Adult-directed Speech Research Articles

Fathers' Infant-Directed Speech in a Small-Scale Society.

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.

Audio-Visual Perception of Gender by Infants Emerges Earlier for Adult-Directed Speech.

Early multisensory perceptual experiences shape the abilities of infants to perform socially-relevant visual categorization, such as the extraction of gender, age, and emotion from faces. Here, we investigated whether multisensory perception of gender is influenced by infant-directed (IDS) or adult-directed (ADS) speech. Six-, 9-, and 12-month-old infants saw side-by-side silent video-clips of talking faces (a male and a female) and heard either a soundtrack of a female or a male voice telling a story in IDS or ADS. Infants participated in only one condition, either IDS or ADS. Consistent with earlier work, infants displayed advantages in matching female relative to male faces and voices. Moreover, the new finding that emerged in the current study was that extraction of gender from face and voice was stronger at 6 months with ADS than with IDS, whereas at 9 and 12 months, matching did not differ for IDS versus ADS. The results indicate that the ability to perceive gender in audiovisual speech is influenced by speech manner. Our data suggest that infants may extract multisensory gender information developmentally earlier when looking at adults engaged in conversation with other adults (i.e., ADS) than when adults are directly talking to them (i.e., IDS). Overall, our findings imply that the circumstances of social interaction may shape early multisensory abilities to perceive gender.

Are Homophones Acoustically Distinguished in Child-Directed Speech?

ABSTRACTMany approaches to early word learning posit that children assume a one-to-one mapping of form and meaning. However, children’s early vocabularies contain homophones, words that violate that assumption. Children might learn such words by exploiting prosodic differences between homophone meanings that are associated with lemma frequency (Gahl, 2008). Such differences have not yet been documented in children’s natural language experience and the exaggerated prosody of child-directed speech could either mask the subtle distinctions reported in adult-directed speech or enhance them. This study measured the duration, vowel characteristics, and pitch information of homophone tokens taken from a corpus of child-directed speech. The results show that homophone meanings are acoustically distinct in child-directed speech as a function of lemma frequency, particularly in utterance-final positions. Such distinctions may allow children to maintain separate phonetic representations of homophones until their cognitive and linguistic abilities are robust to violations of the one-to-one bias.

Who's my little monkey? Effects of infant-directed speech on visual retention in infant rhesus macaques.

Both human and nonhuman primate adults use infant-directed facial and vocal expressions across many contexts when interacting with infants (e.g., feeding, playing). This infant-oriented style of communication, known as infant-directed speech (IDS), seems to benefit human infants in numerous ways, including facilitating language acquisition. Given the variety of contexts in which adults use IDS, we hypothesized that IDS supports learning beyond the linguistic domain and that these benefits may extend to nonhuman primates. We exposed 2.5-month-old rhesus macaque infants (N=15) to IDS, adult-directed speech (ADS), and a non-social control (CTR) during a video presentation of unrelated stimuli. After a 5- or 60-minute delay, infants were shown the familiar video side-by-side with a novel video. Infants exhibited a novelty preference after the 5-minute delay, but not after the 60-minute delay, in the ADS and CTR conditions, and a novelty preference in the IDS condition only after the 60-minute delay. These results are the first to suggest that exposure to IDS affects infants' long-term memory, even in non-linguistic animals.

Infant-directed speech reduces English-learning infants' preference for trochaic words.

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.

Infant-directed speech is consistent with teaching.

Infant-directed speech (IDS) has distinctive properties that differ from adult-directed speech (ADS). Why it has these properties-and whether they are intended to facilitate language learning-is a matter of contention. We argue that much of this disagreement stems from lack of a formal, guiding theory of how phonetic categories should best be taught to infantlike learners. In the absence of such a theory, researchers have relied on intuitions about learning to guide the argument. We use a formal theory of teaching, validated through experiments in other domains, as the basis for a detailed analysis of whether IDS is well designed for teaching phonetic categories. Using the theory, we generate ideal data for teaching phonetic categories in English. We qualitatively compare the simulated teaching data with human IDS, finding that the teaching data exhibit many features of IDS, including some that have been taken as evidence IDS is not for teaching. The simulated data reveal potential pitfalls for experimentalists exploring the role of IDS in language learning. Focusing on different formants and phoneme sets leads to different conclusions, and the benefit of the teaching data to learners is not apparent until a sufficient number of examples have been provided. Finally, we investigate transfer of IDS to learning ADS. The teaching data improve classification of ADS data but only for the learner they were generated to teach, not universally across all classes of learners. This research offers a theoretically grounded framework that empowers experimentalists to systematically evaluate whether IDS is for teaching. (PsycINFO Database Record

