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.