Phonological Variation in Child-Directed Speech is Modulated by Lexical Frequency.

We investigate whether child-directed speech (CDS) contains a higher proportion of canonical pronunciations compared to adult-directed speech (ADS), focusing on Korean noun stem-final obstruent variation. In a word-teaching task, we observed that mothers use a higher rate of canonical pronunciation when addressing infants than when addressing adults. In a follow-up experiment, adults exhibited a higher rate of canonical pronunciation for high- than low-frequency words. Additional analyses conducted with only the high-frequency monosyllabic words from the two experiments found no evidence for simplified phonology in CDS when lexical frequency was controlled for. Our findings suggest that the higher rate of canonical forms in CDS, with respect to Korean morphophonological rules, is mediated by the frequency of word usage. Thus, the didactic function of CDS phonology appears to be a byproduct of mothers using familiar words with children. These results highlight the importance of considering word usage in investigating the nature of CDS.

Validation of an open source, remote web-based eye-tracking method (WebGazer) for research in early childhood.

Measuring eye movements remotely via the participant's webcam promises to be an attractive methodological addition to in-person eye-tracking in the lab. However, there is a lack of systematic research comparing remote web-based eye-tracking with in-lab eye-tracking in young children. We report a multi-lab study that compared these two measures in an anticipatory looking task with toddlers using WebGazer.js and jsPsych. Results of our remotely tested sample of 18-27-month-old toddlers (N = 125) revealed that web-based eye-tracking successfully captured goal-based action predictions, although the proportion of the goal-directed anticipatory looking was lower compared to the in-lab sample (N = 70). As expected, attrition rate was substantially higher in the web-based (42%) than the in-lab sample (10%). Excluding trials based on visual inspection of the match of time-locked gaze coordinates and the participant's webcam video overlayed on the stimuli was an important preprocessing step to reduce noise in the data. We discuss the use of this remote web-based method in comparison with other current methodological innovations. Our study demonstrates that remote web-based eye-tracking can be a useful tool for testing toddlers, facilitating recruitment of larger and more diverse samples; a caveat to consider is the larger drop-out rate.

Korean infants' perceptual responses to Korean and Western music based on musical experience.

This study investigates infants' enculturation to music in a bicultural musical environment. We tested 49 12- to 30-month-old Korean infants on their preference for Korean or Western traditional songs played by haegeum and cello. Korean infants have access to both Korean and Western music in their environment as captured on a survey of infants' daily exposure to music at home. Our results show that infants with less daily exposure to any kind of music at home listened longer to all music types. The infants' overall listening time did not differ between Korean and Western music and instruments. Rather, those with high exposure to Western music listened longer to Korean music played with haegeum. Moreover, older toddlers (aged 24-30 months) maintained a longer interest in songs of an origin with which they are less familiar, indicating an emerging orientation towards novelty. Early orientation of Korean infants toward the novel experience of music listening is likely driven by perceptual curiosity, which drives exploratory behavior that diminishes with continued exposure. On the other hand, older infants' orientation towards novel stimuli is led by epistemic curiosity, which motivates an infant to acquire new knowledge. Korean infants' lack of differential listening likely reflects their protracted period of enculturation to ambient music due to complex input. Further, older infants' novelty-orientation is consistent with findings in bilingual infants' orientation towards novel information. Additional analysis showed a long-term effect of music exposure on infants' vocabulary development. A video abstract of this article can be viewed at https://www.youtube.com/watch?v=Kllt0KA1tJk RESEARCH HIGHLIGHTS: Korean infants showed novelty-oriented attention to music such that infants with less daily exposure to music at home showed longer listening times to music. 12- to 30-month-old Korean infants did not show differential listening to Korean versus Western music or instruments, suggesting a protracted period of perceptual openness. 24- to 30-month-old Korean toddlers' listening behavior indicated emerging novelty-preference, exhibiting delayed enculturation to ambient music compared to Western infants reported in earlier research. 18-month-old Korean infants with a greater weekly exposure to music had higher CDI scores a year later, consistent with the well-known music-to-language transfer effect.

Mothers' use of touch across infants' development and its implications for word learning: Evidence from Korean dyadic interactions.

