Adult-directed Speech Research Articles

Infants' Preference for ID Speech in Face and Voice Extends to a Non‐Native Language

ABSTRACTInfants prefer infant‐directed (ID) speech. Concerning talking faces, previous research showed that 3‐ and 5‐month‐olds prefer faces that produce native ID than native adult‐directed (AD) speech, regardless of background speech being ID, AD or silent. Here, we explored whether infants also show a preference for non‐native ID speech. We presented 3‐ and 6‐month‐old infants with pairs of talking faces, one producing non‐native ID speech and the other non‐native AD speech, either in silence (Experiment 1) or accompanied by non‐native ID or AD background speech (Experiment 2). Results from Experiment 1 showed an overall preference for the silent ID talking faces across both age groups, suggesting a reliance on cross‐linguistic, potentially universal cues for this preference. However, Experiment 2 showed that preference for ID faces was disrupted at 3 months when auditory speech was present (ID or AD). At 6 months, infants maintained a preference for ID talking faces, but only when accompanied by ID speech. These findings show that auditory non‐native speech interferes with infants' processing of ID talking faces. They also suggest that by 6 months, infants start associating ID features from faces and voices irrespective of language familiarity, suggesting that infants' ID preference may be universal and amodal.

A longitudinal investigation of the acoustic properties of infant-directed speech from 6 to 18 months.

Caregivers often modulate their speech when interacting with infants, adapting a register that has been suggested to have attentional, affective and didactic purposes. The present preregistered study examined the longitudinal trajectories of a diverse range of acoustic features of infant-directed speech (IDS) and compared these with adult-directed speech (ADS), in Norwegian parents of 6- to 18-month-old infants. Sixty-nine families participated. Throughout five laboratory visits across one year, parents were recorded reading a picture-book to their infant (IDS) and an experimenter (ADS). The book was designed to tightly control for the linguistic content and context of speech between participants, timepoints and registers. Analyses of a total of 54 594 vowels and 22 958 phrases revealed, first, an overall effect of register: parents used higher pitch, wider pitch range, slower articulation rate, longer vowel duration and more variable and less distinct vowels in IDS than in ADS. Second, significant register-by-age interactions indicated that parents' IDS, compared with their ADS, featured wider pitch range, larger vowel space and shorter vowel duration in older as compared with younger infants, while pitch, articulation rate and vowel variability and distinctiveness remained relatively stable with age. Results are discussed in the context of the proposed functions of IDS.

Appreciation of singing and speaking voices is highly idiosyncratic.

Voice preferences are an integral part of interpersonal interactions and shape how people connect with each other. While a large number of studies have investigated the mechanisms behind (speaking) voice attractiveness, very little research was dedicated to other types of vocalizations. In this Registered Report, we proposed to investigate voice preferences with an integrative approach. To this end, we used a newly recorded and validated stimulus set of contrasting vocalizations by 22 highly trained female singers speaking and singing the same material (in Brazilian Portuguese) in contrasting styles (sung as a lullaby, as a pop song or as an opera aria; and spoken aloud as if directed to an adult audience and as if directed to an infant). We asked 62 participants to rate these vocalizations in terms of how much they liked them; and we compared the amount of shared taste (that is, how much participants agreed in their preferences) across styles. We found highly idiosyncratic preferences across all styles. Our predictions concerning shared taste were not confirmed: although shared taste was higher for lullaby than for pop singing, it was unexpectedly higher for operatic than pop singing, and higher for infant-directed than adult-directed speech. Conversely, our prediction of limited consistency in average preferences for some singers across styles was confirmed, contradicting sexual selection-based ideas of singing and speaking as 'backup' signals of individual fitness. Our findings draw attention to the role of individual differences in voice preferences and highlight the need for a broader approach to understanding the underlying mechanisms of voice preferences. Stage 1 recommendation and review history: https://rr.peercommunityin.org/articles/rec?id=357. Stage 2 recommendation and review history: https://rr.peercommunityin.org/articles/rec?id=802.

Testing the relationship between preferences for infant-directed speech and vocabulary development: A multi-lab study.

