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

Developing automaticity in neural speech discrimination in typically developing bilingual Italian-German and monolingual German children

Many studies have shown that input in more than one language influences children's phonemic development. In this study, we examined the neural processes supporting perception of Voice Onset Time (VOT) in bilingual Italian-German children and their monolingual German peers. While German contrasts short-lag and long-lag, Italian contrasts short-lag and voicing lead. We examined whether bilinguals' phonetic/phonological systems for the two languages develop independently or whether they influence each other, and what role language input plays in the formation of phonetic/phonological categories. Forty five-year-old children (16 monolingual German, 24 bilingual Italian-German) were tested in an oddball design expected to elicit a neural Mismatch Response (MMR). The stimuli were bilabial stop VOT contrasts with the short-lag stop, common to both languages, as the standard. Four deviant VOTs were selected: 92 ms and 36 ms lag for German; 112 ms and 36 ms voicing lead for Italian. Bilingual children's language background was assessed using a caregiver questionnaire. Italian-German bilingual 5-year-old children and German monolingual controls showed similar MMRs to German long-lag and Italian voicing lead VOT, except for the 36 ms long-lag deviant; this acoustically difficult distinction did not elicit a robust negative MMR in the bilingual children. The lack of a difference between the bilinguals and monolinguals for voicing lead suggests that the amount of input in Italian for the bilinguals was not sufficient to lead to an advantage compared to the monolingual German children. Alternatively, the finding could indicate that voicing lead is easier to discriminate than voicing lag.

English Vowel Perception in Spanish-English Bilingual Preschoolers: Multiple-Talker Input Is Only Beneficial for Children With High Language Exposure Levels

PURPOSES

This study examines English vowel perception in Spanish-English bilingual preschoolers, comparing bilinguals' perception patterns to those of monolinguals and examining how child internal (age) and external variables (input quantity and input diversity) predict perceptual performance.

METHOD

Sixty children between 3;6 and 5;6 (years;months) of age participated in the study, 28 of whom were Spanish-English bilinguals and 32 English monolinguals. Perception was assessed through a forced-choice minimal-pair identification task in which children heard synthesized audio stimuli (i.e., "sheep" and "ship") that varied systematically along the /i-ɪ/ continuum and were asked to match them with one of two pictures. The data were analyzed with Bayesian mixed-effects logistic regression analyses, modeling responses as a function of continuum step, language background (monolingual or bilingual), age, English exposure (i.e., input quantity), and number of English input providers (i.e., input diversity).

RESULTS

The results indicate that, despite displaying nonnative English stop voicing perception in a previous study, the same bilingual children showed English /i-ɪ/ perception patterns that did not differ from those of monolinguals. While age did not predict vowel perception, input quantity and diversity jointly interacted to moderate how well children perceived the /i-ɪ/ contrast. Specifically, diverse input promoted perceptual performance in children who received high levels of English exposure-and who presumably had more advanced English language skills, whereas it limited perceptual performance in children with more limited English exposure and skills.

CONCLUSIONS

This study shows that bilingual children can show monolingual-like perception patterns for some sounds while displaying nontarget perception for others. This is the first study to demonstrate that language exposure mediates the role of input diversity on speech sound development, suggesting that varied input can be more or less beneficial for speech sound development based on the learner's language learning stage.

Neural correlates of lexical-tone and vowel-quality processing in 6- and 9-month-old German-learning infants and adults

We examined the neurophysiological underpinnings of lexical-tone and vowel-quality perception in learners of a non-tonal language. We tested 25 6- and 25 9-month-old German-learning infants, as well as 24 German adults and expected developmental differences for the two linguistic properties, as they are both carried by vowels, but have a different status in German. In adults, both lexical-tone and vowel-quality contrasts elicited mismatch negativities, with a stronger response to the vowel-quality contrast. Six-month-olds showed positive mismatch responses for lexical-tone and vowel-quality contrasts, with an emerging negative mismatch response for vowel-quality only. The negative mismatch responses became more pronounced for the vowel-quality contrast at 9 months, while the lexical-tone contrast elicited mainly positive mismatch responses. Our data reveal differential developmental changes in the processing of vowel properties that differ in their lexical relevance in the ambient language.

