When looking at #TheDress, some saw white and gold stripes and others saw blue and black stripes. However the original photo, which was posted on the social media platform Tumblr in March, contained pixels of either blue or brown.

Scientists decided to dig deeper into this internet brain teaser. They conducted a study and concluded that this is one of the most dramatic examples of color perception. It all has to do with how the brain filters light.

A study of more than 1400 participants, including 300 who had not viewed the photo before, found that people either saw blue and black, white and gold or blue and brown. U.S. neuroscientist Dr. Bevil Conway of Massachusetts Institute of Technology said that which color stripes a person saw in the photo depended upon whether their brains expected to experience natural outdoor light or artificial indoor light.

He concluded that people who saw white and gold may be more accustomed to outdoor light whereas people who saw blue and black may be more accustomed to indoor light. And the people who saw blue and brown fell somewhere in the middle.

Conway said that the larger question is “what causes these differences in the population.” He said that one way of looking at it would be to consider how “light is contaminated by outside illumination, such as a blue sky or incandescent light.”

He added that a person’s brain has to make a decision. It either has to get rid of shorter blue wavelengths of light or longer redder ones. That decision has an impact on how a person sees The Dress.

Conway also said that perception varied by sex and age. Women and older people were more likely to see white and gold whereas a larger amount of younger people saw blue and black.

Conway’s paper on #TheDress was one of three published in the scientific journal Current Biology.