Child Development, September/October 2007, Volume 78, Number 5, Pages 1510– 1525 Using Speech Sounds to Guide Word Learning: The Case of Bilingual Infants Christopher T. Fennell University of Ottawa Krista Byers-Heinlein and Janet F. Werker University of British Columbia Despite the prevalence of bilingualism, language acquisition research has focused on monolingual infants. Monolinguals cannot learn minimally different words (e.g., ‘‘bih’’ and ‘‘dih’’) in a laboratory task until 17 months of age (J. F. Werker, C. T. Fennell, K. M. Corcoran, & C. L. Stager, 2002). This study was extended to 14- to 20-month- old bilingual infants: a heterogeneous sample (English and another language; N 5 48) and two homogeneous samples (28 English – Chinese and 25 English – French infants). In all samples, bilinguals did not learn similar- sounding words until 20 months, indicating that they use relevant language sounds (i.e., consonants) to direct word learning developmentally later than monolinguals, possibly due to the increased cognitive load of learning two languages. However, this developmental pattern may be adaptive for bilingual word learning. The vast majority of experimental work in language development, particularly in the area of early lexical acquisition, has focused on monolingual infants. Yet, due to immigration, official language policies, and cultural preferences and norms, many infants are raised in a bilingual environment. The simultaneous exposure to two languages, each with different sound inventories and lexicons, leads to a very different set of acquisition challenges for bilingual infants. To date, it is unknown whether the burgeoning literature linking speech perception to early word learning in monolinguals will generalize to all infants. The set of experiments presented in this article will explore the theoretical and empirical claims about the relation- ship between speech perception and word learning by extending this line of research to infants raised in a bilingual environment. The task of learning two languages from birth is potentially not an easy one. Bilingual infants must accomplish dual language learning in an environ- ment that is not always overtly structured with respect to language exposure. Many infants hear their two languages from a multitude of sources (e.g., parents, other family members, close friends, sur- rounding community). Even though they may not have systematic language division, bilingual infants acquire words in both of their languages from the beginning of lexical acquisition (Pearson, Ferna ´ndez, & Oller, 1995; Quay, 1995). When compared to mono- linguals, they pass language milestones at similar ages (de Houwer, 1995; Oller, Eilers, Urbano, & Cobo- Lewis, 1997; Pearson & Fernandez, 1994; Petitto et al., 2001) and have similar-sized vocabularies, when taking words from both languages into account (Pearson & Fernandez; Pearson, Ferna ´ndez, & Oller, 1993; Petitto et al.). Although suggestive of important similarities between monolinguals and bilinguals, these outcome measures reveal little about the process by which bilingual infants build their lexicons, spe- cifically how they use their speech perception skills to guide word learning. Do the steps bilingual-learning infants take in linking speech perception to word learning mirror those taken by monolinguals, or do bilingual-learning infants take a different path to achieve similar outcomes? Speech Perception Before beginning the process of word learning in earnest, infants must first refine their perceptual sensitivities to the sound contrasts that distinguish one word from another in their native language, and bilingual-learning infants must accomplish this goal for each of their native languages. For example, an English-learning infant needs to attend to the measur- able and perceptible information that distinguishes [b] from [d], as these sounds can differentiate English words (e.g., ‘‘bad’’ from ‘‘dad’’). The term phonetic denotes these physical properties of speech sounds; This research was funded by a Social Sciences and Humanities Research Council of Canada Grant (410-2004-0744) and a Human Frontiers Science Program Grant (RGP 68/2002) to J. Werker and an O’Brien Foundation Fellowship to C. Fennell and K. Byers-Heinlein acknowledge the support of Natural Sciences and Engineering Research Council of Canada Graduate Scholarships. We thank Laurel Fais for her insightful comments on drafts of this paper. We also thank all the parents and infants who participated in these studies. Correspondence concerning this article should be addressed to Christopher Fennell, School of Psychology, University of Ottawa, 145 Jean-Jacques-Lussier, Ottawa, Ontario, Canada K1N 6N5. Electronic mail may be sent to fennell@uottawa.ca. # 2007 by the Society for Research in Child Development, Inc. All rights reserved. 0009-3920/2007/7805-0007