There is a viral YouTube video with over 16 million views that dramatically demonstrates that a young orangutan can be fooled by a magic trick. Watch it before you read any further.
Now that you've watched – the orangutan clearly understands that the fruit is in the cup; it's been watching very carefully. The cup is capped, briefly goes out of sight and comes back with the cap still on it. You can almost feel the orangutan's puzzlement when the cover is removed and the cup is shown to be empty. And then there is an almost human response, as the orangutan realizes the impossibility of what it's seen and roles on the ground in laughter.
The developmental psychologist Jean Piaget is famous for his studies on the development of cognitive abilities in infants and children. Among other things, Piaget studied the development of object permanence – the realization that an object still exists, even when it disappears from sight. The game of "peek-a-boo" you've played with an infant exploits this idea. For infants less than a certain age you disappear when you cover your face with your hands. Open your hands and say "peek-a-boo" – you reappear and are rewarded with smiles and happy squeals and gurgling sounds from the infant. Wait a few years and the reaction is decidedly different.
One of Piaget's early experiments with object permanence involved placing a toy under a piece of cloth in front of an infant. Very young infants fail to search for the toy, but, at about 9 months, the infant will pick up the cloth, revealing the toy. At that age the child has realized that objects still exist, even when out of sight. Piaget extended this experiment by using two pieces of cloth. In full view of the child he hid the toy under the first cloth. Then, still in full view, he removed the toy from under the first cloth and moved it under the second cloth. A young infant responds by lifting the first cloth; only older infants will lift the second cloth.
I first read about Piaget's experiments and theories of cognitive development when my daughter was around one and a half to two years old. I was curious about her developmental stage so I conducted the two cloth test described above. Then I sat back and watched. Was my daughter going to be a genius for her age or an ordinary child? She hesitated, seemed to collect her thoughts, then leaned forward and, using both hands, picked up both cloths simultaneously!
Object permanence is useful for not only humans, but animals as well. Suppose a squirrel is walking in the woods and sees a bear or other predator ahead. The predator moves out of sight, behind a bush. Without the knowledge that objects can still exist even if not seen the squirrel would keep on walking in the same direction, with disastrous consequences.
Not only will the sense of object permanence reduce the chance that you'll fall victim to a large predator it will enable you to enjoy a performance of magic as much as an orangutan. Unfortunately most people have never had the pleasure of seeing a live performance of close-up magic in which things appear, change and/or disappear right under their noses. Many of these take advantage of the object permanence bias that we all learned as infants. As examples, I encourage you to view these videos of this beautiful card trick, Slydini fooling Dick Cavett with coins and this trick with a single cup and ball. You probably won't roll on the floor laughing like an orangutan, but I bet you'll be smiling.