential (ERP)-based studies have previously detected several ERP components related to SON processing; however, as most of these studies used SON as a deviant stimulus, it was not possible to determine whether these components were SON-specific. To identify SON-specific ERP components, we adopted a passive listening task with EEG data recording involving 25 subjects. The auditory stimuli were a SON, a friend's name (FN), an unfamiliar name (UN) selected from other subjects' names and seven different unfamiliar names (DUNs). The experimental settings included Equal-probabilistic, Frequent-SON, Frequent-FN and Frequent-UN conditions. The results showed that SON consistently evoked a frontocentral SON-related negativity (SRN) within 210-350 ms under all conditions, which was not detected with the other names. Meanwhile, a late positive potential evoked by SON was found to be affected by stimulus probability, showing no significant difference between the SON and the other names in the Frequent-SON condition, or between the SON and a FN in the Frequent-UN condition. Taken together, our findings indicated that the SRN was a SON-specific ERP component, suggesting that distinct neural mechanism underly the processing of a SON.

Storm on predictive brain: A neurocomputational account of ketamine antidepressant effect

For the past decade, ketamine, an N-methyl-D-aspartate receptor (NMDAr) antagonist, has been considered a promising treatment for major depressive disorder (MDD). Unlike the delayed effect of monoaminergic treatment, ketamine may produce fast-acting antidepressant effects hours after a single administration at subanesthetic dose. Along with these antidepressant effects, it may also induce transient dissociative (disturbing of the sense of self and reality) symptoms during acute administration which resolve within hours. To understand ketamine's rapid-acting antidepressant effect, several biological hypotheses have been explored, but despite these promising avenues, there is a lack of model to understand the timeframe of antidepressant and dissociative effects of ketamine. In this article, we propose a neurocomputational account of ketamine's antidepressant and dissociative effects based on the Predictive Processing (PP) theory, a framework for cognitive and sensory processing. PP theory suggests that the brain produces top-down predictions to process incoming sensory signals, and generates bottom-up prediction errors (PEs) which are then used to update predictions. This iterative dynamic neural process would relies on N-methyl-D-aspartate (NMDAr) and α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic receptors (AMPAr), two major component of the glutamatergic signaling. Furthermore, it has been suggested that MDD is characterized by over-rigid predictions which cannot be updated by the PEs, leading to miscalibration of hierarchical inference and self-reinforcing negative feedback loops. Based on former empirical studies using behavioral paradigms, neurophysiological recordings, and computational modeling, we suggest that ketamine impairs top-down predictions by blocking NMDA receptors, and enhances presynaptic glutamate release and PEs, producing transient dissociative symptoms and fast-acting antidepressant effect in hours following acute administration. Moreover, we present data showing that ketamine may enhance a delayed neural plasticity pathways through AMPAr potentiation, triggering a prolonged antidepressant effect up to seven days for unique administration. Taken together, the two sides of antidepressant effects with distinct timeframe could constitute the keystone of antidepressant properties of ketamine. These PP disturbances may also participate to a ketamine-induced time window of mental flexibility, which can be used to improve the psychotherapeutic process. Finally, these proposals could be used as a theoretical framework for future research into fast-acting antidepressants, and combination with existing antidepressant and psychotherapy.

Revisiting the relationship between illusory hand ownership induced by visuotactile synchrony and cardiac interoceptive accuracy

Multisensory integration plays an important role in the experience of the bodily self. Recently, the relationship between exteroception and interoception has been actively debated. The first evidence was a report that the susceptibility of the sense of ownership over a fake hand (i.e., illusory hand ownership: IHO) in the typical rubber hand illusion is negatively modulated by the accuracy of the heartbeat perception (i.e., cardiac interoceptive accuracy: CIA). If reliable, this would suggest an antagonism between the exteroceptive and interoceptive cues underlying the bodily self. However, some inconsistent data have been reported, raising questions about the robustness of the initial evidence. To investigate this robustness, we estimated the extent of the modulatory effect of CIA on IHO susceptibility by applying Bayesian hierarchical modeling to two independent datasets. Overall, our results did not support that IHO susceptibility is modulated by CIA. The present estimates with high uncertainty cannot exclude the hypothesis that the relationship between IHO susceptibility and CIA is so weak as to be negligible. Further studies with larger sample sizes are needed to reach a conclusion about the extent of the modulatory effect. These findings highlight the lack of robustness of key evidence supporting the "antagonism hypothesis".

