Developmental Laterality Research: Infancy

Abstract

The first comprehensive chapter of the book examines in depth the developmental literature on early laterality . It reviews recent publications both on manual behavior and on findings related to the brain. The research reviewed is organized by age and cuts fine. It keeps the age range limited in each section of the chapter in order to present a clear developmental picture. The chapter begins with research in the prenatal period and continues with the newborn and early months of life, before moving on to the second half of the first year and then the second year. The major empirical issue is when laterality first manifests in the infant , because one of the major views is that the brain is equi-potential early in life and that manual behavior does not demonstrate its normal right-hand preference . In contrast, the major opposing view in this regard is that the early brain is specialized already along adult lines, which is the approach of invariant lateralization . The research demonstrates that when tasks and measures are used that are age specific, whether examining manual specialization or hemispheric specialization , the empirical results reflect the later adult pattern, supportive of the invariant lateralization model. In this regard, there is sufficient data even in the prenatal period that the developing fetus demonstrates a right-hand preference for behaviors indicative of manual preference . Moreover, associated brain development findings support that early hemispheric specialization at this age period is organized in a way that parallels later left hemisphere verbal skills and later right hemisphere visuo-spatial ones. Moreover, the models that can best explain the findings include the one of activation-inhibition coordination. The model of cascades in development helps explain longitudinal findings.