Jack is an infant who loves to play peek-a-boo with his father. he seems amazed that his father "reappears" after hiding his face behind his hands. jack probably enjoys peek-a-boo because he does not yet understand:

The correct answer is known as "object permanence".

Object permanence is described as the knowledge that items continue to exist even when they can not be perceived (visible, heard, touched, smelled or sensed in any way). consistent with this view, it is through touching and dealing with gadgets that babies develop item permanence.