6 - Hemispheric Asymmetry in Processing of Dichotically Presented Speech and Nonspeech Stimuli by Infants

Abstract

This chapter discusses the hemispheric asymmetry in processing of dichotically presented speech and nonspeech stimuli by infants. It presents the view that hemispheric asymmetry takes several years to develop and suggest that it is present in early infancy, possibly even at birth. The results of the study reviewed in the chapter indicates that infants between the ages of 22 and 140 days displayed the typical adult pattern of lateral asymmetry for dichotically presented speech and nonspeech stimuli. Functional asymmetries thus appear to be present at a very early age, possibly even at birth. The equipotentiality of the infant brain, whereby one side can readily take over the functions of the other, must be attributed to plasticity, rather than to a lack of hemispheric specialization. In the development of functional hemispheric asymmetry, the prospective significance of each hemisphere might be to mediate specific functions—in most persons this means, for instance, that the prospective significance of the left hemisphere is to be responsible for verbal skills. In the event of injury to one hemisphere, the intact hemisphere may have the prospective potency to mediate functions normally subserved by the damaged region, provided that the damage occurs prior to determination that is before prospective significance has been achieved.