The infantile stimulus-barrier, a concept derived from Freud's hypothetical Reizschutz, has at least two interpretations: as a non-selective passive shield and as an active proto-defense mechanism. It serves to limit external stimuli so as to minimize overstimulation. Stages of neurological maturation are cited to demonstrate its existence. Recent infant studies, however, strongly contradict this: neonatal avoidant responses do not act categorically to minimize internal states of excitation, but are selective. Alternative formulations to the barrier-against-penetration model of stimulus processing propose that infants regulate perceptual experience within a framework of object attachment and information processing. Infants seek out stimuli they can assimilate and accommodate to; the mother provides appropriate stimulation and protects the child from inappropriate sensory experiences at each level of development.