An infant's early crying sounds are largely limited to frontal vowels, such as in "dada," and a few consonants; the remaining vowel and consonant sounds gradually appear, first produced in a babbling manner, and the first meaningful words may appear at ten months. By the end of the second year, the infant's active vocabulary may reach 250 words. One of the key reasons infants can produce more sounds is the developing larynx, or voice box, which "descends" between the ages of 11/2 to 2 years. Thus, as the infant's vocal tract develops, the wider the range of sounds. See voice.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.