Distortion of body image in the obese: a sensory phenomenon.

Body weight in 42 obese and normal weight subjects was measured using a video TV monitor. Tasks included a continuous task where subjects manipulated the width of their body image on TV, and a discrete task, where they judged the accuracy of their TV image which was presented as either normal, too heavy, or too thin. Subjects rated their full body, body regions which included face, waist, and thighs, and two inanimate control objects. Results from the continuous task revealed that obese subjects overestimated body size more than normals. There was also a significant difference in the ratings of the four body regions, with all regions overestimated. Judgements were more accurate for body regions and control objects on ascending trials where the subjects had to increase the width of the image. No differences were obtained between obese and normals on judgements of the control objects. On the discrete discrimination task, a signal detection analysis revealed sensory sensitivity differences between obese and normal weight subjects. Obese subjects were poorer at detecting size distortions of the body regions. The thin/normal discrimination was more difficult than the heavy/normal discrimination. No response criterion differences were found between obese and control subjects, although subjects adopted a more strict criterion with the thin/normal discriminations. Implications of these findings for clinical intervention in eating disorders are discussed.