The self and the Bayesian brain: Testing probabilistic models of body ownership through a self-localization task

Simple multisensory manipulations can induce the illusory misattribution of external objects to one's own body, allowing to experimentally investigate body ownership. In this context, body ownership has been conceptualized as the result of the online Bayesian optimal estimation of the probability that one object belongs to the body from the congruence of multisensory inputs. This idea has been highly influential, as it provided a quantitative basis to bottom-up accounts of self-consciousness. However, empirical evidence fully supporting this view is scarce, as the optimality of the putative inference process has not been assessed rigorously. This pre-registered study aimed at filling this gap by testing a Bayesian model of hand ownership based on spatial and temporal visuo-proprioceptive congruences. Model predictions were compared to data from a virtual-reality reaching task, whereby reaching errors induced by a spatio-temporally mismatching virtual hand have been used as an implicit proxy of hand ownership. To rigorously test optimality, we compared the Bayesian model versus alternative non-Bayesian models of multisensory integration, and independently assess unisensory components and compare them to model estimates. We found that individually measured values of proprioceptive precision correlated with those fitted from our reaching task, providing compelling evidence that the underlying visuo-proprioceptive integration process approximates Bayesian optimality. Furthermore, reaching errors correlated with explicit ownership ratings at the single individual and trial level. Taken together, these results provide novel evidence that body ownership, a key component of self-consciousness, can be truly described as the bottom-up, behaviourally optimal processing of multisensory inputs.

Psychedelics in the treatment of eating disorders: Rationale and potential mechanisms

Eating disorders are serious illnesses showing high rates of mortality and comorbidity with other mental health problems. Psychedelic-assisted therapy has recently shown potential in the treatment of several common comorbidities of eating disorders, including mood disorders, post-traumatic stress disorder, and substance use disorders. The theorized therapeutic mechanisms of psychedelic-assisted therapy suggest that it could be beneficial in the treatment of eating disorders as well. In this review, we summarize preliminary data on the efficacy of psychedelic-assisted therapy in people with anorexia nervosa, bulimia nervosa, and binge eating disorder, which include studies and case reports of psychedelic-assisted therapy with ketamine, MDMA, psilocybin, and ayahuasca. We then discuss the potential therapeutic mechanisms of psychedelic-assisted therapy in these three eating disorders, including both general therapeutic mechanisms and those which are relatively specific to eating disorders. We find preliminary evidence that psychedelic-assisted therapy may be effective in the treatment of anorexia nervosa and bulimia nervosa, with very little data available on binge eating disorder. Regarding mechanisms, psychedelic-assisted therapy may be able to improve beliefs about body image, normalize reward processing, promote cognitive flexibility, and facilitate trauma processing. Just as importantly, it appears to promote general therapeutic factors relevant to both eating disorders and many of their common comorbidities. Lastly, we discuss potential safety concerns which may be associated with these treatments and present recommendations for future research.

Multisensory decisions from self to world

Classic Bayesian models of perceptual inference describe how an ideal observer would integrate 'unisensory' measurements (multisensory integration) and attribute sensory signals to their origin(s) (causal inference). However, in the brain, sensory signals are always received in the context of a multisensory bodily state-namely, in combination with other senses. Moreover, sensory signals from both interoceptive sensing of one's own body and exteroceptive sensing of the world are highly interdependent and never occur in isolation. Thus, the observer must fundamentally determine whether each sensory observation is from an external (versus internal, self-generated) source to even be considered for integration. Critically, solving this primary causal inference problem requires knowledge of multisensory and sensorimotor dependencies. Thus, multisensory processing is needed to separate sensory signals. These multisensory processes enable us to simultaneously form a sense of self and form distinct perceptual decisions about the external world. In this opinion paper, we review and discuss the similarities and distinctions between multisensory decisions underlying the sense of self and those directed at acquiring information about the world. We call attention to the fact that heterogeneous multisensory processes take place all along the neural hierarchy (even in forming 'unisensory' observations) and argue that more integration of these aspects, in theory and experiment, is required to obtain a more comprehensive understanding of multisensory brain function. This article is part of the theme issue 'Decision and control processes in multisensory perception'.

Impact of supplementary sensory feedback on the control and embodiment in human movement augmentation

In human movement augmentation, the number of controlled degrees of freedom could be enhanced by the simultaneous and independent use of supernumerary robotic limbs (SRL) and natural ones. However, this poses several challenges, that could be mitigated by encoding and relaying the SRL status. Here, we review the impact of supplementary sensory feedback on the control and embodiment of SRLs. We classify the main feedback features and analyse how they improve control performance. We report the feasibility of pushing body representation beyond natural human morphology and suggest that gradual SRL embodiment could make multisensory incongruencies less disruptive. We also highlight shared computational bases between SRL motor control and embodiment and suggest contextualizing them within the same theoretical framework. Finally, we argue that a shift towards long term experimental paradigms is necessary for successfully integrating motor control and embodiment.

