Development of Early Handedness, Manual Specialization, and Hemispheric Specialization

Abstract

The development of handedness is related to the development of specialized manual function but follows its own developmental trajectory. Specialized lateralized hand function is referred to as manual specialization and is considered a reflection of underlying hemispheric specialization—for example, in terms of the left hemisphere's superior fine motor and language skills and the right hemisphere's superior spatial skills. The two major models used to explain laterality development concern an early equipotential and then a progressive lateralization of development versus an invariant model—for example, in which the two hemispheres exhibit from early in life the characteristics of adult hemispheric specialization. This entry critically examines the development of handedness, manual specialization, and hemispheric specialization, and, novel to the literature, shows that the equipotential and invariant models are not contradictory. It examines research for both lateralized behavior and brain structure and function from one age period to the next (prenatal to preschool). The research points to connectivity and network models as new ways of explaining left–right differences in brain and behavior, which tie into a proposed activation–inhibition coordination model. The origins of laterality in behavior and brain are shown to lie in biological and environmental influences, including genetically and culturally.