Developmental shift in the discrimination of vowel contrasts in bilingual infants: is the distributional account all there is to it?

Lack of early sensitivity and gradual emergence of native phoneme categories: A pattern from underrepresented language learners

Perceptual narrowing of speech perception supposes that young infants can discriminate most speech sounds early in life. During the second half of the first year, infants' phonetic sensitivity is attuned to their native phonology. However, supporting evidence for this pattern comes primarily from learners from a limited number of regions and languages. Very little evidence has accumulated on infants learning languages spoken in Asia, which accounts for most of the world's population. The present study examined the developmental trajectory of Korean-learning infants' sensitivity to a native stop contrast during the first year of life. The Korean language utilizes unusual voiceless three-way stop categories, requiring target categories to be derived from tight phonetic space. Further, two of these categories-lenis and aspirated-have undergone a diachronic change in recent decades as the primary acoustic cue for distinction has shifted among modern speakers. Consequently, the input distributions of these categories are mixed across speakers and speech styles, requiring learners to build flexible representations of target categories along these variations. The results showed that among the three age groups-4-6 months, 7-9 months, and 10-12 months-we tested, only 10-12-month-olds showed weak sensitivity to the two categories, suggesting that robust discrimination is not in place by the end of the first year. The study adds scarcely represented data, lending additional support for the lack of early sensitivity and prolonged emergence of native phonology that are inconsistent with learners of predominant studies and calls for more diverse samples to verify the generality of the typical perceptual narrowing pattern. RESEARCH HIGHLIGHTS: We investigated Korean-learning infants' developmental trajectory of native phoneme categories and whether they show the typical perceptual narrowing pattern. Robust discrimination did not appear until 12 months, suggesting that Korean infants' native phonology is not stabilized by the end of the first year. The prolonged emergence of sensitivity could be due to restricted phonetic space and input variations but suggests the possibility of a different developmental trajectory. The current study contributes scarcely represented Korean-learning infants' phonetic discrimination data to the speech development field.

Revisiting perceptual sensitivity to non-native speech in a diverse sample of bilinguals

Werker and Tees (1984) prompted decades of research attempting to detail the paths infants take towards specialisation for the sounds of their native language(s). Most of this research has examined the trajectories of monolingual children. However, it has also been proposed that bilinguals, who are exposed to greater phonetic variability than monolinguals and must learn the rules of two languages, may remain perceptually open to non-native language sounds later into life than monolinguals. Using a visual habituation paradigm, the current study tests this question by comparing 15- to 18-month-old monolingual and bilingual children's developmental trajectories for non-native phonetic consonant contrast discrimination. A novel approach to the integration of stimulus presentation software with eye-tracking software was validated for objective measurement of infant looking time. The results did not support the hypothesis of a protracted period of sensitivity to non-native phonetic contrasts in bilingual compared to monolingual infants. Implications for diversification of perceptual narrowing research and implementation of increasingly sensitive measures are discussed.

Sensitivity to visual cues within motion events in monolingual and bilingual infants

It is well known that infants undergo developmental change in how they respond to language-relevant visual contrasts. For example, when viewing motion events, infants' sensitivities to background information ("ground-path cues," e.g., whether a background is flat and continuous or bounded) change with age. Prior studies with English and Japanese monolingual infants have demonstrated that 14-month-old infants discriminate between motion events that take place against different ground-paths (e.g., an unbounded field vs a bounded street). By 19 months of age, this sensitivity becomes more selective in monolingual infants; only learners of languages that lexically contrast these categories, such as Japanese, discriminate between such events. In this study, we investigated this progression in bilingual infants. We first replicated past reports of an age-related decline in ground-path sensitivity from 14 to 19 months in English monolingual infants living in a multilingual society. English-Mandarin bilingual infants living in that same society were then tested on discrimination of ground-path cues at 14, 19, and 24 months. Although neither the English nor Mandarin language differentiates motion events based on ground-path cues, bilingual infants demonstrated protracted sensitivity to these cues. Infants exhibited a lack of discrimination at 14 months, followed by discrimination at 19 months and a subsequent decline in discrimination at 24 months. In addition, bilingual infants demonstrated more fine-grained sensitivities to subtle ground cues not observed in monolingual infants.

Connecting perception and production in early Catalan-Spanish bilingual children: language dominance and quality of input effects

This study investigates perception and production of the Catalan mid-vowel /e/-/ɛ/ contrast by two groups of 4.5-year-old Catalan-Spanish bilingual children, differing in language dominance. Perception was assessed with an XAB discrimination task involving familiar words and non-words. Production accuracy was measured using a familiar-word elicitation task. Overall, Catalan-dominant bilingual children outperformed Spanish-dominant bilinguals, the latter showing high variability in production accuracy, while being slightly above chance level in perception. No correlation between perception and production performance could be established in this group. The effect of language dominance alone could not explain the Spanish-dominant participants' performance, but quality of Catalan input (native vs. accented speech) was identified as an important factor behind familiar-word production and the inaccurate representation of the target contrast in the lexicon of the bilinguals' less-dominant language. More fine-grained measurements of experience-related factors are needed for a full understanding of the acquisition of challenging contrasts in bilingual contexts.

