Infant Directed Speech in Natural Interaction—Norwegian Vowel Quantity and Quality

An interactive face-to-face setting is used to study natural infant directed speech (IDS) compared to adult directed speech (ADS). With distinctive vowel quantity and vowel quality, Norwegian IDS was used in a natural quasi-experimental design. Six Norwegian mothers were recorded over a period of 6 months alone with their infants and in an adult conversation. Vowel duration and spectral attributes of the vowels /a:/, /i:/ and /u:/, and their short counterparts /a/ /i/ and /u/ were analysed. Repeated measures analyses show that effects of vowel quantity did not differ between ADS and IDS, and for back vowel qualities, the vowel space was shifted upwards in IDS compared to ADS suggesting that fronted articulations in natural IDS may visually enhance speech to infants.     

When infants talk,infants listen: pre‐babbling infants prefer listening to speech with infant vocal properties

To learn to produce speech, infants must effectively monitor and assess their own speech output. Yet very little is known about how infants perceive speech produced by an infant, which has higher voice pitch and formant frequencies compared to adult or child speech. Here, we tested whether pre‐babbling infants (at 4–6 months) prefer listening to vowel sounds with infant vocal properties over vowel sounds with adult vocal properties. A listening preference favoring infant vowels may derive from their higher voice pitch, which has been shown to attract infant attention in infant‐directed speech (IDS). In addition, infants' nascent articulatory abilities may induce a bias favoring infant speech given that 4‐ to 6‐month‐olds are beginning to produce vowel sounds. We created infant and adult /i/ (‘ee’) vowels using a production‐based synthesizer that simulates the act of speaking in talkers at different ages and then tested infants across four experiments using a sequential preferential listening task. The findings provide the first evidence that infants preferentially attend to vowel sounds with infant voice pitch and/or formants over vowel sounds with no infant‐like vocal properties, supporting the view that infants' production abilities influence how they process infant speech. The findings with respect to voice pitch also reveal parallels between IDS and infant speech, raising new questions about the role of this speech register in infant development. Research exploring the underpinnings and impact of this perceptual bias can expand our understanding of infant language development.     

Slow Speech Enhances Younger But Not Older Infants' Perception of Vocal Emotion

Infants attend more to infant-directed speech (IDS) than to adult-directed speech (ADS), but infants also prefer speech judged to be high in positive emotion over less emotional speech regardless of whether it is IDS or ADS. Emotion in voices is often conveyed by absolute pitch, pitch contours, and tempo (or duration). The purpose of our study was to explore how perceived emotion in speech is enhanced or attenuated by duration. We tested 18- and 32-week-old infants for attention to IDS that was either high or low in emotion (as judged by adults) and at two different durations (normal vs. slow). The results showed that 18-week-olds attended more to slow IDS (with affect constant), attended more to high affect (with duration constant), and showed equal attention when affect and duration were juxtaposed. In contrast, 32-week-olds showed greater attention to normal IDS regardless of its emotional level. Slower IDS may enhance younger infants' perception of vocal emotion but does not increase attention in older infants perhaps because they no longer rely on this acoustic cue for emotion. We suggest future studies to help tease apart these interpretations.     

Mommy is only happy! Dutch mothers’ realisation of speech sounds in infant-directed speech expresses emotion,not didactic intent

Exaggeration of the vowel space in infant-directed speech (IDS) is well documented for English, but not consistently replicated in other languages or for other speech-sound contrasts. A second attested, but less discussed, pattern of change in IDS is an overall rise of the formant frequencies, which may reflect an affective speaking style. The present study investigates longitudinally how Dutch mothers change their corner vowels, voiceless fricatives, and pitch when speaking to their infant at 11 and 15 months of age. In comparison to adult-directed speech (ADS), Dutch IDS has a smaller vowel space, higher second and third formant frequencies in the vowels, and a higher spectral frequency in the fricatives. The formants of the vowels and spectral frequency of the fricatives are raised more strongly for infants at 11 than at 15 months, while the pitch is more extreme in IDS to 15-month olds. These results show that enhanced positive affect is the main factor influencing Dutch mothers’ realisation of speech sounds in IDS, especially to younger infants. This study provides evidence that mothers’ expression of emotion in IDS can influence the realisation of speech sounds, and that the loss or gain of speech clarity may be secondary effects of affect.     

