Brain researchers hypothesize that this effect, known as the Ebbinghaus illusion, plays its trick based on how our brains interpret depth. From a lifetime of looking at things, we remember that smaller items tend to be farther away, while larger ones are closer. In this image, the brain reads the left ring of large, black circles as nearby and the right, smaller set as distant. Simultaneously, the brain also groups the orange circles with their black surroundings. So the left one is also seen as nearby, and the right one farther away. When the brain compares the orange circles, the only way for the right one to be more distant is if it’s larger than the left circle.