Patterning of infant vocal behavior

Three-month-old infants received two consecutive 5-minute periods of adult social stimulation. In both periods the adult talked, smiled, and touched the infant and in a natural manner tried to elicit vocalizations from the infant. In the first period the adult became unresponsive for 5 sec contingent upon each infant vocalization (time-out, negative reinforcement). In the second period the infant received the same number of time-out periods at the same intervals but independently of vocal responding (yoked, noncontingent control). Negative reinforcement did not suppress infant vocal rate, but the contingent withdrawal of social stimulation did cause the infant to pause more frequently between vocal responses. These pauses generally occurred immediately after the contingently, as compared with the noncontingently, delivered time-out period. The infant appears to recognize the difference between contingent and noncontingent stimulation and pauses after the occurrence of the former. Adult social reinforcement changes the pattern and not the rate of infant vocal responding.     

Learning how to learn from social feedback: The origins of early vocal development

Infants’ prelinguistic vocalizations reliably organize vocal turn-taking with social partners, creating opportunities for learning to produce the sound patterns of the ambient language. This social feedback loop supporting early vocal learning is well-documented, but its developmental origins have yet to be addressed. When do infants learn that their non-cry vocalizations influence others? To test developmental changes in infant vocal learning, we assessed the vocalizations of 2- and 5-month-old infants in a still-face interaction with an unfamiliar adult. During the still-face, infants who have learned the social efficacy of vocalizing increase their babbling rate. In addition, to assess the expectations for social responsiveness that infants build from their everyday experience, we recorded caregiver responsiveness to their infants’ vocalizations during unstructured play. During the still-face, only 5-month-old infants showed an increase in vocalizing (a vocal extinction burst) indicating that they had learned to expect adult responses to their vocalizations. Caregiver responsiveness predicted the magnitude of the vocal extinction burst for 5-month-olds. Because 5-month-olds show a vocal extinction burst with unfamiliar adults, they must have generalized the social efficacy of their vocalizations beyond their familiar caregiver. Caregiver responsiveness to infant vocalizations during unstructured play was similar for 2- and 5-month-olds. Infants thus learn the social efficacy of their vocalizations between 2 and 5 months of age. During this time, infants build associations between their own non-cry sounds and the reactions of adults, which allows learning of the instrumental value of vocalizing.     

Some Personality Characteristics of the Culturally Disadvantaged

The relationship between sensitive maternal behavior and mother-infant vocalization during feedings was examined in an effort to determine this situational meaning of Ainsworth's concept of sensitivity. Ss were 28 white, middle-class mothers and their infants. Excerpts of home feedings videotaped at 6 and 9 months were coded for frequency of contingent vocal interaction and quality of vocal affect. Sensitive mothers were distinguished from insensitive mothers at each age period by differing vocal patterns. At 6 months, infants of sensitive mothers vocalized significantly less than did infants of insensitive mothers. Mothers in both groups responded to their infants' vocalizations equally as often. At 9 months, infants in both groups vocalized the same amount, while sensitive mothers vocalized more often in response to their infants than did insensitive mothers. The only significant difference in vocal affect was found in the greater positive affect among sensitive mothers at 9 months.     

Fifteen-Month-Old Infants Match Vocal Cues to Intentional Actions

Fifteen-month-old infants detected a violation when an actor performed an action that did not match her preceding vocal cue: The infants looked reliably longer when the actor expressed a humorous vocal cue followed by a sweet action or expressed a sweet vocal cue followed by a humorous action, than when the vocal cue was followed by a matching action. The infants failed to detect the mismatch when one person expressed the vocal cue and another performed the action. The results suggest that by 15 months of age, infants are capable of distinguishing between two types of vocal cues and actions along the positive emotional spectrum: humor and sweetness. Furthermore, they match humorous vocal cues to humorous actions and sweet vocal cues to sweet actions only when the cues and actions are made by the same person.     

Imitation and repetition of prosodic contour in vocal interaction at 3 months

This study investigates vocal imitation of prosodic contour in ongoing spontaneous interaction with 10- to 13-week-old infants. Audio recordings from naturalistic interactions between 20 mothers and infants were analyzed using a vocalization coding system that extracted the pitch and duration of individual vocalizations. Using these data, the authors categorized a sample of 1,359 vocalizations on the basis of 7 predetermined contours. Pairs of identical successive vocalizations were considered to be imitations if they involved both partners or repetitions if they were produced by the same partner. Results show that not only do mothers and infants imitate and repeat prosodic contour types in the course of vocal interaction but they do so selectively. Indeed, different contours are imitated and repeated by each partner. These findings suggest that imitation and repetition of prosodic contours have specific functions for communication and vocal development in the 3rd month of life.     

