Object Permanence is a Montessori principle that is often shown in the 9-12 month age group. Working in child care you often find around this age children become "clingy" or not wanting their caregiver to leave their sight.
Giving Mason the opportunity to explore these Object permanence boxes reinforces that even though you may not see something it is still there.
As he drops the ball into the hole, he looses sight of it and has to open the draw to find it. This focus' on his hand eye coordination,fine motor skills and starts the process of his memory understanding object permanence.