Eighteen-month-old babies display object permanence,but they also display the A-not-B error.

A-not-B Error

A cognitive error observed in infants during the sensorimotor stage, where they reach for an object at a location where it was previously found (A) rather than its new location (B).

Object Permanence

The understanding that objects continue to exist even when they cannot be seen, heard, or touched.

Eighteen-month-old Babies

Infants who have reached the age of 18 months, a developmental stage characterized by significant growth in motor skills, language acquisition, and personal social awareness.