Implicit and explicit changes in body satisfaction evoked by body size illusions: Implications for eating disorder vulnerability in women

Investigating the role of weight in body representation through the Rubber Hand Illusion: when individual weight concerns matter

Bodily weight is a physical characteristic involved in body dissatisfaction. We investigated whether the cognitive body representation can be updated to include weight variations using the Rubber Hand Illusion. Moreover, we aimed to explore the role of the individual expression of weight concerns and fat-phobia. Twenty-eight healthy-weight women participated to a Rubber Hand Illusion study, in which an over- and an under-weight rubber hand were tested together with a normal-weigh rubber hand. We verified the effect of hand's weight on the proprioceptive drift and the subjective experience of illusion. Moreover, we measured the individual expression of weight concerns. As with the normal-weight rubber hand, both the underweight and overweight ones produced significant rubber hand illusion effects, as quantified by proprioceptive judgments and questionnaire ratings. Moreover, higher levels of body image concerns were linked to higher shift towards the under-weight rubber hand, as well as higher expression of fat-phobia increased higher illusory subjective experience towards the normal-weight hand. Hands of different weights can be successfully embodied, in line with previous evidence relative to whole body illusions. Nevertheless, we underlined the role of weight concerns in modulating the illusion. Our results are meaningful for those psychopathological conditions characterized by profound changes in individual weight.

Screening of the Risk of Eating Disorders Among Medical Students in the MENA region and Its Associated Factors: A Multinational Cross-Sectional Study

BACKGROUND

Eating disorders (EDs) are a group of mental diseases marked by disrupted eating behaviors, and are associated with several factors. Medical students are highly exposed to this mental disorder with a prevalence of 17.35% in 2022.

OBJECTIVE

To evaluate the risk of EDs and its associated factors among medical students in the Middle East and North Africa (MENA) region.

METHODS

A web-based cross-sectional study was conducted among medical students in the MENA region during the months of June and July 2024. The primary data collection instrument was a comprehensive questionnaire that contained the Eating Attitudes Test (EAT-26) and sociodemographic and clinical features and designed using Google Forms and distributed via social media platforms.

RESULTS

The total number of participants was 5061. The mean age in our population was 22.58 ± 3.27. Our population's average EAT-26 score was 13.87 ± 10.7, with ranges varying from 0 to 72. Based on their EAT-26 scores being 20 or above, 1254 people (24.8%) were deemed to be at risk of EDs. Among the participants, 8% were underweight. The multivariable logistic regression model revealed several eating disorder risk factors such as T1DM, schizophrenia, autism, female gender, IBD, and daily exposure to thin body ideal. Regular sports practice and weight satisfaction were protective factors.

CONCLUSION

There exists a higher prevalence of individuals at risk for the development of EDs in the MENA region especially females, students with comorbidities, and those having conflictual relationships with their parents. Regular sports practice and weight satisfaction are protective factors.

Gender differences in bodily experience: Insights from virtual reality body illusion

Virtual Reality has significantly improved the understanding of body experience, through techniques such as Body Illusion. Body Illusion allows individuals to perceive an artificial body as their own, changing body perceptual and affective components. Prior research has predominantly focused on female participants, leaving the impact of Body Illusion on males less understood. This study seeks to fill this gap by examining the nuanced bodily experiences of men in comparison to women. 40 participants (20 females and 20 males) were proposed with visuo-tactile synchronous and asynchronous Body Illusion to explore changes in body satisfaction and body size estimation across three critical areas: shoulders, hips, and waist. Results revealed significant initial disparities, with females displaying greater body dissatisfaction and a tendency to overestimate body size. After Body Illusion, females adjusted the hips perceived body size closer to that of the virtual body and reported increased body satisfaction independent of the condition. Conversely, males showed changes only in waist size estimation only after synchronous stimulation without significant shifts in body satisfaction. These results suggest a higher sensitivity of women to embodied experiences, potentially due to societal influences and a greater inclination towards self-objectification. These insights pave the way for creating more refined and effective interventions for body image issues, highlighting the importance of incorporating gender-specific considerations in VR-based prevention and therapeutical programs.

Emotional body representations: more pronounced effect of hands at a more explicit level of awareness

To understand conditions such as body dysmorphic disorder, we need to understand healthy individuals' perceptual, conceptual, and emotional representations of their bodies. Not much is known about the differences in these representations across body districts, for example, hands, feet, and whole-body, despite their differences at sensory and functional levels. To understand this, we developed more implicit and explicit measures of body satisfaction for these body districts. Sixty-seven participants (age M = 30.66, SD = 11.19) completed a series of online Implicit Association Tests (IAT) and a Body Image Satisfaction Visual Analogue Scale (BISVAS; explicit) for each body district (hands/feet/whole body). The results show no differences in the more implicit level of awareness in hands, feet and whole body, while differences are apparent at a more explicit level of awareness, with higher scores for body image satisfaction for the hands than the whole body and marginally significant lower scores for feet than hands. Those findings suggest that visual attention, level of concern attributed to a body district, and disgust drivers are possible factors affecting the experience of attitudinal body image satisfaction.

