Plasticity in unimodal and multimodal brain areas reflects multisensory changes in self-face identification.

Nothing provides as strong a sense of self as seeing one's face. Nevertheless, it remains unknown how the brain processes the sense of self during the multisensory experience of looking at one's face in a mirror. Synchronized visuo-tactile stimulation on one's own and another's face, an experience that is akin to looking in the mirror but seeing another's face, causes the illusory experience of ownership over the other person's face and changes in self-recognition. Here, we investigate the neural correlates of this enfacement illusion using fMRI. We examine activity in the human brain as participants experience tactile stimulation delivered to their face, while observing either temporally synchronous or asynchronous tactile stimulation delivered to another's face on either a specularly congruent or incongruent location. Activity in the multisensory right temporo-parietal junction, intraparietal sulcus, and the unimodal inferior occipital gyrus showed an interaction between the synchronicity and the congruency of the stimulation and varied with the self-reported strength of the illusory experience, which was recorded after each stimulation block. Our results highlight the important interplay between unimodal and multimodal information processing for self-face recognition, and elucidate the neurobiological basis for the plasticity required for identifying with our continuously changing visual appearance.

Delving into the relationship between regular physical exercise and cardiac interoception in two cross-sectional studies.

Cardiac interoception, the ability to sense and process cardiac afferent signals, has been shown to improve after a single session of acute physical exercise. However, it remains unclear whether repetitive engagement in physical exercise over time leads to long-term changes in cardiac interoceptive accuracy. It is also unknown whether those changes affect the neural activity associated with the processing of afferent cardiac signals, assessed by the heart-evoked potential (HEP). In this study, we aimed to investigate this hypothesis through two cross-sectional studies, categorizing participants as active or inactive based on physical fitness (Study I; N = 45) or self-reported physical activity levels (Study II; N = 60). Interoception was assessed at rest using the HEP (Studies I and II), the Heartbeat Counting task (Study II), and the Rubber Hand Illusion (RHI) (Study II). Study I showed strong evidence of better cardiovascular fitness in the active group than in the inactive group as well as robust between-group differences in electrocardiogram (ECG) recordings. Study 2 replicated the clear differences in ECG as a function of regular physical activity. Those results were expected due to clear differences in physical activity habits. In contrast, our analysis revealed no robust differences between groups across cardiac interoception tasks and the RHI, although the direct relevance of these measures to interoception remains under investigation. In sum, our results do not provide convincing evidence to support a strong version of the notion that regular physical exercise is associated with an enhanced in cardiac interoception.

Understanding and treating body image disturbances in eating disorders through body illusion interventions: a scoping review protocol.

BACKGROUND: We plan a scoping review aimed to synthesize what is known about the use of sensory-driven body illusion (BI) interventions for understanding and treating body image disturbance (BID) in people diagnosed with clinical eating disorders (EDs) and people with subclinical ED symptomatology. Our study will provide an outline of the current literature, identify gaps within the literature, and suggest novel directions for future research. METHODS/DESIGN: The scoping review process will be guided by the methodological framework of Arksey and O'Malley, subsequent recommendations by Levac et al., and the Preferred Reporting Items for Systematic Reviews and Meta-analysis Protocols Extension for Scoping Reviews guidelines. The following electronic databases will be systematically searched: MEDLINE (via PubMed), Web of Science, PsycINFO, and Scopus. Furthermore, to identify additional studies, we will use a search engine such as Google Scholar, and for grey literature, we will include Proquest for Dissertations and Theses. A search strategy has been identified and agreed upon by the research team in conjunction with a research librarian. Two researchers will screen the titles and abstracts independently and then assess the full text of the selected citations for the inclusion criteria. A third reviewer will be involved in cases of disagreement. Data will be extracted, collated, and charted to summarize all the relevant methods, outcomes, and key findings in the articles. DISCUSSION: A better understanding of this topic will aid in the development and refinement of current treatments aimed at treating BID in people with EDs. Implications and recommendations for research, policy, and practice in the context of the ED community will be discussed. SYSTEMATIC REVIEW REGISTRATION: https://osf.io/3bcm6/?view_only=83b2e8a2445d4266909992e3dfb51929.

Active and passive-touch during interpersonal multisensory stimulation change self-other boundaries.

