A square composed of horizontal lines appears taller and narrower than an identical square made up of vertical lines. Reporting this illusion, Hermann von Helmholtz noted that such illusions, in which filled space seems to be larger than unfilled space, were common in everyday life, adding the observation that ladies’ frocks with horizontal stripes make the figure look taller. As this assertion runs counter to modern popular belief, we have investigated whether vertical or horizontal stripes on clothing should make the wearer appear taller or fatter. We find that a rectangle of vertical stripes needs to be extended by 7.1% vertically to match the height of a square of horizontal stripes and that a rectangle of horizontal stripes must be made 4.5% wider than a square of vertical stripes to match its perceived width.
First of all, very few of us are shaped anything like the lovely little figure used in this research. Then there’s the psychological factor. Maybe stripes really don’t make a difference but if we look at a, shall we say, rather wide person wearing stripes and we think the stripes make her look fatter does it really matter whether or not we can prove scientifically that they do or do not make her look fatter? Also, the color, contrast, and width of the stripes probably make a difference.
Fashion is all about optical illusion, and eyes are easily fooled. (My eyes are really easily fooled.) I’ve never questioned the conventional wisdom in this matter. Perhaps I should.