Hypoarticulation in infant-directed speech

Speakers design their multimodal communication according to the needs and knowledge of their interlocutors, phenomenon known as audience design. We use more sophisticated language (e.g., longer sentences with complex grammatical forms) when communicating with adults compared with children. This study investigates how speech and co-speech gestures change in adult-directed speech (ADS) versus child-directed speech (CDS) for three different tasks. Overall, 66 adult participants (Mage = 21.05, 60 female) completed three different tasks (story-reading, storytelling and address description) and they were instructed to pretend to communicate with a child (CDS) or an adult (ADS). We hypothesised that participants would use more complex language, more beat gestures, and less iconic gestures in the ADS compared with the CDS. Results showed that, for CDS, participants used more iconic gestures in the story-reading task and storytelling task compared with ADS. However, participants used more beat gestures in the storytelling task for ADS than CDS. In addition, language complexity did not differ across conditions. Our findings indicate that how speakers employ different types of gestures (iconic vs beat) according to the addressee's needs and across different tasks. Speakers might prefer to use more iconic gestures with children than adults. Results are discussed according to audience design theory.

Japanese has traditionally been called “mora-timed,” but studies have shown that this intuition is based not on durational tendencies but rather on phonological, structural factors in the language. Meanwhile, infant-directed speech (IDS) is said to “exaggerate” certain properties of adult-directed speech (ADS), including rhythm. If so, then it is possible that the mora rhythm of Japanese is more strongly observed in IDS than ADS. To investigate this possibility, the present study utilized the RIKEN Japanese Mother-Infant Conversation Corpus, which contains approximately 11 h of IDS by 22 mothers talking with their 18-to-24-month-old infants, and 3 h of ADS by the same mothers. Results from durational analyses showed that aspects of mora rhythm, such as the distinction between phonemically short and long vowels and singleton and geminate consonants, and the tendency toward isochrony of moras, were not greater in IDS than ADS. Mora duration in IDS was instead more variable, partly stemming from greater phrase-final lengthening and non-phonemic, emphatic lengthening. Results from structural analysis, however, showed that non-CV moras such as moraic nasals that characterize Japanese rhythm occurred more frequently in IDS than ADS. These results suggest that even in IDS, Japanese rhythm is manifested structurally, not durationally. [Work supported by JSPS.]

Both theoretical models of infant language acquisition and empirical studies posit important roles for attention to speech in early language development. However, deaf infants with cochlear implants (CIs) show reduced attention to speech as compared with their peers with normal hearing (NH; Horn, Davis, Pisoni, & Miyamoto, 2005; Houston, Pisoni, Kirk, Ying, & Miyamoto, 2003), which may affect their acquisition of spoken language. The main purpose of this study was to determine (a) whether infant-directed speech (IDS) enhances attention to speech in infants with CIs, as compared with adult-directed speech (ADS), and (b) whether the degree to which infants with CIs pay attention to IDS is associated with later language outcomes. We tested 46 infants-12 prelingually deaf infants who received CIs before 24 months of age and had 12 months of hearing experience (CI group), 22 hearing experience-matched infants with NH (NH-HEM group), and 12 chronological age-matched infants with NH (NH-CAM group)-on their listening preference in 3 randomized blocks: IDS versus silence, ADS versus silence, and IDS versus ADS. We administered the Preschool Language Scale-Fourth Edition (PLS-4; Zimmerman, Steiner, & Pond, 2002) approximately 18 months after implantation to assess receptive and expressive language skills of infants with CIs. In the IDS versus silence block, all 3 groups looked significantly longer to IDS than to silence. In the ADS versus silence block, both the NH-HEM and NH-CAM groups looked significantly longer to ADS relative to silence; however, the CI group did not show any preference. In the IDS versus ADS block, whereas both the CI and NH-HEM groups preferred IDS over ADS, the NH-CAM group looked equally long to IDS and ADS. IDS preference quotient among infants with CIs in the IDS versus ADS block was associated with PLS-4 Auditory Comprehension and PLS-4 Expressive Communication measures. Two major findings emerge: (a) IDS enhances attention to speech in deaf infants with CIs; (b) the degree of IDS preference over ADS relates to language development in infants with CIs. These results support a focus on input in developing intervention strategies to mitigate the effects of hearing loss on language development in infants with hearing loss.

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.