How do deaf infants attain first signs?

In this study the development and alternation of nonreferential gestures were examined longitudinally in terms of the acquisition of Japanese sign language. Parent–child free‐play sessions in their home were videotaped at every monthly visit. Hand activities produced by two deaf infants of deaf parents are described and analyzed. Nonreferential gestures were observed frequently just before the occurrences of the first signs. They consisted of many rhythmic and repetitious movements. Nonreferential gestures became more complex and the number of them also increased as infants grew up. The comparison of nonreferential gestures and first signs revealed the continuity between them in terms of movements. In conclusion, nonreferential gestures are equivalent to a manual analog of vocal babbling.     

A detector of sonic and ultrasonic vocalizations with frequency readout

An electronic apparatus to detect vocalizations between 4 and 50 kHz and to provide frequency readout is described. A frequency-to-voltage converter changes vocalizations to their analog. A peak-and-hold circuit retains and gates the maximal value of this analog voltage while it is accessed by a chart recorder or computer. Provision is made to lock out noise by inhibiting the device’s response to all signals lower than those associated with a selectable cutoff frequency. In preliminary tests of the apparatus, vocal signals of two rats in a common cage were recorded while the animals were subjected to a brief, intermittent bout of faradic shock to the feet. All recorded vocalizations occurred at frequencies below 26 kHz.     

Temporal Relationships Between Gaze and Vocal Behavior in Prelinguistic and Linguistic Communication

This work reports longitudinal evaluation of the temporal relationships between gaze and vocal behavior addressed to interactive partners (mother or experimenter) in a free-play situation. Thirteen children were observed at the ages of 1;0 and 1;8 during laboratory sessions, and video recordings of free-play interactions with mother and a female experimenter were coded separately for children's vocal behavior (vocalizations and words) and gaze toward their interactive partners. The difference between the observed and expected cooccurrence of these two communicative behaviors was evaluated by transformation into z-scores. The most important findings are related to differences in the temporal relationship observed at age 1;0 between gaze and vocalizations and at age 1;8 between gaze and words. At the earlier age, the infants who exhibited greater coordination between gaze and vocal behavior than was expected by chance (z-score > +1.96) preferred to look at the interlocutor at the beginning of the vocal turn. Instead, when they were older and began to produce words, they frequently looked at the interlocutor at the end of the vocal turn. These results are interpreted as referring to characteristics of conversational competence in the prelinguistic and linguistic periods. Moreover, looking at the interlocutor at the beginning of the vocal turn at age 1;0 was found to be related to language production at age 1:8, highlighting a significant relationship between conversational competence during the prelinguistic period and language acquisition.     

People and objects affect the quality of vocalizations in infants with down syndrome

The vocalizations of eight infants with Down syndrome were recorded longitudinally in relation to different social and non-social contexts. The infants were observed biweekly from 8 to 24 weeks and monthly up to 40 weeks. At each visit the infants were presented with their mother, a female stranger, and a rattle puppet, each alternately active and passive. Each condition lasted 60 sec. The results showed that by 4 months of age, the infants produced different types of vocal sounds in relation to environmental contexts. They produced significantly more melodic (speechlike) sounds, vocalic (non-speechlike) sounds, and emotional (crying, laughing and fussing) sounds when facing people than objects. By 6 months of age, these utterances began to be distinguished between mother and female stranger and active and passive adults. However, within the communicative context the overall amount of vocalic (non-speechlike) sounds produced was larger than the amount of melodic (speechlike) sounds. It is suggested that this low output of melodic sounds in the overall vocal production of these infants may adversely affect the development of more appropriate vocal behaviour.     

