Imagine you’re walking on the sidewalk with a friend and you see a pile of stones—two side by side, and then a chain beneath them forming a curved line. It reminds you of a smile. “Look,” you say. “A face.”
Days later, you’re making pancakes for your toddler, and you pull out some blueberries to put on top. The shape of the pancake reminds you of something: you put two blueberries side by side forming eyes, and then a row beneath them to form a happy face. “Look,” says your two-year-old. “A face.”
Of course, it is difficult not to see a face in these instances—because you see faces frequently, your mind is accustomed to them, and therefore begins to perceive them in other contexts. In this case, you are making use of a psychological set: a group of expectations that guides our perceptions and behaviors. Because your mind is used to things being a certain way, the psychological set colors your expectations, and helps you perceive the world in ways consistent with your views. While the face perception example describes a “perceptual set,” psychological sets are called “mental sets” when they inform how we solve problems.