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.     

Perception of audiovisual infant directed speech

Infant perception often deals with audiovisual speech input and a first step in processing this input is to perceive both visual and auditory information. The speech directed to infants has special characteristics and may enhance visual aspects of speech. The current study was designed to explore the impact of visual enhancement in infant-directed speech (IDS) on audiovisual mismatch detection in a naturalistic setting. Twenty infants participated in an experiment with a visual fixation task conducted in participants’ homes. Stimuli consisted of IDS and adult-directed speech (ADS) syllables with a plosive and the vowel /a:/, /i:/ or /u:/. These were either audiovisually congruent or incongruent. Infants looked longer at incongruent than congruent syllables and longer at IDS than ADS syllables, indicating that IDS and incongruent stimuli contain cues that can make audiovisual perception challenging and thereby attract infants’ gaze.     

Exploring priming effects of social and non-social attention getters on older infants’ preferences for infant-directed speech

In infant research, various auditory/visual events are often used as attention getters to orient infants to a screen and alert them to upcoming information for their detection, discrimination, and/or recognition. Importantly, the influence of attention-getters on infants’ performance has rarely been systematically evaluated, even though these attention cues could be affecting subsequent information processing. This study investigated whether specific attention-getters could prime infants’ preferences for infant-directed speech (IDS) compared to adult-directed speech (ADS). Both a non-social and a social prime were chosen with the prediction that the social prime would strengthen infants' attention to IDS on a subsequent trial, but the non-social prime would have no differential effect on subsequent attention to either speech type. A total of 20 12- to 18-month old infants were presented with either a nonsocial (rotating form + chimes) or social (smiling female + voice) prime in an infant-controlled, speech preference procedure with both IDS and ADS speech types. Given previous research, we predicted that infants would show significantly more attention on trials during which looking produced IDS, but that this preference would be significantly augmented for infants in the condition receiving a social attention-getter before each trial. Results did not bear out this prediction, although we found a consistent, robust preference for IDS. The results will be discussed in terms of why these attention getters did not affect subsequent processing of two very different speech types, and what future modifications may be necessary in order to examine roles of attention getters in affecting experimental outcomes in infancy research. A secondary benefit of the findings is that we empirically established a growing preference for IDS in infants as old as 18-months of age.     

Does Infant-Directed Speech Help Phonetic Learning? A Machine Learning Investigation

A prominent hypothesis holds that by speaking to infants in infant-directed speech (IDS) as opposed to adult-directed speech (ADS), parents help them learn phonetic categories. Specifically, two characteristics of IDS have been claimed to facilitate learning: hyperarticulation, which makes the categories more separable, and variability, which makes the generalization more robust. Here, we test the separability and robustness of vowel category learning on acoustic representations of speech uttered by Japanese adults in ADS, IDS (addressed to 18- to 24-month olds), or read speech (RS). Separability is determined by means of a distance measure computed between the five short vowel categories of Japanese, while robustness is assessed by testing the ability of six different machine learning algorithms trained to classify vowels to generalize on stimuli spoken by a novel speaker in ADS. Using two different speech representations, we find that hyperarticulated speech, in the case of RS, can yield better separability, and that increased between-speaker variability in ADS can yield, for some algorithms, more robust categories. However, these conclusions do not apply to IDS, which turned out to yield neither more separable nor more robust categories compared to ADS inputs. We discuss the usefulness of machine learning algorithms run on real data to test hypotheses about the functional role of IDS.     

