Normal language acquisition.

Long before they start talking, children are skilled at using eye contact, facial expression, and nonverbal gestures to communicate with other people. They also are able to discriminate speech sounds from an early age. Vocabulary learning builds on the child's knowledge about objects, actions, locations, properties, and stages gained as a result of sensorimotor development. Early word combinations allow children to express semantic relationships between these various referents. During the period from 2 to 4 years of age, children move from expressing their ideas in simple telegraphic speech to being able to ask questions, use negation, talk about past and future events, and describe complicated situations using sentences constructed according to complex grammatical rules.