How thin is too thin? Evidence from visual aftereffects in body size estimation.

Exposure to unrealistic body ideals on social media may distort individuals' body image, potentially leading to increased body dissatisfaction. One proposed mechanism for this phenomenon is visual adaptation: prolonged exposure to thin bodies can shift subsequent judgments of body size, leading to subsequent bodies being perceived as fatter than they are. This study investigated whether exposure to body images of varying thinness alters judgments of body size relative to one's own bodyand whether individual differences in body image concerns moderate these aftereffects. Thirty-four young women completed a psychophysical task in which they judged whether test bodies were thinner or fatter than themselves, following adaptation to either an extremely thin or a slightly thinner (but closer-to-self) body. Results showed stronger aftereffects following exposure to extreme-thin adaptors, with lower points of subjective equality (PSEs), indicating a shift toward judging thinner bodies as equivalent to one's own body size. The point of subjective equality (PSE) is the body size at which participants are equally likely to judge a test body as thinner or fatter than their own. Adaptation to both close-thin and extreme-thin bodies resulted in lower PSEs, consistent with a contrastive aftereffect in which test stimuli were perceived as larger following exposure to thin adaptors. Higher body concern was positively associated with larger baseline PSEs, indicating greater perceived body size. These findings support the role of visual adaptation in shaping perceptual judgments of body size and suggest that individual differences in body concern influence this process. Opponent coding may underlie this mechanism, as greater aftereffects were observed for more extreme adaptors.