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the first two years


An average, or standard, measurement, calculated from the measurements of many individuals within a specific group or population


A point on a ranking scale of 0 to 100. Example: a child who is at the 50th percentile for height means that half of all children his age are taller and half are shorter.

shaken baby syndrome

A life-threatening condition that occurs when an infant is forcefully shaken back and forth, rupturing blood vessels in the brain and breaking neural connections


The mental processing of sensory information, when the brain interprets a sensation.

gross motor skills

Physical abilities involving large body movements, such as walking and jumping.

fine motor skills

Physical abilities involving small body movements, especially of the hands and fingers, such as drawing and picking up a coin.


A responsive movement that seems automatic because it almost always occurs in reaction to a particular stimulus.


A situation in which a seemingly healthy infant, at least 2 months of age, suddenly stops breathing and dies unexpectedly while asleep.

primary circular reactions

The first of three types of feedback loops in sensorimotor intelligence, this one involving the infant's own body. Includes reflexes and early adaptations.

secondary circular reactions

The second of three types of feedback loops in sensorimotor intelligence, this one involving people and objects.

tertiary circular reactions

The third of three types of feedback loops in sensorimotor intelligence, this one involving active exploration and experimentation.

object permanence

The realization that objects (including people) still exist when they cannot be seen, touched, or heard.

information-processing theory

A perspective that compares human thinking processes, by analysis, to computer analysis of data, including sensory input, connections, stored memories, and output,


The extended repetition of certain syllables, such as ba-ba-ba, that begins between 6 and 9 months of age.

social smile

A smile evoked by a human face, normally evident in infants about 6 weeks after birth.

stranger wariness

An infant's expression of concern-a quiet stare, clinging to a familiar person, or sadness-when a stranger appears.

separation anxiety

An infant's distress when a familiar caregiver leaves; most obvious between 9 and 14 months.


A person's realization that he or she is a distinct individual, with body, mind, and actions that are separate from those of other people.

social learning

Learning by observing others.


Inborn differences between one person and another in emotion, activity, and self-control.


According to Ainsworth, "an affectional tie" that an infant forms with the caregiver- a tie that binds them together in space and endures over time.


The intersections where the axons of one neuron meet the dendrites of another neuron.


A viral infection that can cause blindness, deafness, and brain damage in a fetus if contracted by a pregnant woman.

sensorimotor stage

In Piaget's theory, the stage (birth to 2 yrs) during which infants know the world mostly in terms of their sensory impressions and motor activities.

depth perception

Our ability to perceive the distance of objects from us.

trust vs. mistrust

According to Erikson, first stage of personality development in which the infant's basic sense of trust or mistrust develops as a result of consistent or inconsistent care.

social referencing

An infant's use of another person's emotional cues to interpret unfamiliar events.

15-17 hours per day

The amount of time a newborn typically spends sleeping.


Anything that stimulates our five senses.


A nerve cell; the basic building block of the nervous system.

prefrontal cortex

Located in the anterior frontal lobe of the brain. Assists in planning, self-control and self regulation. Very immature in the newborn.


Already acute at birth, with infants turning their heads toward sounds, particularly a human voice.


The least mature sense at birth; infants see only objects between 4 and 30 inches away.


Present at birth; rapidly adapts to the social world.

Babinski reflex

When infants' feet are stroked, their toes fan upward.

Moro reflex

Infants fling their arms outward and then bring them together when startled.

Benefits of breastfeeding

Helps prevent illness--particularly allergies, ear infections, stomach upsets & asthma--provides antibodies against disease, provides a balance of nutrients that adjusts to the age of the baby


A sign that infants are thinking as they learn from experience. Includes assimilation (in which new experiences are reinterpreted to fit into old ideas) and accommodation (in which old ideas are restructured to include new experiences).

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