Law of Figure-Ground Perception

This is the mind eventual focusing on a certain plot or pattern that creates a familiar image and disregards the other image which is present in the background usually represented with contrasting colors such as black and white. Then when the brain focus's on the background it becomes harder to see the initial image. In the image below, if you focus on the white shape you might see a vase, not noticing the to black faces looking at each other in the background.