Science & Technology

The Neurological Reason Why Black Clothes Are Slimming

Fashion has a lot of rules. Most of them, however, are outdated (it's fine if your belt doesn't match your shoes), arbitrary ("no white after Labor Day" is just a rule thanks to 19th-century Mean Girls), or just plain wrong (horizontal stripes don't actually make you look wider). But there's one rule of thumb that goes beyond tradition and into the realm of neuroscience: Black garments are slimming. It all comes down to how your visual system processes light.

Does This Illusion Make Me Look Fat?

You wouldn't normally expect an article about fashion to start with a 19th-century German scientist best known for a landmark discovery in physics, but this isn't a normal article about fashion. Hermann von Helmholtz made fundamental contributions to a wide variety of subjects, and his 1867 "Handbook of Physiological Optics" was no exception: It's been called "the foundation work of visual perception" and "the greatest book ever written on vision." Within explanations of how physics, physiology, and psychology play a role in what we see, he included several visual illusions that illustrate exactly how this all happens with our own eyes.

Below is what Helmholtz dubbed the "irradiation illusion." The "holes" in each square are identical in size, yet the white hole looks bigger than the black hole.

This is precisely the phenomenon that makes you look slimmer in black slacks than you do in white denim — the color of the slacks makes them appear smaller. But why? Well, that's a question that's centuries old.

Helmholtz wasn't the first to notice this illusion. In the 1500s, Galileo Galilei noticed that some of the planets looked larger when viewed with the naked eye than they did when viewed through a telescope, making the white glow of Venus appear eight to ten times larger than Jupiter in the night sky. He knew something strange must be going on with his vision to cause this illusion, but he wasn't sure what. Luckily, scientists never stopped wondering, and in 2014, they figured it out.

Nice Day for a White Warping

For the study looking into this, researchers at the State University of New York College of Optometry used electrodes to record the electrical signals from neurons in the visual areas of cat, monkey, and human brains. The human and animal participants gazed at light shapes on dark backgrounds and dark shapes on light backgrounds, just like in the irradiation illusion above, along with light or dark shapes on gray backgrounds. The electrode sensors showed that not all visual neurons behave the same way.

Your visual system operates via two main channels: "on" neurons that are sensitive to light things and "off" neurons that are sensitive to dark things. When it came to the dark "off" neurons, the researchers found that they responded predictably to dark shapes on a light background — the greater the contrast between the two, the more active these neurons were. But the light "on" neurons behaved bizarrely. Even with the same amount of contrast, light objects on a dark background triggered a greater response in these neurons.

This makes some sense, evolutionarily speaking. In the dark of night, you'd want to be able to take in every bit of light you can get, so a visual system that exaggerates light objects on a dark background could come in handy. It's not that hard to see dark objects in the light of day, so the opposite wouldn't be true. But this has side effects in the colors of your outfit and in the appearance of the planets — the brighter appearance of Venus in the night sky makes it look bigger than the comparably darker Jupiter.

So the next time you're picking out an outfit, just think "the neuronal nonlinearity of the human visual system!" (It really rolls off the tongue, trust us). If you want to look smaller and slimmer, then go for darker hues and stay away from whites and pastels. Keep those visual neurons activating like clockwork.

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For more visual trickery, check out "The Ultimate Book of Optical Illusions" by Al Seckel. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Ashley Hamer August 30, 2018

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