Speech rate has been reported to be slower in infant-directed speech (IDS) than in adult-directed speech (ADS). Studies have also found phrase-final lengthening to be more exaggerated in IDS compared with ADS. In our study we asked whether the observed overall slower rate of IDS is due to exaggerated utterance-final syllable lengthening. Two mothers of preverbal English-learning infants each participated in two recording sessions, one with her child, and another with an adult friend. The results showed an overall slower rate in IDS compared to ADS. However, when utterance-final syllables were excluded from the calculation, the speech rate in IDS and ADS did not differ significantly. The duration of utterance-final syllables differed significantly for IDS versus ADS. Thus, the overall slower rate of IDS was due to the extra-long final syllable occurring in relatively short utterances. The comparable pre-final speech rate for IDS and ADS further accentuates the final syllable lengthening in IDS. As utterances in IDS are typically phrases or clauses, the particularly strong final-lengthening cue could potentially facilitate infants’ segmentation of these syntactic units. These findings are consistent with the existing evidence that pre-boundary lengthening is important in the processing of major syntactic units in English-learning infants.

SummaryInfant-directed speech (IDS) plays a central role in early communication, initially expressing emotion and later supporting language development. This study examined how the brain’s functional network organization responds to infant-directed speech (IDS) versus adult-directed speech (ADS) during early infancy. Electroencephalography (EEG) data were collected from 49 healthy infants at 0, 4, and 9 months as they listened to the same fairy tale spoken in both IDS and ADS. Brain connectivity was assessed using phase lag synchronization across six frequency bands, and network topology was characterized using minimum spanning tree analysis. The delta network showed greater hierarchical and cost-efficient organization in response to IDS, particularly over frontal regions, with these differences becoming more pronounced with age. Over time, network integration increased and shifted toward the left hemisphere. These findings highlight how functional brain networks dynamically adapt to socially relevant speech input, reflecting the evolving communicative function of IDS during the first year of life.

Extensive experience in written language might provide children the opportunity to learn to read in the same manner they learn spoken language. One potential type of written language immersion is reading aloud to children, which is additionally valuable because the vocabulary in picture books is richer and more extensive than that found in child-directed speech. This study continues a comparison between these 2 communication media by evaluating their relative linguistic and cognitive complexity. Although reading grade level has been used only to assess the complexity of written language, it was also applied to both child-directed and adult-directed speech. Five measures of reading grade level gave an average grade level of 4.2 for picture books, 1.9 for child-directed speech, and 3.0 for adult-directed speech. The language in picture books is more challenging than that found in both child-directed and adult-directed speech. It is proposed that this difference between written and spoken language is the formal versus informal genre of their occurrence rather than their text or oral medium. The value of reading books aloud therefore exposes children to a linguistic and cognitive complexity not typically found in speech to children.

The goal of this research is to understand how bilingual and monolingual parents adjust their speech when talking to infants. We examined pitch characteristics of infant-directed speech (IDS) and adult-directed speech (ADS) with Spanish-English bilingual and English monolingual parents and their infants (8–20 months of age). Thirty-eight parent-infant dyads participated in two naturalistic play tasks. Parents spoke with a bilingual researcher to collect samples of ADS. Results showed that both parent groups produced higher maximum and average fundamental frequency in IDS than ADS, suggesting that caregivers adjust pitch similarly in IDS across registers. However, for bilinguals, the IDS versus ADS difference was larger in English than Spanish; bilingual parents differentiated IDS adjustments across languages. The analyses across word repetitions revealed that in bilingual parents’ IDS, there was no change in pitch across the first and second repetitions of target words, even when repetitions occurred in different languages. Taken together, results suggest that bilingual parents adjust their IDS pitch similarly to English-speaking monolinguals, but they differentiate English and Spanish IDS adjustments. Overall, this project contributes to our understanding of parents’ register adjustments across multilingual language learning contexts.

Investigations of the phonetics of infant-directed speech (IDS) have mainly focused on prosodic aspects, showing extreme values or overspecifications in comparison to adult-directed speech (ADS). On the other hand, studies of segmental properties, especially consonantal ones, are very rare. The lack of knowledge of phonetic characteristics of the infant’s speech input is problematic, considering that the infant’s perceptual development seems to be attuned towards properties in the ambient language, as suggested by infant perception experiments. In the present study voice onset time (VOT) was measured in Swedish mothers’ IDS and in their ADS. VOT was significantly shorter in IDS than in ADS in both voiced and voiceless stops. The impact of stress was very clear in both IDS and ADS, showing significantly longer VOT in stressed positions as compared to the unstressed. The results are discussed in a framework assuming a differential weighting system of different phonetic aspects such as prosodic, consonantal and vocalic, as a function of infant development.

