Here were the simple instructions given by a Harvard University assistant professor to people participating in a recent cognitive science study:
“Imagine the following scene. Visualize it in your mind’s eye, as vividly as you can: a person walks into a room and knocks a ball off a table.”
The professor, Tomer Ullman, then asked those in the study about nine properties of their mental images, including the color and size of the ball, the shape and size of the table, and the person’s hair color and height. If you are anything like the people in the study, you only visualized a subset of all of these properties. Did you see how big the ball was? How about the person’s hair color? Most participants visualized the former but not the latter.