by Beth Stillman

Created on: February 16, 2009

It is no small task to start from a nearly invisible single cell to becoming a walking, talking, functioning human being. And, as with any seemingly insurmountable task, growth and development has to be broken down into smaller, more manageable tasks that build on each other to slowly create the ever evolving human being. These tasks (that involve brain and physical development, emotional development, social development, et cetera, and the interactions of all these pieces) that we go through throughout life are referred to as stages, and within each of these stages is what we call a sensitive period.

A sensitive period is a time in development where specific areas of growth are more likely to develop than at other times. This sensitive period is a window of opportunity or sorts, and conversely, a window of special vulnerability to disturbances in that specific development. The sensitive period is the time where something is the most likely to be developed or retarded, based on the environmental influences. For example, in the second trimester of pregnancy, a baby is growing and developing its internal organs and limbs. A disturbance to the fetal environment, for example, exposure to chemicals, in the second trimester will harm the development of the baby's organs and limbs more than it would, say, in the third trimester, when the organs have finished their prenatal development and growth is focused on becoming larger and more viable. As a developing child, the first year is the time when the baby is learning about how loving and trustworthy and nurturing his world is, and if the baby is nurtured, the nurturing establishes this sense of trust and safety more strongly in this first year that at any other time. If the baby is not nurtured until later, such as if the child was in an orphanage and abused, the baby will not be able to develop the sense of safety and trust as readily as he would have in his first year. He will be connected with caregivers in an atypical way, either by being completely detached and uncomfortable with affection, or he will constantly need affection and be continually seeking it from others.

Theorists continue to debate on if there are sensitive' periods or critical' ones. Sensitive periods imply a period of greater opportunity and development, and if this period is missed, there still exists the opportunity to learn these skills, although it is diminished. For example, we are most susceptible to picking up a new language in infancy, but we can still learn a new language later in life, albeit not as readily. Critical periods mean that once the opportunity to develop the skill or physical capacity is missed, the person will forever be stuck' in that period and will never learn it later on and be able to move forward. For example, research has shown that when an area of the brain is deprived of stimuli, that area of the brain will not develop at all. If that stimuli is provided later, the brain may not be able to recover the lack of development and be able to interpret or integrate the stimuli.

Many theorists have developed ideas on what children need specifically and when, and many people who work with children can readily see when a child is missing developmental experiences or became harmed during developmental experiences. Children's needs change as they grow, from needing nurturing, structure, emotional and behavioral regulation, independence, and so on. Providing the right experience at the right time helps a person to successfully move from a single cell into a functional adult, tackling challenging task after challenging task along the way.

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