When speaking to infants, mothers often alter their speech compared to how they speak to adults, but findings for fathers are mixed. This study examined interactions (N=30) between fathers and infants (Mage ±SD=7.8±4.3months) in a small-scale society in Vanuatu and two urban societies in North America. Fundamental frequency (F0 ) and speech rate were measured in infant-directed and adult-directed speech. When speaking to infants, fathers in both groups increased their F0 range, yet only Vanuatu fathers increased their average F0 . Conversely, North American fathers slowed down their speech rate to infants, whereas Vanuatu fathers did not. Behavioral traits can vary across distant cultures while still potentially solving similar communicative problems.

Over the past couple of decades, research has established that (1) infant-directed speech (IDS) facilitates speech, language, and cognitive development; and (2) infants are sensitive to the rhythmic structures in the ambient language. However, little is known about the role of IDS in infants' processing of rhythmic structures. Building on these two lines of research, whether IDS enhances infants' sensitivity to the predominant stress pattern (trochaic) in English was asked. To address this question, 9-month-old American infants were familiarized and tested with both trochaic (e.g., lazy) and iambic (e.g., cartoon) words presented in either IDS or adult-directed speech (ADS). Infants showed listening preference for the trochaic over iambic words when the speech was presented in ADS, but not in IDS. These results suggest that IDS attenuates infants' preference for trochaic stress pattern. Further acoustical analyses demonstrated that IDS provided less salient spectral cues for the contrasts between stressed and unstressed syllables in trochaic words. These findings encourage further efforts to explore the effects of IDS on language acquisition from a broader perspective.

This study explored the impact of infant‐directed speech (IDS) versus adult‐directed speech (ADS) on neural activity to familiar and unfamiliar words in 6‐ and 13‐month‐old infants. Event‐related potentials were recorded while infants listened to familiar words in IDS, familiar words in ADS, unfamiliar words in IDS, and unfamiliar words in ADS. The results indicated that IDS elicited increased neural activity compared to ADS for both age groups. Six‐month‐olds showed a boost in neural activity to IDS for familiar words only. Thirteen‐month‐olds exhibited increased brain activity to IDS for both familiar and unfamiliar words. The results suggested that IDS changed as a function of development and word familiarity and served as an attentional spotlight to increase brain activity to potentially meaningful words.

Typically, the point vowels [i,ɑ,u] are acoustically more peripheral in infant-directed speech (IDS) compared to adult-directed speech (ADS). If caregivers seek to highlight lexically relevant contrasts in IDS, then two sounds that are contrastive should become more distinct, whereas two sounds that are surface realizations of the same underlying sound category should not. To test this prediction, vowels that are phonemically contrastive ([i-ɪ] and [eɪ-ε]), vowels that map onto the same underlying category ([æ- ] and [ε- ]), and the point vowels [i,ɑ,u] were elicited in IDS and ADS by American English mothers of two age groups of infants (four- and eleven-month-olds). As in other work, point vowels were produced in more peripheral positions in IDS compared to ADS. However, there was little evidence of hyperarticulation per se (e.g. [i-ɪ] was hypoarticulated). We suggest that across-the-board lexically based hyperarticulation is not a necessary feature of IDS.

Infants’ preference for faces with direct compared to averted eye gaze, and for infant-directed over adult-directed speech, reflects early sensitivity to social communication. Here, we studied whether infant-directed speech (IDS), could affect the processing of a face with direct gaze in 4-month-olds. In a new ERP paradigm, the word ‘hello’ was uttered either in IDS or adult-direct speech (ADS) followed by an upright or inverted face. We show that the face-specific N290 ERP component was larger when faces were preceded by IDS relative to ADS. Crucially, this effect is specific to upright faces, whereas inverted faces preceded by IDS elicited larger attention-related P1 and Nc. These results suggest that IDS generates communicative expectations in infants. When such expectations are met by a following social stimulus – an upright face – infants are already prepared to process it. When the stimulus is a non-social one –inverted face – IDS merely increases general attention.

Is responsiveness to multimodal, infant-directed talk affected by CNS damage and exposure to cocaine?