Are Words Easier to Learn From Infant‐ Than Adult‐Directed Speech? A Quantitative Corpus‐Based Investigation

We investigate whether infant‐directed speech (IDS) could facilitate word form learning when compared to adult‐directed speech (ADS). To study this, we examine the distribution of word forms at two levels, acoustic and phonological, using a large database of spontaneous speech in Japanese. At the acoustic level we show that, as has been documented before for phonemes, the realizations of words are more variable and less discriminable in IDS than in ADS. At the phonological level, we find an effect in the opposite direction: The IDS lexicon contains more distinctive words (such as onomatopoeias) than the ADS counterpart. Combining the acoustic and phonological metrics together in a global discriminability score reveals that the bigger separation of lexical categories in the phonological space does not compensate for the opposite effect observed at the acoustic level. As a result, IDS word forms are still globally less discriminable than ADS word forms, even though the effect is numerically small. We discuss the implication of these findings for the view that the functional role of IDS is to improve language learnability.     

Detecting ‘infant‐directedness' in face and voice

Five‐ and 3‐month‐old infants' perception of infant‐directed (ID) faces and the role of speech in perceiving faces were examined. Infants' eye movements were recorded as they viewed a series of two side‐by‐side talking faces, one infant‐directed and one adult‐directed (AD), while listening to ID speech, AD speech, or in silence. Infants showed consistently greater dwell time on ID faces vs. AD faces, and this ID face preference was consistent across all three sound conditions. ID speech resulted in higher looking overall, but it did not increase looking at the ID face per se. Together, these findings demonstrate that infants' preferences for ID speech extend to ID faces.     

Parent coaching at 6 and 10 months improves language outcomes at 14 months: A randomized controlled trial

Previous studies reveal an association between particular features of parental language input and advances in children's language learning. However, it is not known whether parent coaching aimed to enhance specific input components would (a) successfully increase these components in parents' language input and (b) result in concurrent increases in children's language development. The present randomized controlled trial assigned families of typically developing 6‐month‐old infants to Intervention (parent coaching) and Control (no coaching) groups. Families were equivalent on socioeconomic status, infants' gender, and infants' age. Parent coaching took place when infants were 6 and 10 months of age, and included quantitative and qualitative linguistic feedback on the amount of child‐directed speech, back‐and‐forth interactions, and parentese speech style. These variables were derived from each family's first‐person LENA recordings at home. Input variables and infant language were measured at 6, 10, and 14 months. Parent coaching significantly enhanced language input as measured by two social interaction variables: percentage of speech directed to the child and percentage of parentese speech. These two variables were correlated, and were both related to growth in infant babbling between 6 and 14 months. Intervention infants showed greater growth in babbling than Control infants. Furthermore, at 14 months, Intervention infants produced significantly more words than Control infants, as indicated by LENA recordings and parent report via the MacArthur‐Bates Communicative Developmental Inventory. Together, these results indicate that parent coaching can enrich specific aspects of parental language input, and can immediately and positively impact child language outcomes. A video abstract of this article can be viewed at: https://youtu.be/7wqR28gPiwo     

Infant directed speech and the development of speech perception: Enhancing development or an unintended consequence?

Infant directed speech (IDS) is a speech register characterized by simpler sentences, a slower rate, and more variable prosody. Recent work has implicated it in more subtle aspects of language development. Kuhl et al. (1997) demonstrated that segmental cues for vowels are affected by IDS in a way that may enhance development: the average locations of the extreme “point” vowels (/a/, /i/ and /u/) are further apart in acoustic space. If infants learn speech categories, in part, from the statistical distributions of such cues, these changes may specifically enhance speech category learning. We revisited this by asking (1) if these findings extend to a new cue (Voice Onset Time, a cue for voicing); (2) whether they extend to the interior vowels which are much harder to learn and/or discriminate; and (3) whether these changes may be an unintended phonetic consequence of factors like speaking rate or prosodic changes associated with IDS. Eighteen caregivers were recorded reading a picture book including minimal pairs for voicing (e.g., beach/peach) and a variety of vowels to either an adult or their infant. Acoustic measurements suggested that VOT was different in IDS, but not in a way that necessarily supports better development, and that these changes are almost entirely due to slower rate of speech of IDS. Measurements of the vowel suggested that in addition to changes in the mean, there was also an increase in variance, and statistical modeling suggests that this may counteract the benefit of any expansion of the vowel space. As a whole this suggests that changes in segmental cues associated with IDS may be an unintended by-product of the slower rate of speech and different prosodic structure, and do not necessarily derive from a motivation to enhance development.     

