Dual language statistical word segmentation in infancy: Simulating a language-mixing bilingual environment.

Infants are sensitive to syllable co-occurrence probabilities when segmenting words from fluent speech. However, segmenting two languages overlapping at the syllabic level is challenging because the statistical cues across the languages are incongruent. Successful segmentation, thus, relies on infants' ability to separate language inputs and track the statistics of each language. Here, we report three experiments investigating how infants statistically segment words from two overlapping languages in a simulated language-mixing bilingual environment. In the first two experiments, we investigated whether 9.5-month-olds can use French and English phonetic markers to segment words from two overlapping artificial languages produced by one individual. After showing that infants could segment the languages when the languages were presented in isolation (Experiment 1), we presented infants with two interleaved languages differing in phonetic cues (Experiment 2). Both monolingual and bilingual infants successfully segmented words from one of the two languages-the language heard last during familiarization. In Experiment 3, a conceptual replication, we replicated the findings of Experiment 2 with a different population and with different cues. As before, when 12-month-old monolingual infants heard two interleaved languages differing in English and Finnish phonetic cues, they learned only the last language heard during familiarization. Together, our findings suggest that segmenting words in a language-mixing environment is challenging, but infants possess a nascent ability to recruit phonetic cues to segment words from one of two overlapping languages in a bilingual-like environment. A video abstract of this article can be viewed at https://www.youtube.com/watch?v=92pNcpxZguw.

Perceptual narrowing in the context of increased variation: Insights from bilingual infants.

Human infants become native-language listeners through a process of perceptual narrowing. Monolingual infants are initially sensitive to a wide range of language-relevant contrasts. However, as they mature and gain native-language experience, their sensitivity to nonnative contrasts declines. Here, we consider the case of infants growing up bilingual as a window into how increased variation affects early perceptual development. These infants encounter different meaningful contrasts in each of their languages, and must also attend to contrasts that occur between their languages. Bilingual infants share many classic developmental patterns with monolinguals. However, they also show unique developmental patterns in the perception of native distinctions such as U-shaped trajectories and dose-response relationships, and show some enhanced sensitivity to nonnative distinctions. Analogous developmental patterns can be observed in individuals exposed to two nonlinguistic systems in domains such as music and face perception. Some preliminary evidence suggests that bilingual individuals might retain more sensitivity to nonnative contrasts, reaching a less narrow end state than monolinguals. Nevertheless, bilingual infants do become perceptually specialized native listeners to both of their languages, despite increased variation and differing patterns of perceptual development in comparison to monolinguals.

Object Familiarity Enhances Infants' Use of Phonetic Detail in Novel Words.

Infants greatly refine their ability to discriminate language sounds by 12 months, yet 14-month-olds appear to confuse similar-sounding novel words. Two explanations could account for this phenomenon: infants initially have incomplete phoneme representations, suggesting developmental discontinuity; or word-learning demands interfere with use of established phonetic detail. These hypotheses were tested at 14 months by pairing a novel word with an object preexposed to half the infants and novel to the other half. If demands are key, only preexposed infants should efficiently use phonetic detail; there is no need to concurrently learn object details with the word. If representations lack detail, object familiarity should not matter. Only infants preexposed to the object noticed a change in its label, thus challenging the discontinuity position and demonstrating the impact of object familiarity on early word learning.

A multi-lab study of bilingual infants: Exploring the preference for infant-directed speech.

From the earliest months of life, infants prefer listening to and learn better from infant-directed speech (IDS) than adult-directed speech (ADS). Yet, IDS differs within communities, across languages, and across cultures, both in form and in prevalence. This large-scale, multi-site study used the diversity of bilingual infant experiences to explore the impact of different types of linguistic experience on infants' IDS preference. As part of the multi-lab ManyBabies 1 project, we compared lab-matched samples of 333 bilingual and 385 monolingual infants' preference for North-American English IDS (cf. ManyBabies Consortium, 2020: ManyBabies 1), tested in 17 labs in 7 countries. Those infants were tested in two age groups: 6-9 months (the younger sample) and 12-15 months (the older sample). We found that bilingual and monolingual infants both preferred IDS to ADS, and did not differ in terms of the overall magnitude of this preference. However, amongst bilingual infants who were acquiring North-American English (NAE) as a native language, greater exposure to NAE was associated with a stronger IDS preference, extending the previous finding from ManyBabies 1 that monolinguals learning NAE as a native language showed a stronger preference than infants unexposed to NAE. Together, our findings indicate that IDS preference likely makes a similar contribution to monolingual and bilingual development, and that infants are exquisitely sensitive to the nature and frequency of different types of language input in their early environments.

What paradox? Referential cues allow for infant use of phonetic detail in word learning.

Past research has uncovered a surprising paradox: Although 14-month-olds have exquisite phonetic discrimination skills (e.g., distinguishing [b] from [d]), they have difficulty using phonetic detail when mapping novel words to objects in laboratory tasks (confusing bin and din). While some have attributed infants' difficulty to immature word learning abilities, the hypothesis presented herein is that infants are powerful word learners and this apparent difficulty occurs only when the referential status of the novel word is unclear. Across 2 experiments, 14-month-old infants (N=44) used phonetic detail to map novel words to objects when conditions were conducive to word-referent mapping (clear sentential contexts and word-referent training), thus revealing no fundamental discontinuity in its use from speech perception to word learning.

Fourteen-month-old infants learn similar-sounding words.