Twenty-month-olds categorically discriminate similar sounding vowels regardless of vocabulary level, an event related potentials (ERP) study

The current study investigated whether vocabulary relates to phonetic categorization at neural level in early childhood. Electoencephalogram (EEG) responses were collected from 53 Dutch 20-month-old children in a passive oddball paradigm, in which they were presented with two nonwords "giep" [ɣip] and "gip" [ɣɪp] that were contrasted solely by the vowel. In the multiple-speaker condition, both nonwords were produced by twelve different speakers; while, in the single-speaker condition, one single token of each word was used as stimuli. Infant positive mismatch responses (p-MMR) were elicited in both conditions without significant amplitude differences. When the infants were median split based on vocabulary level, the large and small vocabulary groups showed comparable p-MMR amplitudes yet different scalp distribution in both conditions. These results suggest successful phonetic categorization of native similar sounding vowels at 20 months, and a close relationship between speech categorization and vocabulary development.

Maturation of the mismatch response in pre-school children: Systematic literature review and meta-analysis

Event-related potentials (ERPs), specifically the Mismatch Response (MMR), holds promise for investigating auditory maturation in children. It has the potential to predict language development and distinguish between language-impaired and typically developing groups. However, summarizing the MMR's developmental trajectory in typically developing children remains challenging despite numerous studies. This pioneering meta-analysis outlines changes in MMR amplitude among typically developing children, while offering methodological best-practices. Our search identified 51 articles for methodology analysis and 21 for meta-analysis, involving 0-8-year-old participants from 2000 to 2022. Risk of Bias assessment and methodology analysis revealed shortcomings in control condition usage and reporting of study confounders. The meta-analysis results were inconsistent, indicating large effect sizes in some conditions and no effect sizes in others. Subgroup analysis revealed the main effects of age and brain region, as well as an interaction of age and time-window of the MMR. Future research requires a specific protocol, larger samples, and replication studies to deepen the understanding of the auditory discrimination maturation process in children.

The effect of simultaneous exposure on the attention selection and integration of segments and lexical tones by Urdu-Cantonese bilingual speakers

In the perceptual learning of lexical tones, an automatic and robust attention-to-phonology system enables native tonal listeners to adapt to acoustically non-optimal speech, such as phonetic conflicts in daily communications. Previous tone research reveals that non-native listeners who do not linguistically employ lexical tones in their mother tongue may find it challenging to attend to the tonal dimension or integrate it with the segmental features. However, it is unknown whether the attentional interference initially caused by a maternal attentional system would continue influencing the non-optimal tone perception for simultaneous bilingual teenagers. From an endpoint in the age of language acquisition, we investigate whether the tone-specific attention mechanism developed by the Urdu-Cantonese simultaneous bilinguals is automatic enough to assist them in adapting to a phonetically-conflicting environment. Three groups of teenagers engaged in a four-condition ABX task: Urdu-Cantonese simultaneous bilinguals, Cantonese native listeners, and Urdu-speaking, late learners of Cantonese. The results showed that although the simultaneous bilinguals could phonologically process Cantonese tones in a Cantonese-like way under a conflict-free listening condition, they still failed in adapting to the phonetic conflicts, especially the segment-induced ones. It thus demonstrated that the simultaneous exposure and years of regular education in Hong Kong local schools still could not automatically guarantee simultaneous bilingual processing of Cantonese tones. In interpreting the findings, it hypothesized that, except for simultaneous exposure, the development of a tone-specific attention mechanism is also likely to be L1-inhibitory, tone experience-driven, and language-specific for simultaneous bilinguals.

Cross-Language Transfer and Attentional Control in Early Bilingual Speech

PURPOSE

This study investigated the roles of cross-language transfer of first language (L1) and attentional control in second-language (L2) speech perception and production of sequential bilinguals, taking phonological overlap into account.