Moving away from deficiency models: Gradiency in bilingual speech categorization

For much of its history, categorical perception was treated as a foundational theory of speech perception, which suggested that quasi-discrete categorization was a goal of speech perception. This had a profound impact on bilingualism research which adopted similar tasks to use as measures of nativeness or native-like processing, implicitly assuming that any deviation from discreteness was a deficit. This is particularly problematic for listeners like heritage speakers whose language proficiency, both in their heritage language and their majority language, is questioned. However, we now know that in the monolingual listener, speech perception is gradient and listeners use this gradiency to adjust subphonetic details, recover from ambiguity, and aid learning and adaptation. This calls for new theoretical and methodological approaches to bilingualism. We present the Visual Analogue Scaling task which avoids the discrete and binary assumptions of categorical perception and can capture gradiency more precisely than other measures. Our goal is to provide bilingualism researchers new conceptual and empirical tools that can help examine speech categorization in different bilingual communities without the necessity of forcing their speech categorization into discrete units and without assuming a deficit model.

Input quality and speech perception development in bilingual infants' first year of life

Individual differences in infants' native phonological development have been linked to the quantity and quality of infant-directed speech (IDS). The effects of parental and infant bilingualism on this relation in 131 five- and nine-month-old monolingual and bilingual Spanish and Basque infants (72 male; 59 female; from white middle-class background) were investigated. Bilingualism did not affect the developmental trajectory of infants' native and non-native speech perception and the quality of maternal speech. In both language groups, vowel exaggeration in IDS was significantly related to speech perception skills for 9-month-olds (r = -.30), but not for 5-month-olds. This demonstrates that bilingual and monolingual caregivers provide their infants with speech input that assists their task of learning the phonological inventory of one or two languages.

Experience with research paradigms relates to infants' direction of preference

Interpreting and predicting direction of preference in infant research has been a thorny issue for decades. Several factors have been proposed to account for familiarity versus novelty preferences, including age, length of exposure, and task complexity. The current study explores an additional dimension: experience with the experimental paradigm. We reanalyzed the data from 4 experiments on artificial grammar learning in 12-month-old infants run using the head-turn preference procedure (HPP). Participants in these studies varied substantially in their number of laboratory visits. Results show that the number of HPP studies is related to direction of preference: Infants with limited experience with the HPP setting were more likely to show familiarity preferences than infants who had amassed more experience with this paradigm. This evidence has important implications for the interpretation of experimental results: Experience with a given method or, more broadly, with the laboratory environment may affect infants' patterns of preferences.

Perceptual sensitivity to vowel quality and vowel length in the first year of life

The perceptual attunement to native vowel categories has been reported to occur at 6 months of age. However, some languages contrast vowels both in quality and in length, and whether and how the acquisition of spectral and duration-cued contrasts differs is uncertain. This study traced the development of infants' sensitivity to native (Czech) vowel-length and vowel-quality contrasts. The results suggest that in a vowel-length language, infants learn to categorize vowels in terms of length earlier and/or more robustly than in terms of quality, the representation of which may still be relatively underdeveloped at 10 months of age.

Neural Indices of Vowel Discrimination in Monolingual and Bilingual Infants and Children

OBJECTIVES

To examine maturation of neural discriminative responses to an English vowel contrast from infancy to 4 years of age and to determine how biological factors (age and sex) and an experiential factor (amount of Spanish versus English input) modulate neural discrimination of speech.

DESIGN

Event-related potential (ERP) mismatch responses (MMRs) were used as indices of discrimination of the American English vowels [ε] versus [I] in infants and children between 3 months and 47 months of age. A total of 168 longitudinal and cross-sectional data sets were collected from 98 children (Bilingual Spanish-English: 47 male and 31 female sessions; Monolingual English: 48 male and 42 female sessions). Language exposure and other language measures were collected. ERP responses were examined in an early time window (160 to 360 msec, early MMR [eMMR]) and late time window (400 to 600 msec, late MMR).

RESULTS

The eMMR became more negative with increasing age. Language experience and sex also influenced the amplitude of the eMMR. Specifically, bilingual children, especially bilingual females, showed more negative eMMR compared with monolingual children and with males. However, the subset of bilingual children with more exposure to English than Spanish compared with those with more exposure to Spanish than English (as reported by caretakers) showed similar amplitude of the eMMR to their monolingual peers. Age was the only factor that influenced the amplitude of the late MMR. More negative late MMR was observed in older children with no difference found between bilingual and monolingual groups.

CONCLUSIONS

Consistent with previous studies, our findings revealed that biological factors (age and sex) and language experience modulated the amplitude of the eMMR in young children. The early negative MMR is likely to be the mismatch negativity found in older children and adults. In contrast, the late MMR amplitude was influenced only by age and may be equivalent to the Nc in infants and to the late negativity observed in some auditory passive oddball designs.

Perception of English phonetic contrasts by Dutch children: How bilingual are early-English learners?

