Exploration of vocal tract properties during serial production of vowels by full term and preterm infants

Abstract

This study examines the acoustic characteristics of individual vowels and those produced in sequences of three or more during vocal play by full term and preterm at age 6 months. Laboratory and home audiotape recordings of infant vowel sounds were made and digitized for acoustic analysis. Of interest was whether, during production of vowel sequences compared to those produced singly, infants explored the relation between tongue height and tongue advancement, as measured acoustically by the first formant (F1) and second formant (F2) frequencies, respectively. In both groups of infants, the region of F1-F2 space for individually produced vowels was significantly greater than for vowels produced in sequence. High correlation coefficients for F1 and F2 during exploration of vowels produced in sequence were apparent in full term, but not preterm infants. The data support the claim that vowels produced in sequence occupy a more limited region of the vocal tract than those produced singly, and that infants explore the characteristics of their vocalizations within sequences.