Mechanisms of a neonatal rightward turning bias: A reply to Liederman and Kinsbourne

Abstract

Liederman and Kinsbourne have presented interesting data concerning possible mechanisms involved in the newborn infant's rightward turning bias. They have not, however, justified their contention that they have identified the mechanism of the neonatal rightward turning bias. They have attempted to advance their position by presenting, as alternative possibilities, a sensory and a motor hypothesis and then choosing between the two. It is my contention that given the state of our current knowledge, these are neither reasonable nor necessary alternatives. Furthermore, their study does not successfully address the issue presented so that if it were desirable to choose between a sensory and a motor hypothesis it would not be possible to do so on the basis of the data presented. In addition to a sensory or a motor hypoth.esis it is clearly possible to entertain a sensory and a motor hypothesis. In fact, although I have stressed the sensory asymmetry (because it is less obvious), the hypotheses advanced and the data thus far collected by me and my collaborators indicate that the right-turning bias of infants reflects both motor and sensory asymmetries and that both of these are influenced by the infants' prior head position. As regards a motor asymmetry, in the first paper in which we reported a right-turning bias in response to somesthetic stimulation of the perioral region we also noted infants were more likely to turn right than left when their heads were released from a midline position even when such release was not preceded by perioral stimulation (Turkewitz, Gordon, & Birch, 1965). In a subsequent study we showed that even after a treatment known to eliminate differential responding to stimulation of the two sides, infants over 12 hours of age are still more likely to turn fight than left tbllowing release from a midline position (Turkewitz & Creighton, 1974), clearly a finding likely to be due at least in part to a motor asymmetry. With regard to a sensory asymmetry, we have found differences in the