Phrasing in prelinguistic vocalizations

Assessing vocal development in infants and toddlers

The purpose of this study was to examine changes in prelinguistic vocal production during the first 20 months of life. Vocalizations were classified into 23 mutually exclusive and exhaustive types, and grouped into five ascending levels using the Stark Assessment of Early Vocal Development-Revised (SAEVD-R). Data from 30 typically developing infants, aged 0-20 months, show that older infants attained higher developmental levels on the SAEVD-R than younger infants. Infants 0-2, 3-5, and 6-8 months of age primarily produced vocalizations from Levels 1 (Reflexive), 2 (Control of Phonation), and 3 (Expansion). Infants 9-20 months of age also produced vocalizations from Level 4 (Basic Canonical Syllables). Only infants from 16-20 months of age produced Level 5 (Advanced Forms) vocalizations in significant quantities. The outcomes indicate that the SAEVD-R is a valuable instrument for evaluating prelinguistic vocal development.

Infant vocal-motor coordination: precursor to the gesture-speech system?

This study was designed to provide a general picture of infant vocal-motor coordination and test predictions generated by Iverson and Thelen's (1999) model of the development of the gesture-speech system. Forty-seven 6- to 9-month-old infants were videotaped with a primary caregiver during rattle and toy play. Results indicated an age-related increase in frequency of vocal-motor coordination, greater coordination with arm (specifically right arm) than leg or torso movements, and a temporal pattern similar to that in adult gesture-speech coproductions. Rhythmic vocalizations (consonant-vowel repetitions) were more likely to occur with than without rhythmic movement, and with rhythmic manual than with nonmanual activity, and the rate of vocal-manual coordination was higher in babblers than in prebabblers.

Beyond ba-ba and gu-gu: challenges and strategies in coding infant vocalizations

Infant vocal behaviors are extremely complex. Consequently, coding these behaviors is difficult and is typically associated with low reliability across observers. Various difficulties that arise when dealing with prelinguistic vocalizations, especially in the first 6 months of life, are outlined here. A proposed database of digitized infant vocalizations that illustrates strategies used to deal with these difficulties is then described. These strategies are based on theoretical infraphonological constructs, empirical observations, and information about the nature of mature phonological systems. Furthermore, the strategies are open-ended and can be modified as new information becomes available regarding infant vocal behaviors. At present, a preliminary database is available on the Web that illustrates some of these strategies. As the database is expanded, it is expected to provide a general framework for observers to categorize infant vocalizations and thereby enhance observer reliability.

Lateral asymmetries in infancy: implications for the development of the hemispheres

Cerebral asymmetry of cognitive processing of stimulus information is commonly viewed as a neocortical phenomenon. However, a number of lines of evidence give innate asymmetry of brainstem motivating systems, which anticipate experience, a key role. Spontaneous asymmetries of gesture and emotion can be observed in infants, who entirely lack language and visuo-constructive skills. Motives for communication in early life may direct subsequent development of complementary cognitive systems in left and right hemispheres. In split-brain monkeys, lateralized motive sets, intentions for manipulation by one hand, can determine which hemisphere will see and learn. Evolutionary antecedents of cerebral asymmetry appear to affect motivation, social signalling and bimanual coordination, with secondary effect in perceptual processing and learning. The hemispheres of adult humans differ in links with neurochemical system that regulate motor initiatives, exploration and attention, and the approach/withdrawal balance in social encounters. Asymmetries in emotional and communicative behaviour in infancy support evidence that an Intrinsic Motive Formation emerging in the embryo human brain stem regulates asymmetries in development and in functioning of the cerebral cortex.