Teal or Pink? Explanation From a Neuro-Ophthalmologist

Alfredo Sadun, MD, PhD

Dr. Alfredo Sadun, world-renowned neuro-ophthalmologist, explains why two people can look at the same object and see different colors.

Colors, and brightness, are not perceived in the absolute sense. This was understood by Edward Land [scientist, inventor and co-founder of the Polaroid Corporation] and is called “The retinex” theory. Most simply, the brain takes into account the surrounding lights and colors and uses them to make a relative calculation. So, in fact, a white piece of paper on your desk right now looks white even though it reflects less light than my grey trousers do outside (where the sun makes everything much brighter, but the relative lack of brightness of my trousers down-grades it to be perceived as grey). The same for colors.

The French Impressionists knew that (to use Monet) a bright blue parasol will make the opposite color, orange look more orange in the adjacent poppies. But, in addition to the comparisons of colors and brightness in the field, there is also the memory of what colored things usually are. We know strawberries are red, so when in doubt we attribute a little redness to them which can also make something next to them that is “less red” look green when in fact, the photo is only in black and white. So when we make an assumption of one thing, it can change another thing.

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