Body mass index and flanker size: does (over)weight modulate the Baldwin illusion?

© 2020 The Author(s). This open access article is distributed under a Creative Commons Attribution (CC-BY) 4.0 license. Visuospatial processing is a complex process that is vulnerable to bias. Line bisection paradigms are used to help detect the factors that balance left and right hemispatial attention that go beyond the domains of perception and action. For example, studies have indicated the “pseudoneglect” phenomenon in the bisection of horizontally presented lines in healthy subjects. Among the modified versions of the traditional line bisection task is the “Baldwin illusion”. In the Baldwin illusion, the subjective midpoint of a line flanked by squares of different sizes is displaced towards the small square. The goal of the study was two-fold. First, we wanted to investigate whether there is an asymmetry in the Baldwin effect depending on leftward or rightward arrangement of the small square and second whether obesity (as measured by body mass index—BMI) would affect bisection of Baldwin-like flanked lines. Thirty-one healthy, right-handed female subjects (20 normal-weight and 11 overweight) had to repeatedly bisect a horizontal straight line using a series of Baldwin-type stimuli, including a photography of their own and the experimenter’s body. As predicted, this displacement was larger when the small square was on the left end of the line (M = −1.80 mm, SD = 2.71 mm, t = −10.48, p = <0.001) than when it flanked the right end (M = +0.71 mm, SD = 2.90 mm; t = 3.83, p = t = 4.35, p = <0.001). Across all stimulus types (irrespective of the size or type of a flanker), overweight subjects placed the subjective midpoint more leftward than the normal-weight subjects. In 13 out of 16 types the results differed significantly and in the remaining 3 types the tendency was clear (0.074 < p < 0.13). Limitations were addressed. Our results confirmed our asymmetry hypothesis. Also, these preliminary results demonstrated an influence of BMI on line bisection performance, i.e. a larger pseudoneglect for the overweight/obese subjects.