Levels of prominence in Spanish infant-directed speech

Research on Spanish prosody in adult-directed speech (ADS) (Ortega-Llebaria & Prieto 2005, Ortega-Llebaria & Prieto 2011) shows evidence for three acoustic levels of prominence: stressed and focused, stressed and unfocused, and unstressed and unfocused. We tested whether Spanish infant-directed speech (IDS) contains the same levels of prosodic prominence as ADS. In order to test this hypothesis, 30-minute play sessions between adult Spanish-speaking females of Latin American origin (n = 12) and 12-month old infants were recorded. We extracted target words from the recordings containing stressed and unstressed /a/, /e/, /i/, and /o/ in non-final position. Voicesauce (Shue et al 2011) was then used to obtain acoustic correlates of stress in Spanish: pitch, duration, intensity. We also labeled pitch accents using SpToBI conventions (Estebas Vilaplana & Prieto 2009). Latent class analyses to be performed on the data will determine the number of distinct prominence levels present in Spanish IDS as realized by Latin American speakers.

Acoustic correlates to word order in Infant- and adult directed speech: A cross-linguistic study

The acoustic realization of phrasal prominence correlates systematically with the order of Verbs and Objects in natural languages. Prominence is realized as a durational contrast in V(erb)-O(bject) languages (English: short-long, to [Ro]me), and as a pitch/intensity contrast in O(bject)-V(erb) languages (Japanese: high-low, [‘To] kyo ni). Seven-month-old infants can use phrasal prominence to segment unknown artificial languages. This information might thus allow prelexical infants to learn the basic word order of their native language(s). The present study investigates whether this differing realization of phrasal prominence is also found in I(nfant) D(irected) S(peech), previously unexamined speech style. We recorded 15 adult native talkers of languages with opposite word orders producing target phrases (English: VO, e.g., behind furniture, Japanese: OV, e.g., jisho niwa) embedded in carrier sentences, both in A(dult) D(irected) S(peech) and IDS, and conducted acoustic analysis of the phrases (i.e., pitch maximum, mean pitch and intensity, duration). The results revealed the expected contrast in pitch in Japanese IDS and a similar trend in ADS. In English, the predicted durational contrast was found in ADS, additionally accompanied by a pitch contrast. Interestingly, a pitch contrast but no durational contrast was found in IDS.

Developmental progressions in the harmonic structure of infant-directed speech

Caregivers speak differently to infants than to adults early in life. Previous studies of this special register, “motherese,” have sought to identify key differences in voice quality between infant-directed and adult-directed speech. Acoustic properties most salient to infants appear to reside in exaggerations of prosodic structure, but these findings are limited by speech analysis techniques that do not fully capture the acoustic structure of the maternal voice or the way motherese changes over the course of development. In this study, multitaper analysis was used to measure developmental progressions in the complete harmonic structure of the maternal voice. Samples of adult- and infant-directed speech were extracted from home audio recordings of 20 mothers collected monthly from 0-24 months using LENA technology. Multitaper analysis was used to calculate the time-varying amplitude and phase of every harmonic component, the residual noise component, and the spectral envelope, permitting a complete statis...

Mature neural responses to Infant-Directed Speech but not Adult-Directed Speech in Pre-Verbal Infants.

Infant directed speech (IDS), the speech register adults use when talking to infants, has been shown to have positive effects on attracting infants’ attention, language learning, and emotional communication. Here event related potentials (ERPs) are used to investigate the neural coding of IDS and ADS (adult directed speech) as well as their discrimination by both infants and adults. Two instances of the vowel /i/, one extracted from ADS and one from IDS, were presented to 9-month-old infants and adults in two oddball conditions: ADS standard/IDS deviant and IDS standard/ADS deviant. In Experiment 1 with adults, the obligatory ERPs that code acoustic information were different for ADS and IDS; and discrimination, indexed by mismatch negativity (MMN) responses, showed that IDS and ADS deviants were discriminated equally well; although, the P3a response was larger for IDS suggesting it captured adults’ attention more than did ADS. In infants the obligatory responses did not differ for IDS and ADS, but for discrimination, while IDS deviants generated both a slow-positive mismatch response (MMR) as well as an adult-like MMN, the ADS deviants generated only an MMR. The presence of a mature adult-like MMN suggests that the IDS stimulus is easier to discriminate for infants.

Utterances in infant-directed speech are shorter, not slower

It has become a truism in the literature on infant-directed speech (IDS) that IDS is pronounced more slowly than adult-directed speech (ADS). Using recordings of 22 Japanese mothers speaking to their infant and to an adult, we show that although IDS has an overall lower mean speech rate than ADS, this is not the result of an across-the-board slowing in which every vowel is expanded equally. Instead, the speech rate difference is entirely due to the effects of phrase-final lengthening, which disproportionally affects IDS because of its shorter utterances. These results demonstrate that taking utterance-internal prosodic characteristics into account is crucial to studies of speech rate.

