An important feature of the sensory-motor stage is the baby’s inability to symbolize. In other words, the child cannot hold an image of an object in his or her mind when it is no longer physically present. When the object is “out of sight,” it is “out of mind.” Piaget’s concept of object permanence illustrates this phenomenon. If you dangle an object in front of a young baby and then remove the object, the child will not search for the object when it is hidden from view. The child’s attention will simply drift to the next interesting event. However, after the age of eight months (give or take), the baby will search for an interesting object hidden from view. If you hide the rattle behind a pillow, the child will move the pillow to look for the rattle.