A sensory basis for the lateral difference in the newborn infant's response to somesthetic stimulation

To determine whether lateral differences in the newborn infant's response to somesthetic stimulation are a consequence of lateral differences in sensitivity or whether they are the result of lateral differences in motor tendencies, cardiac response to stimulation of the left and right perioral region was examined. Cardiac acceleration occurred significantly more frequently to stimulation of the right than to stimulation of the left. Ipsilateral head turning also occurred more reliably to stimulation of the infant's right side than to stimulation of his left side. Evidence of reliable lateral differences in cardiac acceleration responses even under conditions in which the effects of lateral differences in head turning were removed suggested that the laterally differentiated cardiac responsiveness was not merely a function of increased motor activity consequent upon stimulation of the infant's right side but reflected a difference in sensitivity at the infant's two sides as well.