While common in research using animal models, the approach is difficult to establish in epidemiological studies and virtually nonexistent in human clinical trials. Evidence for critical/sensitive periods or nutritional programming requires a systematic manipulation of the age at which nutritional conditions or supplements are implemented. It is implicit in these hypotheses that the fetal period is a time during which metabolic and physiological systems are malleable and thus susceptible to either insult or enhancement by nutrient intake. The notion of nutritional programming, central to the Barker/Developmental Origins hypotheses of health and disease, represents a variant of the critical/sensitive period concept. Once that period has passed, the activity can still be learned although it will not be.

This chapter reviews research in the context of the development of social preferences and sensory systems, with a summary of the criteria for defining such a period and the evidence necessary to establish its existence. A sensitive period is a time when a childs brain is most receptive to a certain type of stimuli. Roberts made the idea of a critical period in language acquisition public in the end of the 1950s. Critical or sensitive periods in the life of an organism during which certain experiences or conditions may exert disproportionate influence (either for harm or benefit) on long-term developmental outcomes have been the subject of investigation for over a century. The concept of a sensitive period for second language acquisition goes back to research and theoretical models regarding first language acquisition.

Sensitive period notion definition