METHOD

Twenty-five monolingual Dutch-speaking and 25 sequential bilingual Turkish-Dutch-speaking 3- and 4-year-olds were tested using picture identification tasks for speech perception in L1 Turkish and L2 Dutch, single-word tasks for speech production in L1 and L2, and a visual search task for attentional control. Phonological overlap was manipulated by dividing the speech tasks into subsets of phonemes that were either shared or unshared between languages.

RESULTS

In Dutch speech perception and production, monolingual children obtained higher accuracies than bilingual peers. Bilinguals showed equal performance in L1 and L2 perception but scored higher on L1 than on L2 production. For speech perception of shared phonemes, linear regression analyses revealed no direct effects of attention and L1 on L2. For speech production of shared phonemes, attention and L1 directly affected L2. When exploring unshared phonemes, direct effects of attentional control on L2 were demonstrated not only for speech production but also for speech perception.

CONCLUSIONS

The roles of attentional control and cross-language transfer on L2 speech are different for shared and unshared phonemes. Whereas L2 speech production of shared phonemes is also supported by cross-language transfer of L1, L2 speech perception and production of unshared phonemes benefit from attentional control only. This underscores the clinical importance of considering phonological overlap and supporting attentional control when assisting young sequential bilinguals' L2 development.

Language Learning Under Varied Conditions: Neural Indices of Speech Perception in Bilingual Turkish-German Children and in Monolingual Children With Developmental Language Disorder (DLD)

Lateral temporal measures of the auditory evoked potential (AEP) including the T-complex (positive Ta and negative Tb), as well as an earlier negative peak (Na) index maturation of auditory/speech processing. Previous studies have shown that these measures distinguish neural processing in children with typical language development (TD) from those with disorders and monolingual from bilingual children. In this study, bilingual children with Turkish as L1 and German as L2 were compared with monolingual German-speaking children with developmental language disorder (DLD) and monolingual German-speaking children with TD in order to disentangle effects of limited language input vs. reduced perceptual abilities in the processing of speech and non-speech stimuli. Sensory processing reflected by the T-complex (or from lateral temporal electrode sites) was compared in response to a German vowel and a sine-wave tone in the three groups of children, ages 5 through 6 years. Stimuli were presented while children watched a muted video. Auditory evoked potentials (AEPs) were time-locked to the vowels and tones. AEPs to the frequent (standard) stimuli within an oddball paradigm were analyzed at the left (T7) and right (T8) temporal electrode sites.The results revealed language status (monolingual, bilingual, and DLD), stimulus (vowel and tone), and language test measures (receptive and expressive) all influenced the T-complex amplitudes. Particularly, the peak amplitude of Ta was modulated by language status and stimulus type. Bilingual children had significantly more negative Ta responses than the monolingual children with TD for both vowels and tones while DLD children differed from TD children only for the vowel stimulus. The amplitude of the T-complex was overall more negative at the left than at the right site. The Na peak latency was longer for the bilingual group than that observed for the two monolingual groups. The Tb latency was shorter for DLD and bilingual groups than that for TD children in the vowel condition, but no such latency difference between DLD and bilingual children was found. We suggest that the attenuated T-complex for bilingual children indicates continued plasticity of the auditory cortex to allow for learning of novel, second-language speech sounds.

P-MMR and LDN beside MMN as Speech-evoked Neural Markers in Children with Cochlear Implants: A Review

This review mainly explores less-reported neural markers to speech-evoked contrasts in children with cochlear implants (CI). Databases and electronic journals were searched with keywords of "mismatch responses" AND "positive mismatch response" (p-MMR) AND "late discriminate negativity" (LDN). P-MMR likely is as a measurement of brain immaturity in CI children while the developmental trajectories of LDN remain unexplained in older CI children. In CI children, there is a p-MMR-MMN-LDN sequence to speech stimuli developmentally. Whereas these aforementioned neural responses anticipate developmental changes in CI groups, it is still uncertain about the cutoff age for disappearance of p-MMR and LDN.

