Final answer:
Depth perception develops when infants become mobile later in infancy, while fear of heights varies from person to person and may not be directly related to depth perception.
Step-by-step explanation:
Depth perception, or the ability to see in three dimensions, fully develops in infants when they become mobile later in infancy. Before that, newborns lack depth perception. The ability to perceive depth continues to develop throughout early childhood. Fear of heights, on the other hand, is a psychological response that can vary from person to person and may not be directly related to depth perception.