The aim of this study was to investigate whether early-English education benefits the perception of English phonetic contrasts that are known to be perceptually confusable for Dutch native speakers, comparing Dutch pupils who were enrolled in an early-English programme at school from the age of four with pupils in a mainstream programme with English instruction from the age of 11, and English-Dutch early bilingual children. Children were 4-5-year-olds (start of primary school), 8-9-year-olds, or 11-12-year-olds (end of primary school). Children were tested on four contrasts that varied in difficulty: /b/-/s/ (easy), /k/-/ɡ/ (intermediate), /f/-/θ/ (difficult), /ɛ/-/æ/ (very difficult). Bilingual children outperformed the two other groups on all contrasts except /b/-/s/. Early-English pupils did not outperform mainstream pupils on any of the contrasts. This shows that early-English education as it is currently implemented is not beneficial for pupils' perception of non-native contrasts.

Sibling experience prevents neural tuning to adult faces in 10-month-old infants

Early facial experience provided by the infant's social environment is known to shape face processing abilities, which narrow during the first year of life towards adult human faces of the most frequently encountered ethnic groups. Here we explored the hypothesis that natural variability in facial input may delay neural commitment to face processing by testing the impact of early natural experience with siblings on infants' brain responses. Event-Related Potentials (ERPs) evoked by upright and inverted adult and child faces were compared in two groups of 10-month-old infants with (N = 21) and without (N = 22) a child sibling. In first-born infants, P1 ERP component showed specificity to upright adult faces that carried over to the subsequent N290 and P400 components. In infants with siblings no inversion effects were observed. Results are discussed in the context of evidence from the language domain, showing that neural commitment to phonetic contrasts emerges later in bilinguals than in monolinguals, and that this delay facilitates subsequent learning of previously unencountered sounds of new languages.

Statistical Learning and Bilingualism

Purpose

Over the last 2 decades, research on statistical learning has demonstrated its importance in supporting language development. Notably, most of the research to date has focused on monolingual populations (or has not reported the language background of participants). Several recent studies, however, have begun to focus on the impact of bilingualism on statistical learning. To date, the results have been quite mixed, with a handful of studies finding differences between monolinguals and bilinguals and several other studies reporting no differences. Thus, the purpose of this manuscript is to review the literature to date on how bilingualism impacts statistical learning abilities.

Method

We review the contemporary literature, organized by the age of participants and by task when relevant.

Conclusions

We note that there are many discrepant findings within this nascent field, although some trends have emerged. For instance, differences in performance may be attributed to factors such as age of acquisition. However, we note that the state of the field does not yet permit firm clinical recommendations.

Lexical Learning May Contribute to Phonetic Learning in Infants: A Corpus Analysis of Maternal Spanish

In their first year, infants begin to learn the speech sounds of their language. This process is typically modeled as an unsupervised clustering problem in which phonetically similar speech-sound tokens are grouped into phonetic categories by infants using their domain-general inference abilities. We argue here that maternal speech is too phonetically variable for this account to be plausible, and we provide phonetic evidence from Spanish showing that infant-directed Spanish vowels are more readily clustered over word types than over vowel tokens. The results suggest that infants' early adaptation to native-language phonetics depends on their word-form lexicon, implicating a much wider range of potential sources of influence on infants' developmental trajectories in language learning.

Developmental change in tone perception in Mandarin monolingual, English monolingual, and Mandarin-English bilingual infants: Divergences between monolingual and bilingual learners

Most languages use lexical tone to discriminate the meanings of words. There has been recent interest in tracking the development of tone categories during infancy. These studies have focused largely on monolingual infants learning either a tone language or a non-tone language. It remains to be seen how bilingual infants learning one tone language (e.g., Mandarin) and one non-tone language (e.g., English) discriminate tones. Here, we examined infants' discrimination of two Mandarin tones pairs: one salient and one subtle. Discrimination was investigated in three groups: Mandarin-English bilinguals, English monolinguals, and Mandarin monolinguals at 6 months and 9 months of age in a cross-sectional design. Results demonstrated relatively strong Mandarin tone discrimination in Mandarin monolinguals, with salient tone discrimination at 6 months and both salient and subtle tone discrimination at 9 months. English monolinguals discriminated neither contrast at 6 months but discriminated the salient contrast at 9 months. Surprisingly, there was no evidence for tone discrimination in Mandarin-English bilingual infants. In a second experiment, 12- and 13-month-old Mandarin-English bilingual and English monolingual infants were tested to determine whether bilinguals would demonstrate tone sensitivity at a later age. Results revealed a lack of tone sensitivity at 12 or 13 months in bilingual infants, yet English monolingual infants were sensitive to both salient and subtle Mandarin tone contrasts at 12 or 13 months. Our findings provide evidence for age-related convergence in Mandarin tone discrimination in English and Mandarin monolingual infants and for a distinct pattern of tone discrimination in bilingual infants. Theoretical implications for phonetic category acquisition are discussed.

No perceptual reorganization for Limburgian tones? A cross-linguistic investigation with 6- to 12-month-old infants

Despite the fact that many of the world's languages use lexical tone, the majority of language acquisition studies has focused on non-tone languages. Research on tone languages has typically investigated well-known tone languages such as Mandarin and Cantonese Chinese. The current study looked at a Limburgian dialect of Dutch that uses lexical pitch differences, albeit in a rather restricted way. Using a visual habituation paradigm, 6- to 12-month-old Limburgian and Dutch infants were tested for their ability to discriminate Limburgian tones. The results showed that both Limburgian and Dutch infants discriminate the Limburgian tones throughout their first year of life. The role of linguistic experience, acoustic salience, and the degree of similarity to the native prosodic system are discussed.

