Perception of bodily width has long been a point of interest for psychologists, especially amongst those with an interest in eating disorders such as anorexia and bulimia. Numerous studies over the years have identified a trend for people with eating disorders to over-estimate the width of their body parts, including the waist and hips. However, there has been considerably less investigation into representations of body part width in non-clinical populations and how these differ across the whole body. Many would assume that, in order for us to accurately navigate our surroundings, the way we perceive our body’s width and length should be fairly accurate for those who do not suffer from any form of bodily dysmorphia.

PhD student Lettie Wareing, in conjunction with Lancaster academics Dr Megan Readman, Professor Trevor Crawford, Dr Sally Linkenauger, Dr Lisa Lin of Justus-Liebig University Giessen in Germany and Birkbeck’s Professor Matthew Longo set out to test this hypothesis – with surprising results.

The team conducted the study with participants with no history of eating disorders. In four experiments, these participants were asked to estimate how many of their hand lengths or widths made up the length or width of a variety of their own or another person’s body parts – including the length of the full body, torso, leg, arm, head, and foot, and the width of the , shoulders, hips, thigh, back, torso and head–to see if there was any pattern in over- or underestimation across the group for certain limbs. Participants also made the same estimates using a hand-sized stick as the measuring tool, and when in different postures (standing, sitting on a chair, or sitting on a stool) to determine whether the metric used or posture had any impact on the ability to accurately gauge their width. Additionally, participants were also asked to provide the same estimates for another individual to see if there were any difference in accuracy between self-perception and the perception of others.

Interestingly, the team found very little in the way of consistent patterns of over- or underestimation of limb width across the experiments. Instead, accuracy of width estimation varied across individuals, body parts, and experiments. This lack of a stable representation of body part width may seem counterintuitive for navigating the world around us. However, previous studies have shown that people are capable of judging whether or not they can pass through a gap simply by the angle of the opening in relation to their eye height.

Therefore, Lancaster team suggest that given the energetic demands of our perceptual systems, if we do not need a stable representation of our body width in order to navigate our environments, we may not maintain this representation. This means that when individuals are asked to estimate their body width, the inconsistencies observed may come from participants simply attempting to guess their body width. Additionally, given that a human’s width can be subject to rapid change, often through the clothes we wear or the objects we carry, having a fixed idea of limb width may not be particularly for carrying out daily tasks, especially since we would need to be able to quickly adapt to these changes. The full results of the team’s experiments were recently published in the scientific journal Cognition.

On the findings of this study, Lettie Wareing commented: "We often assume that our representations of our bodies are accurate. Here, we add to a growing body of evidence that suggests this is not the case. Across a series of experiments in which participants were asked to estimate the width of their body parts relative to their hand, we did not observe a consistent pattern of over- or underestimation of body part width. Ecological accounts of perception argue that redundant perceptual information is too energetically costly for our brains to maintain. From this perspective, given that stable representations of the width of our bodies may not be required to navigate our environments safely, we may not store a representation of our body width as it is not required. The findings of this study pave the way towards an enhanced understanding of how the body is represented in non-clinical populations. We are hoping to use these results to inform future investigations into body distortions in eating disorders and the possible mechanisms involved in these."