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Visual biases in judging body weight

Lookup NU author(s): Dr Katri Cornelissen, Lucinda Gledhill, Dr Piers Cornelissen, Dr Martin Tovee



Objectives: There has been a steady rise in obesity levels in western countries and a contributory factor is people’s failure to recognise weight gain. Two important visual perceptual biases, which have hitherto been ignored in the obesity literature, could contribute to this problem; contraction bias and Weber’s law. Contraction bias predicts that the weight of obese bodies will be under-estimated and the degree of underestimation will increase as BMI increases. Weber’s law predicts that change in the body size will become progressively harder to detect as their BMI increases. Methods: In experiment 1, twenty nine female participants estimated the weight of 120 women varying in their body mass. In experiment 2, twenty-eight female participants judged which body was the heavier in a 2-alternative forced choice paradigm. Results: In Experiment 1, as predicted the participants showed a progressive under estimation of over-weight and obese bodies, β1 = 0.71, t = 26.96, p < .0001.For experiment 2, there was a significant effect of the BMI of the bodies being judged on the just noticeable difference needed to discriminate between them: F(1,196) = 89.39, p<.0001 for 3D bodies and F(1,86.5) = 44.57, p<.0001 for digital photographs. Conclusions: 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 recognise weight gain and undertake compensatory weight control behaviours.

Publication metadata

Author(s): Cornelissen KK, Gledhill LJ, Cornelissen PL, Tovée MJ

Publication type: Article

Publication status: Published

Journal: British Journal of Health Psychology

Year: 2016

Volume: 21

Issue: 3

Pages: 555-569

Print publication date: 01/09/2016

Online publication date: 09/02/2016

Acceptance date: 12/01/2016

Date deposited: 12/01/2016

ISSN (print): 1359-107X

ISSN (electronic): 2044-8287

Publisher: John Wiley & Sons Ltd.


DOI: 10.1111/bjhp.12185


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