Is Infant Holding-Side Bias Related to Motor Asymmetries in Mother and Child? Ce ´line Scola 1 Jacques Vauclair 1,2 1 Research Center in the Psychology of Cognition Language & Emotion University of Provence 29 Ave. Robert Schuman 13621 Aix-en-Provence Cedex 1, France E-mail: jacques.vauclair@univ-provence.fr 2 Institut Universitaire de France ABSTRACT: Studies have revealed a preference for the left hemibody in infant holding in 65–85% of cases. Several investigations have linked this preference to maternal asymmetries. The main goal of the present study was to assess manual and hemispheric asymmetries in both mother and child and delineate their respective influence on holding-side biases. Holding side was assessed by direct observation, and by use of a questionnaire within populations of mother–child dyads. Maternal asymmetries were handedness and hemispheric specialization for perceiving emotions. Infant asymmetries were fetal position, asymmetric tonic neck reflex (ATNR) at birth and handedness at 19 months of age. To that purpose a longitudinal study has been made with infants observed at 2 and 19 months of age. A significant relationship was found between maternal handedness and holding preferences, but no significant relation was obtained between hemispheric specialization and holding preferences. Fetal position in utero but not ATNR, was significantly related to holding-side preferences. Finally, holding side at 2 months was significantly associated with infants’ unimanual preferences. ß 2010 Wiley Periodicals, Inc. Dev Psychobiol 52: 475–486, 2010. Keywords: laterality; postural asymmetry; holding-side biases; mother-child relationships; cradling; fetal position; ATNR INTRODUCTION The majority of mothers prefer to hold their young children on the left side of their body when soothing or calming them (e.g., Salk, 1960). This behavior is commonly called holding bias. The holding bias is present (1) in several cultures (e.g., Saling & Cooke, 1984), (2) in nonhuman primates (e.g., Hopkins, 2004), (3) and in both mothers and nonmothers (e.g., Vauclair & Scola, 2009), as well as young girls (e.g., Saling & Bonert, 1983), and even fathers (Scola & Vauclair, 2009). The generality of this behavior has prompted growing interest in the literature and some researchers have attempted to explain the origin of this bias. As holding-side preference is a postural asymmetry, several studies have examined the relation- ship between the side of holding and the presence of other asymmetries expressed by the mother (e.g., perceptual asymmetries and handedness: Bourne & Todd, 2004; Harris, Almerigi, & Kirsch, 2000; Huggenberger, Suter, Reijnen, & Schachinger, 2009; Manning & Chamberlain, 1991; Vauclair & Donnot, 2005) or by the child (e.g., asymmetric tonic neck reflex or ATNR: Bundy, 1979; Ginsburg, Fling, Hope, Musgrove, & Andrews, 1979; Sieratzki & Woll, 1996). The aim of this article is to identify the respective relations between these various asymmetries and the newborn holding. For that purpose, four studies were carried out. In the first study, we examined the relationship between holding-side biases and maternal handedness. The second study was concerned with mothers’ hemi- spheric specialization in the perception of emotions, measured at three different times (during pregnancy, immediately after delivery, and 19 months later). The third study focused on the relationship between holding bias, fetal position, and ATNR. Lastly, the fourth study explored the possible relation of the mother’s holding- side bias and the child’s manual preferences. One hypothesis that is often advanced to explain the left bias for holding a young child refers to the handedness Developmental Psychobiology Received 17 September 2009; Accepted 9 February 2010 Correspondence to: J. Vauclair Published online 7 April 2010 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/dev.20450 ß 2010 Wiley Periodicals, Inc.