Handedness in Infants’ Tool Use ABSTRACT: In this study, we investigated whether hand preference influences infants’ choice of what hand to use in grasping a new tool presented at the midline, and whether this will change in the course of learning the functionality of a tool. The tool was a rake within reach placed beside an out-of-reach toy presented either to its right or to its left. Forty-eight infants from 16 to 22 months of age were tested. The results show that use of the right-preferred hand to grasp the rake is strong as of 16 months of age and does not change significantly with age in the condition where using the right hand leads to a better outcome than using the left hand. In the condition where using the left-non-preferred hand makes toy retrieval easier, infants increasingly use the left hand with age. Thus, when grasping the tool, younger infants are more influenced by their hand prefer- ence than older infants, who are better at anticipating the most successful strate- gies. ß 2012 Wiley Periodicals, Inc. Dev Psychobiol Keywords: hand preference; tool use; development INTRODUCTION There has long been much interest in the evolution of handedness in tool use, considered as a marker of hemispheric specialization for sequential behaviors requiring the interplay of sensory input and motor out- put. Many indices show that a majority of early homi- nids already preferentially used their right hand to make and manipulate tools 2 millions of years ago (Steele & Uomini, 2005). In modern human adults, the use of a tool such as a hammer is considered one of the best items to evaluate handedness, being among the actions subject to the strongest degree of hand prefer- ence (Corey, Hurley, & Foundas, 2001; Mackenzie & Peters, 2000; Porac, Coren, Steiger, & Duncan, 1980; Steenhuis, Bryden, Schwartz, & Lawson, 1990). Anoth- er tool, the pencil for writing, also elicits a high level of handedness. Writing is an over-practiced skill. For the hammer, adults expect that using it will require finely coordinated action and that they will need their best hand to achieve the precision required in the successive steps of the action. Contrary to adults, infants have little practice and little anticipation of their action with a tool, and one can wonder what will drive their choice of hand when they are presented with a new tool in the mid-sagittal plane, next to an object to be acted upon, before they have a good understanding of the tool’s functionality. Will hand choice go from a slight to a stronger bias in favor of the preferred hand as they come to anticipate the action that the tool is used in? This hypothesis seems compatible with exist- ing data suggesting that tool use develops the most in infants during the second year of life (McCarty, Clifton, & Collard, 2001), and that by this age handedness can already be observed, even though not as strongly as in adults (Dellatolas, Tubert Bitter, & Curt, 1997; Gesell & Ames, 1947). Testing this hypothesis is the goal of the study presented here. The emergence of hand preference in infants has been extensively studied, in particular for unimanual object grasping and manipulation in cross-sectional studies. As soon as grasping emerges there are clear signs of hand preference (Cornwell, Harris, & Fitzgerald, 1991; Fagard & Lockman, 2005; Hawn & Harris, 1983; Lewkowicz & Turkewitz, 1982; McCormick & Maurer, 1988; Michel, Ovrut, & Harkins, 1985; Morange & Bloch, 1996; Ramsay, 1980). This hand preference does not lead to a Developmental Psychobiology Lauriane Rat-Fischer J. Kevin O’Regan Jacqueline Fagard Laboratoire Psychologie de la Perception UMR 8158, CNRS and Universite ´ Paris Descartes 45 rue des Saints-Pe `res 75270 Paris Cedex 06, France E-mail: jacqueline.fagard@parisdescartes.fr Manuscript Received: 14 April 2012 Manuscript Accepted: 6 August 2012 Correspondence to: Jacqueline Fagard Article first published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/dev.21078  ß 2012 Wiley Periodicals, Inc.