Infant holding biases and their relations to hemispheric specializations for perceiving facial emotions.

Since Salk [Salk, L. (1960). The effects of the normal heartbeat sound on the behavior of the new-born infant: implications for mental health. World Mental Health 12, 168-175] reported a left-side preference for cradling an infant, several studies have attempted to elucidate the origin of this bias. Sex and handedness were the first variables tested but none of them is sufficient for explaining this bias. Manning and Chamberlain [Manning, J. T., & Chamberlain, A. T. (1991). Left-side cradling and brain lateralization. Ethology and Sociobiology, 12, 237-244] proposed that the explanation had to do with hemispheric specialization of emotions and suggested that the mother could better monitor her infant's emotional state when holding on the left side than on the right side. Moreover, the infant could monitor its mother's emotional state, since the most expressive side of mother's face (the left) is visible to the infant. We used two Chimeric Figures Tasks in order to assess (1) the preferred visual field for perceiving an emotion and (2) the most expressive side of the face. Holding biases were measured in a concrete situation using an infant doll. Our main objective was to assess the relation between the asymmetric visual perception and the holding direction in a large sample of university students. We replicated a left-holding preference (66%) in our sample and found an effect of participants' holding posture and a limited effect of laterality but no effect of sex. The most significant finding concerns the links between the preferred visual field and the preferred holding side. This effect was observed in the sample of women, in right-handers, and in the sub-group of participants with care-giving skills. These findings suggest a leading role for the right hemisphere for side of holding.