Consonant and Vowel Processing in Word Form Segmentation: An Infant ERP Study

Does the speaker's eye gaze facilitate infants' word segmentation from continuous speech? An ERP study

The environment in which infants learn language is multimodal and rich with social cues. Yet, the effects of such cues, such as eye contact, on early speech perception have not been closely examined. This study assessed the role of ostensive speech, signalled through the speaker's eye gaze direction, on infants' word segmentation abilities. A familiarisation-then-test paradigm was used while electroencephalography (EEG) was recorded. Ten-month-old Dutch-learning infants were familiarised with audio-visual stories in which a speaker recited four sentences with one repeated target word. The speaker addressed them either with direct or with averted gaze while speaking. In the test phase following each story, infants heard familiar and novel words presented via audio-only. Infants' familiarity with the words was assessed using event-related potentials (ERPs). As predicted, infants showed a negative-going ERP familiarity effect to the isolated familiarised words relative to the novel words over the left-frontal region of interest during the test phase. While the word familiarity effect did not differ as a function of the speaker's gaze over the left-frontal region of interest, there was also a (not predicted) positive-going early ERP familiarity effect over right fronto-central and central electrodes in the direct gaze condition only. This study provides electrophysiological evidence that infants can segment words from audio-visual speech, regardless of the ostensiveness of the speaker's communication. However, the speaker's gaze direction seems to influence the processing of familiar words. RESEARCH HIGHLIGHTS: We examined 10-month-old infants' ERP word familiarity response using audio-visual stories, in which a speaker addressed infants with direct or averted gaze while speaking. Ten-month-old infants can segment and recognise familiar words from audio-visual speech, indicated by their negative-going ERP response to familiar, relative to novel, words. This negative-going ERP word familiarity effect was present for isolated words over left-frontal electrodes regardless of whether the speaker offered eye contact while speaking. An additional positivity in response to familiar words was observed for direct gaze only, over right fronto-central and central electrodes.

Probing the Impact of Prematurity on Segmentation Abilities in the Context of Bilingualism

Infants born prematurely are at a high risk of developing linguistic deficits. In the current study, we compare how full-term and healthy preterm infants without neuro-sensorial impairments segment words from fluent speech, an ability crucial for lexical acquisition. While early word segmentation abilities have been found in monolingual infants, we test here whether it is also the case for French-dominant bilingual infants with varying non-dominant languages. These bilingual infants were tested on their ability to segment monosyllabic French words from French sentences at 6 months of (postnatal) age, an age at which both full-term and preterm monolinguals are able to segment these words. Our results establish the existence of segmentation skills in these infants, with no significant difference in performance between the two maturation groups. Correlation analyses failed to find effects of gestational age in the preterm group, as well as effects of the language dominance within the bilingual groups. These findings indicate that monosyllabic word segmentation, which has been found to emerge by 4 months in monolingual French-learning infants, is a robust ability acquired at an early age even in the context of bilingualism and prematurity. Future studies should further probe segmentation abilities in more extreme conditions, such as in bilinguals tested in their non-dominant language, in preterm infants with medical issues, or testing the segmentation of more complex word structures.

Cross-Cultural Sex/Gender Differences in Produced Word Content Before the Age of 3 Years

Does sex/gender matter for language acquisition? Small advantages in vocabulary size for females are well documented. In this study, however, we found that children's early vocabulary composition was a significantly better predictor of sex/gender than their vocabulary size. We conducted classification analysis on word-production data from children (12-36 months old, n = 39,553) acquiring 26 different languages. Children's sex/gender was classified at above-chance levels in 22 of 26 languages. Classification accuracy was significantly higher than for models based on vocabulary size and increased as a function of sample size. Boys produced more words for vehicles and outdoor scenes, whereas girls produced more words for clothing and body parts. Classification accuracy also increased as a function of age and peaked at 30 months, reaching accuracy levels observed in studies of adult word use. These differences in vocabulary are indicative of differences in the lifeworld of children and may themselves cause further differences in development.

Maturation of consonant perception, but not vowel perception, predicts lexical skills at 12 months

Consonants and vowels differentially contribute to lexical acquisition. From 8 months on, infants' preferential reliance on consonants has been shown to predict their lexical outcome. Here, the predictive value of German-learning infants' (n = 58, 29 girls, 29 boys) trajectories of consonant and vowel perception, indicated by the electrophysiological mismatch response, across 2, 6, and 10 months for later lexical acquisition was studied. The consonant-perception trajectory from 2 to 6 months (β = -2.95) and 6 to 10 months (β = -.91), but not the vowel-perception trajectory, significantly predicted receptive vocabulary at 12 months. These results reveal an earlier predictive value of consonant perception for word learning than previously found, and a particular role of the longitudinal maturation of this skill in lexical acquisition.

Early recognition of familiar word-forms as a function of production skills

Growing evidence shows that early speech processing relies on information extracted from speech production. In particular, production skills are linked to word-form processing, as more advanced producers prefer listening to pseudowords containing consonants they do not yet produce. However, it is unclear whether production affects word-form encoding (the translation of perceived phonological information into a memory trace) and/or recognition (the automatic retrieval of a stored item). Distinguishing recognition from encoding makes it possible to explore whether sensorimotor information is stored in long-term phonological representations (and thus, retrieved during recognition) or is processed when encoding a new item, but not necessarily when retrieving a stored item. In this study, we asked whether speech-related sensorimotor information is retained in long-term representations of word-forms. To this aim, we tested the effect of production on the recognition of ecologically learned, real familiar word-forms. Testing these items allowed to assess the effect of sensorimotor information in a context in which encoding did not happen during testing itself. Two groups of French-learning monolinguals (11- and 14-month-olds) participated in the study. Using the Headturn Preference Procedure, each group heard two lists, each containing 10 familiar word-forms composed of either early-learned consonants (commonly produced by French-learners at these ages) or late-learned consonants (more rarely produced at these ages). We hypothesized differences in listening preferences as a function of word-list and/or production skills. At both 11 and 14 months, babbling skills modulated orientation times to the word-lists containing late-learned consonants. This specific effect establishes that speech production impacts familiar word-form recognition by 11 months, suggesting that sensorimotor information is retained in long-term word-form representations and accessed during word-form processing.

