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.     

The Effects of Motor and Vocal Response Interruption and Redirection on Vocal Stereotypy and Appropriate Vocalizations

Stereotypy has been defined as repetitive vocal or motor behaviors that are noncontextual with invariant topographies. One intervention to reduce vocal stereotypy and increase appropriate vocalizations is response interruption and redirection (RIRD). Previous research has suggested that RIRD's behavioral mechanism consists of punishment. The purpose of this study was to extend this research by comparing two procedures, namely, vocal and motor RIRD contingent upon the occurrence of vocal stereotypy and to evaluate concomitant increases in appropriate vocalizations. A multiple treatment reversal design was used to compare the effectiveness of both interventions on five children diagnosed with an Autism Spectrum Disorder. Results suggested that both demand topographies were equally effective in reducing vocal stereotypy and increasing appropriate vocalizations. This research replicates previous findings that have suggested that RIRD is a punishment procedure. Copyright © 2015 John Wiley & Sons, Ltd.     

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.     

Co‐occurences of preverbal vocal behavior and motor action in early infancy

This study reports on co‐occurrence of vocal behaviors and motor actions in infants in the prelinguistic stage. Four Japanese infants were studied longitudinally from the age of 6 months to 11 months. For all the infants, a 40 min sample was coded for each monthly period. The vocalizations produced by the infants co‐occurred with their rhythmic actions with high frequency, particularly in the period preceding the onset of canonical babbling. Acoustical analysis was conducted on the vocalizations recorded before and after the period when co‐occurrence took place most frequently. Among the vocalizations recorded in the period when co‐occurrence appeared most frequently, those that co‐occurred with rhythmic action had significantly shorter syllable duration and shorter formant‐frequency transition duration compared with those that did not co‐occur with rhythmic action. The rapid transitions and short syllables were similar to patterns of duration found in mature speech. The acoustic features remained even after co‐occurrence disappeared. These findings suggest that co‐occurrence of rhythmic action and vocal behavior may contribute to the infant’s acquisition of the ability to perform the rapid glottal and articulatory movements that are indispensable for spoken language acquisition.     

Infants' responses to mothers' imitative behaviors

Several investigators have suggested that young infants' smiles and vocalizations following their mothers' imitative behaviors might reflect infant recognition that the mother's behavior is imitative or at least contingent. This study investigated whether infants smile and vocalize more frequently subsequent to maternal imitative than non-imitative behavior during both spontaneous and imitative face-to-face interactions. Fourteen 3 1/2-month-old infants and their mothers were videotaped in these two face-to-face interaction situations. The infants vocalized more frequently during the imitative situation and infant vocalizations plus simultaneous smiling, and vocalizations occurred more often following maternal imitative than non-imitative behavior. Although these data suggest that infant vocalizations and simultaneous smiles and vocalizations may reflect the infants' recognition of maternal imitative behavior, they do not establish definitively that it is the imitation per se vs. the contingency aspect that is recognized by the infant.     

Influence of a televised model's vocalization pattern on infants

To assess the influence of a televised model's vocalizations on the vocal patterns of infant viewers, 32 infants at 6 months of age were presented either a televised adult model repeating a novel phoneme pattern (/ba/ba/ba/ba) or a control televised presentation of adult conversation selected from typical daytime programming. Sequential analyses of infant vocalizations revealed that infants exposed to the televised model altered their vocalization pattern, as indicated by a significant increase over base line levels in their production of a patterned series of discrete vocalizations. Infants exposed to the televised conversation showned no increase in this pattern of vocalization, and none of the infants in the study produced the novel phoneme (/ba/). The results indicate that televised presentation of discrete, repeated vocalizations can have an influence on the vocalization pattern of infants. The potential role of television in infant development is discussed.     

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.     

What bats have to say about speech and language

Understanding the biological foundations of language is vital to gaining insight into how the capacity for language may have evolved in humans. Animal models can be exploited to learn about the biological underpinnings of shared human traits, and although no other animals display speech or language, a range of behaviors found throughout the animal kingdom are relevant to speech and spoken language. To date, such investigations have been dominated by studies of our closest primate relatives searching for shared traits, or more distantly related species that are sophisticated vocal communicators, like songbirds. Herein I make the case for turning our attention to the Chiropterans, to shed new light on the biological encoding and evolution of human language-relevant traits. Bats employ complex vocalizations to facilitate navigation as well as social interactions, and are exquisitely tuned to acoustic information. Furthermore, bats display behaviors such as vocal learning and vocal turn-taking that are directly pertinent for human spoken language. Emerging technologies are now allowing the study of bat vocal communication, from the behavioral to the neurobiological and molecular level. Although it is clear that no single animal model can reflect the complexity of human language, by comparing such findings across diverse species we can identify the shared biological mechanisms likely to have influenced the evolution of human language.     