Babbling development as seen in canonical babbling ratios: A naturalistic evaluation of all-day recordings

Canonical babbling (CB) is critical in forming foundations for speech. Research has shown that the emergence of CB precedes first words, predicts language outcomes, and is delayed in infants with several communicative disorders. We seek a naturalistic portrayal of CB development, using all-day home recordings to evaluate the influences of age, language, and social circumstances on infant CB production. Thus we address the nature of very early language foundations and how they can be modulated. This is the first study to evaluate possible interactions of language and social circumstance in the development of babbling. We examined the effects of age (6 and 11 months), language/culture (English and Chinese), and social circumstances (during infant-directed speech [IDS], during infant overhearing of adult-directed speech [ADS], or when infants were alone) on canonical babbling ratios (CBR = canonical syllables/total syllables). The results showed a three-way interaction of infant age by infant language/culture by social circumstance. The complexity of the results forces us to recognize that a variety of factors can interact in the development of foundations for language, and that both the infant vocal response to the language/culture environment and the language/culture environment of the infant may change across age.     

Universality and specificity in infant-directed speech: Pitch modifications as a function of infant age and sex in a tonal and non-tonal language

The aim of this study was to investigate the prosodic characteristics of infant-directed speech (IDS) to boys and girls in a tonal (Thai) and non-tonal (Australian English) language. Speech was collected from mothers speaking to infants at birth, and 3, 6, 9, and 12 months, and also to another adult. Mean-F₀, pitch range, and utterance slope-F₀ were extracted, and the integrity of the tonal information in Thai investigated. The age trends across the two languages differed for each of these measures but Australian English IDS was generally more exaggerated than Thai IDS. With respect to sex differences, Australian English mothers used higher mean-F₀, pitch range, and more rising utterances for girls than boys, but Thai mothers used more subdued mean-F₀ and more falling utterances for girls than boys. Despite variations in pitch modifications by Thai and Australian English mothers, overall IDS is more exaggerated than adult-directed speech (ADS) in both languages. Furthermore, tonal information in Thai was only slightly less identifiable in Thai IDS than Thai ADS. The universal features and language-specific differences in IDS are discussed in terms of facilitating infant socialization at younger ages, and language acquisition later in infancy.     

Mothers' and fathers' speech to infants in a teaching situation

The purpose of this study was to compare mothers' and fathers' speech to their preverbal infants in a teaching situation. Thirty-two parents of 16 8-month-olds were asked to teach their infants to put a small cube into a cup. Infant Gender (2) x Birth Order (2) x Parent (2) analyses of variance were performed with repeated measures on parent. Results indicated that fathers issued more utterances and used more words per utterance than did mothers. Although there was no difference in the proportion of imperatives used by mothers and fathers, fathers' imperatives were significantly longer than mothers'; this difference was not evident for utterances that contained indirect instructions. Mothers tended to use more exact repetitions. There were differences in parental speech related to infant gender: Parents directed more utterances, particularly utterances that contained negative statements, imperatives, and exhortations, to girls than to boys. Infant Gender x Parent effects for imperatives and exhortations indicated that these differences were especially true for fathers. Overall, it appeared that fathers made greater efforts to control the situation and to direct their infants' behavior, which might have reflected mothers' and fathers' different perceptions of both their infants' ability and their own role as teachers.     