From early on, infants show a preference for infant-directed speech (IDS) over adult-directed speech (ADS), and exposure to IDS has been correlated with language outcome measures such as vocabulary. The present multi-laboratory study explores this issue by investigating whether there is a link between early preference for IDS and later vocabulary size. Infants' preference for IDS was tested as part of the ManyBabies 1 project, and follow-up CDI data were collected from a subsample of this dataset at 18 and 24 months. A total of 341 (18 months) and 327 (24 months) infants were tested across 21 laboratories. In neither preregistered analyses with North American and UK English, nor exploratory analyses with a larger sample did we find evidence for a relation between IDS preference and later vocabulary. We discuss implications of this finding in light of recent work suggesting that IDS preference measured in the laboratory has low test-retest reliability.

Investigation of mothers' elicited infant-directed speech and singing for preterm infants.

Mother's voice is a salient auditory stimulus commonly experienced during early development; after birth, characteristic acoustic modulations of mothers' infant-directed speech (IDSpeech) and singing (IDSinging) contribute to neurodevelopment. For preterm infants, early separation leads to decreased exposure to mother's voice; the impact on maternal ability to produce IDSpeech/IDSinging and infant perception of mother's voice is unknown. Fifty mother/preterm-infant dyads were enrolled in this prospective cohort study. Forty-four mothers recorded Twinkle, Twinkle Little Star in coached adult-directed speech (ADSpeech), IDSpeech, and IDSinging. Between 34.0-36.9w CGA, infants underwent high-density EEG during exposure to their mother's voice recordings. Acoustic features of mothers' voice and infant cortical response were analyzed and correlated. Acoustic features of recorded maternal ADSpeech, IDSpeech, and IDSinging were significantly different. In 33 infants with EEG, mean fundamental frequency and speech production rate (SPR) variability correlated with infant responses to ADSpeech; SPR and SPR variability correlated with IDSpeech; SPR correlated with IDSinging. Correlations were found at differing scalp locations for speech versus singing. Mothers of hospitalized preterm infants differentially modulate their voice during coached recorded language; features can then be differentiated by their preterm infants thus presenting opportunities for targeted interventions when parents cannot be present. Mothers of preterm infants can record their voice with acoustically quantifiable characteristics of infant-directed singing and speech, even when not at their infant's bedside. Recorded adult- and infant-directed speech stimuli are differentially processed in the brains of hospitalized preterm infants. The ability for mothers to create acoustically-distinct infant-directed speech in the absence of their infant may be driven by coaching to achieve an approximated sense of connection with their infant.

A cross-linguistic examination of young children's everyday language experiences.

We present an exploratory cross-linguistic analysis of the quantity of target-child-directed speech and adult-directed speech in North American English (US & Canadian), United Kingdom English, Argentinian Spanish, Tseltal (Tenejapa, Mayan), and Yélî Dnye (Rossel Island, Papuan), using annotations from 69 children aged 2-36 months. Using a novel methodological approach, our cross-linguistic and cross-cultural findings support prior work suggesting that target-child-directed speech quantities are stable across early development, while adult-directed speech decreases. A preponderance of speech from women was found to a similar degree across groups, with less target-child-directed speech from men and children in the North American samples than elsewhere. Consistently across groups, children also heard more adult-directed than target-child-directed speech. Finally, the numbers of talkers present in any given clip strongly impacted children's moment-to-moment input quantities. These findings illustrate how the structure of home life impacts patterns of early language exposure across diverse developmental contexts.

Young Children's Directed Question Asking in Preschool Classrooms.

