The influence of three-dimensional cues on body size judgements

Abstract

Research has shown that body size judgements are frequently biased, or inaccurate. Critically, judgement biases are further exaggerated for individuals with eating disorders, a finding that has been attributed to difficulties integrating body features into a perceptual whole. However, current understanding of which body features are integrated when judging body size is lacking. In this study, we examine whether individuals integrate three-dimensional (3D) cues to body volume when making body size judgements. Computer-generated body stimuli were presented in a 3D Virtual Reality (VR) environment. Participants (N = 412) were randomly assigned to one of two conditions: in one condition the to-be-judged body was displayed binocularly (containing 3D cues to body volume), in the other, bodies were presented monocularly (2D cues only). Across 150 trials, participants were required to make a body size judgement of a target female body from a third-person point of view using an unmarked visual analogue scale (VAS). It was found that 3D cues significantly influenced body size judgements. Namely, thin 3D bodies were judged smaller, and overweight 3D bodies were judged larger, than their 2D counterpart. Furthermore, to reconcile these effects, we present evidence that the two perceptual biases, regression to the mean and serial dependence, were reduced by the additional 3D feature information. Our findings increase our understanding of how body size is perceptually encoded and creates testable predictions for clinical populations exhibiting integration difficulties.

Sizing up the crowd: Assessing spatial integration difficulties in body size judgements across eating disorder symptomatology

“…This study ensured that on each trial, each body varied in appearance, clothing and overall lighting. Furthermore, in our study, our CG stimuli have the advantage of including stereoscopic (e.g., three-dimensional) cues, which provide further realism and ecological validity, relative to 2D CG stimuli used in previous studies (Turnbull et al, 2022).…”

“…This is a potentially important consideration given research showing that 3D cues can enhance and/or alter sensitivity to objects and object recognition (Bennett and Vuong, 2006;Burke et al, 2007;Bell et al, 2013;Caziot and Backus, 2015). In addition, Turnbull et al (2022) found that 3D cues influence body size judgements by providing viewers with increased stimulus certainty (e.g., addition of volumetric of lower stomach and bust regions). Furthermore, from an ecological perspective, the bodies that we often see in real life are surrounded by other people.…”

“…Forty-nine synthetic computer-generated images (CGI) of female bodies were created for our earlier work (Turnbull et al, 2022), ranging from very underweight (Size 1) to very overweight (Size 7). Using the program Blender 2.79© we created a linear continuum of seven discrete body size categories.…”

“…A second perceptual bias that tends to occur under more brief exposures is serial dependence, in which judgements are biased by and towards prior experience (Fischer and Whitney, 2014). Serial dependence has been observed for body size judgements, with bodies being perceived to be smaller when preceded by a smaller body, and bodies perceived as larger when preceded by a larger body (Alexi et al, 2018(Alexi et al, , 2019bTurnbull et al, 2022). Thirdly, it has long been observed that estimates of large and small magnitudes are biased towards a mean magnitude (Hollingworth, 1910).…”