Look who's talking: speech style and social context in language input to infants are linked to concurrent and future speech development

Language input is necessary for language learning, yet little is known about whether, in natural environments, the speech style and social context of language input to children impacts language development. In the present study we investigated the relationship between language input and language development, examining both the style of parental speech, comparing ‘parentese’ speech to standard speech, and the social context in which speech is directed to children, comparing one‐on‐one (1:1) to group social interactions. Importantly, the language input variables were assessed at home using digital first‐person perspective recordings of the infants' auditory environment as they went about their daily lives (N =26, 11‐ and 14‐months‐old). We measured language development using (a) concurrent speech utterances, and (b) word production at 24 months. Parentese speech in 1:1 contexts is positively correlated with both concurrent speech and later word production. Mediation analyses further show that the effect of parentese speech‐1:1 on infants' later language is mediated by concurrent speech. Our results suggest that both the social context and the style of speech in language addressed to children are strongly linked to a child's future language development.     

Social pretence with mothers and peers at 15 months

Previous research has shown that adults scaffold and direct early infant social pretend play making it difficult to establish infants' own contribution to pretence. To examine infants' social pretence abilities the present study compared infants' social pretend play in interactions with adults and same-age peers, who have similar socio-cognitive competence. Forty-five 15-month-old infants were observed during free-play interactions with their mother and two same-age, same-gender peers. The frequency and duration of parallel and coordinated social pretence were coded during both interactions. Results showed that while infants played pretence with both social partners, they engaged in more and longer coordinated social pretence with their mothers than with peers. Thus, although competent social partners play an important role in scaffolding complex pretence, infants' own socio-cognitive abilities contribute to the development of social pretence and enable them to pretend play with different partners regardless of their competencies.     

The shift in infant preferences for vowel duration and pitch contour between 6 and 10 months of age

This study investigates the influence of the acoustic properties of vowels on 6‐ and 10‐month‐old infants’ speech preferences. The shape of the contour (bell or monotonic) and the duration (normal or stretched) of vowels were manipulated in words containing the vowels /i/ and /u/, and presented to infants using a two‐choice preference procedure. Experiment 1 examined contour shape: infants heard either normal‐duration bell‐shaped and monotonic contours, or the same two contours with stretched duration. The results show that 6‐month‐olds preferred bell to monotonic contours, whereas 10‐month‐olds preferred monotonic to bell contours. In Experiment 2, infants heard either normal‐duration and stretched bell contours, or normal‐duration and stretched monotonic contours. As in Experiment 1, infants showed age‐specific preferences, with 6‐month‐olds preferring stretched vowels, and 10‐month‐olds preferring normal‐duration vowels. Infants’ attention to the acoustic qualities of vowels, and to speech in general, undergoes a dramatic transformation in the final months of the first year, a transformation that aligns with the emergence of other developmental milestones in speech perception.     

Mothers speak differently to infants at‐risk for dyslexia

Dyslexia is a neurodevelopmental disorder manifested in deficits in reading and spelling skills that is consistently associated with difficulties in phonological processing. Dyslexia is genetically transmitted, but its manifestation in a particular individual is thought to depend on the interaction of epigenetic and environmental factors. We adopt a novel interactional perspective on early linguistic environment and dyslexia by simultaneously studying two pre‐existing factors, one maternal and one infant, that may contribute to these interactions; and two behaviours, one maternal and one infant, to index the effect of these factors. The maternal factor is whether mothers are themselves dyslexic or not (with/without dyslexia) and the infant factor is whether infants are at‐/not‐at family risk for dyslexia (due to their mother or father being dyslexic). The maternal behaviour is mothers’ infant‐directed speech (IDS), which typically involves vowel hyperarticulation, thought to benefit speech perception and language acquisition. The infant behaviour is auditory perception measured by infant sensitivity to amplitude envelope rise time, which has been found to be reduced in dyslexic children. Here, at‐risk infants showed significantly poorer acoustic sensitivity than not‐at‐risk infants and mothers only hyperarticulated vowels to infants who were not at‐risk for dyslexia. Mothers’ own dyslexia status had no effect on IDS quality. Parental speech input is thus affected by infant risk status, with likely consequences for later linguistic development.