If you're trying to look slimmer in an outfit, you certainly shouldn't wear horizontal stripes-- right? An optical illusion created by Hermann von Helmholtz in 1867 shows two squares of black and white stripes, one with the stripes going horizontally, and one where they run vertically.
Weirdly, the horizontally striped square looks taller and the vertically striped square appears wider. In 2011, psychologists at the University of York in England tested whether the illusion seen in the 2-D version was also true in 3-D.
Two identical female mannequins wore either horizontal- or vertical-striped outfits.
The team found that the figure sporting vertical stripes appeared wider; in fact, the one donning horizontal stripes would need to be 10.7 percent broader for the two to visually match up.
It seems science trumps fashion sense this time.