When Frederick was 5 months old, he looked at his favorite ball, but when it rolled out of his view, he did not search for it. Now at 9 months old moves around to search for it, reflecting the presence of:

Object permanence.

Explanation:

Object permanence is a knowledge that objects are still in existence even when they are no longer within reach, cannot be seen or even heard. It is developed through touching of such items. At 5 months Fredrick has not developed to be able to recognize this fact, but at 9 months moving around to search for a ball shows that he now recognizes that despite the fact that the ball is not in sight it is still lying around somewhere and he wants to get a hold of it.