Young infants can learn statistical regularities and patterns in sequences of events. Studies have demonstrated a relationship between early sequence learning skills and later development of cog- nitive and language skills. We investigated the relation between infants’ visual response speed to novel event sequences, and their later receptive and productive vocabulary. Using a modified visual expectancy paradigm (VExP; Haith, Wentworth, & Canfield, 1993), we tested 6-month-old infants’ speed at responding to novel but predictable contingent event sequences. In addition, parental reports and behavioral measures of infants’ vocabulary were obtained at 12, 16, and 22 months. In order to estimate the separate effects of linguistic input on vocabulary, maternal speech from a play session at 12 months was analyzed for lexical diversity and quantity. Results suggest that infants’ speed of responding to novel but predictable events at 6 months robustly predicted both receptive and pro- ductive vocabulary at 22 months. This relation cannot be attributed to general cognitive maturity, as measured by a standardized test (Bayley Scales of Infant Development; Bayley, 2005). Maternal input predicted additional unique variance in infant processing speed. The results suggest that infants’ capacity to quickly learn and respond to sequential patterns, over and above the quality of the speech input they receive, contributes to vocabulary size in the second year.

Recent research suggests that infants tend to add words to their vocabulary that are semantically related to other known words, though it is not clear why this pattern emerges. In this paper, we explore whether infants leverage their existing vocabulary and semantic knowledge when interpreting novel label-object mappings in real time. We initially identified categorical domains for which individual 24-month-old infants have relatively higher and lower levels of knowledge, irrespective of overall vocabulary size. Next, we taught infants novel words in these higher and lower knowledge domains and then asked if their subsequent real-time recognition of these items varied as a function of their category knowledge. While our participants successfully acquired the novel label-object mappings in our task, there were important differences in the way infants recognized these words in real time. Namely, infants showed more robust recognition of high (vs. low) domain knowledge words. These findings suggest that dense semantic structure facilitates early word learning and real-time novel word recognition.