Akiyoshi Kitaoka is a veritable treasure. This professor of experimental psychology at Kyoto’s Ritsumeikan University spends his time playing about and trying to better understand visual perception, and as part of that, he often looks at optical illusions, sharing the best of them on his Twitter account.
Kitaoka is well aware that it’s oddly fun knowing our brain is being tricked, and one of his most recent examples is proving to be a particularly good distraction from the world being, you know, on fire, both metaphorically and literally.
You can see his examples of the illusion below, but they all follow the same pattern: an object moves across a board featuring a color or monochrome gradient, appearing to change color to stand out more from the background hue as it goes. Spoiler alert: the moving object’s color remains constant throughout. Cool, right?
Say you’re outside, in a forest or something, and you need to forage or hunt for food. Light levels will constantly vary, which means that there’s a lot for our visual systems to take in when we search for specific things.
First, you’ve got reflectance, which is how much light is bouncing off a surface. Then, you have lightness, which is how you perceive this reflectance, as well as brightness, which is the perceived intensity of light entering the eye. You also have luminance, which is how intense the light that reaches your eye is based on how sensitive your visual system actually is.
There’s a lot for your brain to deal with, but you still need to see objects of varying kinds as standing out even as the ambient light levels change. That’s why you see the same color object, with the exact same ability to reflect light as it did before, the lightness and brightness levels can change in order for it to stand out.
These illusions then are examples of our brain trying to do the right thing based on its experience in natural, 3D environments but getting it wrong in 2D. Funnily enough, the exact mechanisms as to why this happens are a little mysterious. Is it to do with human perception, physiology, or is it thanks to the uncertainties we get from visual stimuli?
One 2007 study got a computer program to look at surfaces under different lighting conditions and found that not only could it accurately tell the differences between surfaces in the same way that we can, but that it fell for the same lightness illusions as we do. That suggests that past learning experience has an effect on the manifestation of these illusions in humans.
In essence, then, an optical illusion is when the source of a stimulus isn’t the same as what our brains calculate to be the most likely source of that stimulus. That cognitive discrepancy causes us to see things incorrectly even though the brain's trying to do its best.
As that same paper puts it, “sometimes the best way to understand how the visual brain works is to understand why it sometimes does not.” These latest illusions from Kitaoka are a perfect example of why illusions like this aren’t just fun, but vital to neurological and cognitive research.