A time span generally in early development during which an organism is uniquely sensitive to specific stimuli. Also referred to as the optimal or sensitive period.
Although the term "critical period" is used in a variety of contexts, it is most closely associated with ethology, the study of innate and learned behavior in the natural environment. The critical period plays an important role in the concept of imprinting, first described by Konrad Lorenz in connection with the earliest process of social attachment in young animals. Imprinting also applies to any irreversible behavioral response acquired early in life. In the most famous example of imprinting involving goslings, Lorenz demonstrated that exposure to an appropriately maternal object during a critical period would activate the "following" instinct; he successfully had a group of goslings follow him after he "impersonated" their absent mother. This concept was popularized in 1996 in the feature film Fly Away Home.
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 and the early months in which birds must be exposed to the characteristic song of their species in order to learn it. The study of critical periods in animal behavioral development eventually led to the search for and analysis of critical periods in human development.
Critical periods in human development
Critical periods, although not as precisely limited in humans as in other species, have been described for behaviors such as smiling, infant-mother attachment, and language development. Researchers such as Maria Montessori described critical, or sensitive, periods for certain aspects of human development. In developing her Montessori method of education, Montessori defined distinct but overlapping "sensitive periods" that were conducive to development in specific areas. For example, from ages one to five, development and learning are conducive through sensory stimulation. Thus, it is important during this period of childhood for children to experience sensory input whenever possible. A related sensitive period described by Montessori is that for language development, occurring between the ages of three and about five months. During this stage, children are sensitive to sounds and able to discriminate between them and thus should be given auditory stimulation to foster successful language development.
The concept of the critical period appears to be supported by studies of the so-called "wild" or feral children who were deprived of human society for an extended period. These children, although relatively few in number,
Candland, Douglas Keith. Feral Children and Clever Animals: Reflections on Human Nature. New York: Oxford University Press, 1993.
Denny, M. Ray. Comparative Psychology: Research in Animal Behavior. Homewood, IL: Dorsey Press, 1970.
Lillard, Paula Polk. Montessori Today: A Comprehensive Approach to Education from Birth to Adulthood. New York: Schocken Books, 1996.
Lorenz, Konrad. The Foundation of Ethology. New York: Springer-Verlag, 1981.