Object permanence is knowing that an object you can no longer see still exists. It is why Peek-a-boo is so fun. The child is not sure if you are around the corner or not. Oh wow! Mommy’s back!
A typical scenario involves a child sitting in a high chair playing with a toy while mom cooks dinner. Mom is talking to the baby and the baby is banging the toy on the high chair tray. Suddenly, the child throws the toy on the floor. She then leans over to see if it still exists. She smiles and is pleased with herself because it does and then starts to fuss because she can no longer reach it. Most often, mom interprets this as a game of fetch. In reality, her child is checking object permanence. It is simply inconvenient that the toy is now on the floor and mom must pick it up again. Having mom hand the toy back is merely a consequence of this exercise in checking object permanence. The best part of the game is looking over the edge and seeing the toy.
Parents can take advantage of this developmental milestone. If you eliminate your child’s pacifier before object permanence develops, it will be easier on your child. He will forget it because it is out of sight. Also, babies no longer get endorphins from nonnutritive sucking (ie. Pacifiers) by 6 months old. For lots of children, learning about object permanence starts around 8 months so throwing away the pacifier at 6 months makes a lot of sense. After 7-8 months, babies are often very noisy just for fun. Pacifiers stifle this and can quickly be a crutch for parents who want their child to be inappropriately quiet.