Sophia R. Baia¹ (), Ashlyn Overby¹, Michael K. McBeath^1,2; ¹Arizona State University, ²Max Planck Institute for Empirical Aesthetics

Introduction: The body tilt illusion is the exaggerated perception of body tilt angle. People tend to overestimate that they are tilted at 45º when only tilted about 30º. Past research confirms this illusion increases with lack of visual and auditory cues and interacts with gender. The present study examines distortion in body tilt perception as a mediating function of people’s center-of-mass to see if it might account for the sex difference. This follows the finding of women generally having a lower center-of-mass compared to men (Elert, 2005). Method: We constructed a see-saw apparatus to measure body center-of-mass point as well as height, weight, and naval location. We used a human-sized 3D gimbal to measure the body tilt illusion, tilting forward, backward, and to the sides, both with eyes open and closed. 10 men and 14 women were tilted in each condition, estimating when they reached 45º, without feedback. Results: The results replicated previous findings with a large overall body tilt illusion for both sexes, a larger tilt illusion to the side compared to forward-backward, and a large increase with eyes closed compared to open. Additionally, we found a non-significant trend for women to exhibit a larger tilt illusion, which was better accounted for by the mediating variable of center-of-mass. Discussion: The findings further support that perception of body tilt is directional, multisensory and consistent with the illusion being functional for helping people keep their balance. In addition, the lack of a gender effect, but trending mediating effect of center-of-mass supports that this is an underlying mediating physical characteristic. The overall pattern of findings supports that the body tilt illusion is relatively universal, likely functional, and that past differences attributed to gender may be more parsimoniously accounted for by individual body shape differences related to physical balance like center-of-mass.