The co‐construction of joint action between mothers and 2–4‐month‐old infants: the mother's role

The purpose of this longitudinal study was to describe object‐centred interactions between mothers and their 2–4‐month‐old infants, before and during the emergence of reaching and grasping movements. We hypothesized that when reaching movements emerge at around 3 months, mothers alternate between attention stimulation and reaching stimulation, before joint actions between mother and infant develop around objects. Twelve dyads were recorded when infants were 2 months, 3 months and 4 months. The interactive sessions lasted 5 min. Three age‐appropriate toys the infant could handle were available to the mother. A principal component analysis (PCA) was performed on verbal and non‐verbal maternal behaviours, motor infant behaviours and co‐occurrences of those behaviours. The developmental course of prehension in infants when playing with their mother follows similar pathways, as was described when they are observed alone. Mothers appeared to early scaffold prehension skills by verbal and non‐verbal means. Moreover, maternal behaviours change according to the infant's behaviour, and conversely, infant's behaviours influence maternal behaviours: mother plays first an active part in joint action, while later on, the infant achieves joint action when motor skills develop. Copyright © 2000 John Wiley & Sons, Ltd.     

Reinforcement of vocalizations through contingent vocal imitation

Maternal vocal imitation of infant vocalizations is highly prevalent during face-to-face interactions of infants and their caregivers. Although maternal vocal imitation has been associated with later verbal development, its potentially reinforcing effect on infant vocalizations has not been explored experimentally. This study examined the reinforcing effect of maternal vocal imitation of infant vocalizations using a reversal probe BAB design. Eleven 3- to 8-month-old infants at high risk for developmental delays experienced contingent maternal vocal imitation during reinforcement conditions. Differential reinforcement of other behavior served as the control condition. The behavior of 10 infants showed evidence of a reinforcement effect. Results indicated that vocal imitations can serve to reinforce early infant vocalizations.     

Infants’ vocalizations at 6 months predict their productive vocabulary at one year

Long before their first words, children communicate by using speech-like vocalizations. These protophones might be indicative of infants’ later language development. We here examined infants’ (n = 56) early vocalizations at 6 months (vocal reactivity scale of the IBQ-R) as a predictor of their expressive and receptive language at 12 months (German version of the CDI). Regression analyses revealed vocalizations to significantly predict expressive, but not receptive language. Our findings in German-learning 6-month-olds extend previous predictive evidence of early vocalizations reported for older infants. Together these findings are informative in light of early assessments monitoring typical and atypical language development.     

Vocal imitation between mothers and infants

The aim of the present mixed cross-sectional and longitudinal study was to observe and describe some aspects of vocal imitation in natural mother-infant interaction. Specifically, maternal imitation of infant utterances was observed in relation to the imitative modeling, mirrored equivalence, and social guided learning models of infant speech development. Nine mother-infant dyads were audio-video recorded. Infants were recruited at different ages between 6 and 11 months and followed for 3 months, providing a quasi-longitudinal series of data from 6 through 14 months of age. It was observed that maternal imitation was more frequent than infant imitation even though vocal imitation was a rare maternal response. Importantly, mothers used a range of contingent and noncontingent vocal responses in interaction with their infants. Mothers responded to three-quarters of their infant's vocalizations, including speech-like and less mature vocalization types. The infants’ phonetic repertoire expanded with age. Overall, the findings are most consistent with the social guided learning approach. Infants rarely imitated their mothers, suggests a creative self-motivated learning mechanism that requires further investigation.     

ACOUSTIC ANALYSIS OF ORAL PRODUCTIONS OF INFANTS LATER DIAGNOSED WITH AUTISM AND THEIR MOTHER

Research on early signs of autism in social interactions often focuses on infants’ motor behaviors; few studies have focused on speech characteristics. This study examines infant‐directed speech of mothers of infants later diagnosed with autism (LDA; n = 12) or of typically developing infants (TD; n = 11) as well as infants’ productions (13 LDA, 13 TD). Since LDA infants appear to behave differently in the first months of life, it can affect the functioning of dyadic interactions, especially the first vocal productions, sensitive to expressiveness and emotions sharing. We assumed that in the first 6 months of life, prosodic characteristics (mean duration, mean pitch, and intonative contour types) will be different in dyads with autism. We extracted infants’ and mothers’ vocal productions from family home movies and analyzed the mean duration and pitch as well as the pitch contours in interactive episodes. Results show that mothers of LDA infants use relatively shorter productions as compared to mothers talking to TD infants. LDA infants’ productions are not different in duration or pitch, but they use less complex modulated productions (i.e., those with more than two melodic modulations) than do TD. Further studies should focus on developmental profiles in the first year, analyzing prosody monthly.     