Babies detect when the timing is right: Evidence from event-related potentials to a contingent mother-infant conversation

Social interactions are vital for healthy brain development. Burgeoning behavioural evidence indicates that a caregiver who provides contingently timed vocal responses to infant vocalisations provides key support for early language development. Understanding how contingently timed vocal responses relate to neurodevelopment in early infancy is lacking. This study compares event-related potentials (ERPs) to contingent and non-contingently timed vocalisations in 6- and 9-month-old infants (n = 36), and adults (n = 24). ERPs were recorded from each age group while listening to a naturalistic 21-minute recording of a mother playing and conversing with her baby. At 6-months, infants showed a significant positive ERP response to contingent vocalisations by the mother and infant. At 9-months infants showed negative ERP response to the mother's contingent speech. Adults showed no differences in ERPs between contingent and non-contingent speech regardless of the talker. We interpret the increased positivity in response to contingent speech as suggesting that infants show an attentional response at 6-months, and the increased negativity at 9-months relates to lexical-semantic processing. Further work is necessary to confirm the development of distinct ERPs shown in response to natural speech.

Infants' discrimination of consonant contrasts in the presence and absence of talker variability

To learn speech-sound categories, infants must identify the acoustic dimensions that differentiate categories and selectively attend to them as opposed to irrelevant dimensions. Variability on irrelevant acoustic dimensions can aid formation of robust categories in infants through adults in tasks such as word learning (e.g., Rost and McMurray, 2009) or speech-sound learning (e.g., Lively et al., 1993). At the same time, variability sometimes overwhelms learners, interfering with learning and processing. Two prior studies (Kuhl & Miller, 1982; Jusczyk, Pisoni, & Mullennix, 1992) found that irrelevant variability sometimes impaired early sound discrimination. We asked whether variability would impair or facilitate discrimination for older infants, comparing 7.5-month-old infants' discrimination of an early acquired native contrast, /p/ vs. /b/ (in the word forms /pIm/ vs. /bIm/), in Experiment 1, with an acoustically subtle, non-native contrast, /n/ vs. /ŋ/ (in /nIm/ vs. /ŋIm/), in Experiment 2. Words were spoken by one or four talkers. Infants discriminated the native but not the non-native contrast, and there were no significant effects of talker condition. We discuss implications for theories of phonological learning and avenues for future research.

Infants Segment Words from Songs-An EEG Study

Children's songs are omnipresent and highly attractive stimuli in infants' input. Previous work suggests that infants process linguistic-phonetic information from simplified sung melodies. The present study investigated whether infants learn words from ecologically valid children's songs. Testing 40 Dutch-learning 10-month-olds in a familiarization-then-test electroencephalography (EEG) paradigm, this study asked whether infants can segment repeated target words embedded in songs during familiarization and subsequently recognize those words in continuous speech in the test phase. To replicate previous speech work and compare segmentation across modalities, infants participated in both song and speech sessions. Results showed a positive event-related potential (ERP) familiarity effect to the final compared to the first target occurrences during both song and speech familiarization. No evidence was found for word recognition in the test phase following either song or speech. Comparisons across the stimuli of the present and a comparable previous study suggested that acoustic prominence and speech rate may have contributed to the polarity of the ERP familiarity effect and its absence in the test phase. Overall, the present study provides evidence that 10-month-old infants can segment words embedded in songs, and it raises questions about the acoustic and other factors that enable or hinder infant word segmentation from songs and speech.

Infants' statistical word segmentation in an artificial language is linked to both parental speech input and reported production abilities

Individual variability in infant's language processing is partly explained by environmental factors, like the quantity of parental speech input, as well as by infant-specific factors, like speech production. Here, we explore how these factors affect infant word segmentation. We used an artificial language to ensure that only statistical regularities (like transitional probabilities between syllables) could cue word boundaries, and then asked how the quantity of parental speech input and infants' babbling repertoire predict infants' abilities to use these statistical cues. We replicated prior reports showing that 8-month-old infants use statistical cues to segment words, with a preference for part-words over words (a novelty effect). Crucially, 8-month-olds with larger novelty effects had received more speech input at 4 months and had greater production abilities at 8 months. These findings establish for the first time that the ability to extract statistical information from speech correlates with individual factors in infancy, like early speech experience and language production. Implications of these findings for understanding individual variability in early language acquisition are discussed.

The consonant bias in word learning is not determined by position within the word: Evidence from vowel-initial words

The current study used an object manipulation task to explore whether infants rely more on consonant information than on vowel information when learning new words even when the words start with a vowel. Canadian French-learning 20-month-olds, who were taught pairs of new vowel-initial words contrasted either on their initial vowel (opsi/eupsi) or following consonant (oupsa/outsa), were found to have learned the words only in the consonant condition and performed significantly better in the consonant condition than in the vowel condition. These results extend to Canadian French-learning infants the consonant bias in word learning previously found in French-learning infants from France and, crucially, shows that vocalic information has less weight than consonant information in new word learning even when it is the initial sound of the target words, confirming the consonant bias at the lexical level postulated by Nespor et al. (2003). The current findings also suggest that French-learning infants are able to segment vowel-initial words as early as 20 months of age.