Statistical learning in infancy predicts vocabulary size in toddlerhood

During the first 2 years of life, an infant's vocabulary grows at an impressive rate. In the current study, we investigated the impact of three challenges that infants need to overcome to learn new words and expand the size of their vocabulary. We used longitudinal eye-tracking data (n = 118) to assess sequence learning, associative learning, and probability processing abilities at ages 6, 10, and 18 months. Infants' ability to efficiently solve these tasks was used to predict vocabulary size at age 18 months. We demonstrate that the ability to make audio-visual associations and to predict sequences of visual events predicts vocabulary size in toddlers (accounting for 20% of the variance). Our results indicate that statistical learning in some, but not all, domains have a role in vocabulary development.