What does it mean to have distorted body image in anorexia nervosa?

Cornelissen, Katri (2016) What does it mean to have distorted body image in anorexia nervosa? Doctoral thesis, Northumbria University.

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Abstract

This thesis explores body image distortion in anorexia nervosa spectrum disorders (ANSD), using 3D computer generated (CGI) stimuli together with psychophysical and behavioural methods. Experiments 1-3 on healthy controls show that not only does participants’ psychological state influence the perception of their body size, but so does their actual body size, indexed by Body Mass Index (BMI). Healthy controls whose BMI is closest to the population average estimate body size accurately, those with lower than average BMIs over-estimate and those with higher than average BMIs under-estimate, demonstrating contraction bias for body size estimations. Furthermore, control participants’ sensitivity to changes in body size follows Weber’s law: larger bodies require proportionately bigger differences between them to be discriminated. In marked contrast, ANSD individuals with the lowest BMI are the most accurate and most sensitive at body size estimation. As these participants’ BMI increases, sensitivity reduces dramatically, and participants rapidly start to overestimate their body size. Experiment 4 mapped the relationship between participants’ behavioural judgements of body size and where they look during the task. This study showed that (i) accurate body size estimators tended to look more in the waist region, and this was independent of clinical diagnosis; (ii) there is a pattern of looking at images of bodies, particularly viewing the upper parts of the torso, which is specific to participants with ANSD but which is independent of accuracy in body size estimation. Experiment 5 is an adaptation based training program for ANSD participants. It succeeded in raising individuals’ perceptual boundary for thin versus fat body sizes. This resulted in reduced psychological concerns about ANSD participants’ own body shape. In conclusion, this thesis brings novel insight into the phenomenon of distorted body image in ANSD. Implications for the treatment of eating disorders are discussed based on these new data.

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