What color is the dress? This question occupied people around the world seven years ago. Everyone has an answer, but it’s always different. The Internet phenomenon also makes experts ponder. A US scientist provides the explanation.
“The drama that split the planet,” headlines the Washington Post in 2015. What is meant is not the refugee crisis or the Paris climate agreement, but a dress – strictly speaking, a photo of a dress. The need for discussion arises with the question: is the dress white and gold or black and blue? Just under the hashtag
At the time, the dress not only made the social media world ponder. As The Wired reports, it also amazed Pascal Wallisch, a neuroscientist from New York University. When he saw the dress for the first time, it appeared to him to be striped in gold and white. However, when he showed it to his wife, she saw something completely different: she was convinced it was black and blue striped. “I was up all night thinking about what could possibly explain that,” Wallisch told the US magazine.
Thanks to years of research, Wallisch believed he had understood the thirty or so steps in the visual processing chain down to the last detail. But “all of that was turned on its head in February 2015 when the dress appeared on social media,” says the scientist. He felt like a biologist who had just learned that doctors had discovered a new organ in the human body.
The spectrum of light we can see — the primary colors red, green, and blue — are specific wavelengths of electromagnetic energy, Wallisch explains. These wavelengths of energy are emitted from a source such as the sun, a lamp, or a candle. For example, when this light hits a lemon, the lemon absorbs some of those wavelengths and the rest bounces off. What’s left enters through the pupil and hits the retina at the back of the eye. There the information is translated into electrochemical neurons that are used by the brain to construct the subjective experience of seeing color.
Since most natural light is a combination of red, green, and blue, a lemon absorbs the blue wavelengths, leaving the red and green on the retina. So we see a yellow lemon. However, the color only exists in our imagination. In principle, yellow is a pipe dream, says the neuroscientist. “The reason we usually agree that lemons are yellow is because all of our brains create pretty much the same image when light hits lemons.”
Disagreement usually only arises when an image seen is in some way ambiguous and the brain agrees on an interpretation. According to Wallisch, the best examples of this are optical illusions, such as the Ruby Vase, which sometimes looks like a vase and sometimes like two people facing each other in silhouette.
But that’s not the case with the viral photo of the dress. Because here the same light enters all eyes and every brain interprets the lines and shapes as a dress. But: Not all brains convert light into the same colors. To find out why, Wallisch examined more than 13,000 subjects and published his results in the journal “Journal of Vision”. He concludes that the differences in perception are due to our assumptions about how the dress was lit.
Study participants who thought the dress was photographed in the shade viewed the garment as gold and white. In contrast, those who assumed it was lit by artificial light tended to interpret it as black and blue, Wallisch says. “The original image was overexposed, so the lighting source was unclear,” he explains in the study. “As a result, we make assumptions about how the dress was lit, which affects the colors we see.”
“Shadows are blue, so mentally we subtract the blue light to see the image, which then appears in light colors — gold and white,” Wallisch says. However, artificial light tends to be yellowish. “When our brain assumes the photo has been lightened, we pull out yellow, leaving a dress that we see as black and blue.” This is a basic cognitive function: “To recognize the color of an object, the lighting source must be taken into account, which the brain is constantly doing.”
Regardless of what colors people see subjectively, the image never seems ambiguous to the individual because people consciously experienced only the results of their processes, and the results were based on the person’s prior experiences with light, Wallisch explains. “So when the truth is uncertain, our brain resolves that uncertainty without our knowing it by creating the most likely reality it can imagine based on our past experiences.”
