Sensitive periods

Sensitive periods is a term coined by the Dutch geneticist Hugo de Vries and adopted by the Italian educator Maria Montessori to refer to important periods of childhood development.

Montessori believed that every human being goes through a series of quantum leaps in learning during the pre-school years. Drawing on the work of de Vries, she attributed these behaviors to the development of specific areas of the human brain, which she called nebulae. She felt this was especially true during the first few years of life, from birth (or before) to the time of essentially complete development of the brain, about age 6 or 7. Montessori observed several overlapping periods during which the child is particularly sensitive to certain types of stimuli or interactions. She describes these as "sensitive periods", a phrase coined by de Vries during his studies on animals.

According to Montessori, during a sensitive period it is very easy for children to acquire certain abilities, such as language, discrimination of sensory stimuli, and mental modeling of the environment. Once the sensitive period for a particular ability is past, the development of the brain has progressed past the point at which information can be simply absorbed. The child must then be taught the ability, resulting in expenditure of conscious effort, and not producing results as great as could be produced if the sensitive period had been taken advantage of. Montessori was not very specific in her published works about the precise number, description, or timing of these sensitive periods. However, in her lectures to teacher trainees she set out several periods with the approximate ages to which they applied. More importantly, she believed, adults should observe the behavior and activities of children to discover what sensitive periods they are in.

Descriptions
There are many descriptions of the sensitive periods and their ages.

Periods by age
MontessoriMom uses the following chart (cited by permission):

AMI descriptions
The Association Montessori Internationale describes the sensitive periods differently in their teacher-training lectures, arranging them by focus rather than by chronology.

Language
This period runs from birth through approximately age 6. During this period the child is extremely sensitive to vocal sounds and to movements of the vocal apparatus. Out of all the sounds in an infants environment, the infant will be attracted to that of human sounds. Deprivation of language stimuli during this period can lead to severe language defects. Without stimulation, the synapses of Broca's area and related language-processing areas of the brain will literally waste away.

Order
The sensitive period for order operates most actively between roughly the ages of one and three years. In this period, the child is organizing a mental schema for the world. In order for firm conclusions to be drawn about the world, the child must be able to impose an order on it in a way that makes sense to the child and is consistent with the observed world of the child. If this need is not met, the child's ability to reason and learn will be precarious, since she may not be able to consider her conclusions reliable.

Sensory refinement
This period lasts from birth to age 4. A child takes in information about the world through his senses. As the brain develops, it becomes able to discriminate between relevant and irrelevant sensory stimuli. The most efficient way to accomplish this is for the brain to pay attention to all sensory stimuli. The most repetitive (and therefore most important) of these will strengthen neural pathways, while the less common, although initially detected, will not provide enough brain activity to develop sensitivity to them. By age 4 or so, the brain has finished its "decision-making" about which stimuli are relevant, and worth attending to. Other stimuli will be ignored. This period, then, is important for helping the child attend to differences in sensory stimuli, which in turn can lead to a greater ability to impose a mental order on his environment.

Refinement of motor skills
This period encompasses the time between roughly 18 months and 4 years of age. By the beginning of this period, the child's gross motor skills are generally rather well developed. At this point, the continuing development of the cerebellum and motor cortex allow the child to increase her fine motor skills. Activity on the part of the child which focuses on fine muscle control (writing with a pencil, picking up and setting down small objects, and so on) will allow the child's muscular skills to develop to a quite advanced level. After this period, neural control of the muscles is relatively fixed, and improvement in fine motor skills comes only with considerable effort.

Sensitivity To small objects
This period, between roughly 18 and 30 months, might be viewed as a consequence of the overlapping of the previous two. As a consequence of the child's attention to sensory stimuli, combined with an interest in activities requiring fine motor coordination, the child takes an interest in observing and manipulating very small objects, which present a greater challenge to the senses and coordination than large ones.

Social behavior
From about 2.5 through 6 years, the child, having become relatively stable in his physical and emotional environment, begins to attend to the social environment. During this time, in an attempt to order this aspect of her surroundings, the child attends closely to the observed and expected behavior of individuals in a group. This attention and ordering will allow her to move through the social environment in a safe and acceptable way. Children who are, for whatever reason, largely or entirely deprived of social interaction during this period will be less socially confident and perhaps more uncomfortable around others, a feeling which may take substantial effort to overcome.