Critical period is a specified time span, also referred to as the optimal or sensitive period, during which certain events or experiences must occur in order for the development of an organism to proceed normally.
Although used in a variety of contexts, the term critical period is most closely associated with ethology, the study of animal behavior in its natural environment through the lens of evolutionary adaptation. The critical period concept plays an important role in the theory of imprinting, first used by Konrad Lorenz (1903–1989) as he observed the earliest process of social bonding in young animals. The term imprinting, how-ever, also applies to any irreversible behavioral response acquired early in life and expressed by a specific triggering stimulus or situation. In the most famous psychological example of imprinting, Lorenz demonstrated that exposure to any maternal object during a critical period activated the following instinct of newborn goslings: Lorenz successfully had a group of goslings follow him after he impersonated their absent mother.
Other examples of critical periods include the initial four months of life during which puppies must be exposed to humans in order to make good pets. Birds must be exposed to the characteristic song of their species in their early months in order to learn it. Critical periods vary in length: The period for identifying one's mother may last only a few hours, whereas the period for learning to identify a mate may take several months.
The term critical period is also used to describe physiological and behavioral phenomena. For example, the embryonic stage in humans is a critical period for certain types of growth (such as the appearance of the heart, eyes, ears, hands, and feet), which must occur for prenatal development to proceed normally.
See also Ethology ; Imprinting ; Lorenz, Konrad.
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