Caregivers' touches that occur alongside words and utterances could aid in the detection of word/utterance boundaries and the mapping of word forms to word meanings. We examined changes in caregivers' use of touches with their speech directed to infants using a multimodal cross-sectional corpus of 35 Korean mother-child dyads across three age groups of infants (8, 14, and 27 months). We tested the hypothesis that caregivers' frequency and use of touches with speech change with infants' development. Results revealed that the frequency of word/utterance-touch alignment as well as word + touch co-occurrence is highest in speech addressed to the youngest group of infants. Thus, this study provides support for the hypothesis that caregivers' use of touch during dyadic interactions is sensitive to infants' age in a way similar to caregivers' use of speech alone and could provide cues useful to infants' language learning at critical points in early development.

Evaluating the Language ENvironment Analysis System for Korean.

Purpose The algorithm of the Language ENvironment Analysis (LENA) system for calculating language environment measures was trained on American English; thus, its validity with other languages cannot be assumed. This article evaluates the accuracy of the LENA system applied to Korean. Method We sampled sixty 5-min recording clips involving 38 key children aged 7-18 months from a larger data set. We establish the identification error rate, precision, and recall of LENA classification compared to human coders. We then examine the correlation between standard LENA measures of adult word count, child vocalization count, and conversational turn count and human counts of the same measures. Results Our identification error rate (64% or 67%), including false alarm, confusion, and misses, was similar to the rate found in Cristia, Lavechin, et al. (2020). The correlation between LENA and human counts for adult word count (r = .78 or .79) was similar to that found in the other studies, but the same measure for child vocalization count (r = .34-.47) was lower than the value in Cristia, Lavechin, et al., though it fell within ranges found in other non-European languages. The correlation between LENA and human conversational turn count was not high (r = .36-.47), similar to the findings in other studies. Conclusions LENA technology is similarly reliable for Korean language environments as it is for other non-English language environments. Factors affecting the accuracy of diarization include speakers' pitch, duration of utterances, age, and the presence of noise and electronic sounds.

Introducing the Ko Corpus of Korean Mother-Child Interaction.

We describe a corpus of speech taking place between 30 Korean mother-child pairs, divided in three groups of Prelexical (M = 0;08), Early-Lexical (M = 1;02), and Advanced-Lexical (M = 2;03). In addition to the child-directed speech (CDS), this corpus includes two different formalities of adult-directed speech (ADS), i.e., family-directed ADS (ADS_Fam) and experimenter-directed ADS (ADS_Exp). Our analysis of the MLU in CDS, family-, and experimenter-directed ADS found significant differences between CDS and ADS_Fam, and between ADS_Fam and ADS_Exp, but not between CDS and ADS_Exp. Our finding suggests that researchers should pay more attention to controlling the level of formality in CDS and ADS when comparing the two registers for their speech characteristics. The corpus was transcribed in the CHAT format of the CHILDES system, so users can easily extract data related to verbal behavior in the mother-child interaction using the CLAN program of CHILDES.

Infant-Mother Acoustic-Prosodic Alignment and Developmental Risk.

Purpose: One promising early marker for autism and other communicative and language disorders is early infant speech production. Here we used daylong recordings of high- and low-risk infant-mother dyads to examine whether acoustic-prosodic alignment as well as two automated measures of infant vocalization are related to developmental risk status indexed via familial risk and developmental progress at 36 months of age. Method: Automated analyses of the acoustics of daylong real-world interactions were used to examine whether pitch characteristics of one vocalization by the mother or the child predicted those of the vocalization response by the other speaker and whether other features of infants' speech in daylong recordings were associated with developmental risk status or outcomes. Results: Low-risk and high-risk dyads did not differ in the level of acoustic-prosodic alignment, which was overall not significant. Further analyses revealed that acoustic-prosodic alignment did not predict infants' later developmental progress, which was, however, associated with two automated measures of infant vocalizations (daily vocalizations and conversational turns). Conclusions: Although further research is needed, these findings suggest that automated measures of vocalizations drawn from daylong recordings are a possible early identification tool for later developmental progress/concerns. Supplemental Material: https://osf.io/cdn3v/.

Korean Mothers Attune the Frequency and Acoustic Saliency of Sound Symbolic Words to the Linguistic Maturity of Their Children.

