We would like to thank support from Cognitive ToyBox, and note that BML and TK are co-founders of Cognitive ToyBox which developed the two tablet applications in Experiment 1. We gratefully acknowledge Jesse Snedeker for the suggestion that led to Experiment 2, as well as for providing materials from de Marchena et al. (2011). Data from Experiment 2 were previously presented in the Proceedings of the Cognitive Science Society Conference in Lewis & Frank (2013).

Given a novel word and a familiar and a novel referent, children have a bias to assume the novel word refers to the novel referent. This bias -- often referred to as "Mutual Exclusivity'' (ME) -- is thought to be a potentially powerful route through which children might learn new word meanings, and, consequently, has been the focus of a large amount of empirical study and theorizing. Here, we focus on two aspects of the bias that have received relatively little attention in the literature: Development and experience. A successful theory of ME will need to provide an account for why the strength of the effect changes with the age of the child. We provide a quantitative description of the change in the strength of the bias across development, and investigate the role that linguistic experience plays in this developmental change. We first summarize the current body of empirical findings via a meta-analysis, and then present two experiments that examine the relationship between a child's amount of linguistic experience and the strength of the ME bias. We conclude that the strength of the bias varies dramatically across development and that linguistic experience is likely one causal factor contributing to this change. In the General Discussion, we describe how existing theories of ME can account for our findings, and highlight the value of computational modeling for future theorizing.

Early parenting practices play an important role in shaping children’s future outcomes. In particular, high-quality early interactions can facilitate language learning and school performance. The rise of phone-based parenting applications (“apps”) could deliver low-cost interventions on parenting style to a wide variety of populations, especially the parents of very young children, who are often difficult to reach in other ways. Yet little is known about the effects of communicating to parents through app-based interventions. In two studies (one preregistered), we showed parents short videos depicting age-appropriate parent-child activities from a parenting app. We found that after watching the video, parents spoke more and made more bids for joint attention, as compared with controls who watched no video (experiment 1) or a science video (experiment 2). These results suggest that activity videos can lead to positive changes in parent engagement, providing support for the use of such videos in parenting interventions.