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.     

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.     

The neuroethology of primate vocal communication: substrates for the evolution of speech

In this article, we review behavioral and neurobiological studies of the perception and use of species-specific vocalizations by non-human primates. At the behavioral level, primate vocal perception shares many features with speech perception by humans. These features include a left-hemisphere bias towards conspecific vocalizations, the use of temporal features for identifying different calls, and the use of calls to refer to objects and events in the environment. The putative neural bases for some of these behaviors have been revealed by recent studies of the primate auditory and prefrontal cortices. These studies also suggest homologies with the human language circuitry. Thus, a synthesis of cognitive, ethological and neurobiological approaches to primate vocal behavior is likely to yield the richest understanding of the neural bases of speech perception, and might also shed light on the evolutionary precursors to language.     

Sensorimotor foundations of speech perception in infancy

The perceptual system for speech is highly organized from early infancy. This organization bootstraps young human learners’ ability to acquire their native speech and language from speech input. Here, we review behavioral and neuroimaging evidence that perceptual systems beyond the auditory modality are also specialized for speech in infancy, and that motor and sensorimotor systems can influence speech perception even in infants too young to produce speech-like vocalizations. These investigations complement existing literature on infant vocal development and on the interplay between speech perception and production systems in adults. We conclude that a multimodal speech and language network is present before speech-like vocalizations emerge.     

Expressive timing and interactional synchrony between mothers and infants: cultural similarities, cultural differences, and the immigration experience

The spontaneous vocal interactions of 30 mothers and their 2- to 5-month-old infants from India, France, and the United States were analyzed using an acoustic analysis method. Similarities and differences in vocal interactional patterns were highlighted between the three groups. On the one hand, in the three cultural contexts mother–infant vocal interaction was found to be organized around hierarchical temporal intervals of the same approximate length, had the same balance between regular rhythm and variation (“expressive timing”), and manifested the same coordination between mother and infant vocalization (“interactional synchrony”). On the other hand, the three groups also revealed cultural variability. The Indian mothers had more togetherness with their babies, as indexed by less space between vocal turns and more overlap of mother and baby vocalizations. They also produced a higher ratio of nonverbal to verbal vocalizations. The spontaneous vocal interactions of a group of 30 Indian immigrant dyads were also studied. With respect to culturally variable characteristics, the vocal interaction of immigrant dyads living in the United States showed signs of change in the direction of the host culture. With respect to characteristics shared by all three nonimmigrant groups, the immigrant dyads showed lower levels of expressive timing and interactional synchrony than the nonimmigrant group as a whole.     

Auditory--visual cross-modal perception of communicative stimuli in tufted capuchin monkeys (Cebus apella)

Research on cross-modal performance in nonhuman primates is limited to a small number of sensory modalities and testing methods. To broaden the scope of this research, the authors tested capuchin monkeys (Cebus apella) for a seldom-studied cross-modal capacity in nonhuman primates, auditory-visual recognition. Monkeys were simultaneously played 2 video recordings of a face producing different vocalizations and a sound recording of 1 of the vocalizations. Stimulus sets varied from naturally occurring conspecific vocalizations to experimentally controlled human speech stimuli. The authors found that monkeys preferred to view face recordings that matched presented vocal stimuli. Their preference did not differ significantly across stimulus species or other stimulus features. However, the reliability of the latter set of results may have been limited by sample size. From these results, the authors concluded that capuchin monkeys exhibit auditory-visual cross-modal perception of conspecific vocalizations.     

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.     

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.     

