A couple was planning a wedding earlier this year when the bride’s mother sent her daughter a photograph of the dress she planned to wear. When the bride showed the picture to her fiancé, the pair couldn’t agree on what they saw.
To the bride, the dress was white and gold. The groom, however, saw blue and black. The couple posted the image on Facebook, asking friends to settle the dispute. Little did they guess that they would set the Internet afire, sparking one of the biggest social media conversations of 2015.
The debate rapidly went viral, as differing perceptions split friends, families and co-workers.
“The image of the dress triggered such a global furor because it challenges our seemingly self-evident and unquestioned assumption that we see the world as it really is, thereby raising questions about perception and reality,” said Bosco Tjan, professor of psychology at the USC Dornsife College of Letters, Arts and Sciences and an expert on visual perception.
Interpreting sensory input
Why do our perceptions differ? What does this say about the way we view the world? Does an objective reality exist?
As for the dress, why did people see it differently?
“Perception is about how your brain interprets your sensory input,” said Tjan, a founding member and co-director of the Dana and David Dornsife Cognitive Neuroimaging Center who studies the human visual system — in particular, the neural computations that underlie the perception of form.
“Our perception of color depends on our perception of the light in a room or scene,” he said. “When cues about ambient light are missing — as was the case in the photograph of the dress — people may perceive different color for the same object because they implicitly make different assumptions about the ambient light.”
This is because color or more precisely “reflectance,” is a physical property of the material — how much light it reflects at different wavelengths, Tjan explained.
A red object, for example, reflects more long-wavelength light than short-wavelength light. Our eyes cannot see reflectance (the color of an object). Instead, we see the light that the object reflects. In order to infer the color of an object, we need to know the color of the light shining on the object or more precisely, the wavelength or spectral distribution of the light. In the case of the dress, we may make different assumptions about the time of day at which it was photographed and hence assume a different color of the light.
“The brain is always working to infer information, and if it doesn’t have access to direct information, it makes assumptions,” said Tjan, whose work addresses questions pertaining to vision loss, restoration and rehabilitation, including object and face recognition, reading, attention and visual navigation.
“Different people’s brains make different but equally reasonable assumptions. Perception is not direct; it is an implicit or unconscious inference process. Our brains are constantly solving these problems for us behind the scenes, very quickly.”
Never assume
The fact is that humans, like all organisms, are simply not equipped with sufficient sensors to eliminate all ambiguity to directly perceive our world, without assumptions.
“Instead, the brain relies on the fact that our world is governed by physical principles to compensate for our inherently limited and incomplete sensory input and make decisions about what we are really dealing with,” Tjan added. As we have to fill in the gaps with what we know about the world — something that varies according to each individual’s experience — there is room for error and diversity.
What is not present in the photo — in this case the light source — forces our brains to infer the color of the dress from the imagined color of the light source, which influences how we see the dress. Our brains make the decision for us, unconsciously about the color of ambient light and consciously about the color of the dress, and once it has done so, we see it that way.
“The pairing of the colors in the dress materials turned out to hit just the right spot where assumption about daylight matters a lot for seeing the colors of the dress,” Tjan said.