Perception of others’ body sizes is predicted by own body size

Previous research demonstrated that estimates of others’ body sizes are biased towards the average body size in the population (Cornelissen, Gledhill, Cornelissen Tovée, 2016). Bodies in the environment not only influence the internal reference of what is perceived as average or “normal”, but also play an essential role in self-body size evaluation via social comparison (Cattarin, Thompson, Thomas Williams, 2000). In two psychophysical experiments, we asked whether there is also an influence of own body size on the perception of others’ body sizes. For Experiment 1, four biometric female avatars with a body mass index (BMI) of 15, 25, 35, and 45 were generated, and then their weight was altered (± 5, ±10, ±15, and ±20 BMI change) based on a statistical body model. For each of the avatar series, female participants spanning the BMI range memorized what the avatar’s body looked like and then responded for the presented bodies varying in weight whether it was the same as the one memorized. Results showed no influence of participants’ BMI on the accuracy of body size estimates, but sensitivity to weight changes was highest for bodies close to one’s own BMI. In Experiment 2, we examined whether this effect was driven by memory or perceptual factors. Specifically, in a 2-alternative forced choice discrimination task, two bodies were presented simultaneously using the same BMI categories as in Experiment 1. If participants’ body size influences sensitivity during simultaneous presentation, it would suggest that the effect found in Experiment 1 is not due to a better memorization of bodies that are close to one’s own body size. Again, sensitivity to differences in body weight was highest for bodies close to one’s own BMI. These results suggest that our own body size influences our perceptual ability to discriminate the sizes of other’s bodies