Examining early word learning and language input through a longitudinal, experimental, and observational lens

Abstract

Children learn hundreds of words in a few short years (e.g., Dale & Fenson, 1996; Fernald, Pinto, & Swingley, 1998), but there is wide variability between children (Fenson, 2007). Some of the variability in children’s language skills can be attributed to differences in their language input (e.g., generally, children who hear more words say more words; Huttenlocher, et al., 1991; Huttenlocher, et al., 2010). However, there are many other factors at play that may influence both children’s language input and their ability to learn from that input over time, such as their own cognitive, social, and linguistic developments (Bergelson, 2020). In this dissertation, I ask if differences in infants’ language input explain changes in their word comprehension, explain gender differences in their early language skills, or predict their later language outcomes years later.In Chapter 1, I review prior work on variation in children’s language experience, how it maps onto their developing language skills, and how children’s own development may affect that input. Chapter 2 investigates how children's word comprehension develops across infancy in an eye-tracking study and a complementary corpus analysis. I find that infants gain semantic precision in word comprehension from age 0;6 to 1;6, but this improvement is not readily explained by changes in their at-home exposure to the tested words. Instead, children's improvements in word comprehension may be driven by cognitive and social developments that aid their word learning. Chapter 3 investigates if differences in children's early language input could drive gender differences in their early language skills. I replicate prior work finding girls have an early word production advantage, but I do not find evidence that they have different language input compared to boys. However, I find that children hear more words once they've said their first word, regardless of gender. These results suggest that children's language input does not vary by gender, but instead by their language abilities. In Chapter 4, I turn to investigating a longer timescale of language input and development. Do children's early language abilities and input in infancy predict their later language outcomes years later? I find that children's early language skills consistently predict their later language skills, and measures of children's early language input do not improve our predictions. In Chapter 5, I summarize and synthesize the results of these three studies and discuss implications and future directions of this work.Across these three studies, I find that language input is not a strong predictor of differences in children’s language skills. Instead, my results suggest that other factors (such as children’s age, gender, and earlier language development) better predict children’s language outcomes.