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.

Developmental changes of bodily self-consciousness in adolescent girls

The body and the self change markedly during adolescence, but how does bodily self-consciousness, the pre-reflexive experience of being a bodily subject, change? We addressed this issue by studying embodiment towards virtual avatars in 70 girls aged 10-17 years. We manipulated the synchrony between participants' and avatars' touch or movement, as well as the avatar visual shape or size relative to each participant's body. A weaker avatar's embodiment in case of mismatch between the body seen in virtual reality and the real body is indicative of a more robust bodily self-consciousness. In both the visuo-tactile and the visuo-motor experiments, asynchrony decreased ownership feeling to the same extent for all participants, while the effect of asynchrony on agency feeling increased with age. In the visuo-tactile experiment, incongruence in visual appearance did not affect agency feeling but impacted ownership, especially in older teenage girls. These findings highlight the higher malleability of bodily self-consciousness at the beginning of adolescence and suggest some independence between body ownership and agency.

Hierarchical and dynamic relationships between body part ownership and full-body ownership

What is the relationship between experiencing individual body parts and the whole body as one's own? We theorised that body part ownership is driven primarily by the perceptual binding of visual and somatosensory signals from specific body parts, whereas full-body ownership depends on a more global binding process based on multisensory information from several body segments. To examine this hypothesis, we used a bodily illusion and asked participants to rate illusory changes in ownership over five different parts of a mannequin's body and the mannequin as a whole, while we manipulated the synchrony or asynchrony of visual and tactile stimuli delivered to three different body parts. We found that body part ownership was driven primarily by local visuotactile synchrony and could be experienced relatively independently of full-body ownership. Full-body ownership depended on the number of synchronously stimulated parts in a nonlinear manner, with the strongest full-body ownership illusion occurring when all parts received synchronous stimulation. Additionally, full-body ownership influenced body part ownership for nonstimulated body parts, and skin conductance responses provided physiological evidence supporting an interaction between body part and full-body ownership. We conclude that body part and full-body ownership correspond to different processes and propose a hierarchical probabilistic model to explain the relationship between part and whole in the context of multisensory awareness of one's own body.

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.

Body perception in pregnant women: a qualitative study

BACKGROUND

Dramatic body changes in pregnancy cause severe concerns among pregnant women about their appearance. Therefore, this study aimed to explore body perception in pregnant women.

MATERIALS AND METHODS

The qualitative study, using the conventional content analysis approach, was conducted on Iranian pregnant women who were in their second or third trimester of pregnancy. Participants were selected through purposeful sampling method. In-depth and semi-structured interviews were held with 18 pregnant women aged 22 to 36 years, using open-ended questions. Sampling was performed until data saturation was reached.

RESULTS

Three main categories were extracted from 18 interviews: (1) "symbols," with two subcategories, including 'motherhood' and 'vulnerability,' (2) "feelings toward body changes," with five subcategories, including 'negative feelings toward skin changes,' 'feeling unfit,' 'attention-drawing body shape,' 'the ridiculous body shape' and 'obesity,' and (3) "attraction and beauty," with two subcategories, including 'sexual attraction' and 'facial beauty.'

CONCLUSION

The results showed that pregnant women's body perception could be described as maternal feelings and feminine attitudes toward changes during pregnancy compared to mental ideals of facial and body beauty. It is recommended that Iranian women's body perception during pregnancy be evaluated using this study results and that counseling interventions be implemented for women with negative body perceptions.

Normal or tingly? A story about hands and feet

AIMS

Spontaneous sensations (SPS) are sensations that are felt in the body in the absence of external stimulation. The literature on SPS has used explicit measures, such as questionnaires to explore SPS, while no studies to date have examined SPS on an implicit level. This study was conducted to collect representative stimuli that can be used to build such a task, for example, an Implicit Association Test.

METHODS

An online survey was completed by 18 participants to identify the most frequent words used to describe our limbs in the presence or absence of SPS.

RESULTS

Individuals who perceive and those who do not perceive SPS in their limbs describe their limbs as normal, while the most frequently described SPS were itching and tingling.

CONCLUSIONS

Thus, we use the same words/adjectives to describe how we perceive our limbs. However, the way we experience SPS varies as we experience more SPS in hands than feet.

