Investigating the influence of personal BMI on own body size perception in females using self-avatars

Previous research has suggested that inaccuracies in own body size estimation can largely be explained by a known error in perceived magnitude, called contraction bias (Cornelissen, Bester, Cairns, Tovée Cornelissen, 2015). According to this, own body size estimation is biased towards an average reference body, such that individuals with a low body mass index (BMI) should overestimate their body size and high BMI individuals should underestimate their body size. However, previous studies have mainly focused on self-body size evaluation of patients suffering from anorexia nervosa. In this study, we tested healthy females varying in BMI to investigate whether personal body size influences accuracy of body size estimation and sensitivity to weight changes, reproducing a scenario of standing in front of a full length mirror. We created personalized avatars with a 4D full-body scanning system that records participants’ body geometry and texture, and altered the weight of the avatars based on a statistical body model. In two psychophysical experiments, we presented the stimuli on a stereoscopic, large-screen immersive display, and asked participants to respond to whether the body they saw was their own. Additionally, we used several questionnaires to assess participants’ self-esteem, eating behavior, and their attitudes towards their body shape and weight. Our results show that participants, across the range of BMI, veridically perceived their own body size, contrary to what is suggested by the contraction bias hypothesis. Interestingly, we found that BMI influenced sensitivity to weight changes in the positive direction, such that people with higher BMIs were more willing to accept bigger bodies as their own. BMI did not influence sensitivity to weight changes in the negative direction