Learnability of prosodic boundaries: Is infant-directed speech easier?

This study explores the long-standing hypothesis that the acoustic cues to prosodic boundaries in infant-directed speech (IDS) make those boundaries easier to learn than those in adult-directed speech (ADS). Three cues (pause duration, nucleus duration, and pitch change) were investigated, by means of a systematic review of the literature, statistical analyses of a corpus of Japanese, and machine learning experiments. The review of previous work revealed that the effect of register on boundary cues is less well established than previously thought, and that results often vary across studies for certain cues. Statistical analyses run on a large database of mother-child and mother-interviewer interactions showed that the duration of a pause and the duration of the syllable nucleus preceding the boundary are two cues which are enhanced in IDS, while f0 change is actually degraded in IDS. Supervised and unsupervised machine learning techniques applied to these acoustic cues revealed that IDS boundaries were consistently better classified than ADS ones, regardless of the learning method used. The role of the cues examined in this study and the importance of these findings in the more general context of early linguistic structure acquisition is discussed.

The Influence of Child-Directed Speech on Word Learning and Comprehension.

This paper describes an investigation into the function of child-directed speech (CDS) across development. In the first experiment, 10-21-month-olds were presented with familiar words in CDS and trained on novel words in CDS or adult-directed speech (ADS). All children preferred the matching display for familiar words. However, only older toddlers in the CDS condition preferred the matching display for novel words. In Experiment 2, children 3-6 years of age were presented with a sentence comprehension task in CDS or ADS. Older children performed better overall than younger children with 5- and 6-year-olds performing above chance regardless of speech condition, while 3- and 4-year-olds only performed above chance when the sentences were presented in CDS. These findings provide support for the theory that CDS is most effective at the beginning of acquisition for particular constructions (e.g. vocabulary acquisition, syntactic comprehension) rather than at a particular age or for a particular task.

Sixteen-Month-Old Infants’ Segment Words from Infant- and Adult-Directed Speech

ABSTRACTOne of the first challenges facing the young language learner is the task of segmenting words from a natural language speech stream, without prior knowledge of how these words sound. Studies with younger children find that children find it easier to segment words from fluent speech when the words are presented in infant-directed speech, i.e., the kind of speech typically directed toward infants, compared to adult-directed speech. The current study examines whether infants continue to display similar differences in their segmentation of infant- and adult-directed speech later in development. We show that 16-month-old infants successfully segment words from a natural language speech stream presented in the adult-directed register and recognize these words later when presented in isolation. Furthermore, there were no differences in infants’ ability to segment words from infant- and adult-directed speech at this age, although infants’ success at segmenting words from adult-directed speech correlated with their vocabulary size.

Quantity of mothers' and fathers' speech to sons and daughters

The literature on child-directed speech has shown that mothers, on average, talk to their children with higher token frequency than fathers, but fathers may use more complex language or more variable word types. Other recent research has shown that mothers may use greater fundamental frequency variability and range when talking to their children, as compared with fathers who showed no fundamental frequency differences between child- and adult-directed speech. There is also some evidence that mothers may talk more often with their daughters than sons. Whether fathers are sensitive to the sex of their children is unknown. This work looks at the quantity of fathers' and mothers' speech to their sons and daughters from a large database of daylong recordings collected from a body-worn recorder on preschool boys and girls in their natural daily environments. The recordings were analyzed offline with automatic speech processing software which tallied the quantity of syllables produced for all individual talkers and the conversational exchanges among mothers and fathers with their sons and daughters. Contrary to previous findings, results indicate that fathers may engage more often with their sons than daughters, but mothers are not sensitive to child sex.

Two Different Communication Genres and Implications for Vocabulary Development and Learning to Read

This study examined potential differences in vocabulary found in picture books and adult’s speech to children and to other adults. Using a small sample of various sources of speech and print, Hayes observed that print had a more extensive vocabulary than speech. The current analyses of two different spoken language databases and an assembled picture book corpus replicated and extended these findings. The vocabulary in picture books was more extensive than that found in child-directed speech (CDS) and even adult-directed speech (ADS). The likelihood of observing a rare word not contained in the most common 5,000 words in English was more likely in a corpus of picture books than in two different corpora of CDS. The likelihood of a rare word in the picture books was even greater than that found in ADS. It is proposed that these differences are more indicative of informal versus formal language rather than the spoken versus written modalities per se. Nonetheless, these results highlight the value of rich read-aloud experiences for vocabulary development and potentially for reading comprehension once written language is acquired. These findings are described in terms of a distinction between formal and informal language, which has implications for views of literacy, cognitive and linguistic development, and learning to read.

