after hatching any object as their mother. This tendency to imprint an attachment to a mother - object occurs during a very short span of time - hence the term critical period. Other investigators (Hebb, 1947; Riesen, 1958; Thompson and Heron, 1954) discovered that if animals were kept under conditions of sensory deprivation (e.g. total darkness) when young, either they were permanently retarded in their development or they took longer than animals reared under normal conditions.
             These experiments led to renewed interest in the possibility originally suggested by Sigmund Freud that there are critical periods in the development if human infants and young children. The experiments also raise the related question of whether a deprived environment leads to permanent retardation, an enriched environment to permanent increments of growth. Evidence described by the Austrian physician René Spitz (1946) suggests that there is a critical period in infants. Spitz observed a condition called maramus (Greek for "wasting away") in babies cared for in hospital nurseries during wartime. He theorized that if an infant is not giving sufficient attention during the first months of life, it might fail to respond to stimulation and, in extreme cases waste away and die. This theory was popularized by Margaret Ribble in her book The Rights of !
             Infants (1943), in which she maintained that mother love is a prerequisite for satisfactory development.
             All types of imprinting exemplify the basic relationship between the survival function of a concrete behavior and its structure. Affectionate (filial) imprinting on ducks and geese must guarantee that the young follow only their mothers. Hence, chicks...