Infants start out with certain broad capacities for speech, and learning to say words depends on maturation of these capacities: both maturation of the anatomy for speech and maturation of the sensorimotor connections between audition and production systems. Learning to say words also depends on hearing other persons say words; a child has to hear their sounds and appreciate how the sounds that are heard relate to sounds the child can say. Infants begin to take account of the speech they hear and to bend their own capacities for soundmaking to accommodate the sounds of speech in the first half year of life. Before the first words appear, the influence of hearing such different languages as French, English, Japanese, and Swedish is already evident in differences in the sounds of babbling. But maturation and phonetic input determine which words are learned and how they are learned only in a social and informational context. It is the personal and interpersonal context that determines which words are learned in the second year.

EARLY VOCABULARIES

A critically important question for studies of the emergence of language is What is a word? Deciding that what a child says qualifies as a word depends on judgments about the sounds emitted in the effort and their relevance to what is going on in the context. The criteria we used to judge that a word was a word were intuitive and similar to those used in other studies: relatively consistent phonetic shape and meaningfulness.