Visual biases in judging body weight.

Normal visual perceptual biases influence our ability to determine body size: contraction bias and Weber's law mean that as bodies become overweight and obese, it is harder to judge their weight and detect any increase in size. These effects may therefore compromise people's ability to recognize weight gain and undertake compensatory weight control behaviours. Statement of contribution What is already known on this subject? It is common knowledge that obesity levels in the West are rapidly rising and that people fail to recognize weight gain. What has not been widely recognized before is that there are sound perceptual reasons for this failure. Here, we identify two such perceptual biases. What does this study add? Weber's law and contraction bias compromise people's ability to recognize weight gain. It becomes progressively harder to discriminate the size of bodies as their body mass index increases. This compromises the ability to recognize weight gain and undertake compensatory behaviours.