Cross-linguistic differences in the size of the infant vowel space

This study examined the effects of linguistic environmental input on babbling in cross-linguistic investigations of vowel space. Speech samples were collected from 10- to 18-month-old infants learning Arabic (N = 31). First (F1) and second (F2) formant frequencies were identified in the selected vowels and used to calculate the compact-diffuse (F2 − F1) and grave-acute ([F2 + F1]/2) values for each vowel and the size of the vowel space was calculated for each infant's vowel space. These vowel space statistics were compared to similar data derived from vowels produced by English-learning infants (N = 20) and French-learning infants (N = 23) as previously described in Rvachew, Mattock, Polka, and Menard (2006). It was found that Arabic infants appeared to achieve a larger vowel space at a younger age compared to the English and French infants, which we attribute to the benefit of a less crowded vowel space in Arabic input compared to English and French input. Expansion of the vowel space toward the diffuse and grave corners was common to all three language groups, but the developmental trajectories for the mean F1 and mean F2 varied with language input. These findings suggest that the development of infant babbling is influenced by a complex interaction of endogenous and exogenous processes, which include the biological development of the vocal tract and language input from the ambient environment.