"Unique yellow" is particularly interesting because it is stable across large populations—everyone agrees on what unique yellow looks like despite the fact that people's eyes and vision are often very different. (Credit: iStockphoto)

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What makes ‘unique yellow’ unique?

We see things differently in winter compared with how we see them in summer, according to a new study that sheds light on how humans process colors, particularly the color known as “unique yellow.”

Humans identify four unique hues—blue, green, yellow, and red—that don’t appear to contain mixtures of other colors.

Unique yellow—meaning no hint of a green or red—is particularly interesting, scientists say, because it is stable across large populations—everyone agrees on what unique yellow looks like despite the fact that people’s eyes and vision are often very different.

In the summer

Researchers wanted to find out why unique yellow is so stable and what factors might make it change. They thought that unique yellow might depend not on the biology of the eye but on the color of the natural world.

“What we are finding is that between seasons our vision adapts to changes in environment,” says Lauren Welbourne, a PhD student at the University of York. “So in summer when there is a much larger amount of foliage, our visual system has to account for the fact that on average we are exposed to far more green.

“In York, you typically have grey, dull winters and then in summer you have greenery everywhere. Our vision compensates for those changes and that, surprisingly, changes what we think ‘yellow’ looks like. It’s a bit like changing the color balance on your TV.”

Dial it to yellow

For the study, published in the journal Current Biology, researchers tested 67 men and women in January and June. Participants were placed in a darkened room, allowed to adjust to the light and then on a machine called a colorimeter asked to adjust a dial backwards and forwards until they felt they had reached the point where it had reached unique yellow.

“I take lots of measurements of the setting in both seasons, and find a shift in the average setting between seasons,” Welbourne says, adding that the research sheds new light on the complex workings of the visual system.

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“This is the first time natural changes in the environment have been shown to affect our perception of color.  Although there’s no disorder that this can fix, the more we learn about how vision and color in particular is processed, the better we can understand exactly how we see the world. “This can have knock on effects on the way we diagnose and treat visual disorders.”

The findings show how humans are constantly adapting to their surroundings.

“Many places in the world have very different environments throughout the year. Think about the changes that the rainy season brings to India, or winter and summer in the arctic. So this process is very useful because you can adapt to these huge seasonal changes in environmental color and continue to see and discriminate between colors accurately.”

Source: University of York

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