object constancy, 1. the ability to perceive an object as unchanging even under different conditions of observation. Lack of object constancy is a primary symptom of borderline personality disorder, adversely affecting the ability to bond with and trust others. 2. (in child development) a step in development, usually achieved before the age of 2, in which a child gains the understanding that just because someone or something is out of sight, it is not gone. Regarding caregivers, the infant learns that the caregiver will return and builds trust and faith in others. See also object permanence.
