Independent Aftereffects of Fat and Muscle: Implications for neural encoding, body space representation, and body image disturbance

Although research addressing body size misperception has focused on socio-cognitive processes, suchas internalization of the “ideal” images of bodies in the media, the perceptual basis of this phenomenonremains largely unknown. Further, most studies focus on body size per se even though this dependson both fat and muscle mass – variables that have very different relationships with health. We testedvisual adaptation as a mechanism for inducing body fat and muscle mass misperception, and assessedwhether these two dimensions of body space are processed independently. Observers manipulatedthe apparent fat and muscle mass of bodies to make them appear “normal” before and after inspectingimages from one of four adaptation conditions (increased fat/decreased fat/increased muscle/decreasedmuscle). Exposure resulted in a shift in the point of subjective normality in the direction of the adaptingimages along the relevant (fat or muscle) axis, suggesting that the neural mechanisms involved in bodyfat and muscle perception are independent. This supports the viability of adaptation as a model of realworldbody size misperception, and extends its applicability to clinical manifestations of body imagedisturbance that entail not only preoccupation with thinness (e.g., anorexia nervosa) but also withmuscularity (e.g., muscle dysmorphia)