critical period

n. A critical period is a window of time in an organism,s life cycle during which the organism exhibits heightened sensitivity to environmental stimuli, which in turn trigger some aspect of development. For example, graylag goslings develop filial imprinting during the first 36 hours of life, becoming irreversibly bonded to the first moving object they encounter. In language acquisition, the critical period hypothesis has been the subject of extensive and inconclusive study. It is unclear whether lack of early exposure to a first language results in failure to acquire a normal system, though case studies of feral children and congenitally deaf adults strongly suggest that this is the case. Studies examining second-language learners consistently report age effects: older learners do not come as close to native-like attainment of the second-language grammar as do younger learners. However, the reported age effects are not always consistent with details of the predictions of a hypothesized critical period for second-language acquisition, particularly because studies have not consistently found evidence of a sharp turning point (e.g., at the onset of adolescence) in levels of ultimate attainment. Instead, the evidence points to a gradual decline that persists well beyond adolescence and through adulthood.

- EMF