Abstract
Although research addressing body size misperception has focused on socio-cognitive processes, such as internalization of the “ideal” images of bodies in the media, the perceptual basis of this phenomenon remains largely unknown. Further, most studies focus on body size per se even though this depends on both fat and muscle mass – variables that have very different relationships with health. We tested visual adaptation as a mechanism for inducing body fat and muscle mass misperception, and assessed whether these two dimensions of body space are processed independently. Observers manipulated the apparent fat and muscle mass of bodies to make them appear “normal” before and after inspecting images from one of four adaptation conditions (increased fat/decreased fat/increased muscle/decreased muscle). Exposure resulted in a shift in the point of subjective normality in the direction of the adapting images along the relevant (fat or muscle) axis, suggesting that the neural mechanisms involved in body fat and muscle perception are independent. This supports the viability of adaptation as a model of real-world body size misperception, and extends its applicability to clinical manifestations of body image disturbance that entail not only preoccupation with thinness (e.g., anorexia nervosa) but also with muscularity (e.g., muscle dysmorphia).
Highlights
Evidence that the relationship between exposure to different bodies and body size misperception may be mediated by a perceptual adaptation effect
The fat ANOVA revealed a significantly more positive ∆PSNf for observers who adapted to images with increased body size (M = 13.5, SE = 2.5), compared to those who adapted to images with decreased body size (M =−16.2, SE = 2.5), F(1,60) = 67.91, p < 0.0005, ηp 2 = 0.53
A similar effect was observed when analysing the effects on perceived muscle mass, where the muscle ANOVA demonstrated a significantly more positive ∆PSNm for observers who adapted to images with increased body size (M = 11.0, SE = 2.6) compared to observers who adapted to images with decreased body size (M =−16.8, SE = 2.7), F(1,60) = 51.59, p < 0.0005 ηp2 = 0.46
Summary
Evidence that the relationship between exposure to different bodies and body size misperception may be mediated by a perceptual adaptation effect. If the examples of body size misperception can be considered to be real-world examples of visual adaptation, as suggested by previous experimental studies, this technique should be capable of producing independent effects of exposure to fat and muscle.
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