Phonetic inventories, 15-24 months: a longitudinal study.

Longitudinal samples of meaningful speech of 34 normally developing children were analyzed to determine the range and types of consonantal phones produced at 15, 18, 21, and 24 months. Separate inventories for word-initial and word-final consonants were constructed for each child at each age level. Group analyses showed that early inventories in initial position were composed primarily of voiced anterior stops, nasals, and glides; by 24 months, voiceless stops, velars, and a few fricatives were also included. In final position, inventories consisted primarily of voiceless stops and alveolar consonants. There was a strong tendency for the voiced stops to appear first in initial position and for [t] and [r] to appear first in word-final. Individual analyses of place and manner of articulation revealed highly similar patterns across subjects. The findings are related to other longitudinal research in early phonological development and to studies of babbling of younger subjects and correct productions of older subjects.