POP! GOES MY HEART
Nothing is more romantic than curling up in front of a fire with your loved one on Valentine's Day as you lovingly whisper “chromostereopsis.” Okay, maybe it's not as passionate as a sonnet—unless you are a vision scientist. Look at the red and blue hearts and examine their depth with respect to the background. Most people find that the red heart pops in front of the blue background, whereas the blue heart sinks beneath the red background.
This illusion comes about because the lenses in our eyes refract blue light more than red. This phenomenon is called chromatic aberration; another example of this effect is seeing a rainbow when you shine white light through a prism. When both eyes view the red and blue images simultaneously, the cornea and lens of the eyes refract different amounts of the colors. The brain deals with this sensory aberration by imagining depth—the red heart is in front of the blue background, and vice versa—even though none actually exists.