Either of vertical or horizontal stripes on clothing makes the wearer look slimmer

There is a widespread belief that wearing horizontal stripes makes individuals look fatter. Thompson and Mikellidou (2011) showed that the Helmholtz and Oppel-Kundt illusions persist when used on cylinders and pictures of a body, suggesting that the belief is wrong. Swami & Harris (2012), however, reported that the body size was recalled larger when wearing horizontal stripes. We would like to investigate how stripes affect judgements about body size when bodies are being presented in a real space. Observers (n = 197 and 407 for Exp. 1 and 2, respectively) watched mannequins dressed either in horizontal, vertical, or diagonal stripes. We asked observers to rank the order according to perceived slimness. In experiment 1, the mannequin appeared the slimmest for horizontal stripes and looked less slim for diagonal stripes than for other stripes. In experiment 2, where the no-stripe condition was included, the mannequins in striped clothing looked slimmer than the mannequin in uniform grey clothing. The results suggest that any stripes on clothing make the wearer look slimmer. This could be due to that the curves of stripes on a body serve as a cue of depth perception, enhance the perceived depth of a body, and lower the relative body width.