A-not-B error

The A-not-B error is an incomplete or absent schema of object permanence, normally observed during the sensorimotor stage of Jean Piaget's Theory of Cognitive Development.

A typical A-not-B task goes like this: An experimenter hides an attractive toy under box "A" within the baby's reach. The baby searches for the toy, looks under box "A", and finds the toy. This activity is usually repeated several times (always with the researcher hiding the toy under box "A"), which means the baby has the ability to pass the object permanence test. Then, in the critical trial, the experimenter moves the toy under box "B", also within easy reach of the baby. Babies of 10 months or younger typically make the perseveration error, meaning they look under box "A" even though they saw the researcher move the toy under box "B", and box "B" is just as easy to reach. Piaget called this phenomenon A-not-B error. This demonstrates a lack of, or incomplete, schema of object permanence, shows that the infant's cognition of the existence of the object at this time still depends on the actions he makes to the object. Children of 12 months or older (in the preoperational stage of Piaget's theory of cognitive development) typically do not make this error.