In the "enfacement" illusion seeing an unfamiliar face being touched at the same time as one's own face evokes changes in self-face recognition. We investigated the contribution of proprioceptive and motor signals derived from self-generated actions in the sensory-driven malleability of self-other boundaries during the "enfacement" illusion. Changes in self-face recognition during active- and passive-touch interpersonal visuo-tactile stimulation were quantified by means of psychophysical and psychometric tasks. Active- and passive-touch evoked comparable changes in the categorical boundaries of self-other distinction, changing the extent to which the other is assimilated into the mental self-representation. Actively touching or simply feeling touch on one's own face with concurrent observed touch on someone else's face seems to elicit comparable changes in self-recognition, suggesting that afferent input might be sufficient for updating one's body-image, although some components of the experience of self-identification seem to be more affected by passive- than by active-touch.

Bodily ownership and self-location: components of bodily self-consciousness.

Recent research on bodily self-consciousness has assumed that it consists of three distinct components: the experience of owning a body (body ownership); the experience of being a body with a given location within the environment (self-location); and the experience of taking a first-person, body-centered, perspective on that environment (perspective). Here we review recent neuroimaging studies suggesting that at least two of these components-body ownership and self-location-are implemented in rather distinct neural substrates, located, respectively, in the premotor cortex and in the temporo-parietal junction. We examine these results and consider them in relation to clinical evidence from patients with altered body perception and work on a variety of multisensory, body-related illusions, such as the rubber hand illusion, the full body illusion, the body swap illusion and the enfacement illusion. We conclude by providing a preliminary synthesis of the data on bodily self-consciousness and its neural correlates.

You, me, and us: Maintaining self-other distinction enhances coordination, agency, and affect.

Coordinating our actions with others changes how we behave and feel. Here, we provide evidence that interacting with others rests on a balance between self-other integration and segregation. Using a group walking paradigm, participants were instructed to synchronize with a metronome while listening to the sounds of 8 virtual partners. By manipulating the similarity and synchronicity of the partners' steps to the participant's own, our novel auditory task disentangles the effects of synchrony and self-other similarity and examines their contribution to both collective and individual awareness. We measured temporal coordination (step timing regularity and synchrony with the metronome), gait patterns, and subjective reports about sense of self and group cohesion. The main findings show that coordination is best when participants hear distinct but synchronous virtual others, leading to greater subjective feelings of agency, strength, dominance, and happiness.

Exploring multisensory integration of non-naturalistic sounds on body perception in young females with eating disorders symptomatology: a study protocol.

BACKGROUND: Bodily illusions can be used to investigate the experience of being in a body by manipulating the underlying processes of multisensory integration. Research suggests that people with eating disorders (EDs) may have impairments in visual, interoceptive, proprioceptive, and tactile bodily perception. Furthermore, people with EDs also show abnormalities in integrating multisensory visuo-tactile and visual-auditory signals related to the body, which may contribute to the development of body image disturbances. Visuo-auditory integration abnormalities have been observed also in people with subthreshold ED symptomatology. However, it remains unclear whether these impairments are specific to bodily signals or if they extend to any auditory signals. METHODS: We will recruit 50 participants (aged 18-24; females assigned at birth) with ED symptomatology (subthreshold group) and 50 control participants. The Eating Disorder Examination Questionnaire will be administered to screen for ED symptomatology and divide the sample into two groups accordingly (control and subthreshold group using a clinical cut-off score of 2.8). The strength of both illusions will be measured implicitly with estimations of body part position and size, and explicitly with self-report questionnaires. As a secondary aim, regression analysis will be run to test the predictive role of susceptibility for both illusions on interoceptive body awareness (measured by the Multidimensional Assessment of Interoceptive Awareness Scale) and sensory-processing sensitivity (measured by the Highly Sensitive Person Scale). DISCUSSION: Our study may contribute to our understanding of the mechanisms underlying body image disturbances. The results may pave the way for novel clinical interventions targeting early symptoms prior to the development of the disorder in young females.

This study aims to investigate whether individuals with subthreshold eating disorder (ED) symptoms show differences in the integration of proprioceptive and auditory cues in relation to body representation, as compared to healthy controls. This will be examined by focusing on two different body parts (finger and waist) with different levels of emotional significance for individuals with EDs. Participants will be screened for ED symptoms and divided into groups accordingly. The strength of the illusions will be measured using estimations of body part position and size, as well as self-report questionnaires. Regression analysis will be used to assess the predictive role of susceptibility to the body illusions on interoceptive body awareness and sensory-processing sensitivity. The results of this study may have implications for understanding the underlying mechanisms of body image disturbances in EDs, and inform the development of clinical interventions for individuals with subthreshold EDs.

The different faces of one's self: an fMRI study into the recognition of current and past self-facial appearances.

