No abstract

Cross-linguistically, when mothers address their infants they produce acoustically more extreme point vowels (/i/, /u/, and /a/) than they produce when speaking to another adult [Kuhl et al., Science 277, 684–686 (1997)]. This study examines three nonpoint vowels in Russian (/e/, /o/, /’i/) and compares their acoustics in infant-directed (ID) and adult-directed (AD) speech with the acoustics of Russian point vowels in AD and ID speech. Six target words containing the nonpoint vowels in stressed syllables were recorded while ten mothers conversed with their infant and another adult. F1, F2, and F0 were measured at vowel onset, center, and offset. As with the point vowels, the acoustic structure of all three vowels differs significantly in ID and AD speech. F2 tends to move to an acoustically more extreme position in each case. In addition, nonpoint ID vowels show more vowel-inherent formant movement across the course of the vowel. Formant movement may provide an important cue to vowel identity, and its exaggeration in ID speech may increase the likelihood that infants incorporate formant movement into their mental representation of a vowel. Significant differences in formant structure were found for vowels in one-, two-, and three-syllable words, including vowels with short mean durations.

Speech input to infants may exert an important influence on the development of language-specific perception by providing infants with information regarding the phonetic and phonological properties of their language. This study compares the acoustic structure of vowels produced by Russian and American mothers conversing with their infants, with the structure of vowels produced by the same women conversing with an adult. Mothers in both countries were asked to play with their infants (aged 2–5 months) using sets of toys whose names contained the target vowels in at least two different consonant contexts (e.g., sheep, bead). They were asked to use the same words in conversation with an adult. All mothers increased the degree of acoustic separation between vowel categories in infant-directed speech by selectively increasing or decreasing F1 and F2 values. Relative to American mothers [P. K. Kuhl et al., Science 277, 684–686 (1997)], Russian mothers showed smaller increases in fundamental frequency and less variation in vocal pitch while speaking to their infants. Nevertheless, mothers in both countries produced highly similar changes in acoustic structure, and comparable increases in the size of the acoustic space delimited by the vowels /i/, /a/, and /u/, when speaking to their infants.