Reference point .................................
If you look at Cosmos episode 1, I'm sure you find an answer there.
Object permanence is the developmental milestone that must be reached before an infant experiences separation anxiety. It is used to describe the ability of a child to know that objects continue to exist despite the fact that they can no longer be perceived that is , seen or heard, touched, smelled, or sensed in any way. This milestone is developed through touching and handling objects by the infants.