Mirror self-recognition is often considered as an index of self-awareness. Neuroimaging studies have identified a neural circuit specialised for the recognition of one's own current facial appearance. However, faces change considerably over a lifespan, highlighting the necessity for representations of one's face to continually be updated. We used fMRI to investigate the different neural circuits involved in the recognition of the childhood and current, adult, faces of one's self. Participants viewed images of either their own face as it currently looks morphed with the face of a familiar other or their childhood face morphed with the childhood face of the familiar other. Activity in areas which have a generalised selectivity for faces, including the inferior occipital gyrus, the superior parietal lobule and the inferior temporal gyrus, varied with the amount of current self in an image. Activity in areas involved in memory encoding and retrieval, including the hippocampus and the posterior cingulate gyrus, and areas involved in creating a sense of body ownership, including the temporo-parietal junction and the inferior parietal lobule, varied with the amount of childhood self in an image. We suggest that the recognition of one's own past or present face is underpinned by different cognitive processes in distinct neural circuits. Current self-recognition engages areas involved in perceptual face processing, whereas childhood self-recognition recruits networks involved in body ownership and memory processing.

Beyond the colour of my skin: how skin colour affects the sense of body-ownership.

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 (VT) 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.

The person in the mirror: using the enfacement illusion to investigate the experiential structure of self-identification.

How do we acquire a mental representation of our own face? Recently, synchronous, but not asynchronous, interpersonal multisensory stimulation (IMS) between one's own and another person's face has been used to evoke changes in self-identification (enfacement illusion). We investigated the conscious experience of these changes with principal component analyses (PCA) 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.

Effects of pitch and musical sounds on body-representations when moving with sound.

The effects of music on bodily movement and feelings, such as when people are dancing or engaged in physical activity, are well-documented-people may move in response to the sound cues, feel powerful, less tired. How sounds and bodily movements relate to create such effects? Here we deconstruct the problem and investigate how different auditory features affect people's body-representation and feelings even when paired with the same movement. In three experiments, participants executed a simple arm raise synchronised with changing pitch in simple tones (Experiment 1), rich musical sounds (Experiment 2) and within different frequency ranges (Experiment 3), while we recorded indirect and direct measures on their movement, body-representations and feelings. Changes in pitch influenced people's general emotional state as well as the various bodily dimensions investigated-movement, proprioceptive awareness and feelings about one's body and movement. Adding harmonic content amplified the differences between ascending and descending sounds, while shifting the absolute frequency range had a general effect on movement amplitude, bodily feelings and emotional state. These results provide new insights in the role of auditory and musical features in dance and exercise, and have implications for the design of sound-based applications supporting movement expression, physical activity, or rehabilitation.

Eye movements and eating disorders: protocol for an exploratory experimental study examining the relationship in young-adult women with subclinical symptomatology.

BACKGROUND: Recent research indicates that patients with anorexia (AN) show specific eye movement abnormalities such as shorter prosaccade latencies, more saccade inhibition errors, and increased rate of saccadic intrusions compared to participants without AN. However, it remains unknown whether these abnormal eye movement patterns, which may serve as potential biomarkers and endophenotypes for an early diagnosis and preventive clinical treatments, start to manifest also in people with subclinical eating disorders (ED) symptomatology. Therefore, we propose a protocol for an exploratory experimental study to investigate whether participants with subclinical ED symptomatology and control participants differ in their performance on several eye movement tasks. METHODS: The sample will be recruited through convenience sampling. The Eating Disorder Examination Questionnaire will be administered as a screening tool to split the sample into participants with subclinical ED symptomatology and control participants. A fixation task, prosaccade/antisaccade task, and memory-guided task will be administered to both groups. Additionally, we will measure anxiety and premorbid intelligence as confounding variables. Means comparison, exploratory Pearson's correlations and discriminant analysis will be performed. DISCUSSION: This study will be the first to elucidate the presence of specific eye movement abnormalities in participants with subclinical ED symptomatology. The results may open opportunities for developing novel diagnostic tools/therapies being helpful to the EDs research community and allied fields.

Body weight distortions in an auditory-driven body illusion in subclinical and clinical eating disorders.

Previous studies suggest a stronger influence of visual signals on body image in individuals with eating disorders (EDs) than healthy controls; however, the influence of other exteroceptive sensory signals remains unclear. Here we used an illusion relying on auditory (exteroceptive) signals to manipulate body size/weight perceptions and investigated whether the mechanisms integrating sensory signals into body image are altered in subclinical and clinical EDs. Participants' footstep sounds were altered to seem produced by lighter or heavier bodies. Across two experiments, we tested healthy women assigned to three groups based on self-reported Symptomatology of EDs (SED), and women with Anorexia Nervosa (AN), and used self-report, body-visualization, and behavioural (gait) measures. As with visual bodily illusions, we predicted stronger influence of auditory signals, leading to an enhanced body-weight illusion, in people with High-SED and AN. Unexpectedly, High-SED and AN participants displayed a gait typical of heavier bodies and a widest/heaviest visualized body in the 'light' footsteps condition. In contrast, Low-SED participants showed these patterns in the 'heavy' footsteps condition. Self-reports did not show group differences. The results of this pilot study suggest disturbances in the sensory integration mechanisms, rather than purely visually-driven body distortions, in subclinical/clinical EDs, opening opportunities for the development of novel diagnostic/therapeutic tools.

