Horizontal Stripes: Friend or Foe?

For years, the fashion world has told us that vertical stripes make the body look slimmer because they draw the eyes up and down.  Horizontal stripes supposedly do the exact opposite, drawing attention to the widest parts of the body and making us look like swollen watermelons.

But consider the two squares below.  Which one is wider?It’s the one on the right…right?

Wrong–the squares are really the same width, same height.  This compelling illusion was first shown by the physicist Helmholtz, who showed that vertical stripes have a widening effect while horizontal stripes make objects look taller.  Based on his finding, Helmholtz encouraged women to wear horizontal stripes in his Handbook of Physiological Optics. So was Helmholtz wrong?  Or is fashion folk wisdom simply misguided?

The main problem with applying Helmholtz’ theory to clothes is that people are not 2-D rectangles.  People have curves and depth cues that interact with vertical and horizontal stripes in tricky ways.  For instance, strong 3-D cues make objects look thinner (Taya & Muira, 2007).  Observe:

In this figure, the vertical stripes are altered until they make the fatso 2-D square look like a fit 3-D cylinder.  The authors claimed that the same thing happens when people wear vertical stripes; the stripes are slimming because they accentuate depth cues from the body.

But do horizontal stripes also highlight 3-D cues from the body?  Thompson (2008) tested this by having subjects compare cartoons of women wearing horizontal or vertical stripes.  In one experiment, the bodies were two-dimensional; in another experiment, they were three-dimensional (i.e., the bodies had shading cues that gave the illusion of depth).  Here are some examples of the stimuli used:

In this figure, the woman on the left has 3-D cues, while the same woman on the right is 2-D.  Which one looks thinner to you?

I asked readers to vote on this in my last post, and the verdict was that the horizontally striped lady appeared thinner.  Now, I have to admit that this wasn’t really a fair comparison since only the horizontally striped woman had 3-D cues; but even when the 3-D cues were equated, Thompson’s subjects still thought that horizontal stripes were more slimming than vertical stripes.  In fact, to equate the two bodies, subjects widened the horizontally striped body by 6% on average.

So horizontal stripes may be more slimming after all, either by making the body look more three-dimensional, elongating the body, or both.  As it happens, horizontal stripes are super trendy this year.  Coincidence?

It does make me wonder…what else did the fashion world get wrong?  Do skinny jeans really make you look skinny?  Are small patterns actually more flattering than larger prints?  And what’s the verdict on mixing and matching?

Here’s one trend I’d love to see killed off someday by science:

Taya, S., & Miura, K. (2007). Shrinkage in the apparent size of cylindrical objects Perception, 36 (1), 3-16 DOI: 10.1068/p5597

Thompson, P. (2010). Does my butt look big in this? Horizontal stripes, perceived body size and the Oppel-Kundt illusion Journal of Vision, 8 (6), 822-822 DOI: 10.1167/8.6.822