FACTORS AFFECTING LATERAL DIFFERENTIATION IN HUMAN NEWBORN

The effect of asymmetry of muscle tonus and of prior somesthetic stimulation on responsiveness to subsequent somesthetic perioral stimulation was examined. Infants were subjected to; asymmetry of tonus (n = 14), somesthetic stimulation of the right cheek (n = 14) or the left cheek (n = 15), or a control condition in which both types of asymmetry were eliminated (n = 13). All experimental treatments significantly increased responsiveness to both right and left stimulation. Since asymmetry of tonus and prestimulation of the right cheek produced significantly more responses to right than to left stimulation, it is likely that both factors contribute to the normally occurring lateral differences in responsiveness. Somesthetic priming of the two sides did not have opposite effects, indicating additional determinants of lateral differentiation. © 1970.