Capturing Early Word Production in Caregiver-Toddler Shared Book-Reading Interactions

In many circumstances, age and experience with language go hand in hand, making it challenging to disentangle their roles in early word learning. Here we use shared book-reading as a vehicle for structured but naturalistic language exposure, allowing us to control age of exposure to new words (i.e. novel nouns). We presented 18-month-olds (n = 24) and 22-month-olds (n = 20) with three novel nouns embedded in a picture book that caregivers read at home over two weeks. Caregiver-child reading sessions were audio-recorded and coded for toddlers’ novel noun production (our outcome measure), and properties of the reading sessions (such as reading session length and extratextual extensions beyond the book text). While 18-month-olds' and 22-month-olds' caregivers said the target words the same number of times during book-sharing, the older toddlers' caregivers engaged in longer reading sessions and used more extratextual extensions. Over the two weeks, nearly all 22-month-olds and over 2/3 of 18-month-olds produced at least one of the novel nouns (and most 22-month-olds produced all 3). Intriguingly, increased caregiver extratextual extensions were associated with a higher likelihood of toddlers producing novel words during reading sessions within each age group, and overall. In addition, toddlers’ overall productive vocabulary (based on a parent-report checklist, the MBCDI) predicted novel word production among 22-month-olds but not 18-month-olds. Together, these findings show that two weeks of naturalistic book-sharing (with about 250 exposures to each of 3 novel nouns) is sufficient to foster new word production. Our results reveal both developmental changes in toddlers’ learning capacities over 18 to 22 months, and the efficacy of certain aspects of caregiver input across this range. Caregivers’ extratextual talk during shared book-reading emerged as a particularly potent support for toddlers’ use of newly learned words even at the earliest stages of productive vocabulary development.