Supernumerary robotic limbs are robotic devices providing additional limbs to the user. Mattia Pinardi and colleagues review the impact of supplementary sensory feedback on the control performance and embodiment of supernumerary robotic limbs.

Quantifying body ownership information processing and perceptual bias in the rubber hand illusion

Bodily illusions have fascinated humankind for centuries, and researchers have studied them to learn about the perceptual and neural processes that underpin multisensory channels of bodily awareness. The influential rubber hand illusion (RHI) has been used to study changes in the sense of body ownership - that is, how a limb is perceived to belong to one's body, which is a fundamental building block in many theories of bodily awareness, self-consciousness, embodiment, and self-representation. However, the methods used to quantify perceptual changes in bodily illusions, including the RHI, have mainly relied on subjective questionnaires and rating scales, and the degree to which such illusory sensations depend on sensory information processing has been difficult to test directly. Here, we introduce a signal detection theory (SDT) framework to study the sense of body ownership in the RHI. We provide evidence that the illusion is associated with changes in body ownership sensitivity that depend on the information carried in the degree of asynchrony of correlated visual and tactile signals, as well as with perceptual bias and sensitivity that reflect the distance between the rubber hand and the participant's body. We found that the illusion's sensitivity to asynchrony is remarkably precise; even a 50 ms visuotactile delay significantly affected body ownership information processing. Our findings conclusively link changes in a complex bodily experience such as body ownership to basic sensory information processing and provide a proof of concept that SDT can be used to study bodily illusions.

Laterality and hemispheric specialization of self-face recognition

Inspired by the pioneering work of Eran Zaidel beginning in the early 1970's on the role of the two cerebral hemispheres of the human brain in self-related cognition, we review research on self-face recognition from a laterality perspective. The self-face is an important proxy of the self, and self-face recognition has been used as an indicator of self-awareness more broadly. Over the last half century, behavioral and neurological data, along with over two decades of neuroimaging research evidence have accumulated on this topic, generally concluding a right-hemisphere dominance for self-face recognition. In this review, we briefly revisit the pioneering roots of this work by Sperry, Zaidel & Zaidel, and focus on the important body of neuroimaging literature on self-face recognition it has inspired. We conclude with a brief discussion of current models of self-related processing and future directions for research in this area.

Correlations between within-subject variability of pain intensity reports and rubber hand illusion proprioceptive drift

INTRODUCTION

Consistent with the Bayesian brain hypothesis, the within-subject variability of pain intensity reports as captured with the Focused Analgesia Selection Test (FAST) might be a surrogate measure of the certainty in ascending noxious signals. The outcomes of a non-pain-related task, the rubber hand illusion, were hypothesized to reflect the same construct. This study aimed to explore whether within-subject differences in variability of pain intensity reports and the outcomes of the rubber hand illusion might be related.

METHODS

Nonclinical participants underwent the classic rubber hand illusion under synchronous (experimental) and asynchronous (control) conditions. Two outcomes were assessed: proprioceptive drift and feeling of ownership. Thereafter, participants underwent the FAST to assess the within-subject variability of pain reports in response to heat stimuli. Intraclass correlation (ICC) and the correlation coefficient (R2) were the main outcomes. Spearman's correlations were used to assess associations between the outcomes of the 2 tasks.

RESULTS

Thirty-six volunteers completed the study. Both FAST outcomes-ICC (Spearman's r = 0.355, p = 0.033) and R2 (Spearman's r = 0.349, p = 0.037)-were positively correlated with proprioceptive drift in the synchronous but not asynchronous conditions (p > 0.05). The subjective feeling of ownership and FAST outcomes did not correlate (p > 0.05).

CONCLUSIONS

The associations between the 2 tasks' outcomes imply that both tasks at least partly assess similar constructs. Current knowledge suggests that this construct represents the person's certainty in perceiving ascending sensory signals, or, in Bayesian terminology, the certainty of the likelihood.

