17 - Manual Specialization in Infancy: Implications for Lateralization of Brain Function

Abstract

This chapter discusses a series of issues involving the development of lateralization of manual behavior and brain functioning in infancy, and the absence of careful longitudinal research precludes their resolution. The exact nature of early hemispheric specialization has not been fully elucidated and its developmental course is still subject to debate. Hemispheric specialization is often referred to in terms of language- or space- related skills, and it appears that girl infants are in advance of boy infants on a variety of language-related variables. There are several possible ways of explaining this advance in left-hemisphere skills in girls. It could be that the left hemisphere matures more quickly in girls, or is more relied on in girls because of greater sensitivity in the auditory channel from early in life, or develops cerebral connections with the right hemisphere more quickly. Careful longitudinal study of manual specialization and of differential hemispheric functioning in infancy is needed and it give results that will help to clarify the issues of which hand is initially preferred in early infancy, which hemisphere is initially dominant, when sex differences and individual differences in lateralization of function begin to emerge, what is the origin of manual specialization and lateralization of hemispheric function, and what is their presumed interrelationship.