Question asking is a prevalent aspect of children's speech, providing a means by which young learners can rapidly gain information about the world. Previous research has demonstrated that children exhibit sensitivity to the knowledge state of potential informants in laboratory settings. However, it remains unclear whether and how young children are inclined to direct questions that support learning deeper content to more knowledgeable informants in naturalistic classroom contexts. In this study, we examined children's question-asking targets (adults, other preschoolers, self-talk) during an open-play period in a US preschool classroom and assessed how the cognitive and linguistic characteristics of questions varied as a function of the intended recipient. Further, we examined how these patterns changed with age. We recorded the spontaneous speech of individual children between the ages of 3 and 6 years (N = 30, totaling 2875 utterances) in 40-min open-period sessions in their preschool day, noting whether the speech was directed toward an adult, another child, or was stated to self. We publish this fully transcribed database with contextual and linguistic details coded as open access to all future researchers. We found that questions accounted for a greater proportion of preschoolers' adult-directed speech than of their child-directed and self-directed speech, with a particular increase in questions that supported broader learning goals when directed to an adult. Younger children directed a higher proportion of learning questions to adults than themselves, whereas older children asked similar proportions of questions to both, suggesting a difference in younger and older children's question-asking strategies. Although children used greater lexical diversity in questions than in other utterances, their question formulation in terms of length and diversity remained consistent across age and recipient types, reflecting their general linguistic abilities. Our findings reveal that children discriminately choose "what" and "whom" to ask in daily spontaneous conversations. Even in less-structured school contexts, preschoolers direct questions to the informant most likely to be able to provide an adequate answer.

Patterns of lexical and syntactic adjustment in early infant-directed speech related to language development in Hungarian

ABSTRACT Infant-directed speech (IDS) is known to be characterised by phonetic and prosodic cues along with reduced vocabulary and syntax compared to adult-directed speech (ADS). However, there is considerable variation between mothers in the degree of lexical and syntactic reduction of their IDS. The present study aims to investigate the correspondences of the inter-individual variation of maternal IDS at 6 and 18 months with infants’ language development at 18 months. 109 dyads of mothers and their firstborn infants participated in the study. Mothers’ ID and AD storytelling based on standard picture stimuli were recorded at 6 and 18 months of their infants’ age. We analysed measures of speech quantity (number of utterances and words), syntactic complexity (mean length of utterance), and lexical diversity (type-token ratio). Language growth was measured bimonthly using the Hungarian adaptation of the MacArthur-Bates CDI W&G form. The results did not reveal any association between characteristics of mothers’ ID narratives and their infants’ concurrent language skills at 18 months. However, we found a longitudinal link between a distinct pattern of linguistic simplification in maternal ID storytelling at 6 months and the development of expressive vocabulary in infants at 18 months. Infants whose mother tends to reduce both lexical and syntactic complexity of ID narratives the most are more likely to exhibit higher language outcomes. Further research is warranted to explore the background factors and longer-term effects of this maternal strategy.

Limited evidence of test-retest reliability in infant-directed speech preference in a large preregistered infant experiment.

Test-retest reliability-establishing that measurements remain consistent across multiple testing sessions-is critical to measuring, understanding, and predicting individual differences in infant language development. However, previous attempts to establish measurement reliability in infant speech perception tasks are limited, and reliability of frequently used infant measures is largely unknown. The current study investigated the test-retest reliability of infants' preference for infant-directed speech over adult-directed speech in a large sample (N=158) in the context of the ManyBabies1 collaborative research project. Labs were asked to bring in participating infants for a second appointment retesting infants on their preference for infant-directed speech. This approach allowed us to estimate test-retest reliability across three different methods used to investigate preferential listening in infancy: the head-turn preference procedure, central fixation, and eye-tracking. Overall, we found no consistent evidence of test-retest reliability in measures of infants' speech preference (overall r=0.09, 95% CI [-0.06,0.25]). While increasing the number of trials that infants needed to contribute for inclusion in the analysis revealed a numeric growth in test-retest reliability, it also considerably reduced the study's effective sample size. Therefore, future research on infant development should take into account that not all experimental measures may be appropriate for assessing individual differences between infants. RESEARCH HIGHLIGHTS: We assessed test-retest reliability of infants' preference for infant-directed over adult-directed speech in a large pre-registered sample (N=158). There was no consistent evidence of test-retest reliability in measures of infants' speech preference. Applying stricter criteria for the inclusion of participants may lead to higher test-retest reliability, but at the cost of substantial decreases in sample size. Developmental research relying on stable individual differences should consider the underlying reliability of its measures.

