The research tackles a puzzle that has long haunted body image science. Many adolescents and women overestimate normal body sizes and pursue slenderness that falls outside healthy ranges, while some individuals with obesity underestimate their own size. This phenomenon, termed body size and shape misperception, is common across cultures and is closely linked to body dissatisfaction and eating disorders. Traditional explanations have emphasized sociocultural pressures, but a newer hypothesis proposes a perceptual mechanism: constant exposure to extreme body shapes, whether on social media, television, or magazine covers, routinely triggers visual adaptation, and repeated adaptation may permanently recalibrate what the brain accepts as normal. The critical open question was whether the aftereffect of adaptation persists long enough to matter outside the lab, because aftereffects from a single short adaptation session typically fade quickly.

To find out, the team ran a series of three experiments with young Chinese women. In the first, forty participants were split into two groups. One group spent seven consecutive days adapting to contracted, thinner-than-normal body images; the other adapted to expanded, larger-than-normal bodies. Each day, the researchers measured the participants’ perception of body normality, essentially the body size they judged to be average, both before and after the adaptation session. The results were striking. Over the week of training, the baseline judgment, measured before any daily adaptation, gradually shifted toward the adapting body shape. Women who viewed thin bodies began to perceive progressively larger figures as normal, while women who viewed expanded bodies shifted in the opposite direction. Meanwhile, the day-to-day adaptation effect itself shrank, because the baseline had already moved so far that there was little room left for further change.

The most consequential finding came from a follow-up test conducted about a month after training ended. For participants who had adapted to contracted bodies, the baseline perception of normality was still significantly shifted compared with day one, retaining roughly 58 percent of the training effect. In the expanded-body group, the retained effect was even larger, about 79 percent, although the researchers caution that fewer participants from that group completed the follow-up, so that comparison should be treated as preliminary. Either way, the message is clear: brief, repeated visual exposure to distorted bodies is sufficient to produce a perceptual bias that endures for weeks, without any feedback, instruction, or conscious effort on the part of the viewer.

The study went beyond behavior and asked what happens in the brain. Using electroencephalography, the researchers recorded event-related potentials, tiny voltage fluctuations time-locked to the presentation of body images, before and after the week of training. They focused on four well-characterized components: P1 and N1, which reflect early structural encoding of bodies in occipito-temporal cortex, likely involving the extrastriate body area; P2, associated with automatic motivated attention; and the late positive potential, or LPP, which reflects later, more controlled attentional processing. Previous work had shown that enlarged bodies reliably elicit larger N1, P2, and LPP responses than normal-weight or underweight bodies, a pattern interpreted as an implicit, stimulus-driven anti-fat bias.

After a week of adapting to thin bodies, that neural bias grew stronger. The enhanced response to expanded bodies, relative to contracted and midsize ones, became significantly more pronounced in the N1 component, and the P2 bias was also greater in the thin-adaptation group. In contrast, participants who had adapted to expanded bodies showed no comparable strengthening. Importantly, responses to non-body control images, pictures of tools, were completely unaffected, ruling out the possibility that the changes simply reflected generic differences between the two EEG sessions. The training appeared to selectively sharpen the early brain response to large body shapes, potentially laying a foundation for the negative attitudes toward larger bodies documented in earlier studies.

A skeptical reader might wonder whether the whole effect is an illusion of geometry. The stimuli were created by horizontally stretching or compressing photographs, so perhaps participants were merely adapting to wide versus narrow shapes rather than to adiposity. The researchers addressed this concern in two ways. First, a rating task showed that more than 80 percent of the stimuli were judged as manipulations of thinness or largeness rather than narrowness or wideness, indicating that the images genuinely altered perceived body fat. Second, a separate experiment tested whether the aftereffect followed the signature of low-level shape adaptation or of high-level norm recalibration. Low-level contrastive processes would sharpen the boundary between thin and large categories, steepening the psychometric function without moving its center. Recalibrative processes, by contrast, shift the entire perceptual norm. The data favored recalibration: adaptation shifted the point of subjective equality without the steepening predicted by contrastive mechanisms, and model comparisons using the Bayesian Information Criterion confirmed that the position parameter, not the slope, carried the effect.

The team then deployed a drift-diffusion model to settle a long-standing debate about whether high-level aftereffects are truly perceptual or merely decisional. In this framework, the drift rate captures how quickly sensory evidence accumulates toward a judgment, while decision boundaries and starting points capture response strategy. After adaptation to contracted bodies, the drift rate for judging a body as thin decreased significantly, meaning participants needed stronger sensory evidence to reach that conclusion. After adaptation to expanded bodies, the drift rate increased. Crucially, the decision-related parameters did not budge in any condition. The aftereffect, in other words, lives in sensory processing, not in a cautious or biased response criterion.

The third experiment brought the findings into the real world. If chronic exposure to thin bodies drives these biases, then people whose professions demand slenderness should show the strongest effects. The researchers compared professionally trained performers, dancers, models, and actresses with at least two years of formal training, against non-performer controls. Despite having a significantly lower average body mass index, the performers were more preoccupied with their appearance and less satisfied with their bodies. Their perception of body normality was significantly thinner than the average body shape of the reference volunteers, while the non-performers’ judgments matched it. Most tellingly, the performers showed a significant neural response bias to expanded bodies across all measured components, including N1 and P2, whereas the non-performers showed a bias only in the later LPP. Across all participants, the magnitude of the N1 and P2 bias correlated negatively with body mass index, and lower body appreciation, extracted through principal component analysis of the questionnaires, was associated with a stronger N1 bias.

The implications reach well beyond the laboratory. The findings support the adaptation-based theory of body size misperception, suggesting that the visual diet of thin bodies consumed daily through media and professional environments can durably recalibrate the brain’s internal norm, making normal-sized bodies look large and fueling the pursuit of unhealthy slenderness. The authors note that eating disorder patients show a distinctive adaptation profile, responding only to expanded bodies and not to contracted ones, with the degree of impairment tracking symptom severity, and that body size overestimation often persists even after successful cognitive behavioral therapy. That raises an intriguing therapeutic possibility: if passive, feedback-free exposure can shift perceptual norms in healthy women, carefully designed adaptation paradigms, perhaps to larger bodies, might one day help correct distorted body perception in clinical populations. The researchers caution that their follow-up covered only one month, that their stimulus technique, while validated, could be improved with modern computer-generated imagery, and that the neural mechanisms linking perceptual and attitudinal body image remain to be mapped with neuroimaging. Still, the core message is hard to ignore: what we look at, repeatedly and passively, quietly rewrites what we believe a body should be.

Subject of Research: Visual adaptation and its persistent effects on body size perception and neural processing

Article Title: Repeated visual adaptation induces persistent behavioral and neural biases in body size perception

Article References: Sang, X., Dong, X., & Bao, M. (2026). Repeated visual adaptation induces persistent behavioral and neural biases in body size perception. iScience, 29(11), Article 117772. https://doi.org/10.1016/j.isci.2026.117772

Image Credits: AI Generated

DOI: 10.1016/j.isci.2026.117772

Keywords: body size perception, visual adaptation, body image, eating disorders, event-related potentials, perceptual norm recalibration, thin-ideal, anti-fat bias, drift-diffusion model, body dissatisfaction, media exposure, neuroscience