Infants use meter to categorize rhythms and melodies: implications for musical structure learning

Little is known about whether infants perceive meter, the underlying temporal structure of music. We employed a habituation paradigm to examine whether 7-month-old infants could categorize rhythmic and melodic patterns on the basis of the underlying meter, which was implied from event and accent frequency of occurrence. In Experiment 1, infants discriminated duple and triple classes of rhythm on the basis of implied meter. Experiment 2 replicated this result while controlling for rhythmic grouping structure, confirming that infants perceived metrical structure despite occasional ambiguities and conflicting group structure. In Experiment 3, infants categorized melodies on the basis of contingencies between metrical position and pitch. Infants presented with metrical melodies detected reversals of pitch/meter contingencies, while infants presented with non-metrical melodies showed no preference. Results indicate that infants can infer meter from rhythmic patterns, and that they may use this metrical structure to bootstrap their knowledge acquisition in music learning.     

The timing of verbal/vocal communications between mothers and their infants: a longitudinal cross-cultural comparison

Early dialogues between parent and child constitute an important factor for the acquisition of culture and hence verbal interaction is considered to be a universal parenting system. Parenting strategies and socialization practices are strongly influenced by the cultural conception of the self, prototypically defined as the model of independence and interdependence. Our study focuses on the temporal organization of spontaneous verbal/vocal behavior of 20 German middle-class and 28 Cameroonian Nso mother–infant dyads. The infants and their mothers were observed weekly in a 5 min free-play interaction scene from 0 to 3 months of age. We hypothesized to find different amounts of vocalization time, synchronous vocalizations, and contingent maternal responses in the verbal/vocal patterns of the two samples. The findings indicate cross-cultural differences in the temporal structure of verbal/vocal interactions already during the first three months of life, reflecting underlying differences in the culture-specific modes of verbal interaction.     

Social feedback to infants' babbling facilitates rapid phonological learning

Infants' prelinguistic vocalizations are rarely considered relevant for communicative development. As a result, there are few studies of mechanisms underlying developmental changes in prelinguistic vocal production. Here we report the first evidence that caregivers' speech to babbling infants provides crucial, real-time guidance to the development of prelinguistic vocalizations. Mothers of 9.5-month-old infants were instructed to provide models of vocal production timed to be either contingent or noncontingent on their infants' babbling. Infants given contingent feedback rapidly restructured their babbling, incorporating phonological patterns from caregivers' speech, but infants given noncontingent feedback did not. The new vocalizations of the infants in the contingent condition shared phonological form but not phonetic content with their mothers' speech. Thus, prelinguistic infants learned new vocal forms by discovering phonological patterns in their mothers' contingent speech and then generalizing from these patterns.     

EVALUATION OF AN ENHANCED STIMULUS‐STIMULUS PAIRING PROCEDURE TO INCREASE EARLY VOCALIZATIONS OF CHILDREN WITH AUTISM

Evidence to support stimulus‐stimulus pairing (SSP) in speech acquisition is less than robust, calling into question the ability of SSP to reliably establish automatically reinforcing properties of speech and limiting the procedure's clinical utility for increasing vocalizations. We evaluated the effects of a modified SSP procedure on low‐frequency within‐session vocalizations that were further strengthened through programmed reinforcement. Procedural modifications (e.g., interspersed paired and unpaired trials) were designed to increase stimulus salience during SSP. All 3 participants, preschoolers with autism, showed differential increases of target over nontarget vocal responses during SSP. Results suggested an automatic reinforcement effect of SSP, although alternative interpretations are discussed, and suggestions are made for future research to determine the utility of SSP as a clinical intervention for speech‐delayed children.     

Infant vocal development during the first 6 months: speech quality and melodic complexity

The early development of infant non‐distress vocalizations was investigated in this study. Thirteen infants, from 4 to 24 weeks of age, and their mothers were observed weekly in a face‐to‐face interaction situation. The speech quality (syllabic versus vocalic) and melodic complexity (simple versus complex) of infant vocalizations were coded independently. Based on speech quality and melodic complexity, four types of infant non‐distress vocalizations were categorized: simple and complex syllabic (speech‐like) vocalizations as well as simple and complex vocalic (non‐speech‐like) vocalizations. Results showed that complex syllabic sounds were of longer duration and complex vocalic sounds were less frequent than the other types of vocalizations. Curvilinear developmental trends were found in the rate of simple vocalic sounds and in the mean duration of complex syllabic sounds. Furthermore, before 4 months of age, vocalic sounds were more likely to be associated with simple melodic contours, after which syllabic sounds were more likely to be associated with complex melodic contours. A dynamic systems perspective on the early development of infant vocalization is discussed. Copyright © 2000 John Wiley & Sons, Ltd.