How Native Prosody Affects Pitch Processing during Word Learning in Limburgian and Dutch Toddlers and Adults

In this study, Limburgian and Dutch 2.5- to 4-year-olds and adults took part in a word learning experiment. Following the procedure employed by Quam and Swingley (2010) and Singh et al. (2014), participants learned two novel word-object mappings. After training, word recognition was tested in correct pronunciation (CP) trials and mispronunciation (MP) trials featuring a pitch change. Since Limburgian is considered a restricted tone language, we expected that the pitch change would hinder word recognition in Limburgian, but not in non-tonal Dutch listeners. Contrary to our expectations, both Limburgian and Dutch children appeared to be sensitive to pitch changes in newly learned words, indicated by a significant decrease in target fixation in MP trials compared to CP trials. Limburgian and Dutch adults showed very strong naming effects in both trial types. The results are discussed against the background of the influence of the native prosodic system.

Bilingual Infants Demonstrate Perceptual Flexibility in Phoneme Discrimination but Perceptual Constraint in Face Discrimination

Perceptual narrowing is a highly significant development associated with the first year of life. It conventionally refers to an orientation toward nativeness whereby infant's perceptual sensitivities begin to align with the phonetic properties of their native environment. Nativeness effects, such as perceptual narrowing, have been observed in several domains, most notably, in face discrimination within other-race faces and speech discrimination of non-native phonemes. Thus, far, nativeness effects in the face and speech perception have been theoretically linked, but have mostly been investigated independently. An important caveat to nativeness effects is that diversifying experiences, such as bilingualism or multiracial exposure, can lead to a reduction or postponement in attunement to the native environment. The present study was designed to investigate whether bilingualism influences nativeness effects in phonetic and face perception. Eleven-month-old monolingual and bilingual infants were tested on their abilities to discriminate native and non-native speech contrasts as well as own-race and other-race face contrasts. While monolingual infants demonstrated nativeness effects in face and speech perception, bilingual infants demonstrated nativeness effects in the face perception but demonstrated flexibility in speech perception. Results support domain-specific effects of bilingual experience on nativeness effects.

Assessing residents' operative skills for external ventricular drain placement and shunt surgery in pediatric neurosurgery

OBJECTIVE The authors previously demonstrated the use of a validated Objective Structured Assessment of Technical Skills (OSATS) tool for evaluating residents' operative skills in pediatric neurosurgery. However, no benchmarks have been established for specific pediatric procedures despite an increased need for meaningful assessments that can either allow for early intervention for underperforming trainees or allow for proficient residents to progress to conducting operations independently with more passive supervision. This validated methodology and tool for assessment of operative skills for common pediatric neurosurgical procedures-external ventricular drain (EVD) placement and shunt surgery- was applied to establish its procedure-based feasibility and reliability, and to document the effect of repetition on achieving surgical skill proficiency in pediatric EVD placement and shunt surgery. METHODS A procedure-based technical skills assessment for EVD placements and shunt surgeries in pediatric neurosurgery was established through the use of task analysis. The authors enrolled all residents from 3 training programs (Baylor College of Medicine, Houston Methodist Hospital, and University of Texas-Medical Branch) who rotated through pediatric neurosurgery at Texas Children's Hospital over a 26-month period. For each EVD placement or shunt procedure performed with a resident, the faculty and resident (for self-assessment) completed an evaluation form (OSATS) based on a 5-point Likert scale with 7 categories. Data forms were then grouped according to faculty versus resident (self) assessment, length of pediatric neurosurgery rotation, postgraduate year level, and date of evaluation ("beginning of rotation," within 1 month of start date; "end of rotation," within 1 month of completion date; or "middle of rotation"). Descriptive statistical analyses were performed with the commercially available SPSS statistical software package. A p value < 0.05 was considered statistically significant. RESULTS Five attending evaluators (including 2 fellows who acted as attending surgeons) completed 260 evaluations. Twenty house staff completed 269 evaluations for self-assessment. Evaluations were completed in 562 EVD and shunt procedures before the surgeons left the operating room. There were statistically significant differences (p < 0.05) between overall attending (mean 4.3) and junior resident (self; mean 3.6) assessments, and between overall attending (mean 4.8) and senior resident (self; mean 4.6) assessment scores on general performance and technical skills. The learning curves produced for the residents demonstrate a stereotypical U- or V-shaped curve for acquiring skills, with a significant improvement in overall scores at the end of the rotation compared with the beginning. The improvement for junior residents (Δ score = 0.5; p = 0.002) was larger than for senior residents (Δ score = 0.2; p = 0.018). CONCLUSIONS The OSATS is an effective assessment tool as part of a comprehensive evaluation of neurosurgery residents' performance for specific pediatric procedures. The authors observed a U-shaped learning curve, contradicting the idea that developing one's surgical technique and learning a procedure represents a monotonic, cumulative process of repetitions and improvement.

