This past February a photograph of a dress nearly broke the Internet. It all started when a proud mother-in-law-to-be snapped a picture of the dress she planned to wear to her daughter's wedding. When she shared her picture with her daughter and almost-son-in-law, the couple could not agree on the color: she saw white and gold, but he saw blue and black. A friend of the bride posted the confusing photo on Tumblr. Followers then reposted it to Twitter, and the image went viral. “The Dress” pitted the opinions of superstar celebrities against one another (Kanye and Kim disagreed, for instance) and attracted millions of views on social media. The public at large was split into white-and-gold and blue-and-black camps. So much attention was drawn, you would have thought the garment was conjured by a fairy godmother and accessorized with glass slippers.
To sort out the conundrum, the media tapped dozens of neuroscientists and psychologists for comment. Pride in our heightened relevance to society gave way to embarrassment as we realized that our scientific explanations for the color wars were not only diverse but also incomplete. Especially perplexing was the fact that people saw it differently on the same device under the same viewing conditions. This curious inconsistency suggests that The Dress is a new type of perceptual phenomenon, previously unknown to scientists.
Although some early explanations for the illusion focused on individual differences in the ocular structure of the eye, such as the patterning and function of rod and cone photoreceptor cells or the light-filtering properties internal to the eye, the most important culprit may be the brain's color-processing mechanisms. These might vary from one person to the next and can depend on prior experiences and beliefs.
For example, people may have different assumptions about color constancy—the phenomenon that enables us to see an object's color as constant despite changing illumination sources [see “Color Contrast and Constancy,” on opposite page]. Light in the natural world typically comes either from direct golden sunlight or from the blue sky, and our perception thus assumes that most illumination has these colors. It follows that people looking at The Dress might assume the fabric is lit by either blue sky or sunlight. If the observers conclude—even unconsciously—that the source of illumination is the blue sky, their brain will helpfully subtract the blue from their perception of the image, and The Dress will appear white and gold. The brain of observers who assume The Dress is sunlit will subtract gold from the image and consequently see it as blue and black.
Before the discovery of The Dress, vision scientists had thought that people with normal vision experienced color illusions similarly. Earlier examples of ambiguous images were constrained to shape effects, such as when people see a vase or two faces in the same picture. Ambiguous shape illusions differ from The Dress in one fundamental aspect, however: whereas observers can usually flip their perception from vase to faces with little trouble, people often appear stuck in either the white-and-gold or the blue-and-black camp. Strangely, these differences can be irreconcilable. It is as if—in addition to clichéd dichotomies such as glass-half-full versus glass-half-empty or cat versus dog people—The Dress has now presented us with a new divide for humanity. Could it be that different people have different prejudices about the color of the light source? Or maybe about the type of fabric (shiny or matte) The Dress is made of?
Perhaps more than any previous perceptual observation, The Dress demonstrates that we can see the world in strikingly different ways depending on what our individual brain brings to the table. Although by and large the reason for the various interpretations of The Dress remains a scientific mystery, vision laboratories all around the world are conducting dozens of experiments to investigate the enigma. Here we offer a roundup of some of the most promising theories to date—and curious readers can visit our blog, Illusion Chasers, (https://blogs.scientificamerican.com/illusion-chasers) for new developments.