An Exploration of Voice Quality in Mothers Speaking Canadian English to Infants

ABSTRACT Research on the acoustic characteristics of Infant Directed Speech (IDS) in North American English indicates that it is generally higher-pitched than Adult Directed Speech (ADS) and has unique prosodic characteristics, which is commonly found across many spoken languages. However, very little research has addressed another important aspect of prosody: voice quality. In the current study, 25 English-speaking mothers from Canada were recorded speaking to their infant children and to an adult peer. Five acoustic measures of voice quality, including glottal constriction, spectral tilt, Harmonic-to-Noise Ratio (HNR), and Cepstral Peak Prominence (CPP), were analyzed. Only CPP, a measure of the breathiness of a speaker’s voice, and corrected H1-A2, a measure of vocal creakiness, were found to be significantly different between the IDS and ADS registers. Sociolinguistic research identifies voice quality as a key indicator of speech style and persona; we connect the pattern of breathiness in IDS to a possible “parental persona” that builds on the affective intent of IDS (rather than the pedagogical intent), with suggestions for future research.

Acoustic characteristics of infant- and foreigner-directed speech with Mandarin as the target language.

The quality of speech input influences the efficiency of L1 and L2 acquisition. This study examined modifications in infant-directed speech (IDS) and foreigner-directed speech (FDS) in Standard Mandarin-a tonal language-and explored how IDS and FDS features were manifested in disyllabic words and a longer discourse. The study aimed to determine which characteristics of IDS and FDS were enhanced in comparison with adult-directed speech (ADS), and how IDS and FDS differed when measured in a common set of acoustic parameters. For words, it was found that tone-bearing vowel duration, mean and range of fundamental frequency (F0), and the lexical tone contours were enhanced in IDS and FDS relative to ADS, except for the dipping Tone 3 that exhibited an unexpected lowering in FDS, but no modification in IDS when compared with ADS. For the discourse, different aspects of temporal and F0 enhancements were emphasized in IDS and FDS: the mean F0 was higher in IDS whereas the total discourse duration was greater in FDS. These findings add to the growing literature on L1 and L2 speech input characteristics and their role in language acquisition.

Toddlers' prior social experience with speakers influences their word learning.

Toddlers prefer to learn from familiar adults, particularly their caregivers, and perform better on word learning tasks when taught by caregivers than by strangers. However, it remains unclear why toddlers learn better from caregivers than from strangers. One possibility is that toddlers are more receptive to learning from individuals whom they have found to be engaging in previous interactions. The current study tested whether toddlers learn more from an unfamiliar adult who was previously engaging than from an unfamiliar adult who was previously unengaging. Toddlers (27-29months, N=40) were taught labels for novel objects by two different experimenters. Prior to word learning, toddlers watched pre-recorded videos of one experimenter utilizing engaging behaviors (i.e., using infant-directed speech, gestures, eye contact, and positive affect) and one experimenter utilizing unengaging behaviors (i.e., using adult-directed speech, no gestures, no eye contact, and neutral affect). Both experimenters were equally engaging during labeling. Word learning was then tested using a looking-while-listening paradigm. The results of linear mixed-effects model, cluster-based permutation, and growth curve analyses suggest heightened performance for words that were taught by the experimenter who was previously engaging. These results begin to reveal the kinds of social experiences that promote success in early word learning.

Evidence for Infant-directed Speech Preference Is Consistent Across Large-scale, Multi-site Replication and Meta-analysis.

There is substantial evidence that infants prefer infant-directed speech (IDS) to adult-directed speech (ADS). The strongest evidence for this claim has come from two large-scale investigations: i) a community-augmented meta-analysis of published behavioral studies and ii) a large-scale multi-lab replication study. In this paper, we aim to improve our understanding of the IDS preference and its boundary conditions by combining and comparing these two data sources across key population and design characteristics of the underlying studies. Our analyses reveal that both the meta-analysis and multi-lab replication show moderate effect sizes (d ≈ 0.35 for each estimate) and that both of these effects persist when relevant study-level moderators are added to the models (i.e., experimental methods, infant ages, and native languages). However, while the overall effect size estimates were similar, the two sources diverged in the effects of key moderators: both infant age and experimental method predicted IDS preference in the multi-lab replication study, but showed no effect in the meta-analysis. These results demonstrate that the IDS preference generalizes across a variety of experimental conditions and sampling characteristics, while simultaneously identifying key differences in the empirical picture offered by each source individually and pinpointing areas where substantial uncertainty remains about the influence of theoretically central moderators on IDS preference. Overall, our results show how meta-analyses and multi-lab replications can be used in tandem to understand the robustness and generalizability of developmental phenomena.