Enhanced music sensitivity in 9-month-old bilingual infants

This study explores the influence of bilingualism on the cognitive processing of language and music. Specifically, we investigate how infants learning a non-tone language perceive linguistic and musical pitch and how bilingualism affects cross-domain pitch perception. Dutch monolingual and bilingual infants of 8-9 months participated in the study. All infants had Dutch as one of the first languages. The other first languages, varying among bilingual families, were not tone or pitch accent languages. In two experiments, infants were tested on the discrimination of a lexical (N = 42) or a violin (N = 48) pitch contrast via a visual habituation paradigm. The two contrasts shared identical pitch contours but differed in timbre. Non-tone language learning infants did not discriminate the lexical contrast regardless of their ambient language environment. When perceiving the violin contrast, bilingual but not monolingual infants demonstrated robust discrimination. We attribute bilingual infants' heightened sensitivity in the musical domain to the enhanced acoustic sensitivity stemming from a bilingual environment. The distinct perceptual patterns between language and music and the influence of acoustic salience on perception suggest processing diversion and association in the first year of life. Results indicate that the perception of music may entail both shared neural network with language processing, and unique neural network that is distinct from other cognitive functions.

Early Prosodic Acquisition in Bilingual Infants: The Case of the Perceptual Trochaic Bias

Infants start learning the prosodic properties of their native language before 12 months, as shown by the emergence of a trochaic bias in English-learning infants between 6 and 9 months (Jusczyk et al., 1993), and in German-learning infants between 4 and 6 months (Höhle et al., 2009, 2014), while French-learning infants do not show a bias at 6 months (Höhle et al., 2009). This language-specific emergence of a trochaic bias is supported by the fact that English and German are languages with trochaic predominance in their lexicons, while French is a language with phrase-final lengthening but lacking lexical stress. We explored the emergence of a trochaic bias in bilingual French/German infants, to study whether the developmental trajectory would be similar to monolingual infants and whether amount of relative exposure to the two languages has an impact on the emergence of the bias. Accordingly, we replicated Höhle et al. (2009) with 24 bilingual 6-month-olds learning French and German simultaneously. All infants had been exposed to both languages for 30 to 70% of the time from birth. Using the Head Preference Procedure, infants were presented with two lists of stimuli, one made up of several occurrences of the pseudoword /GAba/ with word-initial stress (trochaic pattern), the second one made up of several occurrences of the pseudoword /gaBA/ with word-final stress (iambic pattern). The stimuli were recorded by a native German female speaker. Results revealed that these French/German bilingual 6-month-olds have a trochaic bias (as evidenced by a preference to listen to the trochaic pattern). Hence, their listening preference is comparable to that of monolingual German-learning 6-month-olds, but differs from that of monolingual French-learning 6-month-olds who did not show any preference (Höhle et al., 2009). Moreover, the size of the trochaic bias in the bilingual infants was not correlated with their amount of exposure to German. The present results thus establish that the development of a trochaic bias in simultaneous bilinguals is not delayed compared to monolingual German-learning infants (Höhle et al., 2009) and is rather independent of the amount of exposure to German relative to French.

The Language and Literacy Development of Young Dual Language Learners: A Critical Review

The number of children living in the United States who are learning two languages is increasing greatly. However, relatively little research has been conducted on the language and literacy development of dual language learners (DLLs), particularly during the early childhood years. To summarize the extant literature and guide future research, a critical analysis of the literature was conducted. A search of major databases for studies on young typically developing DLLs between 2000-2011 yielded 182 peer-reviewed articles. Findings about DLL children's developmental trajectories in the various areas of language and literacy are presented. Much of these findings should be considered preliminary, because there were few areas where multiple studies were conducted. Conclusions were reached when sufficient evidence existed in a particular area. First, the research shows that DLLs have two separate language systems early in life. Second, differences in some areas of language development, such as vocabulary, appear to exist among DLLs depending on when they were first exposed to their second language. Third, DLLs' language and literacy development may differ from that of monolinguals, although DLLs appear to catch up over time. Fourth, little is known about factors that influence DLLs' development, although the amount of language exposure to and usage of DLLs' two languages appears to play key roles. Methodological issues are addressed, and directions for future research are discussed.

Bilingualism modulates infants' selective attention to the mouth of a talking face

Infants growing up in bilingual environments succeed at learning two languages. What adaptive processes enable them to master the more complex nature of bilingual input? One possibility is that bilingual infants take greater advantage of the redundancy of the audiovisual speech that they usually experience during social interactions. Thus, we investigated whether bilingual infants' need to keep languages apart increases their attention to the mouth as a source of redundant and reliable speech cues. We measured selective attention to talking faces in 4-, 8-, and 12-month-old Catalan and Spanish monolingual and bilingual infants. Monolinguals looked more at the eyes than the mouth at 4 months and more at the mouth than the eyes at 8 months in response to both native and nonnative speech, but they looked more at the mouth than the eyes at 12 months only in response to nonnative speech. In contrast, bilinguals looked equally at the eyes and mouth at 4 months, more at the mouth than the eyes at 8 months, and more at the mouth than the eyes at 12 months, and these patterns of responses were found for both native and nonnative speech at all ages. Thus, to support their dual-language acquisition processes, bilingual infants exploit the greater perceptual salience of redundant audiovisual speech cues at an earlier age and for a longer time than monolingual infants.

