May 14--It set social media on fire. It divided friends and co-workers. It was a cellphone picture of a sequined dress, and now it has become the subject of three scientific papers.
This week the journal Current Biology published three studies that seek to understand how a single picture can be interpreted so differently by so many people.
If you see the dress as blue and black (the color it appears in normal light), you are in the majority. According to one of the studies, 57% of more than 1,400 people surveyed described the dress as blue and black, while 30% saw it as white and gold. (An additional 11% saw it as blue and brown, and 2% fell into an "other category.")
"It's clearly a crappy picture, but it turns out to be an extraordinarily powerful tool for visual neuroscientists," said Bevil Conway, a professor at Wellesley College and the senior author of the study. "There will be dozens and dozens of papers about it over the years. This is just the beginning."
Conway and other experts on vision say the picture of "the dress" is the most extreme example known of a single image that can be seen by different people as entirely different colors.
"We knew that individual differences in perception are bigger than most people realize, but this picture really did take us aback," said Michael Webster of the University of Nevada, Reno, the senior author of another of the papers, which found that our brains are more likely to discount blue tones than other shades.
Webster added that the dress picture is particularly intriguing because people really lock into a single interpretation of the image. For example, the famous optical illusion of a ballerina spinning can be interpreted as the figure spinning either to the left or to the right, but most people can make themselves see it both ways.
That does not seem to be the case with the dress. "I haven't met anyone who could clearly flip," Webster said.
The authors of the three papers are generally in agreement that the discrepancy in how we perceive the colors in the dress picture is due to the way our brains are interpreting the color of the light that is hitting and reflecting off the dress.
If our brains conclude that the image is lighted by a cool illuminant like a blue sky, we will ignore shorter wavelengths and determine that the dress is white and gold. However, if our brains decide that the image is being lighted by a warm illuminant like an incandescent light, we will discount longer wavelengths in the picture and will see the dress as blue and black.
Conway and coauthors Rosa Lafer-Sousa and Katherine Hermann found that women and older people were more likely to see the dress as white and gold, whereas men and younger people were more likely to see it as blue and black.
Although they are not yet sure why that would be, their current hypothesis is that women and older people are more likely to spend their awake time during the day, and therefore more likely to assume that their visual world is contaminated by blue sky.
"You have in your head an internal model of what the colors of the world are, and that helps you resolve ambiguities," Conway said. "The machine in your head says, 'Well, given what we know historically, I'm going to assume it is this color, or that color.' "
Someone who spends more time under artificial lighting may make a different assumption, he explained.
The study also found that even when people were asked the open ended sentence "this is a _____ and _____ dress," they fell into three camps: "white and gold," "blue and black" and "brown and blue." That suggests that the image is what is called "multistable," meaning it has distinct interpretations.
In a smaller study of 15 people that occurred just days after the image went viral, researchers at Giessen University in Germany found that there may be a large variation in how the colors of the dress were being perceived. Participants were asked to look at a picture of the dress on a computer screen and then adjust the color of a disk on the same screen so that it matched the color they were seeing in the dress.
The results suggest that even among groups that said the dress was blue and black or white and gold, the colors in the dress were still being perceived differently.
"We show that the question 'What color is the dress?' has more than two answers," they write.
They add that most people saw some shades of blue in the sequin stripes of the dress, but that people who saw it as a very light blue perceived these tones to be due to the lighting on the dress, rather than coming from the dress itself.
A third study, led by Webster, reports that people are more likely to filter out blue tones than they are other colors, which may explain why the blue in the dress has been interpreted as white by so many people.
"Your visual system is always trying to separate out what color is coming from the lighting and what color is coming from the object, and you do that differently for blue and yellow," Webster said. "When you see a bluish tint you attribute it to the light, and when you see a yellowish tint you attribute it to the object."
When his team flipped the colors of the dress so that what was blue was now yellow, there was no more dichotomy in perception -- most people see the dress clearly as yellow.
Webster believes that the reason for this might be that shadows are bluish, and so the brain is used to discounting the color. "If your brain sees yellow, you think, it can't be coming from the shading, so it has to be the color of the object itself," he said.
In an interview with the Los Angeles Times, Conway said that when he first saw the divisive image, he did not realize its signifcance.
"I thought, 'This is fluff,' " he said.
But eventually he changed his mind.
"It took me about two weeks, when we got our first results, but then I was like, 'This is extraordinarily profound,' " he said. "It hits this little sweet spot that gives you some clue about how the brain works."
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