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...