Phonetic processing when learning words

Infants have remarkable abilities to learn several languages. However, phonological acquisition in bilingual infants appears to vary depending on the phonetic similarities or differences of their two native languages. Many studies suggest that learning contrasts with different realizations in the two languages (e.g., the /p/, /t/, /k/ stops have similar VOT values in French, Spanish, Italian and European Portuguese, but can be confounded with the /b/, /d/, /g/ in German and English) poses a particular challenge. The current study explores how similarity or difference in the realization of phonetic contrasts affects word-learning outcomes. Bilingual infants aged 16 months were tested on their capacity to learn pairs of new words, differing by a phonological feature (voicing versus place) on their initial consonant. Two groups of infants were considered: bilinguals exposed to languages (French and either Spanish, Italian or European Portuguese) in which the contrasts tested are realized relatively similarly (“similar contrast” group) and bilinguals exposed to languages (French and either English or German) in which the contrasts are realized very differently (“different contrast” group). In the present word-learning situation, the “similar contrast” bilinguals successfully processed the relevant phonetic detail of the word forms, while the “different contrast” bilinguals failed. The present pattern reveals the impact on word learning of phonological differences between the two languages, which is consistent with studies reporting slight time course differences among bilinguals in phonological acquisition. In line with a larger literature on bilingual acquisition, these results provide further evidence that linguistic similarity or difference in the two languages influences the pattern of bilingual acquisition.

The effect of age of acquisition, socioeducational status, and proficiency on the neural processing of second language speech sounds

This study investigates the role of age of acquisition (AoA), socioeducational status (SES), and second language (L2) proficiency on the neural processing of L2 speech sounds. In a task of pre-attentive listening and passive viewing, Spanish-English bilinguals and a control group of English monolinguals listened to English syllables while watching a film of natural scenery. Eight regions of interest were selected from brain areas involved in speech perception and executive processes. The regions of interest were examined in 2 separate two-way ANOVA (AoA×SES; AoA×L2 proficiency). The results showed that AoA was the main variable affecting the neural response in L2 speech processing. Direct comparisons between AoA groups of equivalent SES and proficiency level enhanced the intensity and magnitude of the results. These results suggest that AoA, more than SES and proficiency level, determines which brain regions are recruited for the processing of second language speech sounds.

Speech perception and production by sequential bilingual children: a longitudinal study of voice onset time acquisition

The majority of bilingual speech research has focused on simultaneous bilinguals. Yet, in immigrant communities, children are often initially exposed to their family language (L1), before becoming gradually immersed in the host country's language (L2). This is typically referred to as sequential bilingualism. Using a longitudinal design, this study explored the perception and production of the English voicing contrast in 55 children (40 Sylheti-English sequential bilinguals and 15 English monolinguals). Children were tested twice: when they were in nursery (52-month-olds) and 1 year later. Sequential bilinguals' perception and production of English plosives were initially driven by their experience with their L1, but after starting school, changed to match that of their monolingual peers.

First translation equivalents in bilingual toddlers’ expressive vocabulary

Translation equivalents (TEs) characterize the lexicon of bilinguals from the early stages of acquisition, as reported in studies involving English and other languages in which most cross-language synonyms are dissimilar in phonological form. This research explores the emergence of TEs in Spanish-Catalan bilinguals who are acquiring two languages with many cognate words and thus languages with many cross-language synonyms with identical or similar phonological forms. Expressive vocabulary was obtained in two 18-month-old groups (monolingual and bilingual, N = 24 each) through parental report using a bilingual questionnaire. Four different vocabulary size measures were computed in bilinguals, correcting for different types of phonological overlap in words across their two languages. Bilinguals were found comparable to monolinguals in every measure except for Total Vocabulary Size (Spanish + Catalan words) in which they outscored monolinguals due to the high number of form-identical cross-language elements in their expressive vocabularies. Form-similar and dissimilar TEs accounted for less than 2% of the words produced and were only present in infants with larger vocabularies. Results support the hypothesis that phonological form proximity between words across bilinguals' two languages facilitates early lexical acquisition.

A role for the developing lexicon in phonetic category acquisition

Infants segment words from fluent speech during the same period when they are learning phonetic categories, yet accounts of phonetic category acquisition typically ignore information about the words in which sounds appear. We use a Bayesian model to illustrate how feedback from segmented words might constrain phonetic category learning by providing information about which sounds occur together in words. Simulations demonstrate that word-level information can successfully disambiguate overlapping English vowel categories. Learning patterns in the model are shown to parallel human behavior from artificial language learning tasks. These findings point to a central role for the developing lexicon in phonetic category acquisition and provide a framework for incorporating top-down constraints into models of category learning.

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.

