The child cries and fusses for the ball instead of looking for it under the sofa, because he lacks "object permanence", which is the ability to realize that objects they continue to exist even when they cannot be seen, touched or heard directly. Here the child thinks that that ball doesn't exist because he doesn't see it. The child is in the sensorimotor phase of Piaget's stages of cognitive development. The concept of object permanence develops around 8 months of age during Piaget's sensorimotor phase of cognitive development. Example: A baby about 6 months old was given a toy for a short period of time, then his mother took it and kept it under the pillow while the baby looked at it, but the baby starts to get fussy. When her mother shows her the toy, she feels happy. The mother repeats this several times while looking but the child lacks the permanence of the object and every time he can't see the toy he believes it doesn't exist and becomes fussy and starts crying (White,