According to one formulation, the physical status of the newborn makes the perception of stimuli less efficient than later growth potentiates. Freud formulated the concept of the stimulus barrier. As the Reizschutz' efficiency diminishes, object relations develop; the primary

figure of importance in the development of object relations is the mother or her surrogate. Before the nursling can adequately perceive stimuli, the ideal mother serves as a supplementary barrier against traumatic external and internal excitations. Infants whose maternal protective barriers are deficient develop ego weaknesses and inadequate differentiation of ego and id. If the stimulus barrier or the maternal protective barrier is deficient, or if the drive strength of the child is unusually increased, ego development may be disturbed. It follows that if the infant has or has not a "normal" stimulus barrier and drive potentials and the mother adds traumatic stimuli, ego development might be abnormal.