关键词: 体型知觉, 进食障碍, 机制, 偏差, BMI

Abstract:

Body size perception refers to how an individual perceives the size, weight and proportions of his/her body. Distorted body size perception can be a mental health problems, and is associated with psychiatric disorders such as eating disorders, body dysmorphic disorder, depression, and certain psychotic disorders. This is an often-ignored research area, with largely inconsistent evidence.

The extant literature concerning body size perception in patients with eating disorders generally supports four notions. First, anorexia nervosa (AN) patients and bulimia nervosa (BN) patients both overestimate their body size, but the magnitude of such distorted perception varies with different methods estimating one’s body size. Two commonly-used methods for body size estimation are the ‘depictive method’ and the ‘metric method’. The latter method usually generated a higher degree of overestimation in body size than the former method in patients with eating disorders. Second, the distorted body size perception in AN patients may be confounded by their extremely low body mass index (BMI). Yet, this previous finding is inconsistent due to the ecological validity of the ‘depictive’ and ‘metric’ methods. Third, AN and BN patients have different estimates of body size perception for ＂self＂ versus ＂others＂, and such discrepancy may be related to attitudes towards themselves. However, attitudinal factors and its effect on body size perception are seldom studied and thus remain unclear. Lastly, distorted body size perception in patients with eating disorder is correlated with symptom severity and could indicate prognosis of the illness. Body size perception is also one of the intervention targets for treating eating disorders.

The literature remains inconclusive regarding whether healthy people have accurate body size perception, because previous findings vary with different designs in measuring body size perception, sample characteristics (demographics and geographical-cultural aspects). Yet in general, healthy people tend to perceive others’ body size consistently, with overestimation for others with low BMIs, and underestimation for others with high BMIs.

Three cognitive mechanisms underlying distorted body size perception have been proposed, namely contraction bias, adaptive after-effect and serial dependence. These putative mechanisms operate in health people and patients with eating disorders. In view of the above-mentioned review of the literature, we recommended three useful approaches for research in body size perception. First, it is necessary to distinguish two different methods for estimating body size perception, namely the ‘recognition technique’ (which involves the use of a visual analogue as reference in measurements) and the ‘recall technique” (which does not involve any visual analogue). It is likely that the two methods will yield different estimates from subjects, and may partly account for the inconsistent finding in the literature. Second, the problems of unclear definition of “overestimation” in previous studies should be addressed, by developing operational criteria and a standardized definition across different paradigms. Third, male subjects should be included in future study, because this gender has been under-represented in previous research. Lastly, in view of the growing incidence of eating disorders, body size perception is a worthy topic for research in China.

Key words: body size perception, eating disorders, mechanism, inaccuracy, BMI