Contribution of positive affect in infant directed speech: what do amplitude modulations patterns suggest?

Speech perception relies heavily on cortical entrainment of amplitude modulations in speech, which occur at different rates. Following a study by Leong et al. (2017) showing slower modulations have higher power than faster modulations in infant directed speech (IDS), we hypothesized that positive emotions in IDS might drive this pattern. Using the same analyses (spectral amplitude modulation phase hierarchy method and phase synchronization index (PSI) (Leong and Goswami, 2015)), we compared the power of isolated modulation rates (synchronous with neural oscillations) and the synchrony between them in IDS and adult directed speech (ADS), using English stimuli from Many Babies Consortium (Frank et al., 2020). We repeated the same analyses comparing happy and neutral ADS using stimuli of four native English speakers (Pell et al., 2009). Our analysis did not uncover significant power differences between IDS and ADS. However, it revealed happy ADS has higher power at slower rates, with the reversed pattern for neutral ADS (p < 0.001). PSI was higher for two faster rates in neutral ADS (p < 0.0001), as reported by Leong et al. comparing IDS versus ADS. These findings reveal novel acoustic features of vocal emotions that might be important in attracting infant attention to IDS.

Processing of visual stimuli following infant directed speech: Attention-guiding effects of unfamiliar speech.

This study investigates attention modulation as a function of infant directed (ID) versus adult directed (AD) speech in seven-month-old infants using electroencephalographic measures. In three experiments, infants were presented with either ID speech or AD speech as stimuli, followed by highly variable images of inanimate objects as targets. In Experiment 1 (N=18), images were preceded by ID or AD speech with semantic content ("Look here"). Contrary to hypothesis, targets preceded by AD speech elicited increased amplitude of the Negative central (Nc) component compared to targets preceded by ID speech, indicating increased attention. Experiment 2 (N=23) explored whether ID versus AD speech influences attention allocation also without semantic content. The same targets were either preceded by human voice sounds without semantic content ("Uh-Ah") following the prosody of either ID or AD speech register. No differences in attention allocation or object processing were observed. Experiment 3 (N=18) contrasted ID speech with and without semantic content and found enhanced attention allocation following stimuli without semantic content, but increased object processing following stimuli with semantic content. Overall, the effects observed here are consistent with the idea that less familiar speech stimuli increase attention for subsequent objects. Semantic content of stimuli increased the depth of object processing in 7-month-olds.

“It's not just what we say or do, but how we say and do it”

Infant-directed speech (IDS) and infant-directed actions (IDA) represent specific behavioural modifications of adults when they communicate with infants and young children. Infant-directed modifications (IDMs) have specific behavioural representations marked by high positive affection, greater expressiveness, simplification, and increased repetition. Both IDS and IDA appear as part of the same larger behavioural system of IDMs. However, so far, studies have analysed the features and functions of these behaviours separately. Compared to adult-directed speech, IDS is characterised by longer pauses, a slower tempo, more prosodic repetition, higher fundamental frequency, longer vowels, repetitive intonation structures, and greater melodiousness. In IDA, compared to adult-directed actions, the amplitude of movements, simplification, and number of repetitions tend to increase as the distance between communication partners decrease. In this review, we draw a parallel between IDS and IDA to show that adults change both their speech and actions in similar ways and that both actions and speech change depending on the infant’s age and/or developmental stage. We discuss possible (biological) mechanisms that elicit the use of IDS and IDA and argue that this specific type of adult behaviour has a unique impact on how infants perceive and process information. Insights on biological, behavioural, and functional aspects of IDMs could provide a new perspective on the importance of early interactions and knowledge acquisition in both typically developing children and those with developmental disorders.