Can infants, in the very first stages of word learning, use their perceptual sensitivity to the phonetics of speech while learning words? Research to date suggests that infants of 14 months cannot learn two similar-sounding words unless there is substantial contextual support. The current experiment advances our understanding of this failure by testing whether the source of infants' difficulty lies in the learning or testing phase. Infants were taught to associate two similar-sounding words with two different objects, and tested using a visual choice method rather than the standard Switch task. The results reveal that 14-month-olds are capable of learning and mapping two similar-sounding labels; they can apply phonetic detail in new words. The findings are discussed in relation to infants' concurrent failure, and the developmental transition to success, in the Switch task.

Associative word learning in infancy: A meta-analysis of the switch task.

Associative word learning, the ability to pair a concept to a word, is an essential mechanism for early language development. One common method by which researchers measure this ability is the Switch task (Werker, Cohen, Lloyd, Casasola, & Stager, 1998), wherein infants are habituated to 2 word-object pairings and then tested on their ability to notice a switch in those pairings. In this comprehensive meta-analysis, we summarized 141 Switch task studies involving 2,723 infants of 12 to 20 months to estimate an average effect size for the task (random-effect model) and to explore how key experimental factors affect infants' performance (fixed-effect model). The average effect size was low to moderate in size, Cohen's d = 0.32. The use of language-typical and dissimilar-sounding words as well as the presence of additional facilitative cues aided performance, particularly for younger infants. Infants learning 2 languages at home outperformed those learning 1, indicating a bilingual advantage in learning word-object associations. Together, these findings support the Processing Rich Information from Multidimensional Interactive Representations (PRIMIR) theoretical framework of infant speech perception and word learning (e.g., Werker & Curtin, 2005), but invite further theoretical work to account for the observed bilingual advantage. Lastly, some of our analyses raised the possibility of questionable research practices in this literature. Therefore, we conclude with suggestions (e.g., preregistration, transparent data peeking, and alternate statistical approaches) for how to address this important issue. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

The impact of cross-language phonological overlap on bilingual and monolingual toddlers' word recognition.

We examined how L2 exposure early in life modulates toddler word recognition by comparing German-English bilingual and German monolingual toddlers' recognition of words that overlapped to differing degrees, measured by number of phonological features changed, between English and German (e.g., identical, 1-feature change, 2-feature change, 3-feature change, no overlap). Recognition in English was modulated by language background (bilinguals vs. monolinguals) and by the amount of phonological overlap that English words shared with their L1 German translations. L1 word recognition remained unchanged across conditions between monolingual and bilingual toddlers, showing no effect of learning an L2 on L1 word recognition in bilingual toddlers. Furthermore, bilingual toddlers who had a later age of L2 acquisition had better recognition of words in English than those toddlers who acquired English at an earlier age. The results suggest an important role for L1 phonological experience on L2 word recognition in early bilingual word recognition.

Early word learners' ability to access phonetic detail in well-known words.

Several recent studies from our laboratory have shown that 14-month-old infants have difficulty learning to associate two phonetically similar new words to two different objects when tested in the Switch task. Because the infants can discriminate the same phonetic detail that they fail to use in the associative word-learning situation, we have argued that this word-learning failure results from a processing overload. Here we explore how infants perform in the Switch task with already known minimally different words. The experiment involved the same phonetic difference as used in our earlier word-learning studies. Following habituation to two familiar minimal pair object-label combinations (ball and doll), infants of 14 months looked longer to a violation in the object-label pairing (e.g., label 'ball' paired with object doll) than to an appropriate pairing. These results using well known words are consistent with the pattern of data recently obtained by Swingley and Aslin (2002) in which it was found that infants of 14 months look longer to the correct object when the accompanying well known word is spoken correctly rather than mispronounced. We discuss how these results are compatible with the limited resource explanation originally offered by Stager and Werker (1997).

Quality not quantity of television viewing is associated with bilingual toddlers' vocabulary scores.

Previous research examining the relationship between television viewing and vocabulary has produced mixed findings that indicate the quality of television exposure may impact language development more than quantity. However, few infant or toddler studies have included both quality and quantity measures and no study has done so with bilinguals. Caregivers of monolingual English, monolingual French, and English-French bilingual infants and toddlers from the same geographical area completed questionnaires regarding television exposure and vocabulary. Factor analysis of the questionnaire data confirmed that quantity and quality of viewing should be assessed separately. Quantity of television viewing was not correlated with language outcomes in any group. Poor quality viewing (television unintended for children, background television, solitary viewing, and earlier age of viewing) was related to lower vocabulary scores overall, but especially the English vocabulary scores of bilingual toddlers. Possible reasons for this finding are discussed.

Bilingual beginnings to learning words.

At the macrostructure level of language milestones, language acquisition follows a nearly identical course whether children grow up with one or with two languages. However, at the microstructure level, experimental research is revealing that the same proclivities and learning mechanisms that support language acquisition unfold somewhat differently in bilingual versus monolingual environments. This paper synthesizes recent findings in the area of early bilingualism by focusing on the question of how bilingual infants come to apply their phonetic sensitivities to word learning, as they must to learn minimal pair words (e.g. 'cat' and 'mat'). To this end, the paper reviews antecedent achievements by bilinguals throughout infancy and early childhood in the following areas: language discrimination and separation, speech perception, phonetic and phonotactic development, word recognition, word learning and aspects of conceptual development that underlie word learning. Special consideration is given to the role of language dominance, and to the unique challenges to language acquisition posed by a bilingual environment.

Using speech sounds to guide word learning: the case of bilingual infants.

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 = 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.