Directors: Antonio M. Battro and Kurt W. Fischer
Program officer: María Lourdes Majdalani
From sounds to language: the auditory world in the infant brain
Why are native languages acquired during infancy and childhood? Given that language acquisition proceeds rapidly during these periods, it is important to reveal the early development of the biological foundation for language, namely, the brain, in order to answer this fundamental question. Because speech perception precedes speech production during infancy (Jusczyk, 1997), one effective strategy to address this question is to clarify the neural basis underlying auditory and speech processing in infants. By using multi-channel near-infrared spectroscopy (NIRS), which is a noninvasive technique to measure activation in multiple regions of the brain, we conducted a series of studies to examine the mechanisms through which the infant brain perceives speech sounds and non-speech sounds such as tone sequences (Homae et al., 2006; Homae et al., 2007). We found that the infant brain showed functional differentiation in the auditory-related areas, and that a cortical region in the right hemisphere of the brain participated in processing pitch patterns of not only speech sounds but also tone sequences. The pitch information in both speech and non-speech sounds seems to affect the auditory perception in early infancy, whereas the alterations in sensitivity to information during the course of development results in selectivity in infants with regard to pitch information in their native languages. This selective tuning is attributable to two factors: speech information surrounding the infants and brain development. The infant brain is not a miniature version of the adult brain but a continuously self-organizing system that forms functional regions and networks between multiple regions via short-range and long-range connectivity (Homae et al., 2010). We propose that the neural development proceeds in two directions, localization and globalization, for organization of functional networks for perception, cognition, and behavior. Elucidation of the auditory world of infants would enable a deep understanding of infant development and origin of the human nature.