Semantic facilitation in bilingual first language acquisition q Samuel Bilson a , Hanako Yoshida b , Crystal D. Tran b , Elizabeth A. Woods b , Thomas T. Hills c,⇑ a Institute of Mathematics, University of Warwick, United Kingdom b Department of Psychology, University of Houston, United States c Department of Psychology, University of Warwick, United Kingdom article info Article history: Received 31 August 2014 Revised 18 February 2015 Accepted 29 March 2015 Available online 20 April 2015 Keywords: Bilingualism Language acquisition Communicative development inventory Network analysis Mutual exclusivity abstract Bilingual first language learners face unique challenges that may influence the rate and order of early word learning relative to monolinguals. A comparison of the productive vocabularies of 435 children between the ages of 6 months and 7 years—181 of which were bilingual English learners—found that monolinguals learned both English words and all- language concepts faster than bilinguals. However, bilinguals showed an enhancement of an effect previously found in monolinguals—the preference for learning words with more associative cues. Though both monolinguals and bilinguals were best fit by a similar model of word learning, semantic network structure and growth indicated that the two groups were learning English words in a different order. Further, in comparison with a model of two-monolinguals-in-one-mind, bilinguals overproduced translational equivalents. Our results support an emergent account of bilingual first language acquisition, where learning a word in one language facilitates its acquisition in a second language. Ó 2015 Elsevier B.V. All rights reserved. 1. Introduction How does learning two first languages at the same time differ from learning only one first language? This question is the focus of this article but also holds a central place in our understanding of the cognitive prerequisites for lan- guage learning more generally. From a casual perspective, learning two languages at once should make the language learning problem harder, because words and their refer- ents violate the one-to-one mapping we often expect within a language. Most bilingual children, however, seem undaunted. The evidence suggests that bilingual first lan- guage learners have little problem learning two languages (Lanza, 2000), and as we report below, past research sug- gests that the differences are, if anything, subtle. Yet, these differences are important because our theories of language acquisition rely on certain underlying principles, and many of these principles are derived from research on monolin- guals. By understanding bilingual learning better, we bet- ter understand the constraints and generality of our theories. We also better understand what is both a growing form of language learning (UNESCO, 2003) as well as a lan- guage mode that has both lifelong economic and cognitive consequences (Bialystok, 2009; Bialystok, Craik, & Freedman, 2007; Kovács & Mehler, 2009). In this article we focus on a comparative investigation of monolingual and bilingual first language acquisition by asking how learning two languages at once during early childhood influences the rate and order of word learning. We investigate the rate by looking at both word and con- cept learning, two aspects of language learning that have often been difficult to discern between monolingual and bilingual populations because of small sample sizes. We investigate the order both by comparing two recent http://dx.doi.org/10.1016/j.cognition.2015.03.013 0010-0277/Ó 2015 Elsevier B.V. All rights reserved. q Data and code sufficient to reproduce the analyses and figures can be found here: www2.warwick.ac.uk/fac/sci/psych/people/thills/thills/bil- sonetal_data.zip. ⇑ Corresponding author at: Department of Psychology, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, United Kingdom. Tel.: +44 247 652 3183. E-mail address: t.t.hills@warwick.ac.uk (T.T. Hills). Cognition 140 (2015) 122–134 Contents lists available at ScienceDirect Cognition journal homepage: www.elsevier.com/locate/COGNIT