Infant Vocal Development in a Dynamic Communication System: Vocal Exploration Activities in Various Social Settings

Pre-linguistic vocal productions are the manifestations of a unique capacity ofhuman infants.The uniqueness is characterized by voluntaryvocal play and systematic repetition which serveno fixed functions.Such pre-linguistic infant vocalizations are the product of complex processes of internal vocal exploration activities and external social interactions. However,very few studies have incorporated both aspects to understand the nature of early vocal development. Therefore, the current study aims to investigate the relationship between vocal category development and exploration activities in varying social communication circumstances, using a developmentally appropriate coding scheme for infant vocalization.The vocalizations of 7 infants at three different ages (approximately 4, 7, and 11 months) were used. The three vocal types (i.e., vocant, growl, and squeal), the three engagement types (i.e., symmetrical, asymmetrical, and unengaged), and two proximity types (i.e., immediate and distant) were included. Based on observation and reports from prior research, the current dissertation incorporates fundamental frequency (f0) and duration of utterances as parameters to measure vocal exploration activities in various social settings.The findings in this study provides that infants build their vocal categories, producing the three vocal categories distinctively in the acoustic domains of f0 and duration and showing systematic vocal repetition patterns among the categories. These results provide empirical evidence against Jakobson\u27s view that pre-linguistic vocal sounds are mere byproducts of biological functions, and presumably not affected by socialization.The current results seem to suggest that internally driven vocal activities might tend to be more active when social demands are low, indicating that vocal play is a cognitively intensive process requiring attentional resources.In terms of age effect on vocal exploration activities, at the earliest stage we see high exploration ( and thus repetition), and at the latest stage we see consolidated categories( and thus high discriminability). This result provides a significant new perspective on the sequential logic of the two domains in vocal category development.This research also showed infants\u27 systematic tendency to utilize the vocal categories differentially in various social settings early on, suggesting infants\u27 voluntary control efforts on their pre-linguistic vocal productions to respond to constantly changing social circumstances