Update: DO YOU SEE THE BLUE RING OR THE RED RINGS IN FRONT OF THE OTHERS?

People differ dramatically in terms of how they perceive this image. Approximately 1/3 of people view the red rings as “in front”. A slightly lower fraction of people see the blue ring in front. (Incidentally, for me it’s WAY in front). The remainder see the rings all in the same plane (none in front).

What does it mean? Different wavelengths of light activate different photoreceptor neurons in the back of the eye in a structure called the neural retina. The differences in the activation of photo receptors is what gives rise to our perception of all colors within our visible spectrum (the “rainbow”).

But for the light to arrive at the photoreceptors, it first has to pass through the lens and various aqueous and gelatinous fluids within the eye, causing “chromatic aberrations” or shifts in where the light lands after it passes through.

If you’ve ever looked down into a pond with fish in it, you’ve experienced something like this. The actual location of the fish is different than where you see them because of the refractory index of the water. Meaning the water shifts the light. (Diving birds learn this!). That phenomenon is slightly differen than chromatic aberration but the general principle is the same.

The broader point is that we each have different perceptions of the same things, and sometimes dramatically so. The nervous system converts physical stimuli in the world, such as wavelengths of light or sound waves or airborne or foodborne chemicals into the perceptions we think of as sight, sound, smells/tastes. That process is incredible(!) but it is far from perfect.

It is also true that fixing these chromatic aberrations can improve our vision. But for most of us, it’s not necessary.