U-shaped development: an old but unsolved problem

Even today the investigation of U-shaped functions in human development is of considerable importance for different domains of Developmental Psychology. More and more scientific researchers focus their efforts on the challenge to describe and explain the phenomenon by identifying those skills and abilities being affected. The impact of U-shaped functions on diagnostic decision-making and on therapeutic treatment programs highlights the importance of understanding the nature of non-monotonic development. The present article therefore addresses the relevant questions of how U-shaped functions are defined in theory, in which developmental domains such non-monotonic growth curves are suggested to occur, and which implications there are for future methodology and diagnostic practice. Finally, it is recommended to clearly identify those interactions between proximal and distal subcomponents which are expected to contribute to a U-shaped development.

Rapid gains in segmenting fluent speech when words match the rhythmic unit: evidence from infants acquiring syllable-timed languages

The ability to extract word-forms from sentential contexts represents an initial step in infants' process toward lexical acquisition. By age 6 months the ability is just emerging and evidence of it is restricted to certain testing conditions. Most research has been developed with infants acquiring stress-timed languages (English, but also German and Dutch) whose rhythmic unit is not the syllable. Data from infants acquiring syllable-timed languages are still scarce and limited to French (European and Canadian), partially revealing some discrepancies with English regarding the age at which word segmentation ability emerges. Research reported here aims at broadening this cross-linguistic perspective by presenting first data on the early ability to segment monosyllabic word-forms by infants acquiring Spanish and Catalan. Three different language groups (two monolingual and one bilingual) and two different age groups (8- and 6-month-old infants) were tested using natural language and a modified version of the HPP with familiarization to passages and testing on words. Results revealed positive evidence of word segmentation in all groups at both ages, but critically, the pattern of preference differed by age. A novelty preference was obtained in the older groups, while the expected familiarity preference was only found at the younger age tested, suggesting more advanced segmentation ability with an increase in age. These results offer first evidence of an early ability for monosyllabic word segmentation in infants acquiring syllable-timed languages such as Spanish or Catalan, not previously described in the literature. Data show no impact of bilingual exposure in the emergence of this ability and results suggest rapid gains in early segmentation for words that match the rhythm unit of the native language.

Perceptual foundations of bilingual acquisition in infancy

Infants are prepared by biology to acquire language, but it is the native language(s) they must learn. Over the first weeks and months of life, infants learn about the sounds and sights of their native language, and use that perceptual knowledge to pull out words and bootstrap grammar. In this paper, I review research showing that infants growing up bilingual learn the properties of each of the their two languages simultaneously, while nonetheless keeping them apart. Thus, they use perceptual learning to break into the properties of each of the two native languages. While the fundamental process of language acquisition is the same whether one or two languages are being acquired, cognitive advantages accrue from the task of language separation, and processing costs accrue from the more minimal input received in each of the two languages. I conclude by suggesting that when there are sufficient cues to which language is being used, the cognitive advantages that accrue from language separation enable the bilingual infant to move forward in language acquisition even in the face of processing costs.

Influences of lexical tone and pitch on word recognition in bilingual infants

Infants' abilities to discriminate native and non-native phonemes have been extensively investigated in monolingual learners, demonstrating a transition from language-general to language-specific sensitivities over the first year after birth. However, these studies have mostly been limited to the study of vowels and consonants in monolingual learners. There is relatively little research on other types of phonetic segments, such as lexical tone, even though tone languages are very well represented across languages of the world. The goal of the present study is to investigate how Mandarin Chinese-English bilingual learners contend with non-phonemic pitch variation in English spoken word recognition. This is contrasted with their treatment of phonemic changes in lexical tone in Mandarin spoken word recognition. The experimental design was cross-sectional and three age-groups were sampled (7.5months, 9months and 11months). Results demonstrated limited generalization abilities at 7.5months, where infants only recognized words in English when matched in pitch and words in Mandarin that were matched in tone. At 9months, infants recognized words in Mandarin Chinese that matched in tone, but also falsely recognized words that contrasted in tone. At this age, infants also recognized English words whether they were matched or mismatched in pitch. By 11months, infants correctly recognized pitch-matched and - mismatched words in English but only recognized tonal matches in Mandarin Chinese.

The acquisition of phonetic categories in bilingual infants: new data from an anticipatory eye movement paradigm

Contrasting results have been reported regarding the phonetic acquisition of bilinguals. A lack of discrimination has been observed for certain native contrasts in 8-month-old Catalan-Spanish bilingual infants (Bosch & Sebastián-Gallés, 2003a), though not in French-English bilingual infants (Burns, Yoshida, Hill & Werker, 2007; Sundara, Polka & Molnar, 2008). At present, the data for Catalan-Spanish bilinguals constitute an exception in the early language acquisition literature. This study contributes new findings that show that Catalan-Spanish bilingual infants do not lose the capacity to discriminate native contrasts. We used an adaptation of the anticipatory eye movement paradigm (AEM; McMurray & Aslin, 2004) to explore this question. In two experiments we tested the ability of infants from Catalan and Spanish monolingual families and from Catalan-Spanish bilingual families to discriminate a Spanish-Catalan common and a Catalan-specific vowel contrast. Results from both experiments revealed that Catalan-Spanish bilingual infants showed the same discrimination abilities as those shown by their monolingual peers, even in a phonetic contrast that had not been discriminated in previous studies. Our results demonstrate that discrimination can be observed in 8-month-old bilingual infants when tested with a measure not based on recovery of attention. The high ratio of cognates in Spanish and Catalan may underlie the reason why bilinguals failed to discriminate the native vowels when tested with the familiarization-preference procedure but succeeded with the AEM paradigm.