Content words in Hebrew child-directed speech

The goal of the study was to examine whether the ‘noun-bias’ phenomenon, which exists in the lexicon of Hebrew-speaking children, also exists in Hebrew child-directed speech (CDS) as well as in Hebrew adult-directed speech (ADS). In addition, we aimed to describe the use of the different classes of content words in the speech of Hebrew-speaking parents to their children at different ages compared to the speech of parents to adults (ADS). Thirty infants (age range 8:5–33 months) were divided into three stages according to age: pre-lexical, single-word, and early grammar. The ADS corpus included 18 Hebrew-speaking parents of children at the same three stages of language development as in the CDS corpus. The CDS corpus was collected from parent–child dyads during naturalistic activities at home: mealtime, bathing, and play. The ADS corpus was collected from parent–experimenter interactions including the parent watching a video and then being interviewed by the experimenter. 200 utterances of each sample were transcribed, coded for types and tokens and analyzed quantitatively and qualitatively. Results show that in CDS, when speaking to infants of all ages, parents’ use of types and tokens of verbs and nouns was similar and significantly higher than their use of adjectives or adverbs. In ADS, however, verbs were the main lexical category used by Hebrew-speaking parents in both types and tokens. It seems that both the properties of the input language (e.g. the pro-drop parameter) and the interactional styles of the caregivers are important factors that may influence the high presence of verbs in Hebrew-speaking parents’ ADS and CDS. The negative correlation between the widespread use of verbs in the speech of parents to their infants and the ‘noun-bias’ phenomenon in the Hebrew-child lexicon will be discussed in detail.

Phonetic Modification of Vowel Space in Storybook Speech to Infants up to 2 Years of Age

A large body of literature has indicated vowel space area expansion in infant-directed (ID) speech compared with adult-directed (AD) speech, which may promote language acquisition. The current study tested whether this expansion occurs in storybook speech read to infants at various points during their first 2 years of life. In 2 studies, mothers read a storybook containing target vowels in ID and AD speech conditions. Study 1 was longitudinal, with 11 mothers recorded when their infants were 3, 6, and 9 months old. Study 2 was cross-sectional, with 48 mothers recorded when their infants were 3, 9, 13, or 20 months old (n=12 per group). The 1st and 2nd formants of vowels /i/, /ɑ/, and /u/ were measured, and vowel space area and dispersion were calculated. Across both studies, 1st and/or 2nd formant frequencies shifted systematically for /i/ and /u/ vowels in ID compared with AD speech. No difference in vowel space area or dispersion was found. The results suggest that a variety of communication and situational factors may affect phonetic modifications in ID speech, but that vowel space characteristics in speech to infants stay consistent across the first 2 years of life.

Vowel space characteristics of speech directed to children with and without hearing loss.

This study examined vowel characteristics in adult-directed (AD) and infant-directed (ID) speech to children with hearing impairment who received cochlear implants or hearing aids compared with speech to children with normal hearing. Mothers' AD and ID speech to children with cochlear implants (Study 1, n=20) or hearing aids (Study 2, n=11) was compared with mothers' speech to controls matched on age and hearing experience. The first and second formants of vowels /i/, /ɑ/, and /u/ were measured, and vowel space area and dispersion were calculated. In both studies, vowel space was modified in ID compared with AD speech to children with and without hearing loss. Study 1 showed larger vowel space area and dispersion in ID compared with AD speech regardless of infant hearing status. The pattern of effects of ID and AD speech on vowel space characteristics in Study 2 was similar to that in Study 1, but depended partly on children's hearing status. Given previously demonstrated associations between expanded vowel space in ID compared with AD speech and enhanced speech perception skills, this research supports a focus on vowel pronunciation in developing intervention strategies for improving speech-language skills in children with hearing impairment.

Fundamental frequency of speech directed to children who have hearing loss

Studies of child-directed speech (CDS) have shown that when talking to children, parents systematically use (among other strategies) increased fundamental frequency (F0). Lombard effects such as increased F0 have also been documented when addressing a listener who is hard-of-hearing (HH). Here, we examine F0 of mothers and fathers in families with HH versus typically developing (TD) children in CDS and adult-directed speech (ADS) contexts. Whole-day audio recordings were collected by a child-worn audio recorder and analyzed by automatic speech recognition (ASR) software to identify segments of vocal activity by children and their parents (LENA Research Foundation, Boulder, CO). Custom software extracted F0 values in all conditions. We found that (1) mothers are much more systematic in their use of CDS than fathers, (2) parents do not appear to be sensitive to the hearing status of their children, and (3) parents of HH children may have higher overall F0 irrespective of CDS or ADS. Results suggest that mothers and fathers do not use F0 with their children in the same way, and parents of children with hearing loss may have certain global F0 characteristics not shared by parents of TD children.