Child-Directed Speech in Noise: Testing Signal- and Code-Based Phonetic Enhancement.

Talkers adapt their speech according to the demands of their listeners and the communicative context, enhancing the properties of the signal (pitch, intensity) and/or properties of the code (enhancement of phonemic contrasts). This study asked how mothers adapt their child-directed speech (CDS) in ways that might serve the immediate goals of increasing intelligibility, as well as long-term goals of supporting speech and language development in their children. Mothers (N = 28) participated in a real-time interactive speech production/perception paradigm, in which mothers instructed their young (3- to 5-year-old) children, or an adult listener, to select the picture corresponding to a target word. The task was performed at low and high levels (56 vs. 75 dB SPL) of background noise to examine the Lombard effects of decreased audibility on speech production. Acoustic-phonetic analyses of CDS and adult-directed speech (ADS) productions of target words and carrier phrase (e.g., "Find pig") revealed that mothers significantly enhanced the mean pitch, pitch variability, and intensity of target words in CDS, particularly at higher background noise levels and for younger children. Mothers produce CDS with a higher signal-to-noise ratio than ADS. However, limited evidence was found for phonetic enhancement of the segmental properties of speech. Although increased category separation was found in the voice onset time of stop consonants, decreased vowel category separation (an anti-enhancement effect) was observed in CDS. Mothers readily enhance the suprasegmental signal properties of their speech in CDS, but not the acoustic-phonetic properties of phonemes. This study fails to provide evidence of phonetic enhancement in preschool children in a dyadic communication task under noisy listening conditions. https://doi.org/10.23641/asha.24645423.

Fathers' unmodulated prosody in child-directed speech.

Mothers and fathers modify prosodic characteristics of child-directed speech relative to adult-directed speech. Evidence suggests that mothers and fathers may differ in how they use child-directed speech as communicative partners. Thus, fathers create communicative challenges during father-child interaction that facilitate the child's adaptation to a wider potential range of interlocutors. In this paper, speech production differences are examined between mothers and fathers in child-directed speech to toddlers as compared to adult-directed speech. Using a longitudinal, large-scale design of audio recordings in naturalistic environments and automatic speech processing techniques, it was found that mothers, but not fathers, increased their fundamental frequency when addressing their toddlers. The results suggest that fathers do not modulate the prosody of their speech in the same way as mothers when communicating with their toddlers. Findings have implications for emotional and communicative practices of fathers compared to mothers and the differential role each plays in child development.

Seeing a Talking Face Matters: Gaze Behavior and the Auditory-Visual Speech Benefit in Adults' Cortical Tracking of Infant-directed Speech.

In face-to-face conversations, listeners gather visual speech information from a speaker's talking face that enhances their perception of the incoming auditory speech signal. This auditory-visual (AV) speech benefit is evident even in quiet environments but is stronger in situations that require greater listening effort such as when the speech signal itself deviates from listeners' expectations. One example is infant-directed speech (IDS) presented to adults. IDS has exaggerated acoustic properties that are easily discriminable from adult-directed speech (ADS). Although IDS is a speech register that adults typically use with infants, no previous neurophysiological study has directly examined whether adult listeners process IDS differently from ADS. To address this, the current study simultaneously recorded EEG and eye-tracking data from adult participants as they were presented with auditory-only (AO), visual-only, and AV recordings of IDS and ADS. Eye-tracking data were recorded because looking behavior to the speaker's eyes and mouth modulates the extent of AV speech benefit experienced. Analyses of cortical tracking accuracy revealed that cortical tracking of the speech envelope was significant in AO and AV modalities for IDS and ADS. However, the AV speech benefit [i.e., AV > (A + V)] was only present for IDS trials. Gaze behavior analyses indicated differences in looking behavior during IDS and ADS trials. Surprisingly, looking behavior to the speaker's eyes and mouth was not correlated with cortical tracking accuracy. Additional exploratory analyses indicated that attention to the whole display was negatively correlated with cortical tracking accuracy of AO and visual-only trials in IDS. Our results underscore the nuances involved in the relationship between neurophysiological AV speech benefit and looking behavior.

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.