Impact of second-language experience in infancy: brain measures of first- and second-language speech perception

Language experience 'narrows' speech perception by the end of infants' first year, reducing discrimination of non-native phoneme contrasts while improving native-contrast discrimination. Previous research showed that declines in non-native discrimination were reversed by second-language experience provided at 9-10 months, but it is not known whether second-language experience affects first-language speech sound processing. Using event-related potentials (ERPs), we examined learning-related changes in brain activity to Spanish and English phoneme contrasts in monolingual English-learning infants pre- and post-exposure to Spanish from 9.5-10.5 months of age. Infants showed a significant discriminatory ERP response to the Spanish contrast at 11 months (post-exposure), but not at 9 months (pre-exposure). The English contrast elicited an earlier discriminatory response at 11 months than at 9 months, suggesting improvement in native-language processing. The results show that infants rapidly encode new phonetic information, and that improvement in native speech processing can occur during second-language learning in infancy.

The "Perceptual Wedge Hypothesis" as the basis for bilingual babies' phonetic processing advantage: new insights from fNIRS brain imaging

In a neuroimaging study focusing on young bilinguals, we explored the brains of bilingual and monolingual babies across two age groups (younger 4-6 months, older 10-12 months), using fNIRS in a new event-related design, as babies processed linguistic phonetic (Native English, Non-Native Hindi) and non-linguistic Tone stimuli. We found that phonetic processing in bilingual and monolingual babies is accomplished with the same language-specific brain areas classically observed in adults, including the left superior temporal gyrus (associated with phonetic processing) and the left inferior frontal cortex (associated with the search and retrieval of information about meanings, and syntactic and phonological patterning), with intriguing developmental timing differences: left superior temporal gyrus activation was observed early and remained stably active over time, while left inferior frontal cortex showed greater increase in neural activation in older babies notably at the precise age when babies' enter the universal first-word milestone, thus revealing a first-time focal brain correlate that may mediate a universal behavioral milestone in early human language acquisition. A difference was observed in the older bilingual babies' resilient neural and behavioral sensitivity to Non-Native phonetic contrasts at a time when monolingual babies can no longer make such discriminations. We advance the "Perceptual Wedge Hypothesis" as one possible explanation for how exposure to greater than one language may alter neural and language processing in ways that we suggest are advantageous to language users. The brains of bilinguals and multilinguals may provide the most powerful window into the full neural "extent and variability" that our human species' language processing brain areas could potentially achieve.

The interplay between input and initial biases: asymmetries in vowel perception during the first year of life

Vowels with extreme articulatory-acoustic properties act as natural referents. Infant perceptual asymmetries point to an underlying bias favoring these referent vowels. However, as language experience is gathered, distributional frequency of speech sounds could modify this initial bias. The perception of the /i/-/e/ contrast was explored in 144 Catalan- and Spanish-learning infants (2 languages with a different distribution of vowel frequency of occurrence) at 4, 6, and 12 months. The results confirmed an acoustic bias at 4 and 6 months in all infants. However, at 12 months, discrimination was not affected by the acoustic bias but by the frequency of occurrence of the vowel.

Effect of bilingualism on lexical stress pattern discrimination in French-learning infants

Monolingual infants start learning the prosodic properties of their native language around 6 to 9 months of age, a fact marked by the development of preferences for predominant prosodic patterns and a decrease in sensitivity to non-native prosodic properties. The present study evaluates the effects of bilingual acquisition on speech perception by exploring how stress pattern perception may differ in French-learning 10-month-olds raised in bilingual as opposed to monolingual environments. Experiment 1 shows that monolinguals can discriminate stress patterns following a long familiarization to one of two patterns, but not after a short familiarization. In Experiment 2, two subgroups of bilingual infants growing up learning both French and another language (varying across infants) in which stress is used lexically were tested under the more difficult short familiarization condition: one with balanced input, and one receiving more input in the language other than French. Discrimination was clearly found for the other-language-dominant subgroup, establishing heightened sensitivity to stress pattern contrasts in these bilinguals as compared to monolinguals. However, the balanced bilinguals' performance was not better than that of monolinguals, establishing an effect of the relative balance of the language input. This pattern of results is compatible with the proposal that sensitivity to prosodic contrasts is maintained or enhanced in a bilingual population compared to a monolingual population in which these contrasts are non-native, provided that this dimension is used in one of the two languages in acquisition, and that infants receive enough input from that language.

Effects of early bilingualism on learning phonological regularities in a new language

Drawing on structural sensitivity theory, the current study investigated monolingual and bilingual children's ability to learn how phonemes combine to form acceptable syllables in a new language. A total of 186 monolingual and bilingual kindergarteners, first graders, and second graders in Taiwan participated in the study. Bilingual children, regardless of whether they actively used a second language at home or simply had exposure to it, showed an advantage over their monolingual peers in learning the phonological patterns in the new language. The study provides empirical support for structural sensitivity theory and calls for the need to reconceptualize the effects of early bilingualism.