An average, or standard, calculated from many individuals within a specific group or population.

A point on a ranking scale of 0 to 100. The 50th percentile is the midpoint; half the people in the population being studied rank higher and half rank lower.

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

The learned abilities to move some part of the body, in actions ranging from a large leap to a flicker of the eyelid. (The word motor here refers to movement of muscles.)

Physical abilities involving large body movements, such as walking and jumping. (The word gross here means "big.")

Physical abilities involving small body movements, especially of the hands and fingers, such as drawing and picking up a coin. (The word fine here means "small.")

Piaget's term for the way infants think—by using their senses and motor skills—during the first period of cognitive development.

The realization that objects (including people) still exist even if they can no longer be seen, touched, or heard.

The extended repetition of certain syllables, such as ba-ba-ba, when babies are between 6 and 9 months old.

A single word that is used to express a complete, meaningful thought.

Chomsky's term for a hypothesized mental structure that enables humans to learn language, including the basic aspects of grammar, vocabulary, and intonation.

Is more concrete in familiar setting, when repeated, and when infant is motivated.

early dendrite growth

Refers to brain functions that require certain basic common experiences (which an infant can be expected to have) in order to develop normally.

Refers to brain functions that depend on particular, variable experiences and that therefore may or may not develop in a particular infant.