A critical period in developmental biology refers to a stage of maturation in the organism's lifespan during which the nervous system is mainly vulnerable to some kinds of environmental stimuli. If due to certain causes, the organism does not acquire the suitable stimulus at this critical period, to acquire a given trait or skill, it may become tough, eventually less successful, or even not possible, to attain some of the functions in the later stages of the life. The functions, which are essential for the survival of an organism, like vision, are mainly likely to form at these critical periods.