The present study investigates Korean mothers' use of sound symbolism, in particular expressive lengthening and ideophones, in their speech directed to their children. Specifically, we explore whether the frequency and acoustic saliency of sound symbolic words are modulated by the maturity of children's linguistic ability. A total of 36 infant-mother dyads, 12 each belonging to the three groups of preverbal (M = 8-month-old), early speech (M = 13-month-old), and multiword (M = 27-month-old) stage, were recorded in a 40-min free-play session. The results were consistent with the findings in previous research that the ratio of sound symbolic words in mothers' speech decreases with child age and that they are acoustically more salient than conventional words in duration and pitch measures. We additionally found that mothers weaken the prominence for ideophones for older children in mean pitch, suggesting that such prominence of these iconic words might bootstrap infants' word learning especially when they are younger. Interestingly, however, we found that mothers maintain the acoustic saliency of expressive lengthening consistently across children's ages in all acoustic measures. There is some indication that children at age 2 are not likely to have mastered the fine details of scalar properties in certain words. Thus, it could be that they still benefit from the enhanced prosody of expressive lengthening in learning the semantic attributes of scalar adjectives, and, accordingly, mothers continue to provide redundant acoustic cues longer for expressive lengthening than ideophones.

Entrainment of prosody in the interaction of mothers with their young children.

Caregiver speech is not a static collection of utterances, but occurs in conversational exchanges, in which caregiver and child dynamically influence each other's speech. We investigate (a) whether children and caregivers modulate the prosody of their speech as a function of their interlocutor's speech, and (b) the influence of the initiator of the conversation on durational characteristics of the exchange. We analyzed naturalistic conversations from 13 mother-infant/toddler dyads aged 12-30 months across full-day recordings of 3-5 days per dyad using LENA and automated analytic tools. We found small, but significant, effects of mothers and their children influencing each other's speech, particularly in pitch measures. We also found longer utterances and shorter response latencies for the initiator of a conversation. While mothers show more mature conversational capabilities (more entrainment, shorter response latencies), our findings converge with prior research to highlight the active role of young children in the conversational exchange.

Additive effects of lengthening on the utterance-final word in child-directed speech.

PURPOSE: The authors investigated lengthening effects in child-directed speech (CDS) across the sentence, testing the additive effects on duration of Word Position, Register, Focus, and Sentence Mode (statement/question). METHOD: Five theater students produced 6 sentences containing 5 monosyllabic words in a simulated dialogue, varying in Register, Focus, and Sentence Mode. The authors segmented a total of 1,800 sentences using forced-alignment tools, and they analyzed the duration of each word. RESULTS: The results show significant effects of Register, Word Position, and their interactions. The simple effect of Register was significant in all 5 word positions, indicating a global elongation effect in CDS. Interestingly, there was no proportional increase of the final word in CDS. In addition, the 3-way interactions Register × Word Position × Focus and Register × Word Position × Sentence Mode were significant, which converge to the conclusion that the utterance-final word in CDS is additively elongated when it is focused and in a statement. CONCLUSION: Elongation in CDS is a global effect, but the additive effects of duration demonstrated in the authors' data suggest that the effect of enhanced utterance-final lengthening in CDS in naturalistic samples may be a by-product of discourse characteristics of CDS.

It's a question? Infants attend differently to yes/no questions and declaratives.

We examined infants' perception of the intonational characteristics of yes-no questions and declarative sentences in English. Both infants habituated to questions and those habituated to declaratives preferred the question forms at test, suggesting that infants process these two sentence types differently.

Development of perceptual sensitivity to extrinsic vowel duration in infants learning American English.

8- and 14-month-old infants' perceptual sensitivity to vowel duration conditioned by post-vocalic consonantal voicing was examined. Half the infants heard CVC stimuli with short vowels, and half heard stimuli with long vowels. In both groups, stimuli with voiced and voiceless final consonants were compared. Older infants showed significant sensitivity to mismatching vowel duration and consonant voicing in the short condition but not the long condition; younger infants were not sensitive to such mismatching in either condition. The results suggest that infants' sensitivity to extrinsic vowel duration begins to develop between 8 and 14 months.