The contribution of stimulating multiple body parts simultaneously to the illusion of owning an entire artificial body

The full-body ownership illusion exploits multisensory perception to induce a feeling of ownership of an entire artificial body. Although previous research has shown that synchronous visuotactile stimulation of a single body part is sufficient for illusory ownership of the whole body, the effect of combining multisensory stimulation across multiple body parts remains unknown. Therefore, 48 healthy adults participated in a full-body ownership illusion with conditions involving synchronous (illusion) or asynchronous (control) visuotactile stimulation to one, two, or three body parts simultaneously (2×3 design). We used questionnaires to isolate illusory ownership of five specific body parts (left arm, right arm, trunk, left leg, right leg) from the full-body ownership experience and sought to test not only for increased ownership in synchronous versus asynchronous conditions but also for potentially varying degrees of full-body ownership illusion intensity related to the number of body parts stimulated. Illusory full-body ownership and all five body-part ownership ratings were significantly higher following synchronous stimulation than asynchronous stimulation (p-values < .01). Since non-stimulated body parts also received significantly increased ownership ratings following synchronous stimulation, the results are consistent with an illusion that engages the entire body. Furthermore, we noted that ownership ratings for right body parts (which were often but not always stimulated in this experiment) were significantly higher than ownership ratings for left body parts (which were never stimulated). Regarding the effect of stimulating multiple body parts simultaneously on explicit full-body ownership ratings, there was no evidence of a significant main effect of the number of stimulations (p = .850) or any significant interaction with stimulation synchronicity (p = .160), as assessed by linear mixed modelling. Instead, median ratings indicated a moderate affirmation (+1) of an illusory full-body sensation in all three synchronous conditions, a finding mirrored by comparable full-body illusion onset times. In sum, illusory full-body ownership appears to be an 'all-or-nothing' phenomenon and depends upon the synchronicity of visuotactile stimulation, irrespective of the number of stimulated body parts.

The role of affective touch in whole-body embodiment remains equivocal

Previous studies have highlighted that affective touch delivered at slow velocities (1-10 cm/s) enhances body-part embodiment during multisensory illusions, yet its role towards whole-body embodiment is less established. Across two experiments, we investigated the role of affective touch towards subjective embodiment of a whole mannequin body within the full body illusion, amongst healthy females. Participants perceived affective touch to be more pleasant than non-affective touch, but this did not enhance subjective embodiment within the illusion and no interaction between synchrony (Experiment 1), or congruency (Experiment 2), and the velocity of touch was observed. Finally, the perceived pleasantness of touch was not modulated by subthreshold eating disorder psychopathology, as measured by means of a self-report questionnaire. Therefore, the present findings suggest that enhancement of embodiment due to affective touch may be body-part specific, and not generalise to greater ownership towards a whole body.

Measuring recognition of body changes over time: A human-computer interaction tool using dynamic morphing and body ownership illusion

Measuring body image is crucial at both personal and social levels. Previous studies have attempted to quantitatively measure body image but methods for measuring body change recognition over time have not yet been established. The present study proposes a novel human-computer interaction technique using dynamic morphing and body ownership illusion, and we conducted a user study to investigate how body ownership illusion and gender would affect to body change recognition. The results showed that a participant's body change recognition was weak when the body ownership illusion was strong. In addition, female participants were less sensitive than male participants. With our proposed technique, we demonstrated that we were able to quantitatively measure body change recognition and our empirical data indicated that body change recognition varied depending on body ownership illusion and gender, suggesting that our methodology could not only be used in future body image studies but also in eating disorder treatments.

The Spanish Body Image State Scale: Factor Structure, Reliability and Validity in a Colombian Population

OBJECTIVE

Body image is a construct highly dependent on culture and ethnicity. Furthermore, recent studies reveal that body image is not only a trait, but also a momentary state subject to change in diverse situational contexts. However, cultural influences on momentary body image have not been sufficiently investigated. To assess the influence of Latin American culture on momentary body image and to enable its comparison to Western countries, the Spanish translation of an existing state body image scale such as the Body Image States Scale (BISS) is needed. In addition, the factor structure, reliability and general validity of the Spanish BISS (S-BISS) should be evaluated prior to its application in diverse situational contexts.

METHOD

We conducted a cross-sectional study evaluating 1137 individuals between the ages of 18 and 28 years from Barranquilla, Colombia, South America. The original BISS, which assesses body satisfaction, was translated from English to Spanish. Factorial structure, scale score reliability and convergent/divergent validity were assessed.