Deficits in Processing of Lexical Tones in Mandarin-Speaking Children With Developmental Language Disorder: Electrophysiological Evidence

Purpose This study explored the neural marker indexing deficits in discriminating lexical tone changes in Mandarin-speaking children with developmental language disorders (DLDs) using mismatch negativity, an event-related potential component for auditory change detection. Mandarin has four lexical tones characterized by a high-level tone (T1), high-rising tone (T2), low-dipping tone (T3), and high-falling tone (T4), in which the T2/T3 contrast is acoustically less discriminable in developmental groups. Therefore, this study further examined how deficits in children with DLD would vary with tonal contrasts' acoustic saliency. Method Event-related potentials were measured using the multideviant oddball paradigm described by Lee et al. (2012), who used Mandarin syllables [i] in T3 as the standard sound (80%), T1 as the large deviant (10%), and T2 as the small deviant (10%). Twelve children with DLD aged between 4 and 6 years participated in this study, and 12 age-matched children with typical development were selected from the data set of Lee et al. (2012) as the controls. Results The T1/T3 change elicited adultlike mismatch negativity in both the DLD and control groups, while no group difference was revealed. The T2/T3 change elicited a robust positive mismatch response (P-MMR) in children with DLD, while the P-MMR was less significant in the control group. The group comparisons revealed a larger P-MMR in children with DLD than in the control group. Furthermore, children with lower scores in language assessments tend to reveal larger P-MMRs. Conclusions This study demonstrated that deficits in children with DLD in discriminating subtle lexical tone changes reflect greater positivity of P-MMR to T2/T3 change. This implies that MMR to T2/T3 may serve as a neural marker for evaluating language delay in preschoolers.

Neural Representation of the English Vowel Feature [High]: Evidence From /ε/ vs. /ɪ/

Many studies have observed modulation of the amplitude of the neural index mismatch negativity (MMN) related to which member of a phoneme contrast [phoneme A, phoneme B] serves as the frequent (standard) and which serves as the infrequent (deviant) stimulus (i.e., AAAB vs. BBBA) in an oddball paradigm. Explanations for this amplitude modulation range from acoustic to linguistic factors. We tested whether exchanging the role of the mid vowel /ε/ vs. high vowel /ɪ/ of English modulated MMN amplitude and whether the pattern of modulation was compatible with an underspecification account, in which the underspecified height values are [−high] and [−low]. MMN was larger for /ε/ as the deviant, but only when compared across conditions to itself as the standard. For the within-condition comparison, MMN was larger to /ɪ/ deviant minus /ε/ standard than to the reverse. A condition order effect was also observed. MMN amplitude was smaller to the deviant stimulus if it had previously served as the standard. In addition, the amplitudes of late discriminative negativity (LDN) showed similar asymmetry. LDN was larger for deviant /ε/ than deviant /ɪ/ when compared to themselves as the standard. These findings were compatible with an underspecification account, but also with other accounts, such as the Natural Referent Vowel model and a prototype model; we also suggest that non-linguistic factors need to be carefully considered as additional sources of speech processing asymmetries.

Imitation recognition and its prosocial effects in 6-month old infants

The experience of being imitated is theorised to be a driving force of infant social cognition, yet evidence on the emergence of imitation recognition and the effects of imitation in early infancy is disproportionately scarce. To address this lack of empirical evidence, in a within-subjects study we compared the responses of 6-month old infants when exposed to ipsilateral imitation as opposed to non-imitative contingent responding. To examine mediating mechanisms of imitation recognition, infants were also exposed to contralateral imitation and bodily imitation with suppressed emotional mimicry. We found that testing behaviours-the hallmark of high-level imitation recognition-occurred at significantly higher rates in each of the imitation conditions compared to the contingent responding condition. Moreover, when being imitated, infants showed higher levels of attention, smiling and approach behaviours compared to the contingent responding condition. The suppression of emotional mimicry moderated these results, leading to a decrease in all social responsiveness measures. The results show that imitation engenders prosocial effects in 6-month old infants and that infants at this age reliably show evidence of implicit and high-level imitation recognition. In turn, the latter can be indicative of infants' sensitivity to others' intentions directed toward them.