Maternal and infant affect at 4 months predicts performance and verbal IQ at 4 and 7 years in a diverse population

Using existing longitudinal data from 570 infants in the Maternal Lifestyle Study, we explored the predictive value of maternal and infant affect and maternal vocalizations during 2 minutes of face‐to‐face interactions at 4 months on IQ scores at 4.5 and 7 years. After controlling for demographic factors, maternal depression, and prenatal drug exposure, maternal positive affect and maternal positive vocalizations emerged as predictors of both verbal and performance IQ at 4.5 and 7 years. Although infant positive affect during the interaction with the mother was not predictive of these outcome measures, infant positive affect towards an examiner predicted verbal but not performance IQ at 4.5 years. These results suggest that maternal positive affect may index emotional engagement in interaction that facilitates both verbal and nonverbal cognitive development, while infant social positive affect is specifically related to the acquisition of verbal reasoning abilities. These findings are significant because they are based on a discrete snapshot of observable behavior in infancy (just 2 minutes of interaction), because they extend the range of maternal behaviors and characteristics known to support positive developmental outcomes, and because they are derived from high‐risk infants where prevention efforts may be beneficial. Potential mechanisms for these associations are discussed, as are the clinical implications for identifying dyads most in need of targeted interventions.     

Prelinguistic evolution in early hominins: whence motherese?

In order to formulate hypotheses about the evolutionary underpinnings that preceded the first glimmerings of language, mother-infant gestural and vocal interactions are compared in chimpanzees and humans and used to model those of early hominins. These data, along with paleoanthropological evidence, suggest that prelinguistic vocal substrates for protolanguage that had prosodic features similar to contemporary motherese evolved as the trend for enlarging brains in late australopithecines/early Homo progressively increased the difficulty of parturition, thus causing a selective shift toward females that gave birth to relatively undeveloped neonates. It is hypothesized that hominin mothers adopted new foraging strategies that entailed maternal silencing, reassuring, and controlling of the behaviors of physically removed infants (i.e., that shared human babies' inability to cling to their mothers' bodies). As mothers increasingly used prosodic and gestural markings to encourage juveniles to behave and to follow, the meanings of certain utterances (words) became conventionalized. This hypothesis is based on the premises that hominin mothers that attended vigilantly to infants were strongly selected for, and that such mothers had genetically based potentials for consciously modifying vocalizations and gestures to control infants, both of which receive support from the literature.     

Mother–infant behavioral interactions in teenage and adult mothers during the first six months postpartum: Relations with infant development

The purpose of this study was to compare adolescent mothers' (high‐risk group), at‐risk adult mothers' (moderate‐risk group), and no‐risk adult mothers' (low‐risk group) behavioral interactions at one and six months postpartum, and to examine the relationships between maternal behaviors and infant developmental scores on the Bayley scales. Results indicated that high‐risk teenage mothers and moderate‐risk adult mothers vocalized less and had lower contingency rating scores compared to low‐risk adult mothers. Also, infants in the high‐risk and moderate‐risk groups obtained lower mental scores at six months compared to the low‐risk group. Moderate stability across time was found for maternal vocalizations and infant scores on the mental scale. Maternal vocalizations and behavioral contingency rating scores at one month were associated with infants' six‐month performance on the Bayley scales. Specific intervention strategies were discussed with the aim of targeting and improving early maternal behavioral patterns in at‐risk groups. ©2003 Michigan Association for Infant Mental Health.     

Vocal congruence in mother-infant play

Turn-taking is the fundamental temporal structure of adult dialogue. This structure defines two types of joint silence: intrapersonal pause (silence bounded by the vocalizations of a single speaker) and switching pause (silence bounded by the vocalizations of different speakers). Switching pauses mark the boundaries of the turn exchange. In adult conversation the mean durations of both types of pause are characteristically matched between partners. This matching, termed vocal congruence, occurs developmentally earlier in the case of switching pauses. We hypothesized and confirmed that mothers and infants match switching pauses but not intrapersonal pauses at 4 months, even though the infants' vocalizations are prelinguistic. Second, since there are known affective correlates of vocal congruence in adult conversation, we hypothesized a similar affective correlate for mother-infant vocal congruence. We found, for the intrapersonal pause only, that the degree of matching within a dyad correlated with infant affective engagement. We conclude, from switching pause congruence, that a turntaking dialogic structure is being regulated in the mother-infant pair at 4 months in the same way as seen in adult conversation. Thus, both the temporal structure of adult dialogue and its affective correlate are prelinguistic.Supported in part by NIMH grant No. 41675.