The emergence of vowels in an infant.

Recordings of vocal production of an infant (age 16-64 weeks) were subjected to perceptual and acoustic analysis. Sounds resembling the vowel sounds of English were identified, and formant frequency measurements were made from spectrograms. Significant longitudinal trends for individual vowel sounds were not apparent during this period, although formant relationships for some vowels after 38 weeks were consistent with the notion of restructuring of the infant's vocal tract. However, analysis of F1/F2 plots over time revealed the emergence of a well-developed vowel triangle, resembling that of older children and adults. The acute axis of this triangle seems to develop before the grave axis. Implications for anatomical, neuromuscular, and linguistic development are discussed.