The growth of early phonological and lexical development: A longitudinal investigation

This investigation examined the simultaneous development of phonological and lexical skills in children from 12 to 18 months of age. Twenty-three children from diverse socioeconomic backgrounds were followed at two-month intervals as they made the transition from prelinguistic vocalizations to meaningful speech. At the initial visit (12 months), the child's understanding of language was assessed using the Preschool Language Scale - 3 (Zimmerman, Steiner, & Evatt-Pond, 1991), parents completed a vocabulary checklist (MacArthur Communicative Development Inventories: Words and Gestures, Fenson et al., 1993), and a babbling/language sample was obtained as the child interacted with his or her mother. The vocabulary checklist and babbling/language sample were repeated at each of the following visits (14, 16, and 18 months).; The resulting data provide preliminary insights concerning differences in the emerging phonological and lexical skills of children from 12 to 18 months of age. Longitudinal growth-curve modeling techniques were applied to examine differences among the children's lexical and phonological growth curves. Maternal education was found to be more informative than income in explaining differences in the growth-curve models. Differences in the phonological growth-curves at the outset of the investigation were explained by the number of years of maternal education. Conditional models were obtained for two of the lexical outcome variables: number of different words and the percentage of vocalizations classified as lexical. Differences in the intercept and slope values for the number of different words were explained by gender. The number of years of maternal education explained variance in the intercept values for the percentage of vocalizations classified as lexical. This rarely employed measure appears to offer promise in characterizing early lexical development.; In addition, differences in phonological and lexical measures at 18 months were examined as a function of gender and maternal education. Significant differences were observed for all three of the outcome variables: number of different consonants, number of different words, and the percentage of vocalizations classified as lexical. Girls outperformed boys as did children of mothers who had completed “16 plus years” of education when compared to children of mothers who had completed “up to 15 years” of education.