RESULTS

Exploratory and confirmatory factor analyses revealed that a one-factor model with correlated items best described the factorial structure present in the BISS questionnaire. The coefficient of scale score reliability was α = 0.92 (McDonalds ω = 0.93), with similar results for men and women. Significant differences between males and females were found with lesser body satisfaction in females (W = 163260, p = 0.016). Lower S-BISS scores indicating less body satisfaction were associated with higher BMI (r = -0.287, p < 0.001) and obtained in participants who were currently on a diet (t 1135 = -3.98, p < 0.001). The S-BISS was negatively correlated with a trait body image measurement assessing body dissatisfaction (Body Shape Questionnaire, r = -0.577, p < 0.001) and a psychopathology questionnaire (Brief Symptom Inventory 53, r = -0.331, p < 0.001).

CONCLUSION

The S-BISS is a valid and reliable instrument to assess body image in the Colombian population, and exhibits similar psychometric properties to those of the original version. Future studies should examine whether the S-BISS captures change in state body image when applied in diverse situational contexts.

Investigating the Components of Body Image Disturbance Within Eating Disorders

Body image disturbance has been highlighted as a common characteristic within the development and maintenance of clinical eating disorders (EDs), represented by alterations in an individual's bodily experience. However, whilst the perceptual stability of the sense of body ownership has been investigated in ED patients, the stability of the sense of body agency in those with ED is yet to be examined. Therefore, body ownership and body agency were investigated using the moving rubber hand illusion, alongside measures of explicit and implicit body satisfaction. Furthermore, with evidence demonstrating a direct link between perceptual and cognitive-affective components of body image in the healthy population, the relationship between measures of body perception and body satisfaction was investigated. Results showed that both ED and healthy individuals displayed a similar subjective experience of illusory ownership and agency towards the fake hand, following voluntary movement. However, whilst both groups initially overestimated their own hand width prior to the illusion, the ED group displayed a significant reduction in hand size estimation following the illusion, which was not matched to the same degree in healthy individuals. In addition, ED individuals displayed a significantly lower body satisfaction compared with healthy females, on both an explicit and implicit level. Such implicit outcomes were shown to be driven specifically by a weaker association between the self and attractiveness. Finally, a significant relationship was observed between specific perceptual measures and implicit body satisfaction, which highlights the important link between perceptual and cognitive-affective components of one's body image. Together, such findings provide a useful foundation for further research to study the conditions in which these two components relate with regard to body image and its disturbance, particularly in relation to the prognosis and treatment of EDs.

The Effect of a Virtual-Reality Full-Body Illusion on Body Representation in Obesity

Background. The effective illusory ownership over an artificial body in modulating body representations in healthy and eating disorders population has been repeatedly reported in recent literature. In this study, we extended this research in the field of obesity: specifically, we investigated whether ownership over a virtual body with a skinny abdomen might be successfully experienced by participants affected by obesity. Methods. Fifteen participants with obesity and fifteen healthy-weight participants took part at this study in which the VR-Full-Body Illusion was adopted. The strength of illusion was investigated through the traditional Embodiment Questionnaire, while changes in bodily experience were measured through a body size estimation task. Results. Participants with obesity as well as healthy-weight participants reported to experience the illusion. About the body size estimation task, both groups reported changes only in the estimation of the abdomen’s circumference after the experimental condition, in absence of any another difference. Discussion. Participants with obesity reported to experience the illusion over a skinny avatar, but the modulation of the bodily experience seems controversial. Future lines of research exploiting this technique for modulating body representations in obesity, specifically in terms of potential therapeutic use, were discussed.

The Effect of Visual Capture Towards Subjective Embodiment Within the Full Body Illusion

Typically, multisensory illusion paradigms emphasise the importance of synchronous visuotactile integration to induce subjective embodiment towards another body. However, the extent to which embodiment is due to the 'visual capture' of congruent visuoproprioceptive information alone remains unclear. Thus, across two experiments (total N = 80), we investigated how mere visual observation of a mannequin body, viewed from a first-person perspective, influenced subjective embodiment independently from concomitant visuotactile integration. Moreover, we investigated whether slow, affective touch on participants' own, unseen body (without concomitant touch on the seen mannequin) disrupted visual capture effects to a greater degree than fast, non-affective touch. In total, 40% of participants experienced subjective embodiment towards the mannequin body following mere visual observation, and this effect was significantly higher than conditions which included touch to participants own, unseen body. The velocity of the touch that participants received (affective/non-affective) did not differ in modulating visual capture effects. Furthermore, the effects of visual capture and perceived pleasantness of touch was not modulated by subthreshold eating disorder psychopathology. Overall, this study suggests that congruent visuoproprioceptive cues can be sufficient to induce subjective embodiment of a whole body, in the absence of visuotactile integration and beyond mere confabulatory responses.