Distribution of words across the first years of life: A longitudinal analysis of everyday language input to three English-learning infants.

Many in-lab studies have demonstrated that the distribution of word learning moments affects the strength and quality of word representations. How are words distributed in speech to children in their daily lives, and how is distribution related to other input characteristics? The present study analyzes transcripts of language input to English-learning infants from three longitudinal, naturalistic corpora captured between 6 and 39 months of age. To describe how word frequency varies across time, we calculated dispersion scores for all word types for each child. Dispersion quantifies the deviation of observed frequencies in each recording session from expected (uniform across sessions) word frequency, providing a measure of how evenly word utterances were spread across sessions. Dispersion is strongly correlated with frequency and moderately correlated with concreteness across all corpora, such that high frequency and low concreteness words are more evenly dispersed. Correlations with measures of age of acquisition (AoA) varied across corpora, and dispersion did not reliably predict AoA above and beyond frequency and concreteness. The contradiction between the current results and results from in-lab experiments is discussed. This study provides a foundation to explore how word learning unfolds across time and contexts in the real world.