Investigating psychological variables for technologies promoting physical activity.

Background: Many technological interventions designed to promote physical activity (PA) have limited efficacy and appear to lack important factors that could increase engagement. This may be due to a discrepancy between research conducted in this space, and software designers' and developers' use of this research to inform new digital applications. Objectives: This study aimed to identify (1) what are the variables that act as barriers and facilitators to PA and (2) which PA variables are currently considered in the design of technologies promoting PA including psychological, physical, and personal/contextual ones which are critical in promoting PA. We emphasize psychological variables in this work because of their sparse and often simplistic integration in digital applications for PA. Methods: We conducted two systematized reviews on PA variables, using PsycInfo and Association for Computing Machinery Digital Libraries for objectives 1 and 2. Results: We identified 38 PA variables (mostly psychological ones) including barriers/facilitators in the literature. 17 of those variables were considered when developing digital applications for PA. Only few studies evaluate PA levels in relation to these variables. The same barriers are reported for all weight groups, though some barriers are stronger in people with obesity. Conclusions: We identify PA variables and illustrate the lack of consideration of these in the design of PA technologies. Digital applications to promote PA may have limited efficacy if they do not address variables acting as facilitators or barriers to participation in PA, and that are important to people representing a range of body weight characteristics.

Just a heartbeat away from one's body: interoceptive sensitivity predicts malleability of body-representations.

Body-awareness relies on the representation of both interoceptive and exteroceptive percepts coming from one's body. However, the exact relationship and possible interaction of interoceptive and exteroceptive systems for body-awareness remain unknown. We sought to understand for the first time, to our knowledge, the interaction between interoceptive and exteroceptive awareness of the body. First, we measured interoceptive awareness with an established heartbeat monitoring task. We, then, used a multi-sensory-induced manipulation of body-ownership (e.g. Rubber Hand Illusion (RHI)) and we quantified the extent to which participants experienced ownership over a foreign body-part using behavioural, physiological and introspective measures. The results suggest that interoceptive sensitivity predicts the malleability of body representations, that is, people with low interoceptive sensitivity experienced a stronger illusion of ownership in the RHI. Importantly, this effect was not simply owing to a poor proprioceptive representation or differences in autonomic states of one's body prior to the multi-sensory stimulation, suggesting that interoceptive awareness modulates the online integration of multi-sensory body-percepts.

Action Sounds Informing Own Body Perception Influence Gender Identity and Social Cognition.

Sensory information can temporarily affect mental body representations. For example, in Virtual Reality (VR), visually swapping into a body with another sex can temporarily alter perceived gender identity. Outside of VR, real-time auditory changes to walkers' footstep sounds can affect perceived body weight and masculinity/femininity. Here, we investigate whether altered footstep sounds also impact gender identity and relation to gender groups. In two experiments, cisgender participants (26 females, 26 males) walked with headphones which played altered versions of their own footstep sounds that sounded more typically male or female. Baseline and post-intervention measures quantified gender identity [Implicit Association Test (IAT)], relation to gender groups [Inclusion of the Other-in-the-Self (IOS)], and perceived masculinity/femininity. Results show that females felt more feminine and closer to the group of women (IOS) directly after walking with feminine sounding footsteps. Similarly, males felt more feminine after walking with feminine sounding footsteps and associated themselves relatively stronger with "female" (IAT). The findings suggest that gender identity is temporarily malleable through auditory-induced own body illusions. Furthermore, they provide evidence for a connection between body perception and an abstract representation of the Self, supporting the theory that bodily illusions affect social cognition through changes in the self-concept.

Use of a real-life practical context changes the relationship between implicit body representations and real body measurements.

A mismatch exists between people's mental representations of their own body and their real body measurements, which may impact general well-being and health. We investigated whether this mismatch is reduced when contextualizing body size estimation in a real-life scenario. Using a reverse correlation paradigm, we constructed unbiased, data-driven visual depictions of participants' implicit body representations. Across three conditions-own abstract, ideal, and own concrete body-participants selected the body that looked most like their own, like the body they would like to have, or like the body they would use for online shopping. In the own concrete condition only, we found a significant correlation between perceived and real hip width, suggesting that the perceived/real body match only exists when body size estimation takes place in a practical context, although the negative correlation indicated inaccurate estimation. Further, participants who underestimated their body size or who had more negative attitudes towards their body weight showed a positive correlation between perceived and real body size in the own abstract condition. Finally, our results indicated that different body areas were implicated in the different conditions. These findings suggest that implicit body representations depend on situational and individual differences, which has clinical and practical implications.

The Perceived Match Between Observed and Own Bodies, but Not Its Accuracy, Is Influenced by Movement Dynamics and Clothing Cues.

Own-perceived body matching - the ability to match one's own body with an observed body - is a difficult task for both general and clinical populations. Thus far, however, own-perceived body matching has been investigated in situations that are incongruent with how we are used to experience and perceive our body in daily life. In the current study, we aimed to examine own-perceived body matching in a context that more closely resembles real life. More specifically, we investigated the effects of body movement dynamics and clothing cues on own-perceived body matching. We asked participants to match their own body with an externally perceived body that was a 3D-generated avatar based on participants' real bodies, fitted with a computer-generated dress. This perceived body was (1) either static (non-walking avatar) or dynamic (walking avatar), (2) either bigger, smaller, or the same size as participants' own body size, and (3) fitted with a dress with a size either bigger, smaller, or the same as participants' own dress size. Our results suggest that movement dynamics cues did not improve the accuracy of own-perceived body matching, but that confidence about dress fit was higher for dynamic avatars, and that the difference between dynamic and static avatars was dependent on participants' self-esteem. Furthermore, when participants were asked to rate the observed body in reference to how they wanted to represent themselves to others, dynamic avatars were rated lower than static avatars for the biggest-sized bodies only, possibly reflecting the influence of movement cues on amplifying socio-cultural stereotypes. Finally, while smaller body/dress sizes were systematically rated higher than bigger body/dress sizes for several self-report items, the interplay between body and dress size played an important role in participants' self-report as well. Thus, while our research suggests that movement and garment dynamics, allowing for realistic, concrete situations that are reminiscent of daily life, influence own-body perception, these cues did not lead to an improvement in accuracy. These findings provide important insights for research exploring (own-) body perception and bodily self-awareness, with practical (e.g., development of online avatars) and clinical (e.g., anorexia nervosa and body dysmorphic disorder) implications.

Auditory-induced body distortions in children and adults.

Recent studies have shown that body-representations can be altered by dynamic changes in sound. In the so-called "auditory Pinocchio illusion" participants feel their finger to be longer when the action of pulling their finger is paired with a rising pitch. Here, we investigated whether preschool children - an age group in which multisensory body-representations are still fine-tuning - are also sensitive to this illusion. In two studies, sixty adult and sixty child participants heard sounds rising or falling in pitch while the experimenter concurrently pulled or pressed their index finger on a vertical (Experiment 1) or horizontal axis (Experiment 2). Results showed that the illusion was subjected to axis and age: both adults and children reported their finger to be longer in Experiment 1, but not in Experiment 2. However, while in adults the feeling of finger elongation corresponded to a recalibration of the fingertip's felt position upwards, this was not the case in children, who presented a dissociation between the feeling of finger elongation and the perceived fingertip position. Our results reveal that the 'auditory Pinocchio illusion' is constrained to the vertical dimension and suggest that multisensory interactions differently contribute to subjective feelings and sense of position depending on developmental stage.

Altering One's Body-Perception Through E-Textiles and Haptic Metaphors.

Technologies change rapidly our perception of reality, moving from augmented to virtual to magical. While e-textiles are a key component in exergame or space suits, the transformative potential of the internal side of garments to create embodied experiences still remains largely unexplored. This paper is the result from an art-science collaborative project that combines recent neuroscience findings, body-centered design principles and 2D vibrotactile array-based fabrics to alter one's body perception. We describe an iterative design process intertwined with two user studies on the effects on body-perceptions and emotional responses of various vibration patterns within textile that were designed as spatial haptic metaphors. Our results show potential in considering materials (e.g., rocks) as sensations to design for body perceptions (e.g., being heavy, strong) and emotional responses. We discuss these results in terms of sensory effects on body perception and synergetic impact to research on embodiment in virtual environments, human-computer interaction, and e-textile design. The work brings a new perspective to the sensorial design of embodied experiences which is based on "material perception" and haptic metaphors, and highlights potential opportunities opened by haptic clothing to change body-perception.