Patients with Disorders of Consciousness: Are They Nonconscious, Unconscious, or Subconscious? Expanding the Discussion

Unprecedented advancements in the diagnosis and treatment of patients with disorders of consciousness (DoC) have given rise to ethical questions about how to recognize and respect autonomy and a sense of agency of the personhood when those capacities are themselves disordered, as they typically are in patients with DoC. At the intersection of these questions rests the distinction between consciousness and unconsciousness. Indeed, evaluations of consciousness levels and capacity for recovery have a significant impact on decisions regarding whether to discontinue or prolong life-sustaining therapy for DoC patients. However, in the unconsciousness domain, there is the confusing array of terms that are regularly used interchangeably, making it quite challenging to comprehend what unconsciousness is and how it might be empirically grounded. In this opinion paper, we will provide a brief overview of the state of the field of unconsciousness and show how a rapidly evolving electroencephalogram (EEG) neuroimaging technique may offer empirical, theoretical, and practical tools to approach unconsciousness and to improve our ability to distinguish consciousness from unconsciousness and also nonconsciousness with greater precision, particularly in cases that are borderline (as is typical in patients with DoC). Furthermore, we will provide a clear description of three distant notions of (un)consciousness (unconsciousness, nonconsciousness, and subconsciousness) and discuss how they relate to the experiential selfhood which is essential for comprehending the moral significance of what makes life worth living.

Temporal dynamics of the Rubber Hand Illusion

It is widely accepted that the representation of the body is not fixed and immutable, but rather flexible and constantly updated based on a continuous stream of multisensory information. This mechanism can be very useful to adapt to several situations, but it would not be adaptive if the body representation was too malleable or if it wasn't capable of restoring its integrity after a transient modification. Here we used the Rubber Hand Illusion (RHI) to investigate how quickly the body representation can be modified. Previous studies have investigated the timing of the onset and offset of the illusion, however, they did not assess a fine temporal resolution. Here, we used a potentiometer to record a moment-by-moment rating of the feeling of owning the RH for two minutes during the visuo-tactile stimulation and two minutes following the stimulation. Our results suggest that the feeling of Ownership is already established during the first 19 s of stimulation then it continues to grow, but at a much slower pace. The feeling of Ownership disappears within 66 s from the end of the stimulation. This work sheds new light on the temporal dynamics of the RHI and the malleability of the body self-consciousness.

Relating different Dimensions of Bodily Experiences: Review and proposition of an integrative model relying on phenomenology, predictive brain and neuroscience of the self

How we mentally experience our body has been studied in a variety research domains. Each of these domains focuses in its own ways on different aspects of the body, namely the neurophysiological, perceptual, affective or social components, and proposes different conceptual taxonomies. It is therefore difficult to find one's way through this vast literature and to grasp the relationships between the different dimensions of bodily experiences. In this narrative review, we summarize the existing research directions and present their limits. We propose an integrative framework, grounded in studies on phenomenal consciousness, self-consciousness and bodily self-consciousness, that can provide a common basis for evaluating findings on different dimensions of bodily experiences. We review the putative mechanisms, relying on predictive processes, and neural substrates that support this model. We discuss how this model enables a conceptual assessment of the interrelationships between multiple dimensions of bodily experiences and potentiate interdisciplinary approaches.

Combining the Projective Consciousness Model and Virtual Humans for immersive psychological research: a proof-of-concept simulating a ToM assessment

Relating explicit psychological mechanisms and observable behaviours is a central aim of psychological and behavioural science. One of the challenges is to understand and model the role of consciousness, and in particular its subjective perspective as an internal level of representation (including for social cognition) in the governance of behaviour. Toward this aim, we implemented the principles of the Projective Consciousness Model (PCM) into artificial agents embodied as virtual humans, extending a previous implementation of the model. Our goal was to offer a proof-of-concept, based purely on simulations, as a basis for a future methodological framework. Its overarching aim is to be able to assess hidden psychological parameters in human participants, based on a model relevant to consciousness research, in the context of experiments in virtual reality. As an illustration of the approach, we focused on simulating the role of Theory of Mind (ToM) in the choice of strategic behaviours of approach and avoidance to optimise the satisfaction of agents’ preferences. We designed a main experiment in a virtual environment that could be used with real humans, allowing us to classify behaviours as a function of order of ToM, up to the second order. We show that agents using the PCM demonstrated expected behaviours with consistent parameters of ToM in this experiment. We also show that the agents could be used to estimate correctly each other’s order of ToM. Furthermore, in a supplementary experiment, we demonstrated how the agents could simultaneously estimate order of ToM and preferences attributed to others to optimize behavioural outcomes. Future